THE STAR FORMATION NEWSLETTERAn electronic publication dedicated to early stellar/planetary evolution and molecular clouds

No. 264 — 11 December 2014 Editor: Bo Reipurth (reipurth@ifa.hawaii.edu)

The Star Formation Newsletter

Editor: Bo Reipurthreipurth@ifa.hawaii.edu

Technical Editor: Eli Bressertebressert@gmail.com

Technical Assistant: Hsi-Wei Yenhwyen@asiaa.sinica.edu.tw

Editorial Board

Joao AlvesAlan Boss

Jerome BouvierLee Hartmann

Thomas HenningPaul Ho

Jes JorgensenCharles J. Lada

Thijs KouwenhovenMichael R. MeyerRalph Pudritz

Luis Felipe RodrıguezEwine van Dishoeck

Hans Zinnecker

The Star Formation Newsletter is a vehicle forfast distribution of information of interest for as-tronomers working on star and planet formationand molecular clouds. You can submit materialfor the following sections: Abstracts of recentlyaccepted papers (only for papers sent to refereedjournals), Abstracts of recently accepted major re-views (not standard conference contributions), Dis-sertation Abstracts (presenting abstracts of newPh.D dissertations), Meetings (announcing meet-ings broadly of interest to the star and planet for-mation and early solar system community), NewJobs (advertising jobs specifically aimed towardspersons within the areas of the Newsletter), andShort Announcements (where you can inform or re-quest information from the community). Addition-ally, the Newsletter brings short overview articleson objects of special interest, physical processes ortheoretical results, the early solar system, as wellas occasional interviews.

Newsletter Archivewww.ifa.hawaii.edu/users/reipurth/newsletter.htm

List of Contents

Interview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

My Favorite Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Abstracts of Newly Accepted Papers . . . . . . . . . . 17

Abstracts of Newly Accepted Major Reviews . 51

Dissertation Abstracts . . . . . . . . . . . . . . . . . . . . . . . . 52

New Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

New and Upcoming Meetings . . . . . . . . . . . . . . . . . 59

Cover Picture

NGC 1333 is located at a distance of 235±18 pc(determined to the source SVS 13, Hirota et al.PASJ 60, 37, 2008) and most of the cluster mem-bers have an age less than ∼3 Myr, but with a largespread from newly born Class 0 sources to starsaround 10 Myr old. Numerous Herbig-Haro flowscriss-cross the central cloud core.

The image is composed of data from Subaru, DSS,NOAO, and color images by Robert Gendler.Image assembly and processing by Robert Gendlerand Roberto Colombari.http://www.robgendlerastropics.com

http://www.astrobin.com/users/rob77/

Submitting your abstracts

Latex macros for submitting abstractsand dissertation abstracts (by e-mail toreipurth@ifa.hawaii.edu) are appended toeach Call for Abstracts. You can alsosubmit via the Newsletter web inter-face at http://www2.ifa.hawaii.edu/star-formation/index.cfm

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Al Glassgoldin conversation with Bo Reipurth

Q: You came to astronomy from a background in physics.What motivated that move?

A: The move actually took years and was stimulated byseveral interactions with various colleagues. My early re-search in theoretical physics dealt with nuclear scattering,and later I branched out into atomic scattering and ap-plications of the new many-body techniques to nuclear,atomic and low temperature physics. Early on this led toseveral quantitative treatments of spin-exchange scatter-ing between hydrogen atoms, important for understandingastronomical 21 cm radiation. A work more focused on as-trophysics was a paper entitled ’Anisotropic Superfluidityin Neutron Star Matter’, published in the 1970 PhysicalReview Letters with my student Mark Hoffberg and NYUfaculty colleagues, Bob Richardson and Mal Ruderman. In1964, the Russian theorists Ginzburg and Kirzhnitz hadsuggested that neutron stars are superfluid, and Ruder-man asked whether this idea could be pursued further.I responded positively on the basis of the recent theoryof the superfluidity of liquid He-3 based on the Bardeen,Cooper and Schrieffer (BCS) theory of superconductivity.Unlike the spin-zero electron pairs relevant for supercon-ductivity, the special properties of the nuclear forces led to3P2 neutron pairs as the basis of anisotropic superfluidityof neutron star matter. This was Mark Hoffberg’s Ph.D.thesis, and it represented the first quantitative treatmentof superfluidity in neutron stars.

At this point I was in regular contact with Patrick Thad-deus who was becoming active in the new field of sub-mmradio astronomy. I had met him some ten years earlierwhen he was still a graduate student in Charlie Towneslab at Columbia University which I visited in connectionwith my interest in new techniques for atomic physics. Anequally important interaction occurred with the arrival ofBill Langer at NYU in 1971. Together we began to learn

about the interstellar medium and then to start publishingpapers on cloud models in 1973. Bill and I were helpedby a visit with the Townes group at UC Berkeley in thesummer of 1972.

Q: Has your physics background been an advantage foryour work?

A: My physics background has indeed been a primarydriver of my research in astrophysics. Many of my pa-pers have been devoted to the clarification and calcula-tion of physical processes, or to providing the microscopicbackground for complex astrophysical models. A good ex-ample of the latter are the more than a dozen papers withFrank Shu and his collaborators, especially his studentsJoan Najita, Susana Lizano and Sienny Shang with whomI continue to be close. In the papers dealing with themeteoritic implications of the X-wind model, my nuclearphysics background proved helpful.

Q: You started out writing a series of papers in the sev-enties with Bill Langer. An especially noteworthy paperfrom 1974 discussed models of diffuse clouds. What werethe main results?

A: This paper was the first PDR (photo dissociation re-gion) model. The observational motivation for us was theearly Copernicus UV absorption line studies of interstellardiffuse clouds, especially the thicker ones with significantamounts of molecular hydrogen. Many others joined indeveloping this subject, and the scope of the model wasimmensely extended by the 1985 papers by Tielens andHollenbach. The detailed application of the model to dif-fuse clouds was greatly advanced by my student, StevenFederman, and his collaborators. In addition to modelingthe clouds, Steve has been active in observing them, andhe also carried out theoretical and experimental studies ofthe underlying atomic and molecular physics.

Q: Have laboratory studies been helpful in your work oninterstellar clouds?

A: The discovery of extraterrestrial molecules was a chal-lenge to both observers and theorists simply because theirspectra and physical properties were often poorly known,if at all. As our studies of interstellar and circumstellarmatter become progressively more detailed, the results oflaboratory studies are still needed. Hardly a day goes bywithout my searching, often unsuccessfully, for some as-pect of molecular astrophysics. For example, modelingdense molecular regions requires information, now oftenlacking, on the excitation of the products of chemical re-actions and of dissociative recombination. The neededlaboratory studies are carried out by both chemists andphysicists, and the experiments are demanding and costly.Sufficient and durable support is needed for young scien-tists to develop careers in this area. I fear that this supportis now not strong enough.

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Q: In 1991 you and your collaborators explored the for-mation of molecules in protostellar winds. Do models andobservations agree?

A: The 1991 paper with Huggins and Mamon argued thatSiO and other molecules were synthesized in the nascent,inner outflows of young protostars. In the ensuing decadesextensive observations of SiO and some other species havebeen made of bipolar outflows with mm arrays such asPlateau de Bure, CARMA and SMA. But a resolution ofa fraction of an arcsecond isn’t enough to get to the heartof the matter, i.e., the origin of the jet that drives theoutflows. Future observations with ALMA at the highestresolution may finally do the job. Of course the modelsof the outflows need to be improved in light of significantadvances is astrochemistry over the intervening years. Si-enny Shang at ASIAA is pursuing this line of research andalso encouraging the appropriate observations.

Q: Did the discovery of extreme overabundances of for ex-ample SiO and CH3OH in the L1157 outflow and someother flows come as a surprise?

A: More delight than surprise!

Q: Your well cited paper from 1997 deals with X-ray ion-ization of protoplanetary disks, a study you followed up in2004. What is the state of this field today?

A: The role of X-rays is now much better understood inthe context of the further model studies in 2004 of theatmospheres in the inner regions of protoplanetary disks,work done in collaboration with Joan Najita and my stu-dent Javier Igea. Our current picture of the inner diskatmosphere is that it consists of a relatively hot top layer(∼ 5000K), a warm molecular region (∼ 300 − 1000K),and a cool region below (< 300K). The X-rays do notplay a major role in heating, but they are responsible forgenerating hydrogen ions (H+, H2

+. H3+; He+) and the

heavier, easier to observe, molecular ions such as HCO+

and N2H+. Once the FUV photons in the warm molecu-

lar layer are absorbed, the X-ray generated ions becomethe dominant agents for regulating molecular abundances,e.g., by destroying molecules snd by producing reactiveneutral and ionized atoms and more complex radicals.

Q: A few years ago you studied the formation of water inthe warm atmospheres of disks, and among other findingsyou noted that it may not be necessary to invoke transportof water from cooler to warmer regions. Is this of relevancefor the early solar system?

A: The evolution of water over the lifetime of a proto-planetary disk up to and after the formation of planets isbasic for understanding the composition of planetary at-mospheres, including our own solar nebula and the Earth’soxygen-rich atmosphere. Further studies of water in pro-toplanetary disks that include FUV heating, dissociationand absorption show that abundant water forms on rel-

atively short timescales in the inner few AU of the disksaround T Tauri stars. This prediction is consistent withdetections of warm and hot water in these disks obtainedwith Spitzer and other instrumentation. It does not ruleout other processes, such as vertical and radial mixing ofwater and water ice, but it does indicate that the innerregions of protoplanetary disks are able to rapidly processgas phase oxygen into water. The existence of substantialwater vapor in the inner few AU of these disks dependson the details of the chemistry, which in the case of OHand water is sensitive to the gas temperature and to theformation of molecular hydrogen.

Q: In one of your most recent papers you have re-visitedcosmic-ray and X-ray heating of clouds and disks. Whatare the new physical ingredients in these calculations?

A: The main new direction is a more complete analysisof the chemical reactions induced by the primary prod-ucts of X-rays ionization, the H2

+ and H3+ ions. We have

recently extended this idea to FUV photodissociation inmolecular regions. The heating from the absorption ofFUV radiation by neutral species in dense molecular gas isdominated by the energy yield from the chemical reactionsinduced by the products of photodissociation or photoion-ization. The total heating combines heating from the slow-ing down of the initial photo fragments (“direct” heating)and the conversion of the energy released by the ensuingchemical reactions (“chemical” heating). The productsfrom both processes are often excited and, if the densityis high enough, the excitation energy can be convertedinto heating by collisional de-excitation. A good exampleis provided by molecular hydrogen where FUV absorp-tion yields electronically excited molecules whose fluores-cent decay leads to excited ro-vibrational levels. Anotherexample is the photoionization of atomic carbon, wherethe small standard heating of 1.4 eV per photoionizationcomes from the kinetic energy of the products C+ ande−, but the chemical reactions induced by the C+ ion cangenerate much more heating.

Q: What do you consider the main outstanding problemscurrently in understanding the heating and cooling pro-cesses in disks and clouds?

A: I’ll focus on protoplanetary disks because they havebeen the main focus of my research in recent years. Study-ing their physical properties can help us understand molec-ular gas in general. The heating and cooling of protoplan-etary disks remains a challenge. The gas in these diskscovers a wide range of densities and temperatures, rangingfrom nH = 106 − 1016 cm−3 and T = 20 − 5000K. Thusall of the familiar phases of the ISM are encountered –and more. What is unusual about these disk atmospheresis the very high densities in the warm molecular regionsrelevant for spectroscopic observations. This means thatfamiliar processes from the study of more diffuse regions

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may need revision, and of course new processes may alsoenter. Although protoplanetary disks have been observedat many wavelengths, many of the most interesting re-sults such as the detection of water in the near- and mid-infrared, were made at low spatial resolution, making com-parisons between theory and observation difficult. The re-cent mm observations of HL Tau with a spatial resolutionof 35 milli-arcseconds (5 AU) fill us with hope for morefine scale observations of protoplanetary disks.

The 2004 paper you mentioned earlier with Najita andIgea was called ’Heating ProtoplanetaryDisk Atmospheres’.It should have ended with a question mark, and a currentreconsideration of this subject with Joan Najita and MateAdamkovics may well have something like this correctedtitle. The most important heating mechanism for the ISM,grain photoelectric heating, has also been invoked by manymodelers of protoplanetary disk atmospheres. However, itis inadequate unless a very large fraction of the availablecarbon is in small carbonaceous particles (PAHs). But theoccurrence of PAHs in these regions is uncertain becausethe limited, existing observations do not have the spatialresolution to determine the location of the PAHs. In the2004 study, we argued that mechanical heating, proba-bly fueled by viscous dissipation, might heat protoplane-tary disk atmospheres. We argued that the usual α thindisk heating should be considered as a three-dimensionalquantity and that it should be large in disk atmospheres.This picture has since been supported by simulations ofthe magneto-centrifugal instability (MRI) by Turner andHirose (2011) and Bai and Stone (2013), among others.When incorporated into our disk model, accretion heatingdominates the heating, and it gives inner disk tempera-tures suggested by the infrared observations.

More recently we have been exploring FUV heating bymolecules, instead of just photoelectric heating by grainsdiscussed above. Photochemical heating by the watermolecule is quite interesting in this respect. At the top ofthe molecular region at 1AU, the photochemical heatingrate for water is about four times larger than accretionheating. However, with increasing depth the dissociatingradiation becomes optically thick and accretion heatingdominates. Before strong water self-shielding sets in, themolecular transition region may be dominated by FUVphotochemical heating. More generally, our studies indi-cate that the heating of protoplanetary disk atmospheresdepends on the region, and that it may involve more thanone process at any given location.

To answer the question, ’What Heats Protoplanetary DiskAtmospheres?’, one has to consider several competitiveheating processes, in particular the role of PAHs, accre-tion heating, and photochemical heating. A paper that at-tempts to resolve this issue is now under preparation withmy collaborators, Mate Adamkovics and Joan Najita. But

we are still at the beginning of efforts to construct phys-ically sound models of protoplanetary disks that will berelevant in an era when the observations will be madewith greatly improved spatial resolution that can probethe planet forming region of these disks.

Q: For students who wish to be involved in such futuremodeling as you just mentioned, what physics backgrounddo you think is most important to acquire to be able toenter this fruitful field?

The opportunities provided by ALMA challenge theoriststo develop more sophisticated models, as indeed they should.The new generation modeling of protoplanetary disks musttreat the hydrodynamics and the physics (and chemistry)on a unified basis. To build strength in the latter area, it isimportant for graduate students to study in depth atomicand molecular physics and the physics of radiation. Muchof what is required in disk modeling is inter-disciplinary,and the standard courses offered to students are often toonarrow. Some broad inter-department curriculum devel-opment would be very welcome.

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My Favorite Object

GG Tau A:One Ring to Rule Them All

(thanks to J.R.R. Tolkien)

Anne Dutrey

1 The Early Times

Located at about 140 pc, the young (∼ 1 Myr) TTaurisystem GG Tau has been known as a hierarchical stellarsystem ever since the early nineties (Leinert et al 1991).At that time, it was known to consist of a pair of binariesGG Tau A and GG Tau B, the wide binary GG Tau ABbeing separated by 10′′ in the plane of sky. The binary GGTau B has an apparent separation of 1.4′′ and GG Tau A,the focus of this review, of 0.26′′. The four componentsspan spectral types from K7 to M7, and the least mas-sive of these is a brown dwarf (White et al. 1999). The1.3 millimeter flux of GG Tau A measured by the IRAM30-m telescope by Beckwith et al 1990 revealed that it isthe second brightest millimeter-wavelength TTauri source(HL Tau is the brightest), making it an excellent targetfor the generation of mm telescopes which started to oper-ate in the nineties. Skrutskie et al 1993 observed it in COJ=1-0 using the Nobeyama 45m and detected the doublepeaked profile which is now recognized as characteristicof a rotating disk. A CO J=1-0 map made by Kawabeet al 1993 also showed a displacement of the centroids ofthe red-shifted and blue-shifted line emission which can beinterpreted as due to rotation. They also found the COdisk was large and thus necessarily circumbinary and theysuggested the possible existence of a central hole producedby tidal interactions between the binary and the disk. Ko-erner et al 1993 also published the first 13CO J=2-1 mapmade with OVRO. In the midst of this rapidly growing un-

derstanding of TTauri disks, I arrived at IRAM-Grenobleas a young post-doc in December 1991 with a new researchproject to work on: the physics of the recently discoveredTTauri disks.

Figure 1: The four components of GG Tau as seen in an0.81 µm HST image. North is up and east is left. Theclosest pair (A) has a separation of 0.26” and the widerone (B) is a 1.48” binary. From White et al. (1999).

Figure 2: From Simon and Guilloteau 1992. 2.7mm ob-servations of the dust disk surrounding GG Tau A. Thecontour spacing is 2mJy per beam.The beam size is 2.4”by 1.8” with P.A. 50o.

In the fall of 1991, motivated by the very strong mm-wavecontinuum emission of GG Tau A, Michal Simon wrotea successful PdBI proposal to map it. The observations,carried out during winter 1991/1992, were made on thelong baseline configuration. Stephane Guilloteau made apreliminary data reduction and discovered that the sourcewas not seen in the image! He also noticed that the noisewas significantly higher than the thermal contribution in

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Figure 3: Left panel: continuum distribution in the GG Tau A disk at 2.7mm (false color) and three velocity channelsof the 13CO J=1-0 observations from PdBI. From Dutrey et al 1994. Middle panel: the same at 1.3mm and in 13COJ=2-1. From Guilloteau et al 1999. Right panel: IR image at 1.2µm of the dust in the scattered light emission. FromRoddier et al 1996.

the center of the map. He concluded that the source wascompletely resolved on the long baselines and the projectshould be continued in compact configuration. Fig.2 showsthe final image (Simon and Guilloteau 1992). Due to poorand very incomplete uv coverage (baselines between 50and 150m were missing), the algorithm CLEAN could notproperly recover the source structure even though the to-tal flux was conserved (short baseline contribution). Theauthors concluded that the source was resolved in one di-rection but that these first observations could not indicatewhich one.

2 A Ring or a Disk ?

2.1 A Series of Misfortune and Luck

The next step was to search for CO gas and possible Kep-lerian rotation. The new observations were carried out inwinter 1992/1993. We chose to observe the 13CO J=1-0line instead of the more abundant 12CO because of theatmospheric O2 line at 118 GHz which increases the at-mospheric opacity around 115 GHz.

The results from compact configuration was very promis-ing because in the 13CO map, the centroid of the emissionof each velocity channel was moving exactly like expectedfor a disk in rotation. However the final image which in-cludes the medium baselines was very disappointing: therotation had apparently disappeared. However, a few dayslater, a shift in velocity in the absorption lines observed to-wards 3C111 compared to the Kitt Peak spectra revealedthat the PdBI synthetizer had indeed been unlocked. GG

Tau A was then re-observed on the long baselines and theresulting map magically showed again a velocity gradientsuggesting rotation. We also found a way to recover thecorrupted data and the final image had the impressivenumber of 27 baselines, making it among the best mm im-ages produced at that time. The 13CO J=1-0 and 2.7mmthermal dust maps (Dutrey et al. 1994) are presented inFig.3.

2.2 First Gas and Dust Modeling

Left panel of Fig.3 shows the thermal dust emission at2.7mm (false color) and three velocity channels, blue-shifted,systemic velocity and red-shifted, of the 13CO J=1-0 emis-sion. The CO disk extends up to an outer radius of 800 au.The dust distribution does not appear centrally peaked,suggesting a central hole which was confirmed by the fit.The central hole was marginally resolved in the CO mapand the best model clearly confirmed that both the gasand dust disks were truncated at an inner radius of 180 au.The interior truncation of the disk could be attributed totidal interactions with the central binary (Artymowicz etal 1991).

The observations revealed that most of the dust and gasemission is located in a very narrow ring of 80 au width,extending from 180 to 260 au with relatively sharp edges.The best fit of both the dust and 13CO modeling wasobtained for a gaussian shape. Beyond a radius of 260 au,the CO brightness of the outer disk was well reproduced bya radial power law. The narrow ring contains 90% of thedust emission, with only 10% extending beyond 260 au.

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With about 0.13-0.15M⊙, the total (gas+dust) mass, es-timated from the optically thin dust emission (taking theabsorption coefficient from Beckwith et al 1990 and as-suming a gas-to-dust ratio of 100), makes this disk amongthe more massive TTauri disks. Its mass represents about10% of the total stellar mass. The 13CO data and the op-tically thinner C18O J=1-0 and J=2-1 upper limits (fromthe IRAM 30-m telescope) also suggested that the COgas was depleted by about 100. The gas temperature wasabout 20-25 K inside the ring.

Finally, the modeling of the CO line also nicely confirmedthat the ring is in Keplerian rotation around the centralbinary.

3 The Central Cavity

3.1 Sub-Arcsecond Imaging

In 1996, the IRAM array was upgraded, the new receiverswere dual frequency at 115 and 230 GHz and baselineswere extended to ∼400m. Observing at 230 GHz usingthe new baselines increases the angular resolution by afactor 4. The middle panel of Fig.3 presents the newGG Tau A images in 13CO J=2-1 and in continuum at1.3mm, obtained in winter 1996/1997 (Guilloteau et al1999). Compared to the left panel of the same figure, thecentral hole is fully resolved both in line and in continuum.The three velocity channels of 13CO J=2-1 closely followthe dust ring even if the CO emission is significantly moreextended. HCO+ J=1-0 and the dust emission at 3.4mmwere also mapped. The best modeling of the lines anddust emissions essentially confirmed the previous analysis,in particular, the steepness of the inner and outer edgesof the ring. The new data allow the derivation of the gastemperature because the 13CO J=2-1 emission is opticallythick in the ring. At 180 au, the gas temperature is ∼ 35 Kand the best fit gives Tk(r) = 20× (r/300au)−0.9 K, con-firming that most of the CO disk is cold. The continuumvisibilities confirm that about 10-15% of the flux densityarises from the outer disk. Moreover at 1.3mm, an unre-solved central source is seen at the level of about 10mJy,suggesting the presence of one or two inner circumstellardisks associated with GG Tau Aa and Ab.

In hindsight, we realized that we were very lucky in 1992to select 13CO instead of 12CO. The central cavity, whichwas the first to be detected in a TTauri disk, was both seenin the 13CO and dust maps, although marginally resolved.If we had observed in 12CO J=1-0, it would have beendifficult to convince our colleagues that the hole in the dustdistribution was real and not an observational artifact onthe long baselines.

3.2 Millimeter versus NIR Images

GG Tau A was also among the first disks to be imaged inthe Near Infrared (NIR) scattered light. Using the adap-tive optics system they had developed, Roddier et al 1996observed the dust ring in the Near Infrared at the CFHT.The right panel of Fig.3 shows their image at 1.2µm. Thering is brighter in its northern part, the area pointing to-wards us, and has an inner edge at 180 au, as previouslyderived from the mm images, definitively confirming theedge sharpness and the tidal truncation.

The central stars also do not appear located in the cen-ter of the ring. By comparing the 1.2µm optically thickemission of the dust seen in scattered light with the imageof the optically thin thermal dust emission at 1.3mm, weconclude that since the NIR emission is optically thick, thevertical ring thickness at radius 180 au is of the order of120 au and this thickness also explains the apparent shiftof the stars from the ring center (Guilloteau et al 1999).

Interestingly, Roddier et al 1996 noticed that the centralhole does not appear completely devoid of dust, this factwas confirmed by other scattered light images of the dustat NIR or optical wavelengths (e.g., Silber et al 2000, Kristet al. 2005, see Fig. 4).

Figure 4: An HST image of GG Tau A (Krist et al. 2005).

A new image of the 12CO J=2-1 obtained with the IRAMarray in 2001 also revealed the presence of some resid-ual unresolved 12CO gas inside the cavity (Guilloteauand Dutrey 2001) as predicted by theory and hydrody-namical simulations of circumbinary disks (e.g. Bate andBonnell 1997, Artymowicz and Lubow 1996). However,resolving the streamers of gas and dust falling down fromthe outer reservoir of material onto the circumstellar in-ner disks which would not survive without regular replen-ishment was beyond the capabilities of the existing mmarrays. Many questions were left hanging for nearly 15years.

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4 The ALMA Era

During a meeting organized in June 2011 in honor of MikeSimon, at Stony Brook University, Tracy Beck presentedpreliminary images of H2 at 2.12µm of GG Tau obtainedat Gemini North. These images revealed the existence ofhot gas in the cavity of GG Tau A. Beck et al (2012) foundthat a significant fraction of the H2 gas is hot (∼ 1000−1700 K) and that is likely due to heating by accretionshocks. Stimulated by these observations, we decided tojoin our forces to study the GG Tau system by a multi-wavelength approach.

