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

No. 303 — 15 March 2018 Editor: Bo Reipurth (reipurth@ifa.hawaii.edu)

The Star Formation Newsletter

Editor: Bo Reipurthreipurth@ifa.hawaii.edu

Associate Editor: Anna McLeodanna.mcleod@canterbury.ac.nz

Technical Editor: 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Abstracts of Newly Accepted Papers . . . . . . . . . . 11

Dissertation Abstracts . . . . . . . . . . . . . . . . . . . . . . . . 32

New Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Meetings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Summary of Upcoming Meetings . . . . . . . . . . . . . 39

Cover Picture

The two lobes of the bipolar HII region S106 areseparated at the waist by a dark lane with a veryhigh column density which obscures the excitingsource S106IR. S106 is located at a distance ofabout 1.3 kpc. The source is an embedded O9 star,which is part of a small cluster of young stars. Re-cently it has been discovered that S106IR is vari-able with a period of 5 days, and the observationsindicate that the system is composed of two starswith different luminosity orbiting in an elliptic orbitwith moderate eccentricity (Comeron et al. 2018,arXiv:1801.08958).

Image courtesy NASA, ESA, and the Hubble Her-itage Team (STScI/AURA).

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

Riccardo Cesaroniin conversation with Bo Reipurth

Q:What was your thesis about, and who was your advisor?

A: Well, it depends on what you mean with “thesis”. I’mold enough to recall the time when the PhD title simplydidn’t exist in Italy. The university degree was the finaltitle one could get and obviously the most important. Toanswer your question, my degree thesis was on plerionic su-pernova remnants, under the supervision of Franco Pacini.Fortunately, I’m not too old either, so just the year beforeI got my degree in physics, in 1984, Italy had establisheda PhD course, which I could follow. I switched my inter-est from the death to the birth of the stars and my PhDthesis was on water masers in star forming regions, withMarcello Felli and Gianni Tofani as advisors. I’m gratefulto them for introducing me to the fascinating subject ofthe interstellar medium and star formation. Those daysH2O maser observations were still relatively limited andwe took advantage of the Medicina 32-m antenna (whichwe could freely access thanks to a collaboration with theIstituto di Radioastronomia in Bologna) to cover a largenumber of candidate water maser sources. It was a fortu-nate coincidence that the IRAS point source catalogue be-came available at the same time, which allowed us to selectpromising targets based on the far-IR colours, thus boost-ing the success rate of our maser searches. Among themany colleagues who contributed to this observing cam-paigns I wish to pay tribute to the memory of FrancescoPalla, whose original ideas paved the way for several stud-ies on masers associated with massive protostars.

Q: Your first paper, still cited today, was a large catalogof water masers.

A: That was my first paper as first author, though my veryfirst paper, in collaboration with Marcello Felli and BobHjellming, was on a model describing the free-free contin-uum emission from a bright rim evaporated by a nearbymassive star, basically a “champagne flow”, another topic

pretty fashionable in the 80s. It was a problem involving asolution of the radiative transfer equation, and I had a lotof fun working on that. In contrast to the maser cataloguethat you mention, which was certainly not very excitingfor a young inexperienced student. But you’re right thatthis is still cited and has collected 5 times more citationsthan the bright-rim paper, which shows how useful cata-logues are. Those masers were then all observed with theMedicina telescope and a sub-sample was also monitoredby the Arcetri radio group for longer than 20 years, as afollow-up of my PhD thesis. Actually, the main goal ofmy thesis was to investigate H2O maser variability, an-other hot topic in those days. I also published (and thatwas my first paper without collaborators) a model to ex-plain the anticorrelated variability of two lines in the wa-ter maser spectrum of S255 NIRS3. The model assumedthese lines were orginating from a Keplerian disk arounda ∼18 M⊙ star. I think the idea was nice and original,but... subsequent VLA and VLBI imaging of the masersdidn’t confirm it. However, recent SMA observations ofhot-core tracers have found evidence of a Keplerian diskin S255 NIRS3 and derived a stellar mass of ∼20M⊙. Andmy latest publication is just on a radio outburst from thedisk-jet system in this object. So, somehow the circle isclosed and I’ve taken my “revenge”!

Q: After that you also developed an OH maser model.

A: That was one of the many intriguing problems that Ifaced with the inspiring guidance of Malcolm Walmsley,who sadly passed away the past year, leaving an emptyspace not only in my professional life. He was my men-tor when I was a post-doctoral fellow at the MPI fur Ra-dioastronomie in Bonn and initiated me to the world ofOH maser excitation models. His idea was that all ofthe OH microwave transitions in the 2Π1/2 and 2Π3/2 lad-ders could originate under the same physical conditions,namely from the same region, no matter whether thesewere maser or thermal lines. Some of these far-IR transi-tions of OH are so close to each other in frequency thatthey can overlap due to Doppler shifts from expansion ofthe gas. This increases the line opacity and affects thepopulations of the OH levels. As a matter of fact, themodel we developed could reproduce all of the OH mi-crowave lines (absorption, emission, and masers) observedin W3(OH), thus fully confirming Malcolm’s insight.

Q: In the 90s you worked on observations of hot ammoniatoward ultracompact HII regions. What did you learn?