4.1 A Triple System

In 2013 we observed the stellar system using VLT/NaCoand VLTI/PIONIER at ESO and discovered an additionallow-mass companion orbiting GG Tau Ab, and located atprojected separation of the order of 4.5 au (Di Folco etal 2014). Adding the mass of the new star to the bestdetermination of the two others leads to a better agree-ment with the dynamical mass inferred from CO J=2-1measurements. Moreover, the existence of this third com-ponent also explains why Pietu et al 2011 reported the de-tection of a mm dust disk only around GG Tau Aa. Anycircumstellar disk around GG Tau Ab would be tidallytruncated at a radius no greater than 1-2 au. The newtriple system is shown in Fig.5, middle panel.

4.2 First ALMA Images

We applied to ALMA, and received our data in Febru-ary 2012. The observations (about 40 minutes on source)were made with 23 antennas giving 253 baselines, almost afactor 10 more compared to the interferometric data fromDutrey et al 1994. During the reduction process, we foundthat (again!) a velocity shift corrupted the data. Despiteseveral attempts, its origin could not be found but its mag-nitude was determined by correlation with the 12CO J=2-1data.

Left panel of Fig.5 shows the integrated area of the COJ=6-5 observed with ALMA in the GG Tau A system(false color) with an angular resolution of 0.25” or 35 au.The dust thermal emission at 0.5mm (black contours) isseen in the ring and in the circumstellar disk surroundingthe single star GG Tau Aa. The right panel shows the COJ=2-1 integrated area and the dust emission at 1.3mmobserved with the IRAM array in winter 2006. The COJ=6-5 and 1-0 results were presented together (Dutrey etal 2014).

Most of the CO J=6-5 emission arises inside the cavityand shows the morphology of an inhomogeneous filament

or streamer made of several clumps. The outer circumbi-nary disk is hardly seen. This is likely due to both anH2 density insufficient to thermalize the transition andthe lack of short spacings. At large distances from thethree stars, the kinematics of the CO J=6-5 is Keplerian,the gas being in rotation around the triple stars. Near thestars the velocity pattern is disturbed with motions partlycompatible with infall. We also detect some CO gas as-sociated to the disk orbiting GG Tau Aa. The clumpsseen in CO J=2-1 emission are relatively cold (∼ 35 K)and optically thick. The clumps traced by CO J=6-5 arelikely optically thin and correspond to warmer gas (70 K),particularly at the interface between the streamer and theinner disk of Aa. The mass of each CO J=6-5 clump isabout ∼ 5 · 10−5M⊙. Such a mass reaching the Aa diskmay disappear in at most 5000 years assuming a mini-mum accretion rate of 10−8M⊙/yr. In 1 Myr, at least 200fragments of similar mass must have been accreted to sus-tain the 10−3M⊙ disk orbiting Aa (the disk mass beingestimated from the dust emission).

The dust emission from the circumbinary ring is uniformand very well resolved. We analyzed the 0.5 mm ALMAimage with existing 1.3 and 3.4 mm continuum maps ofthe ring and derived the ring temperature profile: Td(r) =13.8 × (r/200au)−1.1 K. This corresponds to 8.5 K at aradius of 300 au. Since the 0.5 mm emission is departingfrom the Rayleigh-Jeans domain, this derivation is almostindependent of the dust properties. A steep slope (r−0.9)was also derived from the 13CO gas distribution, but witha warmer gas temperature of 20 K at 300 au. All re-sults are consistent with the existence of a dense dust diskwhich intercepts most of the stellar light at its inner edge(∼ 180 au), the material beyond is colder because of theshadow and presents a steep temperature profile. The COmolecules are trapped on grains in the mid-plane becausetheir temperature is below the CO freeze-out point (17 K).CO gas is only present in the heated upper layers of thedisk.

Finally, both the CO J=2-1 and J=6-5 maps (Fig.5) showa very puzzling unresolved hot spot located at the ringouter edge (∼ 250 au) at a position angle of ∼ 120o (northto east). This emission may originate from the progenitorof a sub-stellar object similar to the planetary-mass com-panion imaged around a low-mass binary star by Delormeet al (2013). Such a companion would naturally explainthe confinement of 80% of the circumbinary mass in thenarrow ring of 80 au width. We do not detect a gap atthe interface between the ring and the outer disk , butthe existing 13CO data shows at this radius (∼ 260 au) aring/outer disk density contrast of the order of ∼25 whichcan be attributed to an unresolved gap.

Our results demonstrate at least two reasons why the GGTau system is interesting. It is a fundamental object to

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Figure 5: Left panel: integrated area of CO J=6-5 and 0.5mm dust emission in black contours observed with ALMA(Dutrey et al 2014). The beam size is about 0.25” or 35 au. Middle panel: the new triple stellar system (Di Folco etal 2014). Right panel: same as left panel but for the CO J=2-1 line and 1.3mm dust emissions observed with PdBI.Copyright: Nature/ALMA/ESO/IRAM/CNRS/Universite de Bordeaux.

understand how planets can form, survive and migratein a multiple low-mass stellar environment. Also, thanksto its brightness, size, and fortuitous orientation, it is aunique laboratory to investigate many chemical, physicaland dynamical processes widely associated to planet for-mation which cannot be easily investigated in smaller andfainter disks orbiting single TTauri stars. Our next stepsinclude a full characterization of the gas and dust both inthe outer disk and ring and in the cavity.

References:

Artymowicz, P., et al. 1991, ApJ, 370, L35Artymowicz, P. and Lubow, S., 1996, ApJ, 467, L77Bate, M., Bonnell, I., 1997, MNRAS, 285, 33Beck, T., et al. 2012, ApJ, 557, L72Beckwith S.V.W., et al. 1990, AJ, 99, 924Delorme, P., et al. 2013, A&A, 553, L5Di Folco, E., et al. 2014, A&A, 565, L2Dutrey A., et al. 1994, A&A, 286, 149Dutrey, A., et al. 2014, Nat., 514, 600Guilloteau, S., et al. 1999, A&A, 248, 570Guilloteau, S., Dutrey, A., 2001, IAU Symp.200, 229Kawabe, R., et al. 1993, ApJ, 404, L63Koerner, D. W., et al. 1993, ApJ, 408, L93Krist, J. E. et al. 2005, AJ, 130, 2778Leinert Ch., et al. 1991, A&A, 250, 407Pietu, V., et al. 2011, A&A, 528, 81Roddier C., et al. 1996, ApJ, 463, 326Simon, M. and Guilloteau, S., 1992, ApJ, 397, L47Skrutskie, M. F. et al. 1993, ApJ, 409, 422White, R.J. et al. 1999, ApJ, 520, 811

10

Perspective

The Many Facets of YoungStar VariabilityAnn Marie Cody

1 Historical background

Photometric variability is one of the defining characteris-tics of young, low-mass stars in the 1–10 Myr range. Itsstudy dates back to the mid-1800s, when W. C. Bond iden-tified the first variable star in the Orion Nebula, AF Ori(see Herbig 1982). Further variables were picked up on theHarvard plates by H. S. Leavitt, and published in Picker-ing & Leavitt (1904). Follow-up studies identified addi-tional stars exhibiting brightness changes of up to threemagnitudes and associated with molecular clouds. Withprototype T Tauri, these so-called “nebular variables” dis-played irregular light curves unlike any other class of vari-able; examples are shown in Figure 1. They had brightemission in hydrogen and calcium II, and these lines werealso noted to fluctuate with time (Joy 1945). Membersof the new class displayed ultraviolet excesses – initiallyinterpreted as an indicator of a deep chromosphere. Onlya decade later did it become clear that these were pre-main sequence stars (Ambartsumian 1954, Herbig 1962)surrounded by accretion disks (Bertout et al. 1988). Aninfrared excess revealed the presence of warm circumstel-lar dust (e.g., Strom et al. 1972). These objects repre-sented the end state of star formation, with remaining gasaccreting onto the central star.

Photometric characterization of the pre-main sequence TTauri stars and their spectral energy distributions spurrednumerous monitoring campaigns in the optical and even-tually the near-infrared. Both classical (i.e., accreting) TTauri stars and their weak-lined counterparts (“WTTSs”)were subjected to intensive time series monitoring begin-

ning in the 1980s (e.g., Rydgren & Vrba 1983, Herbst et al.1983, Rydgren et al. 1984). Periodic variability predom-inated among the WTTS (Herbst & Koret 1988 and ref-erences therein), whereas the cause of brightness modula-tion in the classical T Tauri stars (“CTTSs”) was the sub-ject of speculation. For example, Rydgren & Vrba (1983)mentioned variable obscuration by dust clouds passingover the stellar disk but favored a model involving hotplages on the stellar surface. Appenzeller & Dearborn(1984) posited that changing surface magnetic fields wereinvolved in the brightness changes via modulation of activeregions. Bertout et al. (1988) instead invoked hot spotscaused by the infall of accretion material.

The pace of variability monitoring picked up further in the1990s, with in-depth studies of starspot properties and ro-tation rates (Bouvier et al. 1995), simultaneous photomet-ric and spectroscopic campaigns (e.g., Vrba et al. 1993),high resolution spectroscopic monitoring (e.g., Johns &Basri 1995). Bouvier et al. (1999) reported eclipses by cir-cumstellar material around AA Tau. Other groups under-took near-infrared monitoring to probe cooler phenomena(e.g., Horrobin et al. 1997, Hodapp 1999, Skrutskie et al.1996, Carpenter et al. 2001). Suggestions as to the causeof variability included changes in the structure of accret-ing material at the disk or stellar surface (Kenyon et al.1994, Simon et al. 1990), variations in geometry, opacity,or temperature of circumstellar gas and dust, or varyinglevels of extinction by surrounding material (e.g., Schmelz1984).

To aid in variability classification efforts, Herbst et al.(1994) assembled a comprehensive catalog of the UBVRIbehavior of 80 T Tauri stars. This study was amongthe first to highlight multiple distinct variability mech-anisms in T Tauri stars: periodic behavior due to persis-tent hot and cool spots, irregular brightness changes dueto variable accretion, as well as month- to year-long fad-ing events attributed to circumstellar obscuration. Thislatter phenomenon was seen only in the early type stars,with UX Ori as their prototype. Prior to this work, manyauthors attempted to attribute CTTS variability to a sin-gle cause, only to find inconsistent results. The Herbst etal. (1994) catalog formed the basis for our modern frame-work of optical variability in young stellar objects (YSOs),providing a taste of the data deluge that was to come.

2 Cool spots, hot spots, and stellarrotation

Despite reports by Herbst et al. (1994) and Bouvier et al.(1999) of fading events suggestive of circumstellar obscu-ration, attention to young star variability remained largelyon starspots as the primary mechanism. In individual

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Figure 1: Young stars in the 1–10 Myr range were discov-ered to be variable in the mid-1800s. Pictured here aresome of the early light curves– in this case for target RWAur (as published by Joy 1945). Initial monitoring didnot provide enough data points to determine light curvemorphology, but it did reveal that these objects could varywith amplitudes up to 3 magnitudes on timescales of min-utes (e.g., flares) to years (e.g., outbursting events).

cases, multi-band photometry revealed whether cool or hotspots on the stellar photosphere was more consistent withperiodic behavior in light curves. Hot spots were a natu-ral consequence of the magnetic accretion flow model putforth by Konigl in 1991. In contrast to the earlier bound-ary layer model (Lynden-Bell & Pringle 1974), flow alongmagnetic field lines from the inner disk to the stellar sur-face explained both spectroscopic evidence of free-fallingmaterial (Edwards et al. 1994, Hartmann et al. 1994) andthe slow rotation rates of T Tauri stars, which required abraking mechanism. It also naturally produced hot spotswhere shocked gas encountered the star at its magneticpoles.

Given this magnetospheric accretion model, a key ques-tion has been whether magnetic fields lock young starsto their disks, transferring angular momentum outwardand thereby preventing stellar spin-up until the disk dis-perses (e.g., Shu et al. 1994). Initial studies (e.g., Bouvieret al. 1993, 1995) reported that photometric rotation rateswere systematically different betweenWTTSs and CTTSs.With the advent of wide-field CCD detectors and extensivecharacterization of star cluster members, further opportu-nities to test this idea arose. Many star formation regionshave now been monitored photometrically, inluding theOrion Nebula Cluster (e.g., Stassun et al. 1999, Rebull2001, Rebull et al. 2006, Rodriguez-Ledesma et al. 2010),Chamaeleon I (Joergens et al. 2001), IC 348 (e.g., Cohen etal. 2003, Littlefair et al. 2005, Cieza & Baliber 2006), NGC2264 (e.g., Makidon et al. 2004, Lamm et al. 2004, Cieza& Baliber 2006), σ Orionis (e.g., Scholz & Eisloffel 2004,Cody & Hillenbrand 2010), and Cepheus OB3 (Littlefair

et al. 2010). Attribution of periodic light curve signaturesto spot modulation enables derivation of photometric rota-tion periods. Investigation of the disk locking question hasproduced conflicting results, with some authors finding noconnection between rotation period and disk or accretionindicators (e.g., Stassun et al. 1999, Makidon et al. 2004,Littlefair et al. 2005), and others detecting a correlationbetween rotation and either Hα equivalent width (a proxyfor accretion) or (near-)infrared excess (e.g., Herbst et al.2002, Rebull et al. 2006, Rodriguez-Ledesma et al. 2010).Complications in the testing of disk locking theory havearisen because there appears to be a mass dependence torotation rates (e.g., Littlefair et al. 2005). In addition, thetime dependent near-infrared excess is an imperfect indi-cator of disk presence, and does not have a perfect cor-respondence with accretion indicators such as Hα, whichmay fluctuate with time. It can also be argued that rota-tion rate measurements are biased by the fact that rapidlyaccreting objects might only display irregular variability.

While for many analyses, high-amplitude aperiodic pho-tometric behavior was considered “contamination” for ro-tation rate samples, several studies did highlight it as aninteresting phenomenon in its own right. Both Cohen etal. (2004) and Littlefair et al. (2005) identified stars inIC 348 with irregular light curves, including some withfading events of up to one magnitude, reminiscent of theUX Ori class. They attributed these events to occul-tations by dust clouds along the line of sight. Scholz& Eisloffel (2004, 2005) as well detected high-amplitude,quasi-periodic variability among a small fraction of theirσ Orionis and ǫ Orionis monitoring samples, suggestingthat hot spots formed in the presence of unsteady accre-tion flow were responsible for this light curve behavior.In Cody & Hillenbrand (2010), we found that ∼30% ofall monitored low-mass I-band variables in the σ Orio-nis cluster displayed erratic aperiodic behavior, of which∼20% involved prominent fading events on hour-to-daytimescales. This work showed that high precision, highcadence photometric monitoring has the capability to re-veal potentially important morphological information inlight curves.

Additional insights into aperiodic variability came whenphotometric monitoring expanded from the optical to near-infrared. Carpenter et al. (2001, 2002), Eiroa et al. (2002),Alves de Oliveira & Casali (2008), Scholz et al. (2009),and Parks et al. (2013) were all able to study the colorvariability in these bands, finding that some objects be-came redder when fainter, while others became bluer. Thewide variety of color behavior among T Tauri stars in thenear-IR supported the hypothesis that multiple types ofvariability are present among disk-bearing objects, includ-ing accretion hot spots, circumstellar extinction changes,and structural changes in the inner disk.

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3 The space photometry era

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While ground-based monitoring of T Tauri stars has pro-vided a wealth of information on the nature of their vari-ations, such efforts have been hampered by sparse timesampling and sometimes low photometric precision. Withthe dawn of the twenty-first century came fantastic oppor-tunities to employ space telescopes in the study of youngstar variability. Although not originally intended for themonitoring of YSOs, the MOST (Microvariability and Os-cillations of Stars; Walker et al. 2003) satellite launched in2003 provided some of the first high cadence (<1 minute),high precision (few millimagnitudes), long time baseline(several weeks) optical light curves of T Tauri and Her-big Ae/Be stars (Rucinski et al. 2008, 2010, Siwak et al.2011a,b, Cody & Hillenbrand 2013, Siwak et al. 2014).These observations unveiled a rich variety of variabilitybehavior, from stochastic “red” noise and transient period-icities to sharp flux dips. For periodic objects, space-basedmonitoring revealed subtle changes in amplitude from cy-cle to cycle, as well as sudden shifts from one variabilitytype to another (see Figure 2). In the case of the T Tauristar SU Aurigae, periodic light curve behavior appeared ata timescale inconsistent with the rotation period predictedfrom the vsinii value, suggesting that interpretation of allperiodicities as starspots may need to be reconsidered. Inaddition to exploring accretion and disk-related variabil-ity in young stars, MOST has been at the forefront of theidentification of δ Scuti pulsation in pre-main sequenceobjects (e.g., Zwintz et al. 2013).

The improved view of young stars provided by MOSTwas further enhanced by the CoRoT (COnvection, RO-tation and planetary Transits; Baglin et al. 2006) mis-sion, launched in 2006. While MOST could only performprecision photometry on objects down to ∼12th magni-tude (thereby limiting the number of young star targets),CoRoT’s limit of R ∼ 18 enabled the first space-basedmonitoring of an entire young star cluster: NGC 2264.This ∼1–5 Myr region was the only one that fell within

one of two CoRoT “eyes”– its fields of view on the sky. Thefirst CoRoT short run (“SRa01”) took place for 23 daysstraight in March 2008, returning hundreds of incrediblyhigh quality (precision <5 millimagnitudes) light curveson both WTTSs and CTTSs. The results of this run arereported in Alencar et al. (2010), Affer et al. (2013), andFonseca et al. (2014). The Alencar et al. study revealed apopulation of low-mass stars exhibiting periodic flux dipssimilar to that seen in AA Tau by Bouvier et al. (2003).Altogether, 30-40% of stars with inner dusty disks (as ob-served with Spitzer) displayed AA Tau-like behavior. Thevariations were consistent with inner disk warps locatednear the corotation radius, with structural changes occur-ing on timescales of a few rotation periods. This work wasthe first to show that the UX Ori phenomenon extendedto lower mass and shorter timescales; AA Tau periods oc-cupy the 3–10 day range. It also confirmed that thereare at least three distinct types of light curve morphologyamong T Tauri stars: periodic spotted, AA Tau-like, and“irregular” (aperiodic and stochastic).

The second study on CoRoT SRa01 light curves of NGC2264 (Affer et al. 2013) focused on the sample of peri-odic stars, deriving rotation rates and comparing thesefor WTTSs and CTTSs. Although rotation rates hadbeen reported previously for NGC 2264 members (Lammet al. 2004), these were subjected to aliasing in ground-based datasets. CoRoT provided high accuracy periodsfor nearly 200 T Tauri stars, and this dataset was com-bined with disk indicators from Spitzer and accretion in-dicators from spectroscopy. The end result was that asignificant difference in rotation properties was detectedbetween accreting and non-accreting stars, thereby bol-stering the disk locking theory (Affer et al. 2013).

Ultimately, multiwavelength variability information is re-quired to fully unravel the origins of young star variabil-ity; this was perhaps the one feature lacking in the CoRoTmonitoring studies. YSOs and their disks are now knownto vary at a wide range of wavelengths, from X-ray to mid-infrared. With the onset of the Spitzer Space Telescope’sWarm Mission, it became feasible to monitor young starclusters in the mid-infrared for up to 40 days at a time. Yetuntil the first observations of IC 1396 (Morales-Calderonet al. 2009) and IC 348 (Muzerolle et al. 2009) were ob-tained, few attempts at mid-infrared monitoring had beenmade, and the results were not definitive (see Rebull 2011for a summary). Spitzer observations immediately revealedubiquitous brightness variations at the 10–50% level. Cap-italizing on this finding, the Young Stellar Object Vari-ability (YSOVAR) project acquired some 790 hours to ob-serve several thousand YSOs in 12 different star formingregions (Rebull et al. 2014). With data in both the 3.6 and4.5 µm bands of the Infrared Array Camera (IRAC), mul-ticolor light curves were available for many of the targets.

13

As reported in Gunther et al. (2014), Wolk et al. (2015),and Poppenhaeger et al. (2015), the majority of YSOs dis-play reddening trends as they become fainter. However,a small number become bluer as they dim. Most of thevariability is consistent with reddening by dust extinction;alternatively, some of it may also be explained by struc-tural rearrangements of the inner disk wall (e.g., Flaherty& Muzerolle 2010). Development of a light curve classifi-cation scheme is currently underway (Rebull et al. 2015).

What is not clear is how the flux variations at very dif-ferent wavelengths are connected. In 2011, we set outto investigate this question by launching the CoordinatedSynoptic Investigation of NGC 2264 (CSI 2264; Cody etal. 2013, 2014), a simultaneous effort with a dozen groundand space-based telescopes in the X-ray, optical, near-infrared, and mid-infrared. Starting in December 2011,the CSI 2264 campaign performed monitoring of severalthousand YSOs in an approximately 1×1 degree field nearthe center of NGC 2264. The focus of the campaignwere observations by the Warm Spitzer Space Telescope(Werner et al. 2004), in tandem with the CoRoT satel-lite. For much of December 2011, CoRoT and Spitzer werejoined by the MOST telescope, along with the Chandra X-ray Observatory and 12 ground-based telescopes, includ-ing the Very Large Telescope and its FLAMES spectro-graph. The unprecedented aspects of CSI 2264 are its highprecision (1% or better for typical photometric points),high cadence (2 hours per IRAC datapoint and <10 min-utes per CoRoT point), and long time baseline (30 days forSpitzer and 40 days for CoRoT). The combination of pre-cision and time sampling has opened a new view of lightcurve morphologies, which is highlighted in the following.

The exquisite data quality of the CSI 2264 campaign en-abled classification of light curves on a finer level than pre-viously carried out. In Cody et al. (2014), we followed anapproach of visually examining and categorizing the lightcurves, and subsequently confirming our decisions withstatistics. A total of eight different morphologies emergedfrom the set of optical and infrared light curves. Not sur-prisingly, one of the most prominent sets of morphologiesinvolves quasi-periodic fading events that become redderas they grow fainter. Though these are the same as theAlencar et al. (2010) AA Tau class, we refer to these as“quasi-periodic dippers.” A similar morphology, which wecall “aperiodic dippers,” involves fading events with no de-tectable periodicity. Also displaying fading behavior butin a strictly periodic manner are the eclipsing binaries ofNGC 2264. The most intriguing of these exhibits aperiodicout-of-eclipse variability indicative of a circumbinary disk(Gillen et al. 2014, 2015). While the dippers and eclipsingbinaries display fading, the opposite behavior appears instars that we refer to as “bursters”– objects with frequentepisodes of rapidly increasing flux. This behavior is asso-

ciated with indicators of strong accretion, such as ultravi-olet excess; it is investigated in Stauffer et al. (2014). Thebursters and dippers exhibit what we refer to as asym-metric flux behavior; these light curves appear differentwhen flipped upside-down. Another set of light curvesdoes not have this distinction; we call those with no de-tectable periodicity “stochastic.” For light curves that doshow periodicity but are not dippers because their fluxesare symmetric about the time axis, we have chosen thelabel “quasi-periodic symmetric.” The term “periodic” isreserved for objects with the most stable periodicities; thisbehavior is usually attributed to rotational modulation ofcool spots on the stellar surface. A schematic displayingour classification system and the fractions of stars foundin each category is shown in Figure 3.

Figure 3: Schematic of different types of light curve mor-phologies found among young disk-bearing stars in theNGC 2264 cluster, in the optical (“opt”) and infrared(“IR”). Morphologies are categorized using two metrics:asymmetry (i.e., whether a light curve looks similar whenflipped upside-down) and stochasticity (degree of period-icity, or lack thereof). From Cody et al. (2014).

Overall, we have evaluated a set of 162 disk-bearing YSOlight curves with both CoRoT and Spitzer data. Exam-ples of these classes are shown in the optical in Figure 4,and in the infrared in Figure 5. Since the publication ofthese variability classes, one additional type of light curvebehavior has been identified in the CoRoT and Spitzerdataset. These are narrow (<1 day), periodic flux dipswith variable depth. Stauffer et al. (2015) explore the na-ture of these flux dips, concluding that they are consistentwith dust structures in or near the inner disk wall.

The CSI 2264 dataset has exposed just how diverse andmultifacted YSO variability can be. From the early classi-fications of periodic, irregular, and UX Ori stars, our mor-phological database has now expanded to include many

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Figure 4: CoRoT space telescope data has recently enabled a high precision, high cadence view of T Tauri stars,revealing eight different classes of optical variability, as depicted here (adapted from Cody et al. 2014).