A: This is yet another study that I started with Malcolm.The early 90s could be called “the golden era of hot molec-ular cores”. Prior to that epoch, most studies were focusedon regions forming solar-type stars, basically because ofthe limited angular resolution at millimeter wavelengths,a serious limitation if you want to investigate objects thatare typically lying beyond 1 kpc. I think that our studies of

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the hot, dense molecular gas associated with ultracompactHii regions, made in collaboration with Ed Churchwell andhis group, were a significant step further in our knowl-edge of massive star formation. Not only did we confirmthe idea that young Hii regions are often associated withdense, hot molecular cores, but we also found evidence forrotation or expansion of these cores and detected hyper-compact Hii regions embedded inside some of them. Weobserved high excitation inversion transitions of ammo-nia with the VLA as well as several rotational transitionsof methyl cyanide with the Plateau de Bure interferome-ter, which had just become fully operative. The advent of(sub)mm interferometers had obviously changed the rulesof the game, to our benefit, of course. We could deter-mine the distribution of temperature and column densityin these cores and hence prove that they are the cradlesof high-mass stars.

Q: You have advocated the existence of disks around mas-sive protostars in a series of papers, including your 2006Nature Progress article on “The critical role of disks inthe formation of massive stars” and the 2007 review inProtostars and Planets V. Please describe the evidence.

A: This issue is tightly related to that of hot molecularcores. We found velocity gradients across several cores,perpendicular to large scale bipolar outflow originatingfrom the cores themselves. We thought this could bedue to unresolved or barely resolved disks rotating aboutthe axes of those outflows. One must keep in mind that20 years ago much less was known about circumstellardisks around young (proto)stars than today, and whatwas known was limited to low-mass objects. Data like therecent impressive ALMA images of HL Tau were noth-ing but a dream... The question of disks associated withearly-type stars became more and more popular with in-creasing resolving power and sensitivity of the (upgraded)millimeter interferometers. One could thus detect Kep-lerian signatures in a limited number of disks and derivethe stellar mass. The importance of such circumstellardisks is related to the possibility of boosting the accretionthrough the disk plane even in the most massive stars,and thus overcome the powerful radiation pressure on theinfalling material. The state of the art is summarized ina recent review by Maite Beltran, a collaborator of mine,and Willem-Jan de Wit. Now with the advent of ALMAthe study of disks around massive stars is entering a newera, as witnessed by the ever growing number of publica-tions on this topic.

Q: IRAS 20126+4104 has been an object of special attrac-tion for you, and on which you and your collaborators havepublished many papers. What is special about this object?

A: Indeed, it is a very special object, and very rewardingfor an observer like me. Actually, it was Marcello Felli whosingled out this object from a sample of targets that he ob-

served with the VLA. With Marcello, Malcolm and otherswe then pursued its investigation, stimulated by the firstintriguing results which strongly indicated the presence ofa disk. The reason why I consider it my favourite “petobject” is that it looks like a theorist’s dream. The Kep-lerian disk rotating about a 104 L⊙ star is detected basi-cally in all hot-core tracers and the associated jet/outflowcan be seen in the centimeter continuum, H2O masers,shock-tracers like SiO, and the near-IR continuum andH2 line. Notably, the outflow is undergoing precession.With Luca Moscadelli and others, we could also recon-struct the 3D expansion velocity of the jet by means ofwater maser proper motions. Moreover, the molecular ma-terial entrained in the outflow appears to be rotating in thesame sense as the disk, suggesting the possible existenceof a disk wind. These “ingredients” of the star formationrecipe are seldom found all in the same source. And in thisrespect, in my opinion, IRAS 20126+4104 represents so farthe best example of a disk+jet+outflow system associatedwith a massive star.

Q How does your past work and your future plans connect?

A: All in all, I think I’ve been very lucky in my career: as astudent I was esteemed and supported by my supervisors;as a post-doctoral fellow I had the privilege to have Mal-colm as a mentor, from whom I learnt so much; and finally,when I became staff I had excellent students, post-docs,and colleagues, whom it’s been a pleasure to work with.The results obtained so far are a very good starting pointfor the future. The problem of disks around high-massstars is far from being solved. While the idea that B-typeand late O-type stars can form through disk-mediated ac-cretion is almost universally accepted, observational evi-dence of disks around the most massive O-type stars isstill lacking. We’ll keep chasing those disks, by meansof ALMA. A related issue is that of variability of mas-sive young stellar objects. Very recently, Alessio Caratti oGaratti and collaborators have detected an IR burst frommy old friend S255 NIRS3S. With the JVLA we have foundthat also the radio emission from the associated thermaljet is undergoing an outburst phase. This is an excitingresult that could represent the rule rather than the ex-ception in these objects, if disk accretion onto the star isepisodic. The new facilities such as the JVLA, ALMA,and IRAM-NOEMA are fast enough to be used for mon-itoring a large number of young stellar objects and thusestablish on a solid statistical ground whether all starsform through episodic accretion. Also connected to theaccretion phenomenon could be the Lyman excess emis-sion that we have found in 1/3 of the compact Hii regionsfrom the CORNISH survey. The extra UV photons couldbe emitted by accretion shocks. That’s yet another ques-tion to explore with the new instruments already availableor that will come on line in the near future.

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My Favorite Object

NGC 6231:A Testbed for Cluster Formation

Michael Kuhn

1 Introduction

Star cluster formation touches on many areas of stellar as-tronomy, and the young cluster NGC 6231 in the Sco OB1association is no exception, containing stellar objects span-ning the full range of the mass distribution, pre–main-sequence stars, post–main-sequence stars, various classesof variable stars, and various classes of binary stars – evenan ejected high-mass X-ray binary (HMXB). NGC 6231has been known since the 17th Century, when it was firstcataloged by Giovanni Battista Hodierna in Palermo. How-ever, for clusters near the Galactic plane, where NGC 6231is located, heavy contamination by foreground and back-ground field stars means that it is difficult to distinguishcluster members (Figure 1). An optical study by Sung etal. (1998) was only able to confirm 19 pre–main-sequencestar in the cluster, out of the thousands that are nowknown to exist.

X-ray observations have dramatically improved our un-derstanding of this cluster. Pre–main-sequence stars arestrong X-ray emitters due to high coronal magnetic activ-ity (Feigelson & Montmerle 1999), and X-ray selection hasproven to be one of the only methods that is effective atidentifying Class III YSOs in Galactic plane fields (Feigel-son et al. 2013). For NGC 6231, observations with XMMNewton lead to the discovery of hundreds of low-mass clus-ter members (Sana et al. 2006a,b, 2007a). More recently,the higher spatial resolution and lower background in the

Figure 1: A VVV mosaic of NGC 6231 using the bandsZ (blue), J (green), and H (red) to create the color im-age. The more distant stars have higher extinction makingthem appear redder in this image.

Figure 2: The Chandra X-ray image of NGC 6231 (K17a).Most X-ray sources are classified as cluster members.

observation by the Chandra X-ray Observatory (Figure 2)lead to the discovery of thousands of additional members(Damiani et al. 2016, Kuhn et al. 2017a,b). In this articlewe use the membership catalog from Kuhn et al. (2017a,henceforth K17a) based on a re-analysis of the Chandradata and multi-epoch photometry from the VISTA Vari-ables in the Vıa Lactea (VVV) survey (Minniti et al. 2010,Saito et al. 2012). This catalog, designated CXOVVV,contains 2148 probable cluster members, which we usedas the basis for a subsequent study of the cluster’s struc-

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ture (Kuhn et al. 2017b, henceforth K17b).

Several properties of NGC 6231 make it an excellent testbedfor early cluster evolution. It has light (AV ≈ 1.4 mag),uniform absorption. It contains more than a hundred Oand B stars and several thousand pre–main-sequence stars.Its stars show a clear age spread, with age estimates rang-ing from 2 to 7 Myr. It has a (partially) known supernovahistory due to the ejected HMXB with a trace-back ageof 3 Myr (Ankey et al. 2001). It is relatively nearby witha distance based on isochrone fitting of ∼1.6 kpc (whichmay soon be refined using Gaia parallax measurements).And, it is covered by deep X-ray imaging and optical andnear-infrared surveys like VVV and VPHAS+ (Drew et al.2014). In particular, the cluster is an excellent example ofwhat is left after molecular clouds are completely dispersedat the end of star formation in a massive star-forming re-gion. There is no evidence for molecular cloud material inthe cluster, although clouds still exist in other parts of theSco OB1 association (Reipurth 2008), the cluster interioris sufficiently devoid of cloud material that stellar windsare free streaming (Massa 2017).

2 Radial Profile

The large, X-ray flux-limited sample of cluster membersprovides an excellent opportunity to study the structureof a young star cluster. In our study, we exclude sourcesbelow the X-ray completeness limit to avoid spatial biasesdue to non-uniformities in the detector.

It is not clear from theory what surface-density profileto expect for a young cluster like NGC 6231. For olderopen clusters, a variety of models have been developedbased on approximate solutions for virialized, gravitation-ally bound groups of stars (Binney & Tremaine 2008), andsuch models have successfully described even very youngclusters like the Orion Nebula Cluster (e.g., Hillenbrand& Hartmann 1998). The two-body virialization timescalefor NGC 6231 is ∼100–300 Myr, much longer than thecurrent age of 2–7 Myr for the stellar population (K17b).For such a young cluster, several processes could affectthe profile, including the initial structure of the molecularcloud, early dynamics of cluster assembly and evolution,and the velocity dispersion of the stars (which may noteven be gravitationally bound).

In K17b we tested a variety of surface density profiles (Fig-ure 3). The models were fitted to the spatial distributionof stars in the cluster by maximizing a likelihood equationthat does not require binning of points (Kuhn et al. 2014).The profiles were based on the functional forms of thePlummer sphere, the Hubble model, scale-invariant power-laws, and the multivariate normal distribution, with clus-ter center and ellipticity as free parameters.

Figure 3: Results from fitting the cluster profile with vari-ous models (K17b). The left panels show maps of residualsafter the model has been fit, with red residuals indicatingexcess stars compared to the model and blue indicatingfewer stars than in the model. The right panels show sur-face density for a slice through the cluster at declination−41◦50′00′′, with the models shown in gray and adaptivesmoothing estimates shown in black.

The candidate models were evaluated through examina-tion of the residual maps (Figure 3, left column) and bycomparison to an estimate of the surface density in thecluster produced by adaptive smoothing (right column).The Hubble model provides the closest agreement withthe data, with the Plummer sphere being second best,but underestimating the number of stars in the core of thecluster. The scale-invariant models, which were proposedfor young clusters by Cartwright & Whitworth (2004), areclearly ruled out in this case. We also exclude a normaldistribution, which could arise if stars fly away from thecluster with a Maxwell-Boltzmann velocity distribution.