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Figure 5: The diversity of infrared light curves from Spitzer infrared monitoring of the NGC 2264 cluster. Black circlesare 3.6 µm datapoints, and grey circles are 4.5 µm points; the latter have had their mean shifted so as to overlapthe 3.6 µm points. Similar to the optical behavior above, these time series show distinct morphological patterns thatcomprise eight different categories.

different types of light curve behavior. How do these newobservational insights build on our earlier knowledge ofvariability mechanisms? It is crucial to keep in mind thatastrophysical variability generally can come not just from

changes in the luminosity, but also from changes in theemission’s beaming, from changes in the extinction, andat infrared wavelengths also from changes in the arrange-ment of the reprocessing dust and gas. We now know that

15

all four play roles in young stars’ variability: luminositycontributed by accretion varies as a function of flow rate,spots modulate the light curve in light-house type fash-ion, disk material blocks the star-light in a time-dependentmanner, and the disk structure itself changes, thereby af-fecting (near-)infrared emission. Thanks to high qualityspace-based monitoring, we now have definitive examplesof light curves with each of these forms of variability. Theaccretion burst objects highlighted by Stauffer et al. (2014)are cases in which variability is dominated by unsteady gasinflow. The sinusoidal light curves predominating amongWTTSs are produced by cool spots. AA-Tau or quasi-periodic dipper behavior is well modeled as dust obscu-ration by a warped disk (Alencar et al. 2010, McGinniset al. 2015). And finally, the ∼10% of disk-bearing starsin which there is little optical variation in the face of sig-nificant (10-30%) mid-infrared brightness fluctuations arelikely cases of inner disk structural changes (Cody et al.2014).

The challenge now is to determine how the remainingclasses of variability (e.g., purely stochastic, aperiodic dip-ping, and quasi-periodic light curves) relate to these phys-ical mechanisms. Are they simply a combination of sev-eral variability types in a single light curve? Or are thereadditional sources of variation, such as hot spots? Fur-ther investigation of color changes in the optical to near-infrared, as well as time series spectroscopy, can illuminatethese questions. For researchers interested in exploring theCoRoT and Spitzer light curves on their own, these datawere recently released to the public and are now availablethrough the Infrared Science Archive at:http://irsa.ipac.caltech.edu/data/SPITZER/CSI2264/

References:

Affer, L. et al. 2013, MNRAS, 430, 1433Alencar, S. et al. 2010, A&A, 519, 88Alves de Oliveira, C. & Casali, M. 2008, A&A, 485, 155Ambartsumian, V. A., 1954, Mem. Soc. R. Sci. Liege, 1, 293Appenzeller, I. & Dearborn, D. S. P. 1984, ApJ, 278, 689Baglin, A. et al. 2006, Proc. The CoRoT Mission Pre-Launch Status-Stellar Seismology and Planet Finding (ESA Special Publication),Vol. 1306, ed. M. Fridlund, A. Baglin, J. Lochard, & L. Conroy(Noordwijk: ESA), 33Bertout, C., Basri, G. & Bouvier, J. 1988, ApJ, 330, 350Bouvier, J. et al. 1993, A&A, 272, 176Bouvier, J. et al. 1995, A&A, 299, 89Bouvier, J. et al. 1999, 349, 619Bouvier, J. et al. 2003, A&A, 409, 169Carpenter, J. M., Hillenbrand, L. A. & Skrutskie, M. F. 2001, 121,3160Carpenter, J. M. et al. 2002, AJ, 124, 1001Cieza, L. & Baliber, N. 2006, ApJ, 649, 862Cieza, L. & Baliber, N. 2007, ApJ, 671, 605Cody, A. M. & Hillenbrand, L. A. 2010, ApJS, 191, 389Cody, A. M. & Hillenbrand, L. A. 2013, AJ, 145, 79Cody, A. M. et al. 2013, AN, 334, 63Cody, A. M. et al. 2014, AJ, 147, 82Cohen, R. E., Herbst, W. & Williams, E. C. 2004, AJ, 127, 1602Edwards, S. et al. 1994, AJ, 108, 1056Eiroa, C. et al. 2002, A&A, 384, 1038

Flaherty, K. M. & Muzerolle, J. 2010, ApJ, 719, 1733Fonseca, N. et al. 2014, A&A, 567, 39Gillen, E. et al. 2014, A&A, 562, 50Gillen, E. et al. 2015, in prep.Gunther, H. M. et al. 2014, AJ, 148, 122Hartmann, L., Hewett, R. & Calvet, N. 1994, ApJ, 426, 669Herbig, G. H. 1962, AdA&A, 1, 47Herbig, G. H. 1982, Ann. NY Acad. Sci., 395, 64Herbst, W., Holtzman, J. A. & Klasky, R. S. 1983, AJ, 88, 1648Herbst, W. & Koret, D. L. 1988, AJ, 96, 1949Herbst, W. et al. 1994, AJ, 108, 1906Herbst, W. et al. 2002, A&A, 396, 513Hodapp, K. W. 1999, AJ, 118, 1338Horrobin, M. J., Casali, M. M. & Eiroa, C. 1997, A&A, 320, 41Joergens, V. et al. 2003, AppJ, 594, 971Johns, C. M. & Basri, G. 1995, AJ, 109, 2800Joy, A. H. 1945, ApJ, 102, 168Kenyon, S. et al. 1994, AJ, 107, 2153Konigl, A. 1991, ApJ, 370, 39Lamm, M. H. et al. 2004, A&A, 417, 557Littlefair, S. P. et al. 2005, MNRAS, 358, 341Littlefair, S. P. et al. 2010, MNRAS, 403, 545Lynden-Bell, D. & Pringle, J. E. 1974, MNRAS, 168, 603Makidon, R. B. et al. 2004, AJ, 127, 2228McGinnis, P., Alencar, S. H. P. et al. 2015, submittedMorales-Calderon, M. et al. 2009, ApJ, 702, 1507Muzerolle, J. et al. 2009, ApJL, 704, 15Parks, R. et al. 2013, ApJS, 211, 3Pickering, E. C. & Leavitt, H. S. 1904, ApJ, 19, 289Poppenhaeger, K. et al. 2015, in prep.Rebull, L. 2001, AJ, 121, 1676Rebull, L. et al. 2006, ApJ, 646, 297Rebull, L. 2011, 16th Cambridge Workshop on Cool Stars, StellarSystems, and the Sun (ASP Conf. Ser. 448), ed. C. Johns-Krull, M.K. Browning, & A. A. West (San Francisco, CA: ASP), 5Rebull, L. et al. 2014, AJ, 148, 92Rebull, L. et al. 2015, in prep.Rodrıguez-Ledesma, M., Mundt, R. & Eisloffel, J. 2010, A&A, 515,13Rucinski, S. M. et al. 2008, MNRAS, 391, 1913Rucinski, S. M. et al. 2010, A&A, 522, 113Rydgren et al. 1984, AJ, 89, 1015Rydgren & Vrba 1983, ApJ, 267, 191Sandage, A. 1958, RA, 5, 149Scholz, A. & Eisloffel, J. 2004, A&A, 419, 249Scholz, A. & Eisloffel, J. 2005, A&A, 429, 1007Scholz, A. et al. 2009, MNRAS, 398, 873Shu, F. et al. 1994, ApJ, 429, 781Simon, T. et al. 1990, AJ, 100, 1957Siwak, M. et al. 2011a, MNRAS, 410, 2725Siwak, M. et al. 2011b, MNRAS, 415, 1119Siwak M. et al. 2014, MNRAS, 444, 327Skrutski, M. F. et al. 1996, AJ, 112, 2168Schmelz, J. T. 1984, AJ, 89, 108Stassun, K. et al. 1999, AJ, 117, 2941Stauffer, J. et al. 2014, AJ, 147, 83Stauffer, J. et al. 2015, AJ, submittedStrom, S. E. et al. 1972, ApJ, 171, 267Vrba, F. J. et al. 1993, AJ, 106, 1608Walker, G. et al. 2003, PASP, 115, 1023Wolk, S. et al. 2015, in prep.Zwintz, K. et al. 2013, A&A, 552, 68

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Abstracts of recently accepted papers

On the Stability of Extrasolar Planetary Systems and other Closely Orbiting Pairs

Fred C. Adams1,2 and Anthony M. Bloch3

1 Physics Department, University of Michigan, Ann Arbor, MI 48109, USA2 Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA3 Mathematics Department, University of Michigan, Ann Arbor, MI 48109, USA

E-mail contact: fca at umich.edu

This paper considers the stability of tidal equilibria for planetary systems in which stellar rotation provides a significantcontribution to the angular momentum budget. We begin by applying classic stability considerations for two bodiesto planetary systems — where one mass is much smaller than the other. The application of these stability criteria to asubset of the Kepler sample indicates that the majority of the systems are not in a stable equilibrium state. Motivatedby this finding, we generalize the stability calculation to include the quadrupole moment for the host star. In general,a stable equilibrium requires that the total system angular momentum exceeds a minimum value (denoted here asLX) and that the orbital angular momentum of the planet exceeds a minimum fraction of the total. Most, but notall, of the observed planetary systems in the sample have enough total angular momentum to allow an equilibriumstate. Even with the generalizations of this paper, however, most systems have too little orbital angular momentum(relative to the total) and are not in an equilibrium configuration. Finally, we consider the time evolution of theseplanetary systems; the results constrain the tidal quality factor of the stars and suggest that 106<∼Q∗

<∼ 107.

Accepted by MNRAS

http://arxiv.org/pdf/1411.2859

Evaporation of grain-surface species by shock waves in protoplanetary disk

Takuhiro Aota1,2, Tsuyoshi Inoue3 and Yuri Aikawa1

1 Dept. of Earth and Planetary Sciences, Kobe University, Japan2 Fuji Soft, Japan3 National Astronomical Observatory of Japan

E-mail contact: aikawa at kobe-u.ac.jp

Recent ALMA (Atacama Large Millimeter/submillimeter Array) observations of young protostellar objects detectedwarm SO emission, which could be associated with a forming protostellar disk. In order to investigate if such warmgas can be produced by accretion shock onto the forming disk, we calculate the sputtering and thermal desorption ofvarious grain surface species in one dimensional shock waves. We find that thermal desorption is much more efficientthan the sputtering in the post-shock region. While H2O can be thermally desorbed, if the accretion velocity is largerthan 8 km s−1 with the pre-shock gas number density of 109 cm−3, SO is desorbed, if the accretion velocity >

∼ 2 kms−1 and >

∼ 4km s−1, with the pre-shock density of 109 cm−3 and 108 cm−3, respectively. We also find that the columndensity of hydrogen nuclei in warm post-shock gas is Nwarm ∼ 1021 cm−2.

Accepted by ApJ

http://arxiv.org/pdf/1412.1178

Depletion of molecular gas by an accretion outburst in a protoplanetary disk

A. Banzatti1, K. M. Pontoppidan1, S. Bruderer2, J. Muzerolle1 and M. R. Meyer3

1 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA2 Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstr. 1, D-85748 Garching bei Munchen, Germany

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3 ETH Zurich, Institut fur Astronomie, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland

E-mail contact: banzatti at stsci.edu

We investigate new and archival 3–5µm high resolution (∼ 3 km s−1) spectroscopy of molecular gas in the inner diskof the young solar-mass star EX Lupi, taken during and after the strong accretion outburst of 2008. The data wereobtained using the CRIRES spectrometer at the ESO Very Large Telescope in 2008 and 2014. In 2008, emissionlines from CO, H2O, and OH were detected with broad profiles tracing gas near and within the corotation radius(0.02–0.3AU). In 2014, the spectra display marked differences. The CO lines, while still detected, are much weaker,and the H2O and OH lines have disappeared altogether. At 3µm a veiled stellar photospheric spectrum is observed.Our analysis finds that the molecular gas mass in the inner disk has decreased by an order of magnitude since theoutburst, matching a similar decrease in the accretion rate onto the star. We discuss these findings in the context ofa rapid depletion of material accumulated beyond the disk corotation radius during quiescent periods, as proposed bymodels of episodic accretion in EXor type young stars.

Accepted by ApJ Letters

http://arxiv.org/pdf/1412.1824

The structure of protoplanetary discs around evolving young stars

Bertram Bitsch1, Anders Johansen1, Michiel Lambrechts1, and Alessandro Morbidelli2

1 Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, 22100 Lund, Sweden2 University Nice-Sophia Antipolis, CNRS, Observatoire de la Cote d’Azur,Laboratoire LAGRANGE, CS 34229, 06304NICE cedex 4, FRANCE

E-mail contact: bert at astro.lu.se

The formation of planets with gaseous envelopes takes place in protoplanetary accretion discs on time-scales of severalmillions of years. Small dust particles stick to each other to form pebbles, pebbles concentrate in the turbulent flow toform planetesimals and planetary embryos and grow to planets, which undergo substantial radial migration. All theseprocesses are influenced by the underlying structure of the protoplanetary disc, specifically the profiles of temperature,gas scale height and density. The commonly used disc structure of the Minimum Mass Solar Nebular (MMSN) is asimple power law in all these quantities. However, protoplanetary disc models with both viscous and stellar heatingshow several bumps and dips in temperature, scale height and density caused by transitions in opacity, which aremissing in the MMSN model. These play an important role in the formation of planets, as they can act as sweetspots for the formation of planetesimals via the streaming instability and affect the direction and magnitude of type-I-migration. We present 2D simulations of accretion discs that feature radiative cooling, viscous and stellar heating,and are linked to the observed evolutionary stages of protoplanetary discs and their host stars. These models allow usto identify preferred planetesimal and planet formation regions in the protoplanetary disc as a function of the disc’smetallicity, accretion rate and lifetime. We derive simple fitting formulae that feature all structural characteristics ofprotoplanetary discs during the evolution of several Myr. These fits are straightforward to apply for modelling anygrowth stage of planets where detailed knowledge of the underlying disc structure is required.

Accepted by A&A

http://arxiv.org/pdf/1411.3255

Reassessing the formation of the Inner Oort cloud in an embedded star cluster II:Probing the inner edge

R. Brasser1,2 and M.E. Schwamb1

1 Institute for Astronomy and Astrophysics, Academia Sinica; 11F AS/NTU, National Taiwan University, 1 RooseveltRd., Sec. 4, Taipei 10617, Taiwan2 Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan

E-mail contact: brasser astro at yahoo.com

The detached object Sedna is likely at the inner edge of the Oort cloud, more precisely the inner Oort cloud (IOC).Until recently it was the sole member of this population. The recent discovery of the detached object 2012 VP113

18

has confirmed that there should be more objects in this region. Three additional IOC candidates with orbits muchcloser to Neptune have been proposed in the past decade since Sedna’s discovery: 2000 CR105, 2004 VN112 and 2010GB174. Sedna and 2012 VP113 have perhelia near 80 AU and semi-major axes over 250 AU. The latter three haveperihelia between 44 AU and 50 AU and semi-major axes between 200 AU and 400 AU. Here we determine whether thelatter three objects belong to the IOC or are from the Kuiper Belt’s Extended Scattered Disc (ESD) using numericalsimulations. We assume that the IOC was formed when the Sun was in its birth cluster. We analyse the evolutionof the IOC and the Scattered Disc (SD) during an episode of late giant planet migration. We examine the impact ofgiant planet migration in the context of four and five planets. We report that the detached objects 2004 VN112 and2010 GB174 are likely members of the IOC that were placed there while the Sun was in its birth cluster or duringan episode of Solar migration in the Galaxy. The origin of 2000 CR105 is ambiguous but it is likely it belongs tothe ESD. Based on our simulations we find that the maximum perihelion distance of SD objects is 41 AU when thesemi-major axis is higher than 250 AU. Objects closer in are subject to mean motion resonances with Neptune thatmay raise their perihelia. The five planet model yields the same outcome. We impose a conservative limit and statethat all objects with perihelion distance q > 45 AU and semi-major axis a > 250 AU belong to the inner Oort cloud.

Accepted by MNRAS

http://arxiv.org/pdf/1411.1184

H2D+ observations give an age of at least one million years for a cloud core forming

Sun-like stars

Sandra Brunken1, Olli Sipila2,3, Edward T. Chambers1, Jorma Harju2, Paola Caselli3,4, Oskar Asvany1,Cornelia E. Honingh1, Tomasz Kaminski5, Karl M. Menten5, Jurgen Stutzki1 and Stephan Schlemmer1

1 I. Physikalisches Institut, Universitat zu Koln, Zulpicher Strasse 77, 50937 Koln, Germany2 Department of Physics, PO Box 64, 00014 University of Helsinki, Finland3 Max-Planck Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85741 Garching bei Munchen, Germany4 School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK5 Max-Planck Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany

E-mail contact: bruenken at ph1.uni-koeln.de

The age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation anddifficult to measure. Some models predict rapid collapse (refs. 1, 2), whereas others predict timescales of more than onemillion years (ref. 3). One possible approach to determining the age is through chemical changes as cloud contractionoccurs, in particular through indirect measurements of the ratio of the two spin isomers (ortho/para) of molecularhydrogen, H2, which decreases monotonically with age (refs.4-6). This has been done for the dense cloud core L183,for which the deuterium fractionation of diazenylium (N2H

+) was used as a chemical clock to infer (ref. 7) that thecore has contracted rapidly (on a timescale of less than 700,000 years). Among astronomically observable molecules,the spin isomers of the deuterated trihydrogen cation, ortho-H2D

+ and para-H2D+, have the most direct chemical

connections to H2 (refs. 8-12) and their abundance ratio provides a chemical clock that is sensitive to greater cloudcore ages. So far this ratio has not been determined because para-H2D

+ is very difficult to observe. The detectionof its rotational ground-state line has only now become possible thanks to accurate measurements of its transitionfrequency in the laboratory (ref. 13), and recent progress in instrumentation technology (refs. 14, 15). Here we reportobservations of ortho- and para-H2D

+ emission and absorption, respectively, from the dense cloud core hosting IRAS16293-2422 A/B, a group of nascent solar-type stars (with ages of less than 100,000 years). Using the ortho/pararatio in conjunction with chemical models, we find that the dense core has been chemically processed for at least onemillion years. The apparent discrepancy with the earlier N2H

+ work (ref. 7) arises because that chemical clock turnsoff sooner than the H2D

+ clock, but both results imply that star-forming dense cores have ages of about one millionyears, rather than 100,000 years.

Accepted by Nature

http://dx.doi.org/10.1038/nature13924

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Recovery of the Candidate Protoplanet HD 100546 b with Gemini/NICI and Detectionof Additional (Planet-Induced?) Disk Structure at Small Separations

Thayne Currie1, Takayuki Muto2, Tomoyuki Kudo1, Mitsuhiko Honda3, Timothy D. Brandt4, CarolGrady5, Misato Fukagawa6, Adam Burrows7, Markus Janson8, Masayuki Kuzuhara9, Michael W.McElwain10, Katherine Follette11, Jun Hashimoto12, Thomas Henning13, Ryo Kandori14, NobuhikoKusakabe14, Jungmi Kwon15, Kyle Mede15, Jun-ichi Morino14, Jun Nishikawa14, Tae-Soo Pyo1, GeneSerabyn16, Takuya Suenaga14, Yasuhiro Takahashi14,15, John Wisniewsk12, Motohide Tamura14,15

1 NAOJ, Subaru Telescope, 650 N Aohoku Pl., Hilo, HI 96720, USA2 Kogashin University, Japan3 Kanagawa University, Japan4 Astrophysics Department, Institute for Advanced Study, Princeton, NJ, USA5 Eureka Scientific, 2452 Delmer, Suite 100, Oakland CA96002, USA6 Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan7 Department of Astrophysical Sciences, Princeton University, 7 Ivy Lane, Princeton, NJ, USA8 Stockholm University, Sweden9 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo152-8551, Japan10 Exoplanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center, Greenbelt, MD 20771,USA11 Department of Astronomy, Steward Observatory, University of Arizona12 H. L. Dodge Department of Physics & Astronomy, University of Oklahoma, 440 W Brooks St Norman, OK 73019,USA13 Max Planck Institute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany14 National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo, 181-8588, Japan15 Department of Astronomy, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan16 Jet Propulsion Laboratory, 4800 Oak Grove Drive, MS 183-900, Pasadena, CA 91109, USA

E-mail contact: currie at naoj.org

We report the first independent, second-epoch (re-)detection of a directly-imaged protoplanet candidate. Using L′

high-contrast imaging of HD 100546 taken with the Near-Infrared Coronagraph and Imager (NICI) on Gemini South,we recover ‘HD 100546 b’ with a position and brightness consistent with the original VLT/NaCo detection from Quanzet al, although data obtained after 2013 will be required to decisively demonstrate common proper motion. HD 100546b may be spatially resolved, up to ≈ 12–13 AU in diameter, and is embedded in a finger of thermal IR bright, polarizedemission extending inwards to at least 0.′′3. Standard hot-start models imply a mass of ≈ 15 MJ. But if HD 100546 bis newly formed or made visible by a circumplanetary disk, both of which are plausible, its mass is significantly lower(e.g. 1–7 MJ). Additionally, we discover a thermal IR-bright disk feature, possibly a spiral density wave, at roughlythe same angular separation as HD 100546 b but 90 degrees away. Our interpretation of this feature as a spiral arm isnot decisive, but modeling analyses using spiral density wave theory implies a wave launching point exterior to ≈ 0.′′45embedded within the visible disk structure: plausibly evidence for a second, hitherto unseen wide-separation planet.With one confirmed protoplanet candidate and evidence for 1–2 others, HD 100546 is an important evolutionaryprecursor to intermediate-mass stars with multiple super-jovian planets at moderate/wide separations like HR 8799.

Accepted by ApJL

http://arxiv.org/pdf/1411.0315

Sub-stellar Companions and Stellar Multiplicity in the Taurus Star-Forming Region

Sebastian Daemgen1, Mariangela Bonavita2, Ray Jayawardhana3, David Lafreniere4 and Markus Janson5

1 Dept. of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, Canada M5H 3H42 The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, U.K.3 Physics & Astronomy, York University, Toronto, Ontario L3T 3R1, Canada4 Department of Physics, University of Montreal, Montreal, QC, Canada5 Department of Astronomy, Stockholm University, Stockholm, Sweden

E-mail contact: daemgen at astro.utoronto.ca

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We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar com-panions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the mostmassive Taurus members at ∼3M⊙ and low-mass stars at ∼0.2M⊙. We detected 74 companion candidates, 34 ofthese reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-upobservations. Four candidate companions are likely unrelated field stars. Assuming physical association with their hoststar, estimated companion masses are as low as ∼2MJup. The inferred multiplicity frequency within our sensitivitylimits between ∼10–1500AU is 26.3+6.6

−4.9%. Applying a completeness correction, 62%±14% of all Taurus stars between

0.7 and 1.4M⊙ appear to be multiple. Higher order multiples were found in 1.8+4.2−1.5% of the cases, in agreement with

previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5–8.8% within our sensitivitylimits from the discovery of two likely bound and three other tentative very low-mass companions. This frequencyappears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution,suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we findevidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of∼2Myr and ∼20Myr, respectively.

Accepted by the Astrophysical Journal

http://arxiv.org/pdf/1411.7031

Testing Magnetic Field Models for the Class 0 Protostar L1527

J.A. Davidson1, Z-Y. Li2, C.L.H. Hull3,12, R.L. Plambeck3, W. Kwon4, R.M. Crutcher5, and L.W.Looney5, G. Novak6, N.L. Chapman6, B.C. Matthews7,8, I.W. Stephens9, J.J. Tobin10, and T.J. Jones11

1 University of Western Australia, School of Physics, 35 Stirling Hwy, Crawley, WA 6009, Australia2 University of Virginia, Astronomy Department, Charlottesville, VA 22904, USA3 University of California, Astronomy Department & Radio Astronomy Laboratory, Berkeley, CA 94720-3411, USA4 SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD, Groningen, The Netherlands5 University of Illinois, Department of Astronomy, 1002 West Green St, Urbana, IL 61801, USA6 Northwestern University, Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and theDepartment of Physics & Astronomy, 2145 Sheridan Road, Evanston, IL 60208, USA7 Herzberg Astronomy & Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC,V9E 2E7, Canada8 University of Victoria, Department of Physics & Astronomy, 3800 Finnerty Road, Victoria, BC, V8P 1A1, Canada9 Boston University, Institute for Astrophysical Research, Boston, MA 02215, USA10 National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA11 University of Minnesota, 116 Church St S.E., Minneapolis, MN, 55455 USA12 Harvard-Smithsonian Center for Astrophysics, 60 Garden St, MS 42, Cambridge, MA 02138, USA

E-mail contact: jackie.davidson at uwa.edu.au

For the Class 0 protostar, L1527, we compare 131 polarization vectors from SCUPOL/JCMT, SHARP/CSO andTADPOL/CARMA observations with the corresponding model polarization vectors of four ideal-MHD, non-turbulent,cloud core collapse models. These four models differ by their initial magnetic fields before collapse; two initially havealigned fields (strong and weak) and two initially have orthogonal fields (strong and weak) with respect to the rotationaxis of the L1527 core. Only the initial weak orthogonal field model produces the observed circumstellar disk withinL1527. This is a characteristic of nearly all ideal-MHD, non-turbulent, core collapse models. In this paper we testwhether this weak orthogonal model also has the best agreement between its magnetic field structure and that inferredfrom the polarimetry observations of L1527. We found that this is not the case; based on the polarimetry observationsthe most favored model of the four is the weak aligned model. However, this model does not produce a circumstellardisk, so our result implies that a non-turbulent, ideal-MHD global collapse model probably does not represent the corecollapse that has occurred in L1527. Our study also illustrates the importance of using polarization vectors coveringa large area of a cloud core to determine the initial magnetic field orientation before collapse; the inner core magneticfield structure can be highly altered by a collapse and so measurements from this region alone can give unreliableestimates of the initial field configuration before collapse.

Accepted by ApJ

http://arxiv.org/pdf/1411.4913

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A Young GMC Formed at the Interface of Two Colliding Supershells: ObservationsMeet Simulations

J.R. Dawson1,2, E. Ntormousi3, Y. Fukui4, T. Hayakawa4, and K. Fierlinger5,6

1 Department of Physics and Astronomy and MQ Research Centre in Astronomy, Astrophysics and Astrophotonics,Macquarie University, NSW 2109, Australia2 Australia Telescope National Facility, CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710,Australia3 Service dAstrophysique, CEA/DSM/IRFU Orme des Merisiers, Bat 709 Gif-sur-Yvette, 91191 France4 Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya, Japan5 University Observatory Munich, Scheinerstr. 1, D-81679 Munchen, Germany6 Excellence Cluster Universe, Technische Universitat Munchen, Boltzmannstr. 2, D-85748, Garching, Germany

E-mail contact: joanne.dawson at mq.edu.au

Dense, star-forming gas is believed to form at the stagnation points of large-scale ISM flows, but observational examplesof this process in action are rare. We here present a giant molecular cloud (GMC) sandwiched between two collidingMilky Way supershells, which we argue shows strong evidence of having formed from material accumulated at thecollision zone. Combining 12CO, 13CO and C18O (J = 1–0) data with new high-resolution, 3D hydrodynamicalsimulations of colliding supershells, we discuss the origin and nature of the GMC (G288.5+1.5), favoring a scenario inwhich the cloud was partially seeded by pre-existing denser material, but assembled into its current form by the actionof the shells. This assembly includes the production of some new molecular gas. The GMC is well interpreted asnon-self-gravitating, despite its high mass (MH2

∼ 1.7×105 M⊙), and is likely pressure confined by the colliding flows,implying that self-gravity was not a necessary ingredient for its formation. Much of the molecular gas is relativelydiffuse, and the cloud as a whole shows little evidence of star formation activity, supporting a scenario in which it isyoung and recently formed. Drip-like formations along its lower edge may be explained by fluid dynamical instabilitiesin the cooled gas.

Accepted by ApJ

http://arxiv.org/pdf/1411.2708

The frequency and nature of cloud-cloud collisions in galaxies

C. L. Dobbs1, J. E. Pringle2 and A. Duarte-Cabral1

1 School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK2 Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK

E-mail contact: dobbs at astro.ex.ac.uk

We investigate cloud–cloud collisions, and GMC evolution, in hydrodynamic simulations of isolated galaxies. Thesimulations include heating and cooling of the ISM, self–gravity and stellar feedback. Over timescales less than 5 Myrmost clouds undergo no change, and mergers and splits are found to be typically two body processes, but evolutionover longer timescales is more complex and involves a greater fraction of intercloud material. We find that mergers, orcollisions, occur every 8-10 Myr (1/15th of an orbit) in a simulation with spiral arms, and once every 28 Myr (1/5thof an orbit) with no imposed spiral arms. Both figures are higher than expected from analytic estimates, as clouds arenot uniformly distributed in the galaxy. Thus clouds can be expected to undergo between zero and a few collisionsover their lifetime. We present specific examples of cloud–10 Myr (1/15th of an orbit) in a simulation with spiral arms,and once every 28 Myr (1/5th of an orbit) with no imposed spiral arms. Both figures are higher than expected fromanalytic estimates, as clouds are not uniformly distributed in the galaxy. Thus clouds can be expected to undergobetween zero and a few collisions over their lifetime. We present specific examples of cloud–cloud interactions oftenbetter resemble a smaller cloud nudging a larger cloud. Our findings are consistent with the view that spiral armsmake little difference to overall star formation rates in galaxies, and we see no evidence that collisions likely producemassive clusters. However, to confirm the outcome of such massive cloud collisions we ideally need higher resolutionsimulations.

Accepted by MNRAS

http://arxiv.org/pdf/1411.0840

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The JCMT Gould Belt Survey: low-mass proto-planetary discs from a SCUBA-2 censusof NGC1333

Peter Dodds1, Jane Greaves1, Aleks Scholz1, Jennifer Hatchell2 and Wayne Holland3

1 SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK2 Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK3 UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

E-mail contact: as110 at st-andrews.ac.uk

NGC 1333 is a 1-2Myr old cluster of stars in the Perseus molecular cloud. We used 850µm data from the GouldBelt Survey with SCUBA-2 on the JCMT to measure or place limits on disc masses for 82 Class II sources in thiscluster. Eight disc-candidates were detected; one is estimated to have mass of about 9 MJupiter in dust plus gas,while the others host only 2-4 MJupiter of circumstellar material. None of these discs exceeds the threshold for the’Minimum Mass Solar Nebula’ (MMSN). This reinforces previous claims that only a small fraction of Class II sourcesat an age of 1-2Myr has discs exceeding the MMSN threshold and thus can form a planetary system like our own.However, other regions with similarly low fractions of MMSN discs (IC348, UpSco, σOri) are thought to be older thanNGC 1333. Compared with coeval regions, the exceptionally low fraction of massive discs in NGC 1333 cannot easilybe explained by the effects of UV radiation or stellar encounters. Our results indicate that additional environmentalfactors significantly affect disc evolution and the outcome of planet formation by core accretion.

Accepted by MNRAS

http://arxiv.org/pdf/1411.5931

Time-monitoring Observations of Brγ Emission from Young Stars

J.A. Eisner1,2, G.H. Rieke1, M.J. Rieke1, K.M. Flaherty1,4, Jordan M. Stone1, T.J. Arnold1, S.R.Cortes1, E. Cox1, C. Hawkins2, A. Cole, S. Zajac2, A.L. Rudolph2

1 Steward Observatory, The University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA2 Department of Physics and Astronomy, California State Polytechnic University, 3801 W Temple Ave, Pomona, CA91768, USA3 Visiting Fellow, JILA, University of Colorado and NIST, Boulder, CO 803094 Current address: Astronomy Department, Wesleyan University, Middletown, CT 06459, USA

E-mail contact: jeisner at email.arizona.edu

We present multiple epochs of near-IR spectroscopy for a sample of 25 young stars, including T Tauri, Herbig Ae/Be,and FU Ori objects. Using the FSPEC instrument on the Bok 90-inch telescope, we obtained K-band spectra of theBrγ transition of hydrogen, with a resolution of ∼3500. Epochs were taken over a span of >1 year, sampling time-spacings of roughly one day, one month, and one year. The majority of our targets show Brγ emission, and in somecases these are the first published detections. Time-variability is seen in approximately half of the targets showingBrγ emission. We compare the observed variability with expectations for rotationally-modulated accretion onto thecentral stars and time-variable continuum emission or extinction from matter in the inner disk. Our observations arenot entirely consistent with models of rotationally-modulated magnetospheric accretion. Further monitoring, over alarger number of epochs, will facilitate more quantitative constraints on variability timescales and amplitudes, and amore conclusive comparison with theoretical models.

Accepted by MNRAS

http://arxiv.org/pdf/1411.5370

Vortex cycles at the inner edges of dead zones in protoplanetary disks

Julien Faure1, Sebastien Fromang1, Henrik Latter2 and Heloise Meheut1

1 Laboratoire AIM, CEA/DSM–CNRS–Universite Paris 7, IRFU/Service d’Astrophysique, CEA-Saclay, 91191 Gif-sur-Yvette, France2 Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for MathematicalSciences, Wilberforce Road, Cambridge, CB3 0WA, UK

23

E-mail contact: julien.faure at cea.fr

In protoplanetary disks, the inner boundary between the turbulent and laminar regions is a promising site for planetformation because solids may become trapped at the interface itself or in vortices generated by the Rossby waveinstability. The disk thermodynamics and the turbulent dynamics at that location are entwined because of theimportance of turbulent dissipation on thermal ionization and, conversely, of thermal ionisation on the turbulence.However, most previous work has neglected this dynamical coupling and have thus missed a key element of the physicsin this region. In this paper, we aim to determine how the the interplay between ionization and turbulence impactson the formation and evolution of vortices at the interface between the active and the dead zones. Using the Godunovcode RAMSES, we have performed a 3D magnetohydrodynamic global numerical simulation of a cylindrical modelof an MRI–turbulent protoplanetary disk, including thermodynamical effects as well as a temperature-dependantresistivity. The comparison with an analogous 2D viscous simulation has been extensively used to help identify therelevant physical processes and the disk’s long-term evolution. We find that a vortex formed at the interface, due toRossby wave instability, migrates inward and penetrates the active zone where it is destroyed by turbulent motions.Subsequently, a new vortex emerges a few tens of orbits later at the interface, and the new vortex migrates inward too.The sequence repeats itself, resulting in cycles of vortex formation, migration, and disruption. This surprising behavioris successfully reproduced using two different codes. In this paper, we characterize this vortex life cycle and discuss itsimplications for planet formation at the dead/active interface. Our results also call for a better understanding of vortexmigration in complex thermodynamical environments. Our simulations highlight the importance of thermodynamicalprocesses for the vortex evolution at the dead zone inner edge.

Accepted by Astronomy and Astrophysics

http://arxiv.org/pdf/1411.3236

The Turbulent Dynamo in Highly Compressible Supersonic Plasmas

Christoph Federrath1, Jennifer Schober2, Stefano Bovino3 and Dominik R. G. Schleicher3

1 Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611, Australia2 Universitat Heidelberg, Zentrum fur Astronomie, Institut fur Theoretische Astrophysik, Albert-Ueberle-Strasse 2,D-69120 Heidelberg, Germany3 Institut fur Astrophysik, Georg-August-Universitat Gottingen, Friedrich-Hund-Platz 1, D-37077 Gottingen, Germany

E-mail contact: christoph.federrath at anu.edu.au

The turbulent dynamo may explain the origin of cosmic magnetism. While the exponential amplification of magneticfields has been studied for incompressible gases, little is known about dynamo action in highly compressible, supersonicplasmas, such as the interstellar medium of galaxies and the early Universe. Here we perform the first quantitativecomparison of theoretical models of the dynamo growth rate and saturation level with three-dimensional magnetohy-drodynamical simulations of supersonic turbulence with grid resolutions of up to 10243 cells. We obtain numericalconvergence and find that dynamo action occurs for both low and high magnetic Prandtl numbers Pm = ν/η = 0.1–10(the ratio of viscous to magnetic dissipation), which had so far only been seen for Pm ≥ 1 in supersonic turbulence. Wemeasure the critical magnetic Reynolds number, Rmcrit = 129+43

−31, showing that the compressible dynamo is almost asefficient as in incompressible gas. Considering the physical conditions of the present and early Universe, we concludethat magnetic fields need to be taken into account during structure formation from the early to the present cosmicages, because they suppress gas fragmentation and drive powerful jets and outflows, both greatly affecting the initialmass function of stars.

Accepted by The Astrophyiscal Journal Letters

http://arxiv.org/pdf/1411.4707

Gaps, Rings, and Non-Axisymmetric Structures in Protoplanetary Disks - From Simu-lations to ALMA Observations

M. Flock1, J.P. Ruge2, N. Dzyurkevich3, Th. Henning4, H. Klahr4 and S. Wolf2

1 CEA UMR AIM Irfu, SAP, CEA-CNRS-Univ. Paris Diderot, Centre de Saclay, 91191 Gif-sur-Yvette, France2 Universitat zu Kiel, Institut fr Theoretische Physik und Astrophysik, Leibnitzstr. 15, 24098 Kiel, Germany

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3 Laboratoire de radioastronomie, UMR 8112 du CNRS, Ecole normale superieure et Observatoire de Paris, 24 rueLhomond, F- 75231 Paris Cedex 05, France4 Max Planck Institute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany

E-mail contact: mario.flock at cea.fr

Recent observations by the Atacama Large Millimeter/submillimeter Array (ALMA) of disks around young starsrevealed distinct asymmetries in the dust continuum emission. In this work we want to study axisymmetric andnon-axisymmetric structures, evocated by the magneto-rotational instability in the outer regions of protoplanetarydisks. We combine the results of state-of-the-art numerical simulations with post-processing radiative transfer (RT)to generate synthetic maps and predictions for ALMA. We performed non-ideal global 3D MHD stratified simulationsof the dead-zone outer edge using the FARGO MHD code PLUTO. The stellar and disk parameters are taken froma parameterized disk model applied for fitting high-angular resolution multi-wavelength observations of circumstellardisks. The 2D temperature and density profiles are calculated consistently from a given surface density profile andMonte-Carlo radiative transfer. The 2D Ohmic resistivity profile is calculated using a dust chemistry model. Themagnetic field is a vertical net flux field. The resulting dust reemission provides the basis for the simulation ofobservations with ALMA. The fiducial model develops a large gap followed by a jump in surface density located atthe dead-zone outer edge. The jump in density and pressure is strong enough to stop the radial drift of particles. Inaddition, we observe the generation of vortices by the Rossby wave instability (RWI) at the jumps location close to 60AU. The vortices are steadily generated and destroyed at a cycle of 40 local orbits which corresponds to a lifetime ofover 19000 years at this location. The RT results and simulated ALMA observations predict the feasibility to observesuch large scale structures appearing in magnetized disks without having a planet.

Accepted by A&A

http://arxiv.org/pdf/1411.2736

IN-SYNC II: Virial Stars from Sub-Virial Cores – The Velocity Dispersion of EmbeddedPre-Main-Sequence Stars in NGC 1333

Jonathan B. Foster1, Michiel Cottaar2, Kevin R. Covey3,4, Hector G. Arce5, Michael R. Meyer2, DavidL. Nidever6, Keivan G. Stassun7,8, Jonathan C. Tan9, S. Drew Chojnowski10, Nicola da Rio9, KevinM. Flaherty11, Luisa Rebull12, Peter M. Frinchaboy13, Steven R. Majewski10, Michael Skrutskie10 andJohn C. Wilson10

1 Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT 06520, USA2 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland3 Lowell Observatory, Flagstaff, AZ 86001, USA4 Current Address: Dept. of Physics & Astronomy, Western Washington Univ., 516 High Street, Bellingham WA98225, USA5 Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520, USA6 Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA7 Department of Physics & Astronomy, Vanderbilt University, VU Station B 1807, Nashville, TN, USA8 Physics Department, Fisk University, Nashville, TN 37208, USA9 Department of Astronomy, University of Florida, Gainesville, FL 32611, USA10 Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA11 Astronomy Department, Wesleyan University, Middletown, CT, 06459, USA12 Spitzer Science Center/Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA13 Department of Physics & Astronomy, Texas Christian University, Fort Worth, TX 76129, USA14 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA

E-mail contact: jonathan.b.foster at yale.edu

The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Usingnear-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity dispersion of young (1-2Myr) stars in NGC 1333 is 0.92±0.12 km s−1 after correcting for measurement uncertainties and the effect of binaries.This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion,but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a sub-virial velocitydispersion of 0.5 km−1. Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement

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provides a strong constraint on the initial velocity dispersion of newly-formed stars. We propose that the differencein velocity dispersion between stars and dense cores may be due to the influence of a 70µG magnetic field acting onthe dense cores, or be the signature of a cluster with initial sub-structure undergoing global collapse.

Accepted by ApJ

http://arxiv.org/pdf/1411.6013

Dense Molecular Clumps associated with the LMC Supergiant Shells LMC 4 and LMC5

Kosuke Fujii1,2, Tetsuhiro Minamidani3, Norikazu Mizuno1,2, Toshikazu Onishi4, Akiko Kawamura2,Erik Muller2, Joanne Dawson5,6, Kenichi Tatematsu2, Tetsuo Hasegawa2, Tomoka Tosaki7, Rie E.Miura2, Kazuyuki Muraoka4, Takeshi Sakai8, Takashi Tsukagoshi9, Kunihiko Tanaka10, Hajime Ezawa2

and Yasuo Fukui11

1 Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 133-0033,Japan;2 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan3 Nobeyama Radio Observatory, 462-2 Nobeyama Minamimaki-mura, Minamisaku-gun, Nagano 384-1305, Japan4 Department of Physical Science, Osaka Prefecture University, Gakuen 1-1, Sakai, Osaka 599-8531, Japan5 Australia Telescope National Facility, CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710,Australia6 Department of Physics and Astronomy and MQ Research Centre in Astronomy, Astrophysics and Astrophotonics,Macquarie University, NSW 2109, Australia7 Joetsu University of Education, Yamayashiki-machi, Joetsu, Niigata 943-8512, Japan8 Graduate School of Informatics and Engineering, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan9 College of Science, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512, Japan10 Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama, Kanagawa223-8522, Japan11 Department of Astrophysics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan

E-mail contact: kosuke.fujii at nao.ac.jp

We investigate the effects of Supergiant Shells (SGSs) and their interaction on dense molecular clumps by observingthe Large Magellanic Cloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC4 and LMC 5. 12CO (J=3–2, 1–0) and 13CO(J=1–0) observations with the ASTE and Mopra telescopes have beencarried out towards these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatialresolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H2)) of the clumps aredistributed from low to high density (103–105 cm−3) and their kinetic temperatures (Tkin) are typically high (greaterthan 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution ofHα, young stellar object candidates, and IR emission. We found that the N48 region is located in the high columndensity H I envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically showhigh n(H2) and Tkin, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor,N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, worksefficiently on the formation of dense molecular clumps and stars.

Accepted by The Astrophysical Journal

http://arxiv.org/pdf/1411.0097

G305.136+0.068: A massive and dense cold core in an early stage of evolution

Guido Garay,1 Diego Mardones,1 Yanett Contreras,1,2 Jaime E. Pineda,3 Elise Servajean,1 and AndresE. Guzman.1,4

1Departamento de Astronomıa, Universidad de Chile, Casilla 36-D, Santiago, Chile

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2CSIRO Astronomy and Space Science, P.O. Box 76, Epping NSW 1710, Australia 3Institute for Astronomy, ETHZurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland4Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, USA

E-mail contact: guido at das.uchile.cl

We report molecular line observations, made with ASTE and SEST, and dust continuum observations at 0.87 mm,made with APEX, towards the cold dust core G305.136+0.068. The molecular observations show that the core isisolated and roughly circularly symmetric and imply that it has a mass of 1.1× 103 M⊙. A simultaneous model fittingof the spectra observed in four transitions of CS, using a non-LTE radiative transfer code, indicates that the coreis centrally condensed, with the density decreasing with radius as r−1.8, and that the turbulent velocity increasestowards the center. The dust observations also indicate that the core is highly centrally condensed and that theaverage column density is 1.1 g cm−2, value slightly above the theoretical threshold required for the formation of highmass stars. A fit to the spectral energy distribution of the emission from the core indicates a dust temperature of17± 2 K, confirming that the core is cold. Spitzer images show that the core is seen in silhouette from 3.6 to 24.0 µmand that is surrounded by an envelope of emission, presumably tracing an externally excited photo-dissociated region.We found two embedded sources within a region of 20 arcsec centered at the peak of the core, one of which is young,has a luminosity of 66 L⊙ and is accreting mass with a high accretion rate, of ∼ 1× 10−4 M⊙ yr−1. We suggest thatthis object corresponds to the seed of a high mass protostar still in the process of formation. The present observationssupport the hypothesis that G305.136+0.068 is a massive and dense cold core in an early stage of evolution, in whichthe formation of a high mass star has just started.

Accepted by ApJ

http://arxiv.org/pdf/1411.5637

IRAS 16547−4247: A New Candidate of a Protocluster Unveiled with ALMA

Aya E. Higuchi1, Kazuya Saigo2, James O. Chibueze2,3, Patricio Sanhueza2, Shigehisa Takakuwa4 andGuido Garay5

1 Ibaraki University, College of Science, 2-1-1 Bunkyo, Mito, 310-8512, Japan2 National Astronomical Observatory of Japan 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan3 Department of Physics and Astronomy, Faculty of Physical Sciences, University of Nigeria, Carver Building, 1University Road, Nsukka, Nigeria4 Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan5 Departamento de Astronomia, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile

E-mail contact: ahiguchi at mx.ibaraki.ac.jp

We present the results of continuum and 12CO(3–2) and CH3OH(7–6) line observations of IRAS 16547−4247 madewith the Atacama Large Millimeter/submillimeter Array (ALMA) at an angular resolution of 0.5 arcsec. The 12CO(3–2) emission shows two high-velocity outflows whose driving sources are located within the dust continuum peak. Thealignment of these outflows do not coincide with that of the wide-angle, large scale, bipolar outflow detected withAPEX in previous studies. The CH3OH(7–6) line emission traces an hourglass structure associated with the cavitywalls created by the outflow lobes.Taking into account our results together with the position of the H2O and class ICH3OH maser clusters, we discuss two possible scenarios that can explain the hourglass structure observed in IRAS16547−4247: (1) precession of a biconical jet, (2) multiple, or at least two, driving sources powering intersectingoutflows. Combining the available evidence, namely, the presence of two cross-aligned bipolar outflows and twodifferent H2O maser groups, we suggest that IRAS 16547−4247 represents an early formation phase of a protocluster.

Accepted by ApJL

http://arxiv.org/abs/1411.7485

A new and simple approach to determine the abundance of hydrogen molecules oninterstellar ice mantles

Ugo Hincelin1, Qiang Chang2,3 and Eric Herbst1

1 Department of Chemistry, University of Virginia, Charlottesville, VA 22904, USA

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2 XinJiang Astronomical Observatory, Chinese Academy of Sciences, 150 Science 1-Street, Urumqi 830011, PR China3 Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008, PR China

E-mail contact: ugo.hincelin at virginia.edu

Water is usually the main component of ice mantles, which cover the cores of dust grains in cold portions of denseinterstellar clouds. When molecular hydrogen is adsorbed onto an icy mantle through physisorption, a common as-sumption in gas-grain rate-equation models is to use an adsorption energy for molecular hydrogen on a pure watersubstrate. However, at high density and low temperature, when H2 is efficiently adsorbed onto the mantle, its surfaceabundance can be strongly overestimated if this assumption is still used. Unfortunately, the more detailed microscopicMonte Carlo treatment cannot be used to study the abundance of H2 in ice mantles if a full gas-grain network isutilized.We present a numerical method adapted for rate-equation models that takes into account the possibility that an H2

molecule can, while diffusing on the surface, find itself bound to another hydrogen molecule, with a far weaker bondthan the H2-water bond, which can lead to more efficient desorption. We label the ensuing desorption ”encounterdesorption”.The method is implemented first in a simple system consisting only of hydrogen molecules at steady state between gasand dust using the rate-equation approach and comparing the results with the results of a microscopic Monte Carlocalculation. We then discuss the use of the rate-equation approach with encounter desorption embedded in a completegas-grain chemical network.For the simple system, the rate-equation model with encounter desorption reproduces the H2 granular coverage com-puted by the microscopic Monte Carlo model at 10 K for a gas density from 104 to 1012 cm−3, and yields up to a factor4 difference above 1012 cm−3. The H2 granular coverage is also reproduced by a complete gas-grain network. We usethe rate-equation approach to study the gas-grain chemistry of cold dense regions with and without the encounterdesorption mechanism. We find that the grain surface and gas phase species can be sensitive to the H2 coverage, upto several orders of magnitude, depending on the species, the density, and the time considered.The method is especially useful for dense and cold environments, and for time-dependent physical conditions, suchas occur in the collapse of dense cores and the formation of protoplanetary disks. It is not significantly CPU timeconsuming, so can be used for example with complex 3D chemical-hydrodynamical simulations.

Accepted by Astronomy & Astrophysics

http://arxiv.org/pdf/1410.7375v2.pdf

Reddening, Distance, and Stellar Content of the Young Open Cluster Westerlund 2

Hyeonoh Hur1, Byeong-Gon Park2, Hwankyung Sung1, Michael S. Bessell3, Beomdu Lim1,2, Moo-Young Chun2, Sangmo Tony Sohn4

1 Department of Astronomy and Space Science, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 143-747,Korea2 Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 305-348, Korea3 Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston CreekACT 2611, Australia4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218

E-mail contact: sungh at sejong.ac.kr

We present deep UBV IC photometric data of the young open cluster Westerlund 2. An abnormal reddening lawof RV,cl = 4.14 ± 0.08 was found for the highly reddened early-type members (E(B − V ) ≥ 1.45), whereas a fairlynormal reddening law of RV,fg = 3.33± 0.03 was confirmed for the foreground early-type stars (E(B − V )fg < 1.05).The distance modulus was determined from zero-age main-sequence (ZAMS) fitting to the reddening-corrected colour-magnitude diagram of the early-type members to be V0 −MV = 13.9± 0.14 (random error) +0.4

−0.1 (the upper limit of

systematic error) mag (d = 6.0 ± 0.4+1.2−0.3 kpc). To obtain the initial mass function, pre-main-sequence (PMS) stars

were selected by identifying the optical counterparts of Chandra X-ray sources and mid-infrared emission stars fromthe Spitzer GLIMPSE source catalog. The initial mass function shows a shallow slope of Γ = −1.1 ± 0.1 down tologm = 0.7. The total mass of Westerlund 2 is estimated to be at least 7,400 M⊙. The age of Westerlund 2 from themain-sequence turn-on and PMS stars is estimated to be <

∼ 1.5 Myr. We confirmed the existence of a clump of PMSstars located ∼1′ north of the core of Westerlund 2, but we could not find any clear evidence for an age difference

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between the core and the northern clump.