We denote the best fit model the “isothermal ellipsoid” be-cause the Hubble model approximates the surface densitydistribution of the isothermal sphere out to several coreradii (Binney & Tremaine 2008). The cluster core radius

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is rc = 1.2 pc and the cluster has a moderate ellipticityof ǫ = 0.33 ± 05. The density of stars at the center ofthe cluster is Σ0 = 460 stars pc−2, which corresponds toa volume density of ρ ∼ 200 stars pc−3. It is more diffi-cult to measure the outer radius for the cluster, becausethe cluster extends beyond the outside of the field of view,and thus it is also difficult to determine the cluster’s totalmass. This is a common problem, which has been dis-cussed by Kroupa et al. (2001) who recommend use of thecore radius as a more robust tracer of cluster properties.Given that the cluster extends out to at least ∼4 core radiiat the edge of the field of view, we use a characteristic ra-dius r4 = 4 rc when comparing NGC 6231’s size or massto other clusters modeled in a similar way. For NGC 6231,this characteristic radius would be 4.6±0.4 pc, containing5700–7500 stars, or 3300–4200 M⊙ (K17b).

In comparison to the Orion Nebula Cluster with a coreradius of rc ∼ 0.2 pc (Hillenbrand & Hartmann 1998),NGC 6231 is much larger and less dense. Both clus-ters have moderate ellipticities, which may be related tothe initial structure of the molecular clouds in both cases(K17b). The size of NGC 6231 is more similar to the∼100 Myr old Pleiades cluster, which also has a notableellipticity (Olivares et al. 2017).

The residual map from the best-fit model (upper left panelof Figure 3) shows an overdensity of stars to the north-west of the cluster center. K17b modeled the main clusterand subcluster with a two-component mixture model (seereview by Kuhn & Feigelson 2018) and found that thetwo-component model is strongly favored over the single-cluster model. The main cluster is centered at 16h54m15.9s

−41◦49′59′′, while the subcluster is centered at 16h54m01.6s

−41◦48′13′′. Overall, the subcluster contributes 4% ofthe stars in the field of view. The O9.7Ia+O8V systemHD 152234 is coincident with the subcluster.

3 Radial Age Gradient?

The various photometric studies of NGC 6231 membersgenerally agree that stellar ages have a significant spreadrelative to the cluster’s young age, although estimates ofthe median age may be affected by differences in evolu-tionary models (Sung et al. 2013; Damiani et al. 2016,K17a). The age spread may influence the cluster’s struc-ture if stars with different ages were in different dynami-cal states. For example, if NGC 6231 were unbound andleaking stars while star formation was ongoing, older starswould be expected to have traveled further from the clus-ter’s center, leading to an age gradient. Age gradientshave been detected in most star-forming regions that havebeen examined, including the Orion Nebula, NGC 2024,and several others (Getman et al. 2014a, 2018).

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Figure 4: Box-and-whisker plot showing distributionsof stellar ages at various distances from the cluster center(K17b). Each box shows the sample mean, the uncertaintyon the mean, the interquartile range, and outlying points.The distributions do not vary significantly with distance.

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Figure 5: Cluster profile models are fit to stars in dif-ferent mass bins (K17b). This plot shows core radius asa function of mass, indicating that higher mass stars aremore centrally concentrated than low mass stars.

Figure 4 shows the distributions of stellar ages in four an-nular regions at different distances from the cluster center.These ages were estimated from the V vs. V − I color-magnitude diagram; however, an alternative age methodbased on near-infrared/X-ray luminosities (Getman et al.2014b) shows the same results. Overall, there is no agegradient. This result implies that the stars in NGC 6231were bound in a compact cluster until the end of star for-mation, when the cluster began to expand as a whole.

4 Mass Segregation

An early study suggested mass segregation in NGC 6231(Raboud & Mermilliod 1998), with OB stars more cen-trally concentrated than low-mass stars. Our cleaner sam-

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ples of low-mass cluster members mean that mass segrega-tion can be tested more rigorously. Indication of statisti-cally significant mass segregation has been found by bothDamiani et al. (2016) and K17b using multiple statisticalmethods. Nevertheless, massive stars are not constrainedto the center of the cluster – systems such as HD 152076(O9.5 III) and HD 152247 (O9 III+O9.7 V) lie more than10′ from the cluster center.

Figure 5 shows one of the mass segregation tests fromK17b. Stars are divided into groups by stellar mass, andeach group is fit with the cluster model from Section 2.The core radius parameter, rc, determines how centrallyconcentrated stars from different groups are. With in-creasing mass the stars are more centrally concentrated,except for the bin containing 1–2 M⊙ stars. This relationcan be empirically described by a −0.29± 0.06 power-law;however, the differences only become statistically signifi-cant for the most massive M > 10 M⊙ group.

Mass segregation as seen in NGC 6231 can be explainedeither as a primordial effect or as a dynamical effect. Inthe latter case, mass segregation is expected to increasewith dynamical age (e.g., Dib et al. 2018). Neverthe-less, for young stellar clusters, there does not appear tobe a straightforward relation between mass segregationand dynamical age given that some very young systems instar-forming regions are segregated down to lower masses(e.g., W40; Kuhn et al. 2010) or more strongly segregated(e.g., clusters in Orion B; Parker 2018) than a dynami-cally older cluster like NGC 6231. This may indicate thatmass segregation seen in young stellar clusters representsa combination of primordial and dynamical effects.