Accepted by MNRAS

http://arxiv.org/pdf/1411.0879

Depletion of chlorine into HCl ice in a protostellar core

M. Kama1, E. Caux2,3, A. Lopez-Sepulcre4,5, V. Wakelam6,7, C. Dominik8,9, C. Ceccarelli4,5, M. Lanza10,F. Lique10, B.B. Ochsendorf1, D.C. Lis11,12,13, R.N. Caballero14 and A.G.G.M. Tielens1

1 Leiden Observatory, P.O. Box 9513, NL-2300 RA, Leiden, The Netherlands2 Universite de Toulouse, UPS-OMP, IRAP, Toulouse, France3 CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France4 Universite de Grenoble Alpes, IPAG, F-38000 Grenoble, France5 CNRS, IPAG, F-38000 Grenoble, France6 Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac, France7 CNRS, LAB, UMR 5804, F-33270, Floirac, France8 Astronomical Institute Anton Pannekoek, Science Park 904, NL-1098 XH Amsterdam, The Netherlands9 Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands10 LOMC - UMR 6294, CNRS-Universite du Havre, 25 rue Philippe Lebon, BP 1123 - 76 063 Le Havre cedex, France11 LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR 8112, F-75014, Paris, France12 Sorbonne Universites, Universite Pierre et Marie Curie, Paris 6, CNRS, Observatoire de Paris, UMR 8112, LERMA,Paris, France13 California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125,USA14 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany

E-mail contact: mkama at strw.leidenuniv.nl

The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-coolingbalance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout ofvarious carriers of elements with abundances < 10−5 has not yet been well studied. Our aim here is to study thedepletion of chlorine in the protostellar core, OMC-2 FIR 4. We observed transitions of HCl and H2Cl

+ towardsOMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysismakes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H2 hyperfine collisionalexcitation rate coefficients. A narrow emission component in the HCl lines traces the extended envelope, and a broadone traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9e-11, a factor of only 0.001that of volatile elemental chlorine. The H2Cl

+ lines are detected in absorption and trace a tenuous foreground cloud,where we find no depletion of volatile chlorine. Gas-phase HCl is the tip of the chlorine iceberg in protostellar cores.Using a gas-grain chemical model, we show that the hydrogenation of atomic chlorine on grain surfaces in the darkcloud stage sequesters at least 90% of the volatile chlorine into HCl ice, where it remains in the protostellar stage.About 10% of chlorine is in gaseous atomic form. Gas-phase HCl is a minor, but diagnostically key reservoir, with anabundance of <1e-10 in most of the protostellar core. We find the 35Cl/37Cl ratio in OMC-2 FIR 4 to be 3.2 ± 0.1,consistent with the solar system value.

Accepted by Astronomy & Astrophysics

http://arxiv.org/pdf/1411.6483

Main-sequence stars masquerading as Young Stellar Objects in the central molecularzone

Christine Koepferl1, Thomas Robitaille1, Esteban Morales1 and Katharine Johnston1

1 Max Planck Institute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany

E-mail contact: koepferl at mpia.de

In contrast to most other galaxies, star-formation rates in the Milky Way can be estimated directly from Young StellarObjects (YSOs). In the Central Molecular Zone (CMZ) the star-formation rate calculated from the number of YSOs

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with 24 microns emission is up to order of magnitude higher than the value estimated from methods based on diffuseemission (such as free-free emission). Whether this effect is real or whether it indicates problems with either or bothstar formation rate measures is not currently known. In this paper, we investigate whether estimates based on YSOscould be heavily contaminated by more evolved objects such as main-sequence stars. We present radiative transfermodels of YSOs and of main-sequence stars in a constant ambient medium which show that the main-sequence objectscan indeed mimic YSOs at 24 microns. However, we show that in some cases the main-sequence models can bemarginally resolved at 24 microns, whereas the YSO models are always unresolved. Based on the fraction of resolvedMIPS 24 microns sources in the sample of YSOs previously used to compute the star formation rate, we estimate thefraction of misclassified ”YSOs” to be at least 63%, which suggests that the star-formation rate previously determinedfrom YSOs is likely to be at least a factor of three too high.

Accepted by ApJ

http://arxiv.org/pdf/1411.4646

Near-IR Imaging Polarimetry toward a Bright-Rimmed Cloud: Magnetic Field in SFO74

Takayoshi Kusune1, Koji Sugitani1, Jingqi Miao2, Motohide Tamura3,4, Yaeko Sato4, Jungmi Kwon3,4,Makoto Watanabe5, Shogo Nishiyama6, Takahiro Nagayama7 and Shuji Sato8

1 Graduate School of Natural Sciences, Nagoya City University, Mizuho-ku, Nagoya 467-8501, Japan2 Centre for Astrophysics & Planetary Science, School of Physical Sciences, University of Kent, Canterbury, Kent CT27NR, UK3 Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan4 National Astronomical Observatory, 2-21-1 Osawa, Mikata, Tokyo 181-8588, Japan5 Department of Cosmosciences, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan6 Faculty of Education, Miyagi University of Education, Sendai 980-0845, Japan7 Department of Physics, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan8 Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan

E-mail contact: t kusune at nsc.nagoya-cu.ac.jp

We have made near-infrared (JHKs) imaging polarimetry of a bright-rimmed cloud (SFO 74). The polarizationvector maps clearly show that the magnetic field in the layer just behind the bright rim is running along the rim,quite different from its ambient magnetic field. The direction of the magnetic field just behind the tip rim is almostperpendicular to that of the incident UV radiation, and the magnetic field configuration appears to be symmetric as awhole with respect to the cloud symmetry axis. We estimated the column and number densities in the two regions (justinside and far inside the tip rim), and then derived the magnetic field strength, applying the Chandrasekhar-Fermimethod. The estimated magnetic field strength just inside the tip rim, 90 uG, is stronger than that far inside, 30uG. This suggests that the magnetic field strength just inside the tip rim is enhanced by the UV radiation inducedshock. The shock increases the density within the top layer around the tip, and thus increases the strength of themagnetic field. The magnetic pressure seems to be comparable to the turbulent one just inside the tip rim, implyinga significant contribution of the magnetic field to the total internal pressure. The mass-to-flux ratio was estimated tobe close to the critical value just inside the tip rim. We speculate that the flat-topped bright rim of SFO 74 could beformed by the magnetic field effect.

Accepted by Astrophysical Journal

http://arxiv.org/pdf/1411.1813

Magnetic field structure in the Flattened Envelope and Jet in the young protostellarsystem HH 211

Chin-Fei Lee1, Ramprasad Rao1, Tao-Chung Ching2, Shih-Ping Lai2, Naomi Hirano1, Paul T.P. Ho1,3

and Hsiang-Chih Hwang1

1 Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan2 Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

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3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

E-mail contact: cflee at asiaa.sinica.edu.tw

HH 211 is a young Class 0 protostellar system, with a flattened envelope, a possible rotating disk, and a collimatedjet. We have mapped it with the Submillimeter Array in 341.6 GHz continuum and SiO J=8-7 at ∼ 0′′. 6 resolution.The continuum traces the thermal dust emission in the flattened envelope and the possible disk. Linear polarizationis detected in the continuum in the flattened envelope. The field lines implied from the polarization have differentorientations, but they are not incompatible with current gravitational collapse models, which predict different orien-tation depending on the region/distance. Also, we might have detected for the first time polarized SiO line emissionin the jet due to the Goldreich-Kylafis effect. Observations at higher sensitivity are needed to determine the fieldmorphology in the jet.

Accepted by ApJL

http://arxiv.org/pdf/1411.2184

A feedback-driven bubble G24.136+00.436: a possible site of triggered star formation

Hong-Li Liu1,2, Yuefang Wu3, JinZeng Li1, Jing-Hua Yuan1, Tie Liu4 and Xiaoyi Dong3

1 National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing100012, China2 University of Chinese Academy of Sciences, 100049 Beijing, China3 Department of Astronomy, Peking University, 100871 Beijing, China4 Korea Astronomy and Space Science Institute 776, Daedeokdae-ro, Yuseong-gu, Daejeon, Republic of Korea 305-348

E-mail contact: hlliu at nao.cas.cn

We present a multi-wavelength study of the IR bubble G24.136+00.436. The J=1-0 observations of 12CO, 13CO andC18O were carried out with the Purple Mountain Observatory 13.7 m telescope. Molecular gas with a velocity of 94.8km s−1 is found prominently in the southeast of the bubble, shaping as a shell with a total mass of ∼ 2× 104 M⊙. Itis likely assembled during the expansion of the bubble. The expanding shell consists of six dense cores. Their dense(a few of 103 cm−3) and massive (a few of 103 M⊙) characteristics coupled with the broad linewidths (> 2.5 km s−1)suggest they are promising sites of forming high-mass stars or clusters. This could be further consolidated by thedetection of compact HII regions in Cores A and E. We tentatively identified and classified 63 candidate YSOs basedon the Spitzer and UKIDSS data. They are found to be dominantly distributed in regions with strong emission ofmolecular gas, indicative of active star formation especially in the shell. The HII region inside the bubble is mainlyionized by a ∼O8V star(s), of the dynamical age ∼1.6 Myr. The enhanced number of candidate YSOs and secondarystar formation in the shell as well as time scales involved, indicate a possible scenario of triggering star formation,signified by the “collect and collapse” process.

Accepted by ApJ

http://arxiv.org/pdf/1411.1226v1.pdf

Herschel/PACS view of disks around low-mass stars and brown dwarfs in the TW Hyaassociation

Yao Liu1,2, Gregory J. Herczeg3, Munan Gong4,5, Katelyn N. Allers6, Joanna M. Brown7, Adam L.Kraus8, Michael C. Liu9, Evgenya L. Shkolnik10, and Ewine F. van Dishoeck11,12

1 Purple Mountain Observatory, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008, China2 Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, 2 West Beijing Road, Nanjing 210008, China3 Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Haidian Qu, Beijing 100871,China4 Tsinghua University, Shuang Qing Lu 30, Haidian Qu, Beijing 100084, China5 Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Peyton Hall, Princeton, NJ 08544, USA6 Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837, USA7 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS 78, Cambridge, MA 02138, USA8 Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, USA

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9 Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Dr., Honolulu, HI 96822, USA10 Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ, 86001, USA11 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands12 Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany

E-mail contact: yliu at pmo.ac.cn

We conducted Herschel/PACS observations of five very low-mass stars or brown dwarfs located in the TW Hyaassociation with the goal of characterizing the properties of disks in the low stellar mass regime. We detected all fivetargets at 70 µm and 100 µm and three targets at 160 µm. Our observations, combined with previous photometry from2MASS, WISE, and SCUBA-2, enabled us to construct SEDs with extended wavelength coverage. Using sophisticatedradiative transfer models, we analyzed the observed SEDs of the five detected objects with a hybrid fitting strategy thatcombines the model grids and the simulated annealing algorithm and evaluated the constraints on the disk propertiesvia the Bayesian inference method. The modelling suggests that disks around low-mass stars and brown dwarfs aregenerally flatter than their higher mass counterparts, but the range of disk mass extends to well below the value foundin T Tauri stars, and the disk scale heights are comparable in both groups. The inferred disk properties (i.e., diskmass, flaring, and scale height) in the low stellar mass regime are consistent with previous findings from large samplesof brown dwarfs and very low-mass stars. We discuss the dependence of disk properties on their host stellar parametersand find a significant correlation between the Herschel far-IR fluxes and the stellar effective temperatures, probablyindicating that the scaling between the stellar and disk masses (i.e., Mdisk ∝ M∗) observed mainly in low-mass starsmay extend down to the brown dwarf regime.

Accepted by A&A

http://arxiv.org/pdf/1411.1858

Simulations of star formation in Ophiuchus, II: Multiplicity

O. Lomax1, A. P. Whitworth1, D. A. Hubber2,3, D. Stamatellos4 and S. Walch5

1 School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, UK2 University Observatory, Ludwig-Maximilians-University Munich, Scheinerstr.1, D-81679 Munich, Germany3 Excellence Cluster Universe, Boltzmannstr. 2, D-85748 Garching, Germany4 Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire, PR1 2HE, UK5 Physikalisches Institut, Universitat zu Koln, Zulpicher Strasse 77, D-50937 Cologne, Germany

E-mail contact: oliver.lomax at astro.cf.ac.uk

Lomax et al. have constructed an ensemble of 60 prestellar cores having masses, sizes, projected shapes, temperaturesand non-thermal radial velocity dispersions that match, statistically, the cores in Ophiuchus; and have simulated theevolution of these cores using SPH. Each core has been evolved once with no radiative feedback from stars, oncewith continuous radiative feedback, and once with episodic radiative feedback. Here we analyse the multiplicitystatistics from these simulations. With episodic radiative feedback, (i) the multiplicity frequency is 60% higher thanin the field; (ii) the multiplicity frequency and the mean semi-major axis both increase with primary mass; (iii) onethird of multiple systems are hierarchical systems with more than two components; (iv) in these hierarchical systemsthe inner pairings typically have separations of a few au and mass ratios concentrated towards unity, whereas theouter pairings have separations of order 100 au and a flatter distribution of mass ratios. The binary statistics arecompatible with observations of young embedded populations, and – if wider orbits are disrupted preferentially byexternal perturbations – with observations of mature field populations. With no radiative feedback, the results aresimilar to those from simulations with episodic feedback. With continuous radiative feedback, brown dwarfs are under-produced, the number of multiple systems is too low, and the statistical properties of multiple systems are at variancewith observation. This suggests that star formation in Ophiuchus may only be representative of global star formationif accretion onto protostars, and hence radiative feedback, is episodic.

Accepted by MNRAS

http://arxiv.org/pdf/1411.7943

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Protostellar Jets Enclosed by Low-velocity Outflows

Masahiro N. Machida1

1 Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan

E-mail contact: machida.masahiro.018 at m.kyushu-u.ac.jp

A protostellar jet and outflow are calculated for ∼ 270yr following the protostar formation using a three dimensionalmagnetohydrodynamics simulation, in which both the protostar and its parent cloud are spatially resolved. A high-velocity (∼ 100 km s−1) jet with good collimation is driven near the disk’s inner edge, while a low-velocity (<∼10 km s−1)outflow with a wide opening angle appears in the outer-disk region. The high-velocity jet propagates into the low-velocity outflow, forming a nested velocity structure in which a narrow high-velocity flow is enclosed by a wide low-velocity flow. The low-velocity outflow is in a nearly steady state, while the high-velocity jet appears intermittently.The time-variability of the jet is related to the episodic accretion from the disk onto the protostar, which is caused bygravitational instability and magnetic effects such as magnetic braking and magnetorotational instability. Althoughthe high-velocity jet has a large kinetic energy, the mass and momentum of the jet are much smaller than those of thelow-velocity outflow. A large fraction of the infalling gas is ejected by the low-velocity outflow. Thus, the low-velocityoutflow actually has a more significant effect than the high-velocity jet in the very early phase of the star formation.

Accepted by The Astrophysical Journal Letters

http://arxiv.org/pdf/1411.7124

Detections of trans-Neptunian ice

M. K. McClure1, C. Espaillat2, N. Calvet1, E. Bergin1, P. D’Alessio3, D. M. Watson4, P. Manoj5,B. Sargent6 and L. I. Cleeves1

1 University of Michigan, USA2 Boston University, USA3 Universidad Nacional Autonoma de Mexico, Mexico4 University of Rochester, USA5 Tata Institute of Fundamental Research, India6 Rochester Institute of Technology, USA

E-mail contact: mmcclure at eso.org

We present Herschel Space Observatory PACS spectra of T Tauri stars, in which we detect amorphous and crystallinewater ice features. Using irradiated accretion disk models, we determine the disk structure and ice abundance in eachof the systems. Combining a model-independent comparison of the ice feature strength and disk size with a detailedanalysis of the model ice location, we estimate that the ice emitting region is at disk radii >30AU, consistent with aproto-Kuiper belt. Vertically, the ice emits most below the photodesorption zone, consistent with Herschel observationsof cold water vapor. The presence of crystallized water ice at a disk location a) colder than its crystallizationtemperature and b) where it should have been re-amorphized in ∼1 Myr suggests that localized generation is occurring;the most likely cause appears to be micrometeorite impact or planetesimal collisions. Based on simple tests with UVmodels and different ice distributions, we suggest that the SED shape from 20 to 50µm may probe the location of thewater ice snow line in the disk upper layers. This project represents one of the first extra-solar probes of the spatialstructure of the cometary ice reservoir thought to deliver water to terrestrial planets.

Accepted by ApJ

http://arxiv.org/pdf/1411.7618

Molecules with a peptide link in protostellar shocks: a comprehensive study of L1157

Edgar Mendoza1,2,3, B. Lefloch2,3, A. Lopez-Sepulcre2,3, C. Ceccarelli2,3, C. Codella4, H. M. Boechat-Roberty1 and R. Bachiller5

1 Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira Pedro Antonio 43, CEP 20080-090, Riode Janeiro, RJ, Brazil2 Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France

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3 CNRS, IPAG, F-38000 Grenoble, France4 INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze, Italy5 IGN, Observatorio Astronomico Nacional, Calle Alfonso XIII, 3 E-28004, Madrid, Spain

E-mail contact: emendoza at astro.ufrj.br, mercurius.em at gmail.com

Interstellar molecules with a peptide link -NH-C(=O)-, like formamide (NH2CHO), acetamide (NH2COCH3) andisocyanic acid (HNCO) are particularly interesting for their potential role in pre-biotic chemistry. We have studiedtheir emission in the protostellar shock regions L1157-B1 and L1157-B2, with the IRAM 30m telescope, as part of theASAI Large Program. Analysis of the line profiles shows that the emission arises from the outflow cavities associatedwith B1 and B2. Molecular abundance of ≈ (0.4 − 1.1) × 10−8 and (3.3 − 8.8) × 10−8 are derived for formamideand isocyanic acid, respectively, from a simple rotational diagram analysis. Conversely, NH2COCH3 was not detecteddown to a relative abundance of a few ≤ 10−10. B1 and B2 appear to be among the richest Galactic sources ofHNCO and NH2CHO molecules. A tight linear correlation between their abundances is observed, suggesting that thetwo species are chemically related. Comparison with astrochemical models favours molecule formation on ice grainmantles, with NH2CHO generated from hydrogenation of HNCO.

Accepted by MNRAS (445, 151-161, 2014)

http://arxiv.org/pdf/1408.4857

Stirring in massive, young debris discs from spatially resolved Herschel images

A. Moor1, A. Kospal1,2, P. Abraham1, D. Apai3, Z. Balog4, C. Grady5, Th. Henning4, A. Juhasz6, Cs.Kiss1, A.V. Krivov7, N. Pawellek7, and Gy. M. Szabo1,8

1 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, PO Box67, H-1525 Budapest, Hungary2 European Space Agency (ESA-ESTEC, SRE-S), P.O. Box 299, 2200 AG, Noordwijk, The Netherlands; ESA fellow3 Department of Astronomy and Department of Planetary Sciences, The University of Arizona, Tucson, AZ 85721USA4 Max-Planck-Institut fur Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany5 Exoplanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center, Greenbelt, MD 20771USA6 Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333 CA Leiden, The Netherlands7 Astrophysikalisches Institut und Universitatssternwarte, Friedrich-Schiller-Universitat Jena, Schillergaßchen 23,07745 Jena, Germany8 ELTE, Gothard Astrophysical Observatory, H-9704 Szombathely, Szent Imre hercegut 112, Hungary

E-mail contact: moor at konkoly.hu

A significant fraction of main-sequence stars are encircled by dusty debris discs, where the short-lived dust particlesare replenished through collisions between planetesimals. Most destructive collisions occur when the orbits of smallerbodies are dynamically stirred up, either by the gravitational effect of locally formed Pluto-sized planetesimals (self-stirring scenario), or via secular perturbation caused by an inner giant planet (planetary stirring). The relativeimportance of these scenarios in debris systems is unknown. Here we present new Herschel Space Observatory imageryof 11 discs selected from the most massive and extended known debris systems. All discs were found to be extended atfar-infrared wavelengths, five of them being resolved for the first time. We evaluated the feasibility of the self-stirringscenario by comparing the measured disc sizes with the predictions of the model calculated for the ages of our targets.We concluded that the self-stirring explanation works for seven discs. However, in four cases, the predicted pace ofoutward propagation of the stirring front, assuming reasonable initial disc masses, was far too low to explain the radialextent of the cold dust. Therefore, for HD 9672, HD 16743, HD 21997, and HD 95086, another explanation is needed.We performed a similar analysis for ß Pic and HR 8799, reaching the same conclusion. We argue that planetary stirringis a promising possibility to explain the disk properties in these systems. In HR 8799 and HD 95086 we may alreadyknow the potential perturber, since their known outer giant planets could be responsible for the stirring process. Ourstudy demonstrates that among the largest and most massive debris discs self-stirring may not be the only activescenario, and potentially planetary stirring is responsible for destructive collisions and debris dust production in anumber of systems.

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Accepted by MNRAS

http://arxiv.org/pdf/1411.5829

New low-mass members of the Octans stellar association and an updated 30–40 Myrlithium age

Simon J. Murphy1,2 and Warrick A. Lawson2

1 Gliese Fellow, Astronomisches Rechen-Institut, Zentrum fur Astronomie der Universitat Heidelberg, D-69120 Hei-delberg, Germany2 School of Physical, Environmental and Mathematical Sciences, University of New South Wales Canberra, ACT 2600,Australia

E-mail contact: murphy at ari.uni-heidelberg.de

The Octans association is one of several young stellar moving groups recently discovered in the Solar neighbourhood,and hence a valuable laboratory for studies of stellar, circumstellar disc and planetary evolution. However, a lack oflow-mass members or any members with trigonometric parallaxes means the age, distance and space motion of thegroup are poorly constrained. To better determine its membership and age, we present the first spectroscopic surveyfor new K and M-type Octans members, resulting in the discovery of 29 UV-bright K5-M4 stars with kinematics,photometry and distances consistent with existing members. Nine new members possess strong Li I absorption, whichallow us to estimate a lithium age of 30–40 Myr, similar to that of the Tucana-Horologium association and bracketedby the firm lithium depletion boundary ages of the β Pictoris (20 Myr) and Argus/IC 2391 (50 Myr) associations.Several stars also show hints in our medium-resolution spectra of fast rotation or spectroscopic binarity. More sothan other nearby associations, Octans is much larger than its age and internal velocity dispersion imply. It maybe the dispersing remnant of a sparse, extended structure which includes some younger members of the foregroundOctans-Near association recently proposed by Zuckerman and collaborators.

Accepted by MNRAS

http://arxiv.org/pdf/1411.5703

Revealing the physical properties of molecular gas in Orion with a large scale survey inJ = 2–1 lines of 12CO, 13CO and C18O

Atsushi Nishimura1,2, Kazuki Tokuda1, Kimihiro Kimura1, Kazuyuki Muraoka1, Hiroyuki Maezawa1,Hideo Ogawa1, Kazuhito Dobashi3, Tomomi Shimoikura3, Akira Mizuno4, Yasuo Fukui5 and ToshikazuOnishi1

1 Department of Physical Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku,Sakai, Osaka 599-8531, Japan2 Nobeyama Radio Observatory, National Astronomical Observatory of Japan, 462-2 Nobeyama, Minamimaki, Mi-namisaku, Nagano, 384-1305, Japan3 Department of Astronomy and Earth Sciences, Tokyo Gakugei University, 4-1-1 Nukuikita-machi, Koganei, Tokyo184-8501, Japan4 Solar-terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan5 Department of Physics and Astrophysics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan

E-mail contact: atsushi.nishimura at nao.ac.jp

We present fully sampled ∼ 3 arcmin resolution images of the 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1)emission taken with the newly developed 1.85-m mm-submm telescope toward the entire area of the Orion A and Bgiant molecular clouds. The data were compared with the J = 1–0 of the 12CO, 13CO, and C18O data taken with theNagoya 4-m telescope and the NANTEN telescope at the same angular resolution to derive the spatial distributionsof the physical properties of the molecular gas. We explore the large velocity gradient formalism to determine thegas density and temperature by using the line combinations of 12CO(J = 2–1), 13CO(J = 2–1), and 13CO(J = 1–0)assuming uniform velocity gradient and abundance ratio of CO. The derived gas density is in the range of 500 to 5000cm−3, and the derived gas temperature is mostly in the range of 20 to 50 K along the cloud ridge with a temperaturegradient depending on the distance from the star forming region. We found the high-temperature region at the cloud

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edge facing to the HII region, indicating that the molecular gas is interacting with the stellar wind and radiation fromthe massive stars. In addition, we compared the derived gas properties with the Young Stellar Objects distributionobtained with the Spitzer telescope to investigate the relationship between the gas properties and the star formationactivity therein. We found that the gas density and star formation efficiency are well positively correlated, indicatingthat stars form effectively in the dense gas region.