5 Cluster Evolution

NGC 6231 is considerably larger than most young stellarclusters observed at earlier stages of development, sug-gesting that NGC 6231 may have expanded from a morecompact state. We can compare NGC 6231’s structure toyoung stellar clusters from the MYStIX study – a studyof nearby massive star-forming regions that used similarmethodologies for identification of members and clusteranalysis (Feigelson et al. 2013, 2018). Given that mostMYStIX regions still have ongoing star formation, theyare generally younger than NGC 6231, although some ofthe regions from the study include stellar subpopulationssimilar in age to NGC 6231. The 1.2 pc core radius forNGC 6231 is ∼15 times larger than the typical core radiusof highly-absorbed subclusters of stars in MYStIX and ∼7times larger than the typical MYStIX young stellar cluster(K17b).

Figure 6 is a scatter plot showing cluster properties (num-ber of stars, median age, and density) for subclusters of

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Figure 6: Scatter plots showing properties of young clus-ters and subclusters from multiple regions (K17b). Thered points indicate NGC 6231, and blue and black pointsindicate clusters and subclusters in MYStIX. Several well-known clusters included in MYStIX are highlighted inblue, such as RCW 38, NGC 2024, W40, Pismis 24,G353.2+0.7, NGC 2362, NGC 6611, and NGC 2244 (fromsmallest to largest in radius).

stars in MYStIX star-forming regions and for NGC 6231(marked by a red point). For the MYStIX subclusters, sta-tistically significant correlations were found between theirproperties, including a positive correlation between clustersize and age, a positive correlation between cluster size andnumber of stars, and negative correlations between clus-ter size and density (Kuhn et al. 2015). These relationsapplied not only to subclusters with few stars, but also towell-known clusters in these regions (marked in blue).

When placing NGC 6231 on this plot, one would not nec-essarily expect this cluster to lie on the same line as theMYStIX clusters. NGC 6231 is a fully-formed cluster witha relatively simple structure, while the MYStIX clustersreside in star-forming regions that often contain multi-ple subclusters. NGC 6231 is also older, larger, and lessdense than most of the MYStIX clusters, and is no longerassociated with a molecular cloud. Nevertheless, it turnsout that NGC 6231 does lie very near the regression linesfound from MYStIX.

The surprising result that NGC 6231 appears to followthe same trend as the MYStIX subclusters (if not coin-

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cidental) suggests that the same cluster formation pro-cesses that determine the properties of MYStIX subclus-ters also determine the properties of fully-formed clusterslike NGC 6231. One of these process could be hierarchicalcluster assembly, in which subclusters merge to buildupmore massive clusters (e.g., Banerjee & Kroupa 2018). Instar-forming regions like MYStIX, with multiple subclus-ters seen in many regions, it seems likely that hierarchicalassembly is occurring, and Kuhn et al. (2015) noted thatthis process could explain the mass-size and size-densityrelations for MYStIX subclusters. Thus, NGC 6231 couldbe the end result of such a process.

6 X-ray Properties of Stars

The large, lightly obscured sample of young cluster mem-bers means that NGC 6231 is also an excellent testbed forX-ray properties of young stars. Figure 7 shows a diagramof X-ray flux versus X-ray spectral hardness. Spectralhardness increases both with increased plasma tempera-ture and increased absorption. However, the foregroundabsorption is sufficiently low that it has no effect on theobserved X-ray properties.

For pre–main-sequence stars, there is a slight increase inmean spectral hardness with increasing X-ray luminosity.This effect is a result of increasing plasma temperaturewith increasing X-ray luminosity, as has been inferred fromX-ray spectroscopic studies of the Orion Nebula Cluster(Preibisch et al. 2005). A minority of objects have partic-ularly hard spectra (ME > 2 keV), which may be a mix-ture of objects with high local absorption (e.g., by edge-ondisks) and background contaminants.

Objects matched to stars with O or B spectral types aremarked by orange circles. X-ray emission from OB starsis thought to come from stellar winds, and is generallymuch softer than X-ray emission from pre–main-sequencestars. On this diagram these sources have X-ray medianenergies ∼1 keV and are among the most luminous X-raysources. Several O-star binaries were studied at multiplepoints in their orbits using a sequence of XMM-Newtonobservations, which showed an orbit-modulated effect ofcolliding stellar winds (e.g., Sana et al. 2007b). However,even these sources appear soft in Figure 7.

Late B stars are not expected to produce X-ray emission,having neither winds nor magnetic activity. Nevertheless,a larger fraction of B stars are detected in X-ray, and thesestars fall on the pre–main-sequence locus of Figure 7. Weinterpret these as multiple-star systems where X-ray emis-sion is dominated by the lower mass pre–main-sequencecompanion. In two cases, strong X-ray flares are detectedin the Chandra data. Based on X-ray properties, K17a es-timate that >35% of B stars in NGC 6231 have low-mass

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]Figure 7: X-ray flux vs. X-ray spectral hardness (K17a).Stars with O and B spectral types are shown by orangepoints, the Wolf-Rayet star is shown by the blue point,and other members (mostly pre–main-sequence stars) areshown by black points. X-ray flux is measured in the 0.5–8.0 keV band. Spectral hardness is measured using theX-ray median energy indicator.

companions, a result consistent with recent results by Moe& Di Stefano (2017).

The Wolf-Rayet star WR 79 is marked in blue in Fig-ure 7, where it stands out both due to its particularly hardX-ray spectrum and its high X-ray luminosity. Damianiet al. (2016) attributed its hardness to both high plasmatemperatures and high absorption. Oskinova et al. (2003)notes that WR 79 is one of the very few carbon enrichedWolf-Rayet stars detected in X-rays, which Damiani et al.(2016) suggest is due to wind-wind collisions in the binarysystem.

7 X-ray Luminosity Evolution

X-ray emission from pre–main-sequence stars is expectedto decline after the first few million years (Preibisch &Feigelson 2005). However, understanding of this declinehas been limited by few X-ray observations of stellar pop-ulations with ages between 5 and 100 Myr. For youngerstars, Gregory et al. (2016) have noted declines in X-ray

9

luminosity with age affected by both stellar mass andposition on the Hayashi or Henyey tracks. Given thatNGC 6231 contains both stars older and younger than5 Myr, it can make a good testbed to look for an ageeffect on X-ray luminosity.

The most notable differences between these samples is thatstars with ages<5 Myr include several tens of objects withX-ray luminosities >1031 erg s−1, while stars with ages5–10 Myr include only one object as bright as that. Thisdifference is found to be statistically significant (Figure 8).This result suggests that early stellar evolution may havea particularly strong effect on the most extreme end of theX-ray luminosity distribution.

8 Outlook

Very young open clusters like NGC 6231 will be excellentobjects for the upcoming Gaia data releases. Gaia’s par-allax and proper-motion measurements will revolutionizestar cluster studies, providing methods to select new mem-bers and opening a window into the internal dynamics ofclusters. While high absorption may limit Gaia studiesof embedded clusters in star-forming regions, this is nota factor for NGC 6231. The X-ray catalog may make auseful testbed for dynamical studies based on Gaia propermotions, which are expected to be precise to 0.1–2 km s−1

for stars in this sample (de Bruijne et al. 2005).

Proper motions will allow direct measurements of clusterproperties that, until now, could only be inferred throughthe spatial distribution of stars in the cluster. One ex-ample is measurements of whether the cluster is dynami-cally bound. K17b argue, based on the size and mass ofNGC 6231, that if the cluster were unbound it would haveexpanded much more significantly than it has since themolecular cloud was dispersed approximately 3 Myr ago.

NGC 6231 is not an isolated cluster, but instead part ofthe much larger Sco OB1 association. However, selectionof association members is particularly difficult at a dis-tance of ∼1.6 kpc among numerous field stars, and thesmall field of view of facilities like Chandra make use ofX-ray observations for selecting members infeasible. Gaiadata, combined with optical and near-infrared surveys likeVPHAS+ and VVV, may provide a better understandingof this association and how clusters like NGC 6231 or Tr 24are connected with its formation.

References:

Ankay, A. et al. 2001, A&A, 370, 170Banerjee, S. & Kroupa, P. 2018, in The Birth of Star Clusters, ed.Stahler, S. (Springer), 424, 119Damiani, F., Micela, G., & Sciortino, S. et al. 2016, A&A, 596, 82de Bruijne, J. et al. 2005, Gaia–JdB–022Dib, S., Schmeja, S., & Parker, R. J. et al. 2018, MNRAS, 473, 849Drew, J. E. et al. 2014, MNRAS, 440, 2036

29.0 30.0 31.0 32.0

05

10

15

20

LX!"erg!s<1#

Age (

VI)

[M

yr]

A

B

C

D

cum

ula

tive

pro

babili

ty

Te30.0 30.5 31.0 31.5

0.0

0.2

0.4

0.6

0.8

1.0

LX!"erg!s<1#

cum

ula

tive

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babili

ty

A: 0.0<age<2.5 Myr

B: 2.5<age<5.0 Myr

C: 5.0<age<7.5 Myr

D: 7.5<age<10 Myr

Figure 8: Left: Age estimates for stars in NGC 6231vs. X-ray luminosity. Stars are subdivided into 4 groupsbased on age. The X-ray luminosity completeness limitfor this sample is LX = 1030 erg s−1. Right: Cumulativedistributions of X-ray luminosity for stars in each group.The differences in the LX distributions are mainly dueto the lack of stars with LX > 1031 erg s−1 for clustermembers older than 5 Myr (K17a).

Feigelson, E. D. & Montmerle, T. 1999, ARA&A, 37, 363Feigelson, E. D. et al. ApJS, 209, 26FFeigelson, E. D. 2018, in The Birth of Star Clusters, ed. Stahler(Springer), 424, 143Getman, K. V., Feigelson, E. D., & Kuhn, M. A. 2014a, ApJ, 787,109Getman, K. V., et al. 2014b, ApJ, 787, 108—. 2014, ApJ, 787, 108—. 2018, MNRAS, 476, 1213Gregory, S. G., Adams, F. C., & Davies, C. L. 2016, MNRAS, 457,3836Hillenbrand, L. A. & Hartmann, L. W. 1998, ApJ, 492, 540Kroupa, P., Aarseth, S., & Hurley, J. 2001, MNRAS, 321, 699Kuhn, M. A. 2010, ApJ, 725, 2485—. 2014, ApJ, 787, 107—. 2015, ApJ, 812, 131—. 2017a, AJ, 154, 214—. 2017b, AJ, 154, 87Kuhn, M. A. & Feigelson, E. D. 2018, in Handbook of Mixture Anal-ysis, ed. Celeux, G. Fruwirth-Schnatter, S., & Robert, C. P. (Chap-man & Hall/CRC)Massa, D. 2017, MNRAS, 465, 1023Minniti, D. et al. 2010, NewA, 15, 433Moe, M. & Di Stefano, R. 2017, ApJS, 230, 15Olivares, J. et al. 2017, A&A, in pressOskinova, L. M. et al. 2003, A&A, 402, 755Parker, R. J. 2018, MNRAS, 476, 617Preibisch, T. & Feigelson, E. D. 2005, ApJS, 160, 390Preibisch, T. et al. 2005, ApJS, 160, 401Raboud, D., & Mermilliod, J.-C. 1998, A&A, 333, 897Reipurth, B. 2008, in Handbook of Star Forming Regions, VolumeII, ed. Reipurth, B. (Astronomical Society of the Pacific MonographPublications), 401Saito, R. K. et al. 2012, A&A, 537, A107Sana, H. et al. 2006a, A&A, 454, 1047—. 2006b, MNRAS, 372, 661—. 2007a, MNRAS, 386, 447—. 2007b, ApJ, 659, 1582Sung, H. et al. 1998, AJ, 115, 734—. 2013, AJ, 145, 37S