Accepted by ApJS

http://arxiv.org/pdf/1412.0790.pdf

Shell instability of a collapsing dense core

Evangelia Ntormousi1, Patrick Hennebelle1,2

1 Laboratoire AIM, Paris-Saclay, CEA/IRFU/SAp - CNRS - Universite Paris Diderot, 91191, Gif-sur-Yvette Cedex,France2 LERMA (UMR CNRS 8112), Ecole Normale Superieure, 75231 Paris Cedex, France

E-mail contact: eva.ntormousi at cea.fr

Understanding the formation of binary and multiple stellar systems largely comes down to studying the circumstancesfor the fragmentation of a condensing core during the first stages of the collapse. However, the probability of frag-mentation and the number of fragments seem to be determined to a large degree by the initial conditions. In thiswork we study the fate of the linear perturbations of a homogeneous gas sphere both analytically and numerically. Inparticular, we investigate the stability of the well-known homologous solution that describes the collapse of a uniformspherical cloud. The difficulty of the mathematical singularity in the perturbation equations is surpassed here byexplicitly introducing a weak shock next to the sonic point. In parallel, we perform adaptive mesh refinement (AMR)numerical simulations of the linear stages of the collapse and compared the growth rates obtained by each method.With this combination of analytical and numerical tools, we explore the behavior of both spherically symmetric andnon-axisymmetric perturbations. The numerical experiments provide the linear growth rates as a function of thecore’s initial virial parameter and as a function of the azimuthal wave number of the perturbation. The overlappingregime of the numerical experiments and the analytical predictions is the situation of a cold and large cloud, and inthis regime the analytically calculated growth rates agree very well with the ones obtained from the simulations. Theuse of a weak shock as part of the perturbation allows us to find a physically acceptable solution to the equations fora continuous range of growth rates. The numerical simulations agree very well with the analytical prediction for themost unstable cores, while they impose a limit of a virial parameter of 0.1 for core fragmentation in the absence ofrotation.

Accepted by A&A

http://arxiv.org/pdf/1411.3177

The role of cosmic rays on magnetic field diffusion and the formation of protostellardiscs

Marco Padovani1,2,3, Daniele Galli3, Patrick Hennebelle4, Benoıt Commercon5 and Marc Joos4

1 Laboratoire Univers et Particules de Montpellier, UMR 5299 du CNRS, Universite de Montpellier II, place E.Bataillon, cc072, 34095 Montpellier, France2 Laboratoire de Radioastronomie Millimetrique, UMR 8112 du CNRS, Ecole Normale Superieure et Observatoire deParis, 24 rue Lhomond, 75231 Paris cedex 05, France3 INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy4 CEA, IRFU, SAp, Centre de Saclay, 91191 Gif-Sur-Yvette, France5 Ecole Normale Superieure de Lyon, CRAL, UMR 5574 du CNRS, Universite Lyon I, 46 Allee d’Italie, 69364 Lyoncedex 07, France

E-mail contact: Marco.Padovani at lupm.univ-montp2.fr

The formation of protostellar discs is severely hampered by magnetic braking, as long as magnetic fields remain frozenin the gas. The latter condition depends on the levels of ionisation that characterise the innermost regions of acollapsing cloud. The chemistry of dense cloud cores and, in particular, the ionisation fraction is largely controlled by

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cosmic rays. The aim of this paper is to evaluate whether the attenuation of the flux of cosmic rays expected in theregions around a forming protostar is sufficient to decouple the field from the gas, thereby influencing the formationof centrifugally supported disc. We adopted the method developed in a former study to compute the attenuationof the cosmic-ray flux as a function of the column density and the field strength in clouds threaded by poloidal andtoroidal magnetic fields. We applied this formalism to models of low- and high-mass star formation extracted fromnumerical simulations of gravitational collapse that include rotation and turbulence. For each model we determinethe size of the magnetic decoupling zone, where collapse or rotation motion becomes unaffected by the local magneticfield. In general, we find that decoupling only occurs when the attenuation of cosmic rays is taken into account withrespect to a calculation in which the cosmic-ray ionisation rate is kept constant. The extent of the decoupling zonealso depends on the dust grain size distribution and is larger if large grains (of radius ∼ 10−5 cm) are formed bycompression and coagulation during cloud collapse. The decoupling region disappears for the high-mass case. Thisis due to magnetic field diffusion caused by turbulence that is not included in the low-mass models. We concludethat a realistic treatment of cosmic-ray propagation and attenuation during cloud collapse may lead to a value ofthe resistivity of the gas in the innermost few hundred AU around a forming protostar that is higher than generallyassumed. Forthcoming self-consistent calculations should investigate whether this effect is strong enough to effectivelydecouple the gas from the field and to compute the amount of angular momentum lost by infalling fluid particles whenthey enter the decoupling zone.

Accepted by Astronomy & Astrophysics

http://arxiv.org/pdf/1408.5901

Primordial mass segregation in simulations of star formation?

Richard J. Parker1, James E. Dale2 and Barbara Ercolano2,3

1 Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool, L3 5RF, UK2 Excellence Cluster ‘Universe’, Boltzmannstraße 2, 85748 Garching, Germany3 Universitats-Sternwarte Munchen, Scheinerstraße 1, 81679 Munchen, Germany

E-mail contact: R.J.Parker at ljmu.ac.uk

We take the end result of smoothed particle hydrodynamics (SPH) simulations of star formation which include feedbackfrom photoionisation and stellar winds and evolve them for a further 10Myr using N -body simulations. We comparethe evolution of each simulation to a control run without feedback, and to a run with photoionisation feedback only.In common with previous work, we find that the presence of feedback prevents the runaway growth of massive stars,and the resulting star-forming regions are less dense, and preserve their initial substructure for longer. The addition ofstellar winds to the feedback produces only marginal differences compared to the simulations with just photoionisationfeedback.

We search for mass segregation at different stages in the simulations; before feedback is switched on in the SPH runs,at the end of the SPH runs (before N -body integration) and during the N -body evolution. Whether a simulationis primordially mass segregated (i.e. before dynamical evolution) depends extensively on how mass segregation isdefined, and different methods for measuring mass segregation give apparently contradictory results. Primordial masssegregation is also less common in the simulations when star formation occurs under the influence of feedback. Furtherdynamical mass segregation can also take place during the subsequent (gas-free) dynamical evolution. Taken together,our results suggest that extreme caution should be exercised when interpreting the spatial distribution of massive starsrelative to low-mass stars in simulations.

Accepted by MNRAS

http://arxiv.org/pdf/1411.3002

Magnetic Fields in High-Mass Infrared Dark Clouds

Thushara Pillai1,2, Jens Kauffmann1,2, Jonathan C. Tan3, Paul F. Goldsmith4, Sean J. Carey5 and KarlM. Menten1

1 MPIfR, Germany2 Caltech, USA

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3 U. Florida, USA4 JPL, USA5 IPAC, Caltech, USA

E-mail contact: tpillai.astro at gmail.com

High-mass Stars are cosmic engines known to dominate the energetics in the Milky Way and other galaxies. However,their formation is still not well understood. Massive, cold, dense clouds, often appearing as Infrared Dark Clouds(IRDCs), are the nurseries of massive stars. No measurements of magnetic fields in IRDCs in a state prior to the onsetof high-mass star formation (HMSF) have previously been available, and prevailing HMSF theories do not considerstrong magnetic fields. Here, we report observations of magnetic fields in two of the most massive IRDCs in the MilkyWay. We show that IRDCs G11.11-0.12 and G0.253+0.016 are strongly magnetized and that the strong magneticfield is as important as turbulence and gravity for HMSF. The main dense filament in G11.11-0.12 is perpendicular tothe magnetic field, while the lower density filament merging onto the main filament is parallel to the magnetic field.The implied magnetic field is strong enough to suppress fragmentation sufficiently to allow HMSF. Other mechanismsreducing fragmentation, such as the entrapment of heating from young stars via high mass surface densities, are notrequired to facilitate HMSF.

Accepted by ApJ

http://arxiv.org/pdf/1410.7390

Infall-Driven Protostellar Accretion and the Solution to the Luminosity Problem

Paolo Padoan1, Troels Haugbølle2 and Ake Nordlund2

1 ICREA & University of Barcelona, Spain2 Center for Star and Planet Formation, University of Copenhagen, Denmark

E-mail contact: ppadoan at icc.ub.edu

We investigate the role of mass infall in the formation and evolution of protostars. To avoid ad hoc initial andboundary conditions, we consider the infall resulting self-consistently from modeling the formation of stellar clustersin turbulent molecular clouds. We show that infall rates in turbulent clouds are comparable to accretion rates inferredfrom protostellar luminosities or measured in pre-main-sequence stars. They should not be neglected in modeling theluminosity of protostars and the evolution of disks, even after the embedded protostellar phase. We find large variationsof infall rates from protostar to protostar, and large fluctuations during the evolution of individuals protostars. Inmost cases, the infall rate is initially of order 10−5 M⊙ yr−1, and may either decay rapidly in the formation of low-massstars, or remain relatively large when more massive stars are formed. The simulation reproduces well the observedcharacteristic values and scatter of protostellar luminosities and matches the observed protostellar luminosity function.The luminosity problem is therefore solved once realistic protostellar infall histories are accounted for, with no needfor extreme accretion episodes. These results are based on a simulation of randomly-driven magneto-hydrodynamicturbulence on a scale of 4 pc, including self-gravity, adaptive-mesh refinement to a resolution of 50 AU, and accretingsink particles. The simulation yields a low star formation rate, consistent with the observations, and a mass distributionof sink particles consistent with the observed stellar initial mass function during the whole duration of the simulation,forming nearly 1,300 sink particles over 3.2 Myr.

Accepted by ApJ

http://arxiv.org/pdf/1407.1445

Characterization of the known T type dwarfs towards the σ Orionis cluster

K. Pena Ramırez1,2, M.R. Zapatero Osorio3, and V.J.S. Bejar4,5

1 Instituto de Astrofısica. Pontificia Universidad Catolica de Chile (IA-PUC), E-7820436 Santiago, Chile2 Millennium Institute of Astrophysics, Santiago, Chile3 Centro de Astrobiologıa (CSIC-INTA), Carretera de Ajalvir km 4, E-28850 Torrejon de Ardoz, Madrid, Spain4 Instituto de Astrofısica de Canarias (IAC), C/. Vıa Lactea s/n, E-38205 La Laguna, Tenerife, Spain5 Universidad de La Laguna, Tenerife, Spain

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E-mail contact: kpena at astro.puc.cl

A total of three T type candidates (S Ori 70, S Ori 73, and S Ori J0538−0213) lying in the line of sight towards σ Orioniswere characterized by means of near-infrared photometric, astrometric, and spectroscopic studies. H-band methaneimages were collected for all three sources and an additional sample of 15 field T type dwarfs using LIRIS/WHT.J-band spectra of resolution of ∼500 were obtained for S Ori J0538−0213 with ISAAC/VLT, and JH spectra ofresolution of ∼50 acquired with WFC3/HST were employed for the spectroscopic classification of S Ori 70 and 73.Proper motions with a typical uncertainty of ±3 mas yr−1 and a time interval of ∼7–9 yr were derived. Using theLIRIS observations of the field T dwarfs, we calibrated this imager for T spectral typing via methane photometry.The three S Ori objects were spectroscopically classified as T4.5±0.5 (S Ori 73), T5±0.5 (S Ori J0538−0213), andT7+0.5

−1.0 (S Ori 70). The similarity between the observed JH spectra and the methane colors and the data of fieldultra-cool dwarfs of related classifications suggests that S Ori 70, 73, and S Ori J053804.65−021352.5 do not deviatesignificantly in surface gravity in relation to the field. Additionally, the detection of K i at ∼1.25 microns in S OriJ0538−0213 points to a high-gravity atmosphere. Only the K-band reddish nature of S Ori 70 may be consistent witha low gravity atmosphere. The proper motions of S Ori 70 and 73 are measurable and are larger than that of thecluster by >3.5σ. The proper motion of S Ori J0538−0213 is consistent with a null displacement. These observationssuggest that none of the three T dwarfs are likely σ Orionis members, and that either planetary-mass objects withmasses below ∼4 MJup may not exist free-floating in the cluster or they may lie at fainter near-infrared magnitudesthan those of the targets (this is H > 20.6 mag), thus remaining unidentified to date.

Accepted by A&A

http://arxiv.org/pdf/1411.3370

Submillimeter Array Observations of Magnetic Fields in G240.31+0.07: An Hourglassin a Massive Cluster-forming Core

Keping Qiu1, Qizhou Zhang2, Karl M. Menten3, Hauyu B. Liu4, Ya-Wen Tang4 and Josep M. Girart5

1 School of Astronomy and Space Science, Nanjing University, 22 Hankou Road, Nanjing 210093, China2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA3 Max-Planck-Institut fr Radioastronomie, Auf dem Hgel 69, D-53121 Bonn, Germany4 Academia Sinica Institute of Astronomy and Astrophysics, P. O. Box 23-141, Taipei 106, Taiwan5 Institut de Cincies de l’Espai (CSIC-IEEC), Campus UAB, Facultat de Cincies, C5p 2, E-08193 Bellaterra, Catalonia,Spain

E-mail contact: kpqiu at nju.edu.cn

We report the first detection of an hourglass magnetic field aligned with a well-defined outflow rotation system in ahigh-mass, star-forming region. The observations were performed with the Submillimeter Array toward G240.31+0.07,which harbors a massive, flattened, and fragmenting molecular cloud core and a wide-angle bipolar outflow. Thepolarized dust emission at 0.88 mm reveals a clear hourglass-shaped magnetic field aligned within 20 of the outflowaxis. Maps of high-density tracing spectral lines, e.g., H13CO

+ (4-3), show that the core is rotating about its minoraxis, which is also aligned with the magnetic field axis. Therefore, both the magnetic field and kinematic propertiesobserved in this region are surprisingly consistent with the theoretical predictions of the classic paradigm of isolatedlow-mass star formation. The strength of the magnetic field in the plane of sky is estimated to be 1.1 mG, resultingin a mass-to-magnetic flux ratio of 1.4 times the critical value and a turbulent-to-ordered magnetic energy ratio of 0.4.We also find that the specific angular momentum almost linearly decreases from r ∼ 0.6 pc to 0.03 pc scales, which ismost likely attributed to magnetic braking.

Accepted by The Astrophysical Journal Letters

http://arxiv.org/pdf/1409.5608

Collisionally Excited Filaments in HST Hα and Hβ Images of HH 1/2

A.C. Raga1, B. Reipurth2, A. Castellanos-Ramırez1, Hsin-Fang Chiang2 and J. Bally3

1 Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Ap. 70-543, 04510 D.F., Mexico2 Institute for Astronomy, University of Hawaii at Manoa, Hilo, HI 96720, USA

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3 Center for Astrophysics and Space Astronomy, University of Colorado, UCB 389, Boulder, CO 80309, USA

E-mail contact: raga@nucleares.unam.mx

We present new Hα and Hβ images of the HH 1/2 system, and we find that the Hα/Hβ ratio has high values in ridgesalong the leading edges of the HH 1 bow shock and of the brighter condensations of HH 2. These ridges have Hα/Hβ= 4 to 6, which is consistent with collisional excitation from the n = 1 to the n = 3 and 4 levels of hydrogen in a gasof temperatures T = 1.5 to 10×104 K. This is therefore the first direct proof that the collisional excitation/ionizationregion of hydrogen right behind Herbig-Haro shock fronts is detected.

Accepted by ApJ Letters

http://arxiv.org/pdf/1411.7972

Fragmentation and Kinematics of dense molecular cores in the filamentary infrared-darkcloud G011.11-0.12

S. E. Ragan1, T. Henning1, H. Beuther1, H. Linz1 and S. Zahorecz1,2

1 Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg, Germany2 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Muenchen, Germany

E-mail contact: S.Ragan at leeds.ac.uk

We present new Plateau de Bure Interferometer observations of a region in the filamentary infrared-dark cloud (IRDC)G011.11-0.12 containing young, star-forming cores. In addition to the 3.2mm continuum emission from cold dust,we map this region in the N2H

+(1-0) line to trace the core kinematics with an angular resolution of 2” and velocityresolution of 0.2 km s−1. These data are presented in concert with recent Herschel results, single-dish N2H

+(1-0) data, SABOCA 350µm continuum data, and maps of the C18O (2-1) transition obtained with the IRAM 30mtelescope. We recover the star-forming cores at 3.2mm continuum, while in N2H

+ they appear at the peaks ofextended structures. The mean projected spacing between N2H

+ emission peaks is 0.18pc, consistent with simpleisothermal Jeans fragmentation. The 0.1 pc-sized cores have low virial parameters on the criticality borderline, whileon the scale of the whole region, we infer that it is undergoing large-scale collapse. The N2H

+ linewidth increases withevolutionary stage, while CO isotopologues show no linewidth variation with core evolution. Centroid velocities of alltracers are in excellent agreement, except in the starless region where two N2H

+ velocity components are detected,one of which has no counterpart in C18O. We suggest that gas along this line of sight may be falling into the quiescentcore, giving rise to the second velocity component, possibly connected to the global collapse of the region.

Accepted by A&A

http://arxiv.org/pdf/1411.1911

Planet-induced disk structures: A comparison between (sub)mm and infrared radiation

Jan Philipp Ruge1, Sebastian Wolf1, Ana L. Uribe2 and Hubert H. Klahr3

1 Universitat zu Kiel, Institut fur Theoretische und Astrophysik, Leibnitzstr. 15, 24098 Kiel, Germany2 University of Chicago, The Department of Astronomy and Astrophysics, 5640 S. Ellis Ave, Chicago, IL 60637, USA3 Max-Planck-Institut fur Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany

E-mail contact: ruge at astrophysik.uni-kiel.de

Young giant planets, which are embedded in a circumstellar disk, will significantly perturb the disk density distribution.This effect can potentially be used as an indirect tracer for planets. We investigate the feasibility of observing planet-induced gaps in circumstellar disks in scattered light. We perform 3D hydrodynamical disk simulations combinedwith subsequent radiative transfer calculations in scattered light for different star, disk, and planet configurations.The results are compared to those of a corresponding study for the (sub)mm thermal re-emission. The feasibility ofdetecting planet-induced gaps in scattered light is mainly influenced by the optical depth of the disk and therefore bythe disk size and mass. Planet-induced gaps are in general only detectable if the photosphere of the disks is sufficientlydisturbed. Within the limitations given by the parameter space here considered, we find that gap detection is possiblein the case of disks with masses below ∼ 10−4...−3 M⊙. Compared to the disk mass that marks the lower AtacamaLarge (Sub)Millimeter Array (ALMA) detection limit for the thermal radiation re-emitted by the disk, it is possible to

40

detect the same gap both in re-emission and scattered light only in a narrow range of disk masses around ∼ 10−4M⊙,corresponding to 16% of cases considered in our study.

Accepted by A&AL

http://arxiv.org/pdf/1411.2735

Young Stellar Object candidates toward the Orion region selected from GALEX

Nestor Sanchez1, Ana Ines Gomez de Castro1, Fatima Lopez-Martinez1, and Javier Lopez-Santiago1

1 S.D. Astronomıa y Geodesia, Fac. CC. Matematicas, Universidad Complutense de Madrid, 28040 Madrid, Spain

E-mail contact: nestorsa at ucm.es

We analyze 359 ultraviolet tiles from the All Sky Imaging Survey of the space mission GALEX covering roughly400 square degrees toward the Orion star-forming region. There is a total of 1,555,174 ultraviolet sources that werecross-matched with others catalogs (2MASS, UCAC4, SDSS, DENIS, CMC15 and WISE) to produce a list of 290,717reliable sources with a wide range of photometric information. Using different color selection criteria we identify 111Young Stellar Object candidates showing both ultraviolet and infrared excesses, of which 81 are new identifications.We discuss the spatial distribution, the spectral energy distributions and other physical properties of these stars. Theirproperties are, in general, compatible with those expected for T Tauri stars. This population of TTS candidates iswidely dispersed around the Orion molecular cloud.

Accepted by A&A

http://arxiv.org/pdf/1411.0532

3D Dust Mapping Reveals that Orion Forms Part of a Large Ring of Dust

E.F. Schlafly1, G. Green2, D.P. Finkbeiner2,3, H.-W. Rix1, W.S. Burgett4, K.C. Chambers4, P.W.Draper5, N. Kaiser4, N.F. Martin6,1, N. Metcalfe5, J.S. Morgan4, P. A. Price7, J.L. Tonry4, R.J.Wainscoat4, C. Waters4

1 Max Planck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg, Germany2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA3 Department of Physics, Harvard University, 17 Oxford Street, Cambridge MA 02138, USA4 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu HI 96822, USA5 Department of Physics, Durham University, South Road, Durham DH1 3LE, UK6 Observatoire Astronomique de Strasbourg, CNRS, UMR 7550, 11 rue de lUniversite, F-67000 Strasbourg, France7 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

E-mail contact: schlafly at mpia.de

The Orion Molecular Complex is the nearest site of ongoing high-mass star formation, making it one of the mostextensively studied molecular complexes in the Galaxy. We have developed a new technique for mapping the 3Ddistribution of dust in the Galaxy using Pan-STARRS1 photometry. We isolate the dust at the distance to Orionusing this technique, revealing a large (100 pc, 14 degree diameter), previously unrecognized ring of dust, which weterm the ”Orion dust ring.” The ring includes Orion A and B, and is not coincident with current Hα features. Thecircular morphology suggests formation as an ancient bubble in the interstellar medium, though we have not been ableto conclusively identify the source of the bubble. This hint at the history of Orion may have important consequencesfor models of high-mass star formation and triggered star formation.

Accepted by ApJ

http://arxiv.org/pdf/1411.5402

The Effects of Initial Abundances on Nitrogen in Protoplanetary Disks

Kamber Schwarz1 and Edwin Bergin1

1 University of Michigan, 1085 South University Ave., Ann Arbor, MI 48109, USA

41

E-mail contact: kamberrs at umich.edu

The dominant form of nitrogen provided to most solar system bodies is currently unknown, though available measure-ments show that the detected nitrogen in solar system rocks and ices is depleted with respect to solar abundances andthe interstellar medium. We use a detailed chemical/physical model of the chemical evolution of a protoplanetary diskto explore the evolution and abundance of nitrogen-bearing molecules. Based on this model we analyze how initialchemical abundances, provided as either gas or ice during the early stages of disk formation, influence which speciesbecome the dominant nitrogen bearers at later stages. We find that a disk with the majority of its initial nitrogen ineither atomic or molecular nitrogen is later dominated by atomic and molecular nitrogen as well as NH3 and HCN ices,where the dominant species varies with disk radius. When nitrogen is initially in gaseous ammonia, it later becomestrapped in ammonia ice except in the outer disk where atomic nitrogen dominates. For a disk with the initial nitrogenin the form of ammonia ice the nitrogen remains trapped in the ice as NH3 at later stages. The model in which most ofthe initial nitrogen is placed in atomic N best matches the ammonia abundances observed in comets. Furthermore theinitial state of nitrogen influences the abundance of N2H

+, which has been detected in protoplanetary disks. StrongN2H

+ emission is found to be indicative of an N2 abundance greater than nN2/nH2

> 10−6, in addition to tracing theCO snow line. Our models also indicate that NO is potentially detectable, with lower N gas abundances leading tohigher NO abundances.

Accepted by The Astrophysical Journal

http://arxiv.org/pdf/1411.1403.pdf

Magnetic field structure around cores with very low luminosity objects

A. Soam1, G. Maheswar1, Chang Won Lee2,7, Sami Dib3,4, H.C. Bhatt5, Tamura Motohide6, andGwanjeong Kim2,7

1 Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital 263002, India2 Korea Astronomy & Space Science Institute (KASI), 776 Daedeokdae-ro, Yuseong-gu, Daejeon, Republic of Korea3 Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, DK-2100, Copenhagen, Denmark4 Centre for Star and Planet Formation, University of Copenhagen, ster Voldgade 5-7., DK-1350, Copenhagen, Den-mark5 Indian Institute of Astrophysics, Kormangala (IIA), Bangalore 560034, India6 National Astronomical Observatory of Japan (NAOJ), Mitaka, Tokyo 181-8588, Japan7 University of Science & Technology, 217 Gajungro, Yuseong-gu, Daejeon, 305-333, Korea

E-mail contact: archana at aries.res.in

We carried out optical polarimetry of five dense cores, (IRAM 04191, L1521F, L328, L673-7, and L1014) which arefound to harbour VeLLO. This study was conducted mainly to understand the role played by the magnetic field in theformation of very low and substellar mass range objects using optical polarisation. The angular offsets between theenvelope magnetic field direction (inferred from optical polarisation measurements) and the outflow position anglesfrom the VeLLOs in IRAM 04191, L1521F, L328, L673-7, and L1014 are found to be 84◦, 53◦, 24◦, 08◦, and 15◦,respectively. The mean value of the offsets for all the five clouds is ∼ 37◦. If we exclude IRAM 04191, the mean valuereduces to become ∼ 25◦. In IRAM 04191, the offset between the projected envelope and the inner magnetic field(inferred from the submillimetre data from SCUPOL) is found to be ∼ 68◦. The inner magnetic field, however, isfound to be nearly aligned with the projected position angles of the minor axis, the rotation axis of the cloud, and theoutflow from the IRAM 04191-IRS. We discuss a possible explanation for the nearly perpendicular orientation betweenthe envelope and core scale magnetic fields in IRAM04191. The angular offset between the envelope magnetic fielddirection and the minor axis of IRAM 04191, L1521F, L673-7, and L1014 are 82◦, 60◦, 47◦, and 55◦, respectively. Themean value of the offsets between the envelope magnetic field and the minor axis position angles for the four cores isfound to be ∼ 60◦. The results obtained from our study on the limited sample of five cores with VeLLOs show thatthe outflows in three of them tend to nearly align with the envelope magnetic field.