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Abstracts of recently accepted papers

A UV-to-NIR Study of Molecular Gas in the Dust Cavity Around RY Lupi

N. Arulanantham1, K. France1, K. Hoadley2, C.F. Manara3,4, P.C. Schneider5, J.M. Alcala6, A.

Banzatti7, H.M. Gunther8, A. Miotello4,9, N. van der Marel10, E.F. van Dishoeck11,12, C. Walsh13,

J.P. Williams14

1 Laboratory for Atmospheric and Space Physics, University of Colorado, 392 UCB, Boulder, CO 80303, USA; 2

Department of Astronomy, California Institute of Technology, 1200 East California Blvd., Pasadena, CA 91125, USA;3 Science Support Office, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC),Keplerlaan 1, 2201 AZ, Noordwijk, The Netherlands; 4 European Southern Observatory, Karl-Schwarzschild-Str. 2,D-85748 Garching bei Munchen, Germany; 5 Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany;6 INAF-Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131, Napoli, Italy; 7 Lunar and PlanetaryLaboratory, The University of Arizona, Tucson, AZ 85721, USA; 8 MIT, Kavli Institute for Astrophysics and SpaceResearch, 77 Massachusetts Avenue, Cambridge, MA 02139, USA; 9 Leiden Observatory, Leiden University, NielsBohrweg 2, 2333 CA Leiden, The Netherlands; 10 Herzberg Astronomy & Astrophysics Programs, National ResearchCouncil of Canada, 5017 West Saanich Road, Victoria, BC, Canada V9E 2E7; 11 Leiden Observatory, Leiden Uni-versity, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands; 12 Max-Planck-Institut fur Extraterrestrische Physik,Giessenbachstrasse 1, 85748 Garching, Germany; 13 School of Physics and Astronomy, University of Leeds, Leeds LS29JT, UK; 14 Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI, USA

E-mail contact: nicole.arulanantham at colorado.edu

We present a study of molecular gas in the inner disk (r < 20 AU) around RY Lupi, with spectra from HST-COS, HST-STIS, and VLT-CRIRES. We model the radial distribution of flux from hot gas in a surface layer between r = 0.1–10AU, as traced by Lyα-pumped H2. The result shows H2 emission originating in a ring centered at ∼3 AU that declineswithin r < 0.1 AU, which is consistent with the behavior of disks with dust cavities. An analysis of the H2 line shapesshows that a two-component Gaussian profile (FWHMbroad,H2

= 105± 15 km s−1; FWHMnarrow,H2= 43± 13 km s−1)

is statistically preferred to a single-component Gaussian. We interpret this as tentative evidence for gas emitting fromradially separated disk regions (〈rbroad,H2

〉 ∼ 0.4± 0.1 AU; 〈rnarrow,H2〉 ∼ 3± 2 AU). The 4.7 µm 12CO emission lines

are also well fit by two-component profiles (〈rbroad,CO = 0.4± 0.1 AU; 〈rnarrow,CO〉 = 15 ± 2 AU). We combine theseresults with 10 µm observations to form a picture of gapped structure within the mm-imaged dust cavity, providingthe first such overview of the inner regions of a young disk. The HST SED of RY Lupi is available online for use inmodeling efforts.

Accepted by ApJ

http://arxiv.org/pdf/1802.05275

Similar complex kinematics within two massive, filamentary infrared dark clouds

A. T. Barnes1,2, J. D. Henshaw3, P. Caselli2, I. Jimnez-Serra4, J. C. Tan5, F. Fontani6, A. Pon7 and S.

Ragan8

1 Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK;2 Max Plank Institute for Extraterrestrial Physics (MPE), Giessenbachstrasse 1, 85748 Garching, Germany; 3 MaxPlank Institute for Astronomy (MPIA), Konigstuhl 17, 69117 Heidelberg, Germany; 4 Queen Mary University ofLondon, Astronomy Unit, Mile End Road, London E1 4NS, UK; 5 Department of Astronomy, University of Florida,Gainesville, FL 32611, USA; 6 NAF - Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, I-50125, Firenze, Italy; 7

Department of Physics and Astronomy, The University of Western Ontario, 1151 Richmond Street, London, N6A 3K7,Canada; 8 School of Physics & Astronomy, Cardiff University, Queen’s building, The parade, Cardiff, CF24 3AA, UK

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

11

Infrared dark clouds (IRDCs) are thought to be potential hosts of the elusive early phases of high-mass star formation.Here we conduct an in-depth kinematic analysis of one such IRDC, G034.43+00.24 (Cloud F), using high sensitivityand high spectral resolution IRAM-30m N2H