Accepted by A&A

http://arxiv.org/pdf/1411.0785

42

Alignment of Protostars and Circumstellar Disks During the Embedded Phase

Christopher Spalding1, Konstantin Batygin1, and Fred C. Adams2,3

1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA2 Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA3 Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA

E-mail contact: cspaldin at caltech.edu

Star formation proceeds via the collapse of a molecular cloud core over multiple dynamical timescales. Turbulencewithin cores results in a spatially non-uniform angular momentum of the cloud, causing a stochastic variation inorientation of the disk forming from the collapsing material. In the absence of star-disk angular momentum coupling,such disk-tilting would provide a natural mechanism for production of primordial spin-orbit misalignments in theresulting planetary systems. However, owing to high accretion rates in the embedded phase of star formation, the inneredge of the circumstellar disk extends down to the stellar surface, resulting in efficient gravitational and accretionalangular momentum transfer between the star and the disk. Here, we demonstrate that the resulting gravitationalcoupling is sufficient to suppress any significant star-disk misalignment, with accretion playing a secondary role. Thejoint tilting of the star-disk system leads to a stochastic wandering of star-aligned bipolar outflows. Such wanderingwidens the effective opening angle of stellar outflows, allowing for more efficient clearing of the remainder of theprotostar’s gaseous envelope. Accordingly, the processes described in this work provide an additional mechanismresponsible for sculpting the stellar Initial Mass Function (IMF).

Accepted by ApJL

http://arxiv.org/pdf/1411.5431

The YSO Population in the Vela-D Molecular Cloud

F. Strafella1, D. Lorenzetti2, T. Giannini2, D. Elia3, Y. Maruccia1, B. Maiolo1, F. Massi4, L. Olmi4, S.Molinari3, S. Pezzuto3

1 Dipartimento di Matematica e Fisica, Universita del Salento, I-73100 Lecce, Italy2 INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio, Italy3 INAF-IAPS, via Fosso del Cavaliere 100, I-00133 Roma, Italy4 INAF-Osservatorio di Arcetri, Largo E.Fermi 5, I-50125 Firenze, Italy

E-mail contact: francesco.strafella at le.infn.it

We investigate the young stellar population in the Vela Molecular Ridge, Cloud-D (VMR-D), a star forming (SF)region observed by both Spitzer/NASA and Herschel/ESA space telescope. The point source, band-merged, Spitzer-IRAC catalog complemented with MIPS photometry previously obtained is used to search for candidate young stellarobjects (YSO), also including sources detected in less than four IRAC bands. Bona fide YSO are selected by usingappropriate color-color and color-magnitude criteria aimed to exclude both Galatic and extragalactic contaminants.The derived star formation rate and efficiency are compared with the same quantities characterizing other SF clouds.Additional photometric data, spanning from the near-IR to the submillimeter, are used to evaluate both bolometricluminosity and temperature for 33 YSOs located in a region of the cloud observed by both Spitzer and Herschel.The luminosity-temperature diagram suggests that some of these sources are representative of Class 0 objects withbolometric temperatures below 70 K and luminosities of the order of the solar luminosity. Far IR observations fromthe Herschel/Hi-GAL key project for a survey of the Galactic plane are also used to obtain a band-merged photometriccatalog of Herschel sources aimed to independently search for protostars. We find 122 Herschel cores located on themolecular cloud, 30 of which are protostellar and 92 starless. The global protostellar luminosity function is obtainedby merging the Spitzer and Herschel protostars. Considering that 10 protostars are found in both Spitzer and Herschellist it follows that in the investigated region we find 53 protostars and that the Spitzer selected protostars account forapproximately two-thirds of the total.

Accepted by ApJ

http://arxiv.org/pdf/1411.2758

43

Herschel Far IR observations of the giant HII region NGC 3603

F. Strafella1, D. Lorenzetti2, T. Giannini2, D. Elia3, Y. Maruccia1, B. Maiolo1, F. Massi4, L. Olmi4, S.Molinari3, S. Pezzuto3

1 Dipartimento di Matematica e Fisica, Universita del Salento, I-73100 Lecce, Italy2 INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio, Italy3 INAF-IAPS, via Fosso del Cavaliere 100, I-00133 Roma, Italy4 INAF-Osservatorio di Arcetri, Largo E.Fermi 5, I-50125 Firenze, Italy

E-mail contact: francesco.strafella at le.infn.it

We observed the giant HII region around the NGC 3603 YC with the 5 broad bands (70, 160, 250, 350, 500 µm) of theSPIRE and PACS instruments, on-board the Herschel Space Observatory. Together with what is currently known ofthe stellar, atomic, molecular and warm dust components, this additional and crucial information should allow us tobetter understand the details of the star formation history in this region. The main objective of the investigation is tostudy, at high spatial resolution, the distribution and main physical characteristics of the cold dust. By reconstructingthe temperature and density maps, we found respectively a mean value of 36 K and log(NH) = 22.0 ± 0.1 cm−2.We carried out a photometric analysis detecting 107 point-like sources, mostly confined to the North and South ofthe cluster. By comparing our data with SED models we found that 35 sources are well represented by YSOs inearly evolutionary phases, from Class 0 to Class I. The Herschel detections also provided far-IR counterparts for 4H2O masers and 11 objects previously known from mid-IR observations. The existence of so many embedded sourcesconfirms the hypothesis of an intense and ongoing star formation activity in the region around NGC 3603 YC.

Accepted by ApJ

http://arxiv.org/pdf/1411.3094

Chains of dense cores in the Taurus L1495/B213 complex

M. Tafalla1 and A. Hacar2

1 Observatorio Astronomico Nacional (IGN), Alfonso XII 3, E-28014 Madrid, Spain2 Institute for Astrophysics, University of Vienna, Turkenschanzstrasse 17, A-1180 Vienna, Austria

E-mail contact: m.tafalla at oan.es

Context. Cloud fragmentation into dense cores is a critical step in the process of star formation. A number of recentobservations show that it is connected to the filamentary structure of the gas, but the processes responsible for coreformation remain mysterious.Aims. We studied the kinematics and spatial distribution of the dense gas in the L1495/B213 filamentary region ofthe Taurus molecular cloud with the goal of understanding the mechanism of core formation.Methods. We mapped the densest regions of L1495/B213 in N2H

+(1–0) and C18O(2–1) with the IRAM 30m telescope,and complemented these data with archival dust-continuum observations from the Herschel Space Observatory.Results. The dense cores in L1495/B213 are significantly clustered in linear chain-like groups about 0.5 pc long.The internal motions in these chains are mostly subsonic and the velocity is continuous, indicating that turbulencedissipation in the cloud has occurred at the scale of the chains and not at the smaller scale of the individual cores. Thechains also present an approximately constant abundance of N2H

+ and radial intensity profiles that can be modeledwith a density law that follows a softened power law. A simple analysis of the spacing between the cores usingan isothermal cylinder model indicates that the cores have likely formed by gravitational fragmentation of velocity-coherent filaments.Conclusions. Combining our analysis of the cores with our previous study of the large-scale C18O emission from thecloud, we propose a two-step scenario of core formation in L1495/B213. In this scenario, named “fray and fragment”,L1495/B213 originated from the supersonic collision of two flows. The collision produced a network of intertwinedsubsonic filaments or fibers (fray step). Some of these fibers accumulated enough mass to become gravitationallyunstable and fragment into chains of closely-spaced cores.

Accepted by Astronomy and Astrophysics

http://arxiv.org/pdf/1412.1083v1

44

Fast molecular jet from L1157-mm

M. Tafalla1, R. Bachiller1, B. Lefloch2,3, N. Rodrıguez-Fernandez4, C. Codella5, A. Lopez-Sepulcre2,3,6

and L. Podio5

1 Observatorio Astronomico Nacional (IGN), Alfonso XII 3, E-28014 Madrid, Spain2 Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France3 CNRS, IPAG, F-38000 Grenoble, France4 CESBIO (UMR 5126), Obs. de Midi-Pyrenees (CNES, CNRS, Univ. Paul Sabatier, IRD), 31401 Toulouse, France5 INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy6 Department of Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan

E-mail contact: m.tafalla at oan.es

Context. L1157-mm powers a molecular outflow that is well-known for its shock-induced chemical activity in severalhot-spots.Aims. We have studied the molecular emission toward L1157-mm searching for a jet component responsible for thesespots.Methods. We used the IRAM 30m telescope to observe the vicinity of L1157-mm in several lines of SiO.Results. The SiO(5–4) and SiO(6–5) spectra toward L1157-mm present blue and red detached components about45 km s−1 away from the ambient cloud. These extremely high-velocity (EHV) components are similar to thosefound in the L1448 and IRAS 04166+2706 outflows and probably arise from a molecular jet driven by L1157-mm.Observations of off-center positions indicate that the jet is unresolved in SiO(5–4) (< 11′′).Conclusions. The EHV jet seen in SiO probably excites L1157-B1 and the other chemically active spots of the L1157outflow.

Accepted by Astronomy and Astrophysics

http://arxiv.org/pdf/1412.1476v1

The massive eruptive Class I variable V723 Carinae

Mauricio Tapia1, Miguel Roth2 and Paolo Persi3

1 Instituto de Astronomia, UNAM, Ensenada, Mexico2 Las Campanas Observatory, CIW, Chile3 INAF- Istituto Astrofisica e Planetologia Spaziale, Rome , Italy

E-mail contact: mt at astrosen.unam.mx

Near-IR observations from 1993 to 2014 of V723 Carinae confirm this to be a young eruptive variable embedded in theCar I PDR/dust cloud in NGC 3372. In 1993, it was fainter than 16.6 in JHK and went into outburst before 2003,reaching K ≃ 12.9 in 2004. Since then, V723 Car has suffered erratic flux variations of up to ∆K = 2 in timescalesof years. The variations are also evident into the mid-infrared. The H −K index shows correlation with K, thoughthe ratio ∆K/∆(H −K) differs from that expected from dust extinction. The 1.91 to 2.48 µm spectrum of V723 Carshows emission lines of H2 and also Brγ, as well as 2.3- 2.4 µm CO overtone band-heads. The system is extremely red(H −K ≥ 4), with mid- and far-IR colours of a Class I object. The fitted parameters of Robitaille et al.’s model tothe 1.6 to 850 µm SED of V723 Car indicate a system composed of a 10M⊙ central star with a 5.6 × 10−3M⊙ diskand a 1.6 × 103M⊙ envelope with AV ∼ 55 of extinction. The total luminosity of the system is about 4 × 103L⊙.V723 Car is the most luminous, most massive, most deeply embedded, and possibly the youngest of all the youngeruptive variables known. Evidence is provided of a 5,000 AU-long jet of shocked gas extending to opposite sites ofthe star. The infrared properties of a nearby 10L⊙ Class I young stellar object, Car I-125, are also described, withvariations in K typical of Herbig Ae/Be stars. Its near-IR spectrum is featureless except for bright Brγ line emission.

Accepted by MNRAS

ftp://ftp.astrosen.unam.mx/iauname/mt/preprints (connect as Guest)

45

Outward Motion of Porous Dust Aggregates by Stellar Radiation Pressure in Proto-planetary Disks

Ryo Tazaki1 and Hideko Nomura2

1 Department of Astronomy, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku,Kyoto 606-8502, Japan2 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo152-8551, Japan

E-mail contact: rtazaki at kusastro.kyoto-u.ac.jp

We study the dust motion at the surface layer of protoplanetary disks. Dust grains in surface layer migrate outwarddue to angular momentum transport via gas-drag force induced by the stellar radiation pressure. In this study, wecalculate mass flux of the outward motion of compact grains and porous dust aggregates by the radiation pressure.The radiation pressure force for porous dust aggregates is calculated using the T-Matrix Method for the Clusters ofSpheres. First, we confirm that porous dust aggregates are forced by strong radiation pressure even if they grow to belarger aggregates in contrast to homogeneous and spherical compact grains to which efficiency of radiation pressurebecomes lower when their sizes increase. In addition, we find that the outward mass flux of porous dust aggregateswith monomer size of 0.1 µm is larger than that of compact grains by an order of magnitude at the disk radiusof 1 AU, when their sizes are several microns. This implies that large compact grains like calcium-aluminum richinclusions (CAIs) are hardly transported to outer region by stellar radiation pressure, whereas porous dust aggregateslike chondritic-porous interplanetary dust particles (CP-IDPs) are efficiently transported to comet formation region.Crystalline silicates are possibly transported in porous dust aggregates by stellar radiation pressure from inner hotregion to outer cold cometary region in the protosolar nebula.

Accepted by ApJ

http://arxiv.org/pdf/1411.4751

Polytropic models of filamentary interstellar clouds – I. Structure and stability

Claudia Toci1 and Daniele Galli2

1 Dipartimento di Fisica e Astronomia, Universita degli Studi di Firenze, Via G. Sansone 1, I-50019 Sesto Fiorentino,Italy2 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy

E-mail contact: claudia at arcetri.astro.it

The properties of filamentary interstellar clouds observed at sub-millimetre wavelengths, especially by the HerschelSpace Observatory, are analysed with polytropic models in cylindrical symmetry. The observed radial density profilesare well reproduced by negative-index cylindrical polytropes with polytropic exponent 1/3 < γp < 2/3 (polytropicindex −3 < n < −3/2), indicating either external heating or non-thermal pressure components. However, the formerpossibility requires unrealistically high gas temperatures at the filament’s surface and is therefore very unlikely. Non-thermal support, perhaps resulting from a superposition of small-amplitude Alfven waves (corresponding to γp = 1/2),is a more realistic possibility, at least for the most massive filaments. If the velocity dispersion scales as the squareroot of the density (or column density) on the filament’s axis, as suggested by observations, then polytropic modelsare characterised by a uniform width. The mass per unit length of pressure-bounded cylindrical polytropes dependson the conditions at the boundary and is not limited as in the isothermal case. However, polytropic filaments canremain stable to radial collapse for values of the axis-to-surface density contrast as large as the values observed onlyif they are supported by a non-isentropic pressure component.

Accepted by M.N.R.A.S.

http://arxiv.org/pdf/1410.6091

Polytropic models of filamentary interstellar clouds – II. Helical magnetic fields

Claudia Toci1 and Daniele Galli2

1 Dipartimento di Fisica e Astronomia, Universita degli Studi di Firenze, Via G. Sansone 1, I-50019 Sesto Fiorentino,

46

Italy2 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy

E-mail contact: claudia at arcetri.astro.it

We study the properties of magnetised cylindrical polytropes as models for interstellar filamentary clouds, extendingthe analysis presented in a companion paper. We formulate the general problem of magnetostatic equilibrium in thepresence of a helical magnetic field, with the aim of determining the degree of support or compression resulting fromthe magnetisation of the cloud. We derive scale-free solutions appropriate to describe the properties of the envelopesof filaments at radii larger than the flat-density region. In these solutions, the polytropic exponent determines theradial profiles of the density and the magnetic field. The latter decreases with radius less steeply than the density,and field lines are helices twisted over cylindrical surfaces. A soft equation of state supports magnetic configurationsthat preferentially compress and confine the filament, whereas in the isothermal limit the field provides support. Foreach value of the polytropic exponent, the Lorentz force is directed outward or inward depending on whether the pitchangle is below or above some critical value which is a function of the polytropic exponent only.

Accepted by MNRAS

http://arxiv.org/pdf/1410.6092

Star formation in Chamaeleon I and III: a molecular line study of the starless corepopulation

A.E. Tsitali1, A. Belloche1, R.T. Garrod2, B. Parise1,3, and K.M. Menten1

1 Max-Planck-Institut fur Radioastronomie, Auf dem Hgel 69, 53121, Bonn, Germany2 Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853-6801, USA3 School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff CF24 3AA, UK

E-mail contact: belloche at mpifr-bonn.mpg.de

The Chamaeleon clouds are excellent targets for low-mass star formation studies. Cha I and II are actively formingstars while Cha III shows no sign of ongoing star formation. We aim to determine the driving factors that have ledto the very different levels of star formation activity in Cha I and III and examine the dynamical state and possibleevolution of the starless cores within them. Observations were performed in various molecular transitions with APEXand Mopra. Five cores are gravitationally bound in Cha I and one in Cha III. The infall signature is seen toward 8–17cores in Cha I and 2–5 cores in Cha III, which leads to a range of 13–28% of the cores in Cha I and 10–25% of the coresin Cha III that are contracting and may become prestellar. Future dynamical interactions between the cores will notbe dynamically significant in either Cha I or III, but the subregion Cha I North may experience collisions between coreswithin ∼0.7 Myr. Turbulence dissipation in the cores of both clouds is seen in the high-density tracers N2H

+ 1–0 andHC3N 10–9. Evidence of depletion in the Cha I core interiors is seen in the abundance distributions of C17O, C18O,and C34S. Both contraction and static chemical models indicate that the HC3N to N2H

+ abundance ratio is a goodevolutionary indicator in the prestellar phase for both gravitationally bound and unbound cores. In the frameworkof these models, we find that the cores in Cha III and the southern part of Cha I are in a similar evolutionary stageand are less chemically evolved than the central region of Cha I. The measured HC3N/N2H

+ abundance ratio and theevidence for contraction motions seen towards the Cha III starless cores suggest that Cha III is younger than Cha ICentre and that some of its cores may form stars in the future. The cores in Cha I South may on the other hand betransient structures.

Accepted by A&A

http://arxiv.org/pdf/1411.3741

The structure of disks around Herbig Ae/Be stars as traced by CO ro-vibrational emis-sion

G. van der Plas1,2,3, M.E. van den Ancker3, L. B. F. M. Waters2,4 and C. Dominik2,5

1 Departamento de Astronomıa, Universidad de Chile, Casilla 36-D, Santiago, Chile2 Astronomical Institute Anton Pannekoek, University of Amsterdam, PO box 94249, 1090 GE, Amsterdam, TheNetherlands

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3 European Southern Observatory, Karl-Schwarzschild-Str.2, D 85748 Garching bei Munchen, Germany4 SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands5 Institute for Astrophysics, Radbout University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands

E-mail contact: info at gerritvanderplas.com

Aims We study the emission and absorption of CO ro-vibrational lines in the spectra of intermediate mass pre-main-sequence stars with the aim to determine both the spatial distribution of the CO gas and its physical properties. Wealso aim to correlate CO emission properties with disk geometry.Methods Using high-resolution spectra containing fundamental and first overtone CO ro-vibrational emission, observedwith CRIRES on the VLT, we probe the physical properties of the circumstellar gas by studying its kinematics andexcitation conditions.Results We detect and spectrally resolve CO fundamental ro-vibrational emission in 12 of the 13 stars observed, andin two cases in absorption.Conclusions Keeping in mind that we studied a limited sample, we find that the physical properties and spatialdistribution of the CO gas correlate with disk geometry. Flaring disks show highly excited CO fundamental emissionup to vu = 5, while self-shadowed disks show CO emission that is not as highly excited. Rotational temperatures rangebetween 250-2000 K. The 13CO rotational temperatures are lower than those of 12CO. The vibrational temperaturesin self-shadowed disks are similar to or slightly below the rotational temperatures, suggesting that thermal excitationor IR pumping is important in these lines. In flaring disks the vibrational temperatures reach as high as 6000 K,suggesting fluorescent pumping. Using a simple kinematic model we show that the CO inner radius of the emittingregion is ≈10 au for flaring disks and ≤ 1 au for self-shadowed disks. Comparison with hot dust and other gas tracersshows that CO emission from the disks around Herbig Ae/Be stars, in contrast to T Tauri stars, does not necessarilytrace the circumstellar disk up to, or inside the dust sublimation radius, Rsubl. Rather, the onset of the CO emissionstarts from ≈Rsubl for self-shadowed disks, to tens of Rsubl for flaring disks. It has recently been postulated that groupI Herbig stars may be transitional disks and have gaps. Our CO observations are qualitatively in agreement with thispicture. We identify the location of the CO emission in these group I disks with the inner rim of the outer disk aftersuch a gap, and suggest that the presence of highly vibrationally excited CO emission and a mismatch between therotational and vibrational temperature may be a proxy for the presence of moderately sized disk gaps in Herbig Ae/Bedisks.

Accepted by Astronomy and Astrophysics

http://arxiv.org/pdf/1412.1311

A direct imaging search for close stellar and sub-stellar companions to young nearbystars

Nikolaus Vogt1, Markus Mugrauer2, Ralph Neuhauser2, Tobias O.B. Schmidt2, Alexander Contreras-Quijada1, and Janos G. Schmidt2

1 Instituto de Fısica y Astronomıa, Universidad de Valparaıso, Chile, Avenida Gran Bretana 1111, Valparaıso, Chile2 Astrophysikalisches Institut und Universitats-Sternwarte Jena, Schillergaßchen 2, D-07745 Jena, Germany

E-mail contact: nikolaus.vogt at uv.cl

A total of 28 young nearby stars (ages ≤60 Myr) have been observed in the Ks-band with the adaptive optics imagerNaos-Conica of the Very Large Telescope at the Paranal Observatory in Chile. Among the targets are ten visualbinaries and one triple system at distances between 10 and 130 pc, all previously known. During a first observingepoch a total of 20 faint stellar or sub-stellar companion-candidates were detected around seven of the targets. Thesefields, as well as most of the stellar binaries, were re-observed with the same instrument during a second epoch, aboutone year later. We present the astrometric observations of all binaries. Their analysis revealed that all stellar binariesare co-moving. In two cases (HD 119022 AB and FG Aqr B/C) indications for significant orbital motions were found.However, all sub-stellar companion-candidates turned out to be non-moving background objects except PZ Tel whichis part of this project but whose results were published elsewhere. Detection limits were determined for all targets,and limiting masses were derived adopting three different age values; they turn out to be less than 10 Jupiter massesin most cases, well below the brown dwarf mass range. The fraction of stellar multiplicity and of the sub-stellarcompanion occurrence in the star forming regions in Chamaeleon are compared to the statistics of our search, andpossible reasons for the observed differences are discussed.

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Accepted by AN

http://arxiv.org/pdf/1411.5438

Expanding Shell and Star Formation in the Infrared Dust Bubble N6

Jing-Hua Yuan1, Yuefang Wu2, Jin Zeng Li1 and Hong-Li Liu1

1 National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing100012, China2 Department of Astronomy, Peking University, 100871 Beijing, China

E-mail contact: jhyuan at nao.cas.cn

We have carried out a multi-wavelength study of the infrared dust bubble N6 to extensively investigate the molecularenvirons and star-forming activities therein. Mapping observations in 12CO J = 1− 0 and 13CO J = 1− 0 performedwith the Purple Mountain Observatory 13.7-m telescope have revealed four velocity components. Comparison betweendistributions of each component and the infrared emission suggests that three components are correlated with N6.There are ten molecular clumps detected. Among them, five have reliable detection in both 12CO and 13CO and havesimilar LTE and non-LTE masses ranging from 200 to higher than 5,000 M⊙. With larger gas masses than virialmasses, these five clumps are gravitationally unstable and have potential to collapse to form new stars. The other fiveclumps are only reliably detected in 12CO and have relatively small masses. Five clumps are located on the borderof the ring structure and four of them are elongated along the shell. This is well in agreement with the collect andcollapse scenario. The detected velocity gradient reveals that the ring structure is still under expansion due to stellarwinds from the exciting star(s). Furthermore, 99 young stellar objects have been identified based on their infraredcolors. A group of YSOs reside inside the ring, indicating active star formation in N6. Although no confirmativefeatures of triggered star formation detected, the bubble and the enclosed HII region have profoundly reconstructedthe natal could and altered the dynamics therein.

Accepted by the Astrophysical Journal

http://arxiv.org/pdf/1411.0767

Kinematics of the Outflow From The Young Star DG Tau B: Rotation in the vicinitiesof an optical jet

Luis A. Zapata1, Susana Lizano1, Luis F. Rodrıguez1, Paul T. P. Ho2,3, Laurent Loinard1,Manuel Fernandez-Lopez3, and Daniel Tafoya1

1Centro de Radioastronomıa y Astrofısica, UNAM, Apdo. Postal 3-72 (Xangari), 58089 Morelia, Mich., Mexico2Academia Sinica Institute of Astronomy and Astrophysics, Taipei, Taiwan3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA4Astronomy Department, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA

E-mail contact: lzapata@crya.unam.mx

We present 12CO(2-1) line and 1300 µm continuum observations made with the Submillimeter Array (SMA) of theyoung star DG Tau B. We find, in the continuum observations, emission arising from the circumstellar disk surroundingDG Tau B. The 12CO(2-1) line observations, on the other hand, revealed emission associated with the disk and theasymmetric outflow related with this source. Velocity asymmetries about the flow axis are found over the entire lengthof the flow. The amplitude of the velocity differences is of the order of 1 – 2 km s−1 over distances of about 300 –400 AU. We interpret them as a result of outflow rotation. The sense of the outflow and disk rotation is the same.Infalling gas from a rotating molecular core cannot explain the observed velocity gradient within the flow. Magneto-centrifugal disk winds or photoevaporated disk winds can produce the observed rotational speeds if they are ejectedfrom a keplerian disk at radii of several tens of AU. Nevertheless, these slow winds ejected from large radii are notvery massive, and cannot account for the observed linear momentum and angular momentum rates of the molecularflow. Thus, the observed flow is probably entrained material from the parent cloud. DG Tau B is a good laboratoryto model in detail the entrainment process and see if it can account for the observed angular momentum.

Accepted by The Astrophysical Journal

http://arxiv.org/pdf/1411.0173

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ALMA reveals a candidate hot and compact disk around the O-type protostar IRAS16547−4247

Luis A. Zapata1, Aina Palau1, Roberto Galvan-Madrid1,2, Luis F. Rodrıguez1, Guido Garay3,James M. Moran4, and Ramiro Franco-Hernandez3

1Centro de Radiostronomıa y Astrofısica, Universidad Nacional Autonoma de Mexico, Morelia, Michoacan, Mexico2European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching, Germany3Departamento de Astronomıa, Universidad de Chile, Casilla 36-D, Santiago, Chile4Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

E-mail contact: lzapata@crya.unam.mx

We present high angular resolution (∼ 0.3′′) submillimeter continuum (0.85 mm) and line observations of the O-type protostar IRAS 16547−4247 carried out with the Atacama Large Millimeter/Submillimeter Array (ALMA).In the 0.85 mm continuum band, the observations revealed two compact sources (with a separation of 2′′), one ofthem associated with IRAS 16547−4247, and the other one to the west. Both sources are well resolved angularly,revealing a clumpy structure. On the other hand, the line observations revealed a rich variety of molecular speciesrelated to both continuum sources. In particular, we found a large number of S-bearing molecules, such as the raremolecule methyl mercaptan (CH3SH). At scales larger than 10,000 AU, molecules (e.g., SO2 or OCS) mostly withlow excitation temperatures in the upper states (Ek

<∼ 300 K) are present in both millimeter continuum sources, and

show a southeast-northwest velocity gradient of 7 km s−1 over 3′′ (165 km s−1 pc−1). We suggest that this gradientprobably is produced by the thermal (free-free) jet emerging from this object with a similar orientation at the base.At much smaller scales (about 1000 AU), molecules with high excitation temperatures (Ek

>∼ 500 K) are tracing a

rotating structure elongated perpendicular to the orientation of the thermal jet, which we interpret as a candidatedisk surrounding IRAS 16547−4247. The dynamical mass corresponding to the velocity gradient of the candidate todisk is about 20 M⊙, which is consistent with the bolometric luminosity of IRAS 16547−4247.

Accepted by The Monthly Notices of the Royal Astronomical Society

http://arxiv.org/pdf/1411.7421

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Abstracts of recently accepted major reviews

Gravitational Collapse and Disk Formation in Magnetized Cores

S. Lizano1 and D. Galli2

1 Centro de Radioastronomia y Astrofisica, UNAM, Apdo. Postal 3-72, 58089 Morelia, Michoacan, Mexico2 NAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Firenze, Italy

E-mail contact: s.lizano at crya.unam.mx

We discuss the effects of the magnetic field observed in molecular clouds on the process of star formation, concentratingon the phase of gravitational collapse of low-mass dense cores, cradles of sunlike stars. We summarize recent analyticwork and numerical simulations showing that a substantial level of magnetic field diffusion at high densities has tooccur in order to form rotationally supported disks. Furthermore, newly formed accretion disks are threaded by themagnetic field dragged from the parent core during the gravitational collapse. These disks are expected to rotate witha sub-Keplerian speed because they are partially supported by magnetic tension against the gravity of the centralstar. We discuss how sub-Keplerian rotation makes it difficult to eject disk winds and accelerates the process ofplanet migration. Moreover, magnetic fields modify the Toomre criterion for gravitational instability via two opposingeffects: magnetic tension and pressure increase the disk local stability, but sub-Keplerian rotation makes the disk moreunstable. In general, magnetized disks are more stable than their nonmagnetic counterparts; thus, they can be moremassive and less prone to the formation of giant planets by gravitational instability.

Accepted by “Magnetic Fields in Diffuse Media”, Springer-Verlag, eds. E. de Gouveia Dal Pino, A. Lazarian, C.Melioli, Chapter 16

http://arxiv.org/pdf/1411.6828

Astrochemistry of dust, ice and gas: introduction and overview

Ewine F. van Dishoeck1

1 Leiden Observatory, Leiden University, The Netherlands

E-mail contact: ewine at strw.leidenuniv.nl

A brief introduction and overview of the astrochemistry of dust, ice and gas and their interplay is presented, aimed atnon-specialists. The importance of basic chemical physics studies of critical reactions is illustrated through a numberof recent examples. Such studies have also triggered new insight into chemistry, illustrating how astronomy andchemistry can enhance each other. Much of the chemistry in star- and planet-forming regions is now thought to bedriven by gas-grain chemistry rather than pure gas-phase chemistry, and a critical discussion of the state of such modelsis given. Recent developments in studies of diffuse clouds and PDRs, cold dense clouds, hot cores, protoplanetarydisks and exoplanetary atmospheres are summarized, both for simple and more complex molecules, with links topapers presented in this volume. In spite of many lingering uncertainties, the future of astrochemistry is bright: newobservational facilities promise major advances in our understanding of the journey of gas, ice and dust from cloudsto planets.

Accepted by Faraday Discussions 2014, vol. 168, 9

http://arxiv.org/pdf/1411.5280

51

Dissertation Abstracts

Submillimeter studies of low mass star forming regions. Star formationin the Chamaeleon cloud complex

Anastasia Tsitali

Max-Planck Institute for Radio Astronomy

Electronic mail: atsitali at gmail.com

Ph.D dissertation directed by: Arnaud Belloche, Karl Menten

Ph.D degree awarded: April 2014

The nearby molecular clouds Chamaeleon I and III (Cha I, Cha III) constitute excellent targets for low-mass starformation studies. Their large starless core population presents the opportunity to explore the earliest phases of starformation, prior to the formation of the protostellar object. The prestellar phase can offer valuable constraints forthe initial conditions necessary for star formation to occur. The apparent similarity between the stellar initial massfunction and the core mass distribution suggests that the prestellar core fragmentation plays a determining role inthe subsequent evolution of the self-gravitating dense cores to stars. A deep understanding of the physical processestaking place during the prestellar phase and the dynamical evolution of these objects is therefore essential in order toconstrain the multiple core collapse models and obtain a complete picture of star formation.

The first part of the thesis focusses on an object in the Cha I molecular cloud, Cha-MMS1. Cha-MMS1 is very likelyto be in the theoretically predicted intermediate evolutionary phase between the prestellar and protostellar phases, thefirst hydrostatic core. The dynamical state of this object is examined through molecular line observations obtainedwith the APEX and Mopra telescopes. The molecular emission is modelled using a radiative transfer code in orderto derive constraints on the kinematics of the envelope, which are then compared to MHD simulations for the firstcore phase. Both the derived internal luminosity of Cha-MMS1 and the constrained infall velocity structure of theenvelope are consistent with predictions of MHD simulations for the first core phase. Excess emission in high-densitytracers additionally suggests the possible presence of a compact, slow outflow driven by Cha-MMS1, which is the mainpredicted observational signature of first cores. Overall, Cha-MMS1 does not belong to the prestellar phase. Thekinematics of its envelope are consistent with a first hydrostatic core candidate, but it cannot be ruled out that thisobject might also be a Class 0 protostar. A future detection of a slow, compact outflow with ALMA would serve asdefinite proof that Cha-MMS1 is indeed a first hydrostatic core.

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The second part of the thesis presents a molecular line survey that was conducted with the APEX and Mopra telescopestoward the starless core populations of the Cha I and III molecular clouds. Cha I is an actively star-forming whereasCha III shows no sign of ongoing star formation. The main goal of this work is to determine the driving factorsthat have led to the strikingly different star formation activities in Cha I and III and to deduce the future dynamicalevolution of the clouds. The kinematics of the starless cores are examined through a virial analysis and a searchfor infall motions. The chemical differences between Cha I and III are investigated through the observed fractionalmolecular abundances of the cores and by a comparison to predictions of chemical models. It is observationallyderived that 15-30% of the Cha I cores and 10-25% of the Cha III cores will likely become prestellar and thereforeform stars in the future. Interactions between the starless cores will not be dynamically significant in either cloud,thus eliminating competitive accretion as a likely process in these clouds. The analysis of the kinematics in the coresshows that turbulence has likely not affected the different star formation activities in Cha I and III. Nevertheless, adifference in chemistry between Cha I and III is seen in the fractional abundances of C18O and CH3OH. The HC3N toN2H+ abundance ratio is then examined as an evolutionary indicator in the prestellar phase through comparison topredictions of collapse and static chemical models. In the framework of these models, this abundance ratio is provento be a good evolutionary tracer. An evolutionary ’gradient’ was thus seen within Cha I, with the cores in its southernpart being younger than the cores in the central region of Cha I. The suggested interpretation is that the southernCha I cores will undertake the same evolutionary path as the central Cha I cores, given that they belong to the samecloud. Interestingly, the Cha III cores have similar HC3N to N2H+ abundance ratios as the southern Cha I cores.Therefore, both the measured HC3N to N2H+ abundance ratio and the detected infall signatures indicate that ChaIII is younger than Cha I, and therefore on the verge of forming stars. This conclusion points to the existence of anevolutionary sequence in the Chamaeleon complex, with the youngest Cha III cloud to the eldest Cha I cloud, and withCha II likely at an intermediate evolutionary state. The dynamical state of Cha II is therefore worth investigating inthe future through both an unbiased, continuum survey as well as molecular line observations.

http://hss.ulb.uni-bonn.de/2014/3770/3770.htm

53

New Jobs

Postdoctoral position in molecular clouds and star formation

The Astrophysics Group at the University of Exeter invites applications for a postdoctoral position (Associate ResearchFellow / Research Fellow) to work with Dr. Chris Brunt in the field of molecular clouds and star formation. Thisfixed-term position is funded by an STFC Consolidated Grant, and is available for 3 years (subject to a 12-monthprobationary period).

The main aim of the project is deducing the 3D structure and dynamics of molecular clouds and relating this tostar formation activity. This is primarily an observational position, though one which involves a substantial degreeof modelling, including the use of supercomputer simulations. We are particularly interested in candidates with abackground in mm/sub-mm spectral line observations, extinction mapping, and infrared continuum observations.Strong mathematical ability and coding proficiency would also be an asset, and applications from candidates from anumerical background will be seriously considered.

Applicants must possess a PhD in astrophysics or a related discipline, or expect to have earned one before taking upthe position. This position is available from April 2015, and start dates up to September 2015 may be possible. Thestarting salary will range from 25,513 on Grade E to 33,242 per annum on Grade F, depending on qualifications andexperience. Extensive supercomputing resources and substantial funding for computing equipment and travel will beavailable.

For further information about the position, or for advice on the application procedure, please contact Chris Brunt(brunt@astro.ex.ac.uk). Please apply via the University of Exeter online application system at jobs.exeter.ac.uk Thejob may be found by searching under ’Key words’ using post reference P48023 (accessible from Dec 1 2014 onwards).The closing date for applications is January 31 2015.

Exeter Astrophysics Group website: http://emps.exeter.ac.uk/physics-astronomy/research/astrophysics/

Information for prospective University of Exeter employees: http://www.exeter.ac.uk/working/prospective/

Details on benefits for University of Exeter employees: http://www.exeter.ac.uk/staff/benefits/benefits/

Postdoctoral position in disc physics and planet migrationUniversity of Central Lancashire, UK

The Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, of the University of Central Lancashire,UK,is seeking to appoint a postdoctoral research assistant to work with Dr. Dimitris Stamatellos on theoretical studies ofplanet formation and migration. This is a 3-year, STFC-funded position and it will be available from 1st April 2015,or as soon as possible thereafter.

The successful applicant will be expected to have previous experience in computational astrophysics. Experiencein hydrodynamics simulations (with SPH and/or grid methods) and in modelling protostellar discs and/or planetformation is highly desirable. Hands-on experience in using grid- and/or particle-based hydrodynamics codes fordisc/planet dynamics simulations (e.g. FARGO, PENCIL, SEREN, GADGET) will be beneficial. The project willmake use of considerable computing resources, including the High Performance Computing facility of the Universityof Central Lancashire, as well as UK supercomputing facilities, such as DIRAC.

The successful applicant will be appointed on Grade G (starting salary 28,695) and will receive the usual benefits foremployees in the UK (pension contribution, health insurance, annual leave, etc). Funds for computing resources andconference/collaboration travelling will also be provided.

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The Jeremiah Horrocks Institute is comprised of nearly 30 staff with a wide range of interests that cover theoreticaland observational aspects of star formation, exoplanets, and life in the Universe (Prof. Derek Ward-Thompson -observational star formation, prestellar cores; Dr. Jason Kirk - observational star formation, prestellar cores; Prof.Don Kurtz - asteroseismology; Prof. Brad Gibson - Galactic habitable zones). The successful applicant will also havethe chance to interact with Prof. S-I, Inutsuka (Nagoya University, Japan) through a collaborative project funded bya Royal Society Daiwa Anglo-Japanese Foundation International Exchanges Award.

The Jeremiah Horrocks Institute is located on the University’s main campus, on a pleasant site in the centre of Preston.Preston itself is nestled on the edge of the beautiful Ribble Valley and the Forest of Bowland Area of OutstandingNatural Beauty. The Lake District, Peak District, and Yorkshire Dales are all within an hour’s drive. Both Manchesterand Liverpool are just 45 minutes away.

The closing date for applications is January 31st 2015. Interviews will be held on March 2nd. For informal inquirespotential applicants may contact Dr Dimitris Stamatellos, either by email at dstamatellos@uclan.ac.uk or bytelephone on +44-(0)-1772-896418. Please apply online via http://www.uclan.ac.uk/jobs/.

Faculty Position in Exoplanet Studies

The School of Earth and Space Exploration (SESE) at Arizona State University invites applications for up to threetenure-track faculty positions in the area of exoplanet studies at either the assistant or associate professor level. Rankand tenure status will be commensurate with experience. Anticipated start date is August 2015. We are especiallyinterested in candidates in the areas of exoplanet detection, interior modeling of exoplanets, atmospheric evolution,and instrumentation. Preference will be given to candidates who demonstrate the potential for interdisciplinarycollaborations with ASU planetary scientists to better characterize exoplanets.

Established in 2006, SESE is the focal point of Earth and space science at Arizona State University, one of the mostdynamic and fastest growing institutions of higher learning in the United States. An essential part of SESE’s missionis to make new discoveries by promoting interdisciplinary science and by integrating science and engineering. SESEfaculty and their research groups benefit from a variety of state-of-the-art facilities including access to the 2x8.4mLarge Binocular Telescope, 6.5m MMT telescope, 6.5m Magellan telescopes and a host of 2m-class telescopes ownedand operated by the State of Arizona. Broad, transdisciplinary collaborations between SESE astronomers, planetaryscientists, Earth scientists, and engineers are actively encouraged (http://sese.asu.edu/people faculty).

Minimum qualifications include: (1) a Ph.D. or equivalent in astronomy or astrophysics, planetary science, or a closelyrelated discipline; (2) a strong research record in exoplanet studies established through publications in internationalpeer-reviewed journals; and (3) a commitment to quality teaching and mentorship at the graduate and undergraduatelevels. Candidates for consideration at the associate level must also have a demonstrated track record of externallyfunded research.

To apply, please submit: 1) a cover letter not more than 3 pages long that includes a description of the applicant’sresearch and teaching interests and experience; 2) a current CV; and 3) the names, addresses, email addresses andtelephone numbers of three references. All materials should be submitted in PDF format to sesenewfac@asu.edu.Refer to Position #11029 in all correspondence.

The application deadline is January 5, 2015; if not filled, reviews will continue weekly until the search is closed. Abackground check is required for employment.

Arizona State University is a VEVRAA Federal Contractor and an Equal Opportunity/Affirmative Action Employer.All qualified applicants will be considered without regard to race, color, sex, religion, national origin, disability,protected veteran status, or any other basis protected by the law.

http://www.asu.edu/aad/manuals/acd/acd401 http://www.asu.edu/titleIX/

The School of Earth & Space Exploration is an academic unit of the College of Liberal Arts and Sciences.

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Three-year postdoctoral position on the formation of massive stars

The Astrophysics Group at the University of Exeter invites applications for a postdoctoral position (Associate Re-search Fellow / Research Fellow) to work with Tim Harries on radiation hydrodynamical simulations of massive starformation. This position is funded by an STFC Consolidated Grant, and is available for 3 years (subject to a 12-monthprobationary period).

The main aim of this project is to investigate the role of radiation pressure and ionisation feedback on the formationof massive stars. This will be done using 3-D radiation hydrodynamical models, and by comparing the simulationswith a broad range of multi-wavelength observational data. We are therefore particularly interested in applicants witha strong background in radiation transfer and/or hydrodynamics; prior work on star formation simulations would alsobe an asset, but all applicants with a good numerical astrophysics background will be seriously considered.

Applicants must possess a PhD in astrophysics or a related discipline, or expect to have earned one before taking upthe position. This position is available from 1st April 2015, although a later start date may be possible. The startingsalary will range from GBP 25,513 on Grade E to GBP 33,242 per annum on Grade F, depending on qualificationsand experience. Extensive supercomputing resources and substantial funding for computing equipment and travel willbe available.

For further information contact Tim Harries (th@astro.ex.ac.uk). Please apply via the University of Exeter onlineapplication system https://jobs.exeter.ac.uk. The job may be found by searching under ’Key words’ using postreference P48022. The closing date for applications is the 31st January 2015.

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Meetings

Gordon Research Conference on Origins of Solar Systems

The 2015 Gordon Research Conference on Origins of Solar Systems will be held from June 28-July 3, 2015.

The Gordon Conference on Origins of Solar Systems brings together a diverse group of scientists to discuss research atthe frontier of understanding how planets and planetary systems form. Invited speakers from the fields of astronomy,astrophysics, cosmochemistry, planetary science, and geochemistry will present their latest findings. Particular topicsof discussion will include: what meteorites tell us about the birth environment of our Solar System and planetarybuilding blocks, how asteroids and icy bodies record the accretion epoch of the Solar System history, new observationaland theoretical constraints on gas and dust in protoplanetary and debris disk systems, and how the properties ofexoplanets are determined and what they tell us about how those planets formed.

Conference website: http://www.grc.org/programs.aspx?id=12345

Workshop: The Formation of the Solar System II

2 - 4 June 2015Berlin / Germany

Although the solar system formed more than 4.5 Gyr ago there still exist a number of indicators to the conditions atthe time of its formation. Meteorites, the composition of the Kuiper belt and even today’ s properties of the solarsystem planets give clues to the solar system’s early history. However, there is an ongoing debate on how to interpretthese properties.

This second workshop ”The Formation of the Solar System II” again has the aim to bring together researchersworking in the various fields involved in this quest. It turns out that this is a truly interdisciplinary endeavour,requiring knowledge of super novae explosions, meteorites, cosmochemistry, structure and evolution of circumstellardiscs, star cluster dynamics, and the early dynamical evolution of planetary systems. Therefore contributions tacklingthe following subjects are welcome:

* Cosmochemical constraints on the physical/chemical conditions in the Solar Nebula

* Time scales of the dust and planetesimal growth for the Solar System

* Models of the Kuiper belt formation

* The role of the stellar environment, with emphasis on star cluster dynamics

* Early planetary system development

* Future evolution of the Solar System

More information can be found at: https://indico.mpifr-bonn.mpg.de/FormationOfTheSolarSystem2

SOC: Melvyn Davies, Matthieu Gounelle, Pavel Kroupa, Alessandro Morbidelli, Simon Portegies Zwart, SusannePfalzner (Chair)

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’From interstellar clouds to star-forming galaxies: universal processes?’

Honolulu, August 3-7, 2015

IAU symposium 315 From interstellar clouds to star-forming galaxies: universal processes? will be held August 3-7,2015 during the IAU General Assembly in Honolulu. The goal of this Symposium is to build a coherent picture of howstar formation is fuelled and proceeds in galaxies. It will gather researchers working on this question with differentviewpoints: from the scale of Galactic molecular clouds to star-forming galaxies at high redshift. Key topics are:

• Atomic and molecular gas reservoirs in galaxies

• From interstellar clouds to dense cores and protostellar disks

• Stellar clusters, low- vs high-mass star formation, origin of the IMF

• Star formation laws, rates, and thresholds in galaxies

• Evolution of star formation with cosmic time and environment

Please see http://astronomy2015.org/symposium_315 for the titles of specific sessions and the full science rationaleof the Symposium.

Deadlines: abstract submission is 2015 March 18, and regular registration is 2015 May 23.

So far, the confirmed invited speakers include:M. Aravena, D. Arzoumanian, S. Basu, G. Chabrier, J. Di Francesco, D. Elbaz, B. Elmegreen, S. Garcıa-Burillo, S.Glover, P. Hopkins, A. Hughes, S. Inutsuka, A. Isella. J. Kenney, K. Kohno, A. Leroy, Z.-Y. Li, S. Madden, M.-M.Mac Low, S. Martın, N. McClure-Griffiths, S. Molinari, F. Motte, P. Myers, S. Offner, M. Putman, L. Tacconi, M.Tafalla, J. Tan, S. Viti, C. Wilson.

With best wishes,Philippe Andre, Pascale Jablonka, Floris van der Takco-Chairs of IAU symposium 315

on behalf of the SOC:Suzanne Aalto, Yuri Aikawa, Frank Bigiel, Alberto Bolatto, Francoise Combes, Steve Eales, Neal Evans, Daisuke Iono,Jeremy Lim, Eve Ostriker, Monica Rubio, Kazushi Sakamoto, Jonathan Williams

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Summary of Upcoming Meetings

The Kinematics of Star Formation: Theory and Observation in the Gaia Era9 January 2015 London, UKhttp://www.star.herts.ac.uk/kinematics

45th “Saas-Fee Advanced Course”:From Protoplanetary Disks to Planet Formation15-20 March 2015, Switzerlandhttp://isdc.unige.ch/sf2015

The Soul of Massive Star Formation15 - 20 March 2015 Puerto Varas, Chilehttp://www.das.uchile.cl/msf2015/

Star and Planet Formation in the Southwest23 - 27 March 2015 Oracle, Arizona, USAhttps://lavinia.as.arizona.edu/~kkratter/SPF1/Home.html

Milky Way Astrophysics from Wide-Field Surveys30 March - 1 April 2015, London, Burlington House at the RAS, UKhttp://astro.kent.ac.uk/~df/gp/index.html

Cloudy Workshop4 - 8 May 2015 Warsaw, Polandhttp://cloud9.pa.uky.edu/~gary/cloudy/CloudySummerSchool/

Triple Evolution & Dynamics in Stellar and Planetary Systems31 May - 5 June 2015 Haifa, Israelhttp://trendy-triple.weebly.com

Workshop on the Formation of the Solar System II2 - 4 June 2015 Berlin, Germanyhttps://indico.mpifr-bonn.mpg/FormationOfTheSolarSystem2

IGM@50: is the Intergalactic medium driving Star Formation?8 - 12 June 2015 Abbazia di Spineto, Italyhttp://www.arcetri.astro.it/igm50

30 Years of Photodissociation regions - A Symposium to honor David Hollenbach’s lifetime in science28 June - 3 July 2015http://pdr30.strw.leidenuniv.nl

Gordon Research Conference on Origins of Solar Systems28 June - 3 July 2015http://www.grc.org/programs.aspx?id=12345

Disc dynamics and planet formation29 June - 3 July 2015 Larnaka, Cyprushttp://www.star.uclan.ac.uk/discs2015

From Interstellar Clouds to Star-forming Galaxies: Universal Processes?3 - 7 August 2015 http://astronomy2015.org/symposium_315

Cosmic Dust17 - 21 August 2015 Tokyo, Japanhttps://www.cps-jp.org/~dust/

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Extreme Solar Systems III29 November - 4 December 2015 Hawaii, USAhttp://ciera.northwestern.edu/Hawaii2015.php

The 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun6 - 10 June 2016 Uppsala, Swedenhttp://www.coolstars19.com

Other meetings: http://www1.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/meetings/

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