+ (1 − 0) and C18O (1 − 0) observations. To disentangle the complexvelocity structure within this cloud we use Gaussian decomposition and hierarchical clustering algorithms. We findthat four distinct coherent velocity components are present within Cloud F. The properties of these components arecompared to those found in a similar IRDC, G035.39-00.33 (Cloud H). We find that the components in both cloudshave: high densities (inferred by their identification in N2H

+), trans-to-supersonic non-thermal velocity dispersionswith Mach numbers of ∼ 1.5?4, a separation in velocity of ∼ 3 km s−1, and a mean red-shift of ∼ 0.3 kms−1 betweenthe N2H

+ (dense gas) and C18O emission (envelope gas). The latter of these could suggest that these clouds sharea common formation scenario. We investigate the kinematics of the larger-scale Cloud F structures, using lower-density-tracing 13CO (1− 0) observations. A good correspondence is found between the components identified in theIRAM-30m observations and the most prominent component in the 13CO data. We find that the IRDC Cloud F isonly a small part of a much larger structure, which appears to be an inter-arm filament of the Milky Way.

Accepted by Monthly Notices of the Royal Astronomical Society

https://arxiv.org/pdf/1801.06538

Dust evolution in protoplanetary discs and the formation of planetesimals. What havewe learned from laboratory experiments?

Jurgen Blum1

1 Institut fur Geophysik und extraterrestrische Physik, Technische Universitat Braunschweig, Mendelssohnstr. 3,38106 Braunschweig, Germany

E-mail contact: j.blum at tu-bs.de

After 25 years of laboratory research on protoplanetary dust agglomeration, a consistent picture of the various processesthat involve colliding dust aggregates has emerged. Besides sticking, bouncing and fragmentation, other effects, like,e.g., erosion or mass transfer, have now been extensively studied. Coagulation simulations consistently show thatµm-sized dust grains can grow to mm- to cm-sized aggregates before they encounter the bouncing barrier, whereassub-µm-sized water-ice particles can directly grow to planetesimal sizes. For siliceous materials, other processes haveto be responsible for turning the dust aggregates into planetesimals. In this article, these processes are discussed, thephysical properties of the emerging dusty or icy planetesimals are presented and compared to empirical evidence fromwithin and without the Solar System. In conclusion, the formation of planetesimals by a gravitational collapse of dust“pebbles” seems the most likely.

Accepted by Space Science Reviews

http://arxiv.org/pdf/1802.00221

The extremely truncated circumstellar disc of V410 X-ray 1:a precursor to TRAPPIST-1?

Dominika M. Boneberg1, Stefano Facchini2, Cathie J. Clarke1, John D. Ilee1, Richard A. Booth1 and

Simon Bruderer2

1 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK; 2 Max-Planck-Institut fur ExtraterrestrischePhysik, Giessenbachstrasse 1, D-85748 Garching, Germany

E-mail contact: boneberg at ast.cam.ac.uk

Protoplanetary discs around brown dwarfs and very low mass stars offer some of the best prospects for formingEarth-sized planets in their habitable zones. To this end, we study the nature of the disc around the very low massstar V410 X-ray 1, whose SED is indicative of an optically thick and very truncated dust disc, with our modellingsuggesting an outer radius of only 0.6 au. We investigate two scenarios that could lead to such a truncation, andfind that the observed SED is compatible with both. The first scenario involves the truncation of both the dust andgas in the disc, perhaps due to a previous dynamical interaction or the presence of an undetected companion. Thesecond scenario involves the fact that a radial location of 0.6 au is close to the expected location of the H2O snowlinein the disc. As such, a combination of efficient dust growth, radial migration, and subsequent fragmentation within

12

the snowline leads to an optically thick inner dust disc and larger, optically thin outer dust disc. We find that a firmmeasurement of the CO J = 2–1 line flux would enable us to distinguish between these two scenarios, by enabling ameasurement of the radial extent of gas in the disc. Many models we consider contain at least several Earth-massesof dust interior to 0.6 au, suggesting that V410 X-ray 1 could be a precursor to a system with tightly-packed innerplanets, such as TRAPPIST-1.

Accepted by MNRAS

https://arxiv.org/pdf/1802.07120

Probing midplane CO abundance and gas temperature with DCO+ in the protoplanetarydisk around HD 169142

M.T. Carney1, D. Fedele2, M.R. Hogerheijde1,3, C. Favre2, C. Walsh4, S. Bruderer5, A. Miotello6, N.M.

Murillo1, P.D. Klaassen7, Th. Henning8, E.F. van Dishoeck1,5

1 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, The Netherlands; 2 INAF–Osservatorio Astrofisico diArcetri, L.go E. Fermi 5, 50125 Firenze, Italy; 3 Anton Pannekoek Institute for Astronomy, University of Amsterdam,Science Park 904, 1098 XH, Amsterdam, The Netherlands; 4 School of Physics and Astronomy, University of Leeds,Leeds LS2 9JT, UK; 5 Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching,Germany; 6 European Southern Observatory, Garching bei Munchen, Germany; 7 UK Astronomy Technology Centre,Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK; 8 Max Planck Institute for Astronomy,Koenigstuhl 17, 69117 Heidelberg, Germany

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

This work aims to understand which midplane conditions are probed by the DCO+ emission in the disk around theHerbig Ae star HD 169142. We explore the sensitivity of the DCO+ formation pathways to the gas temperature andthe CO abundance. The DCO+ J=3–2 transition was observed with ALMA at a spatial resolution of 0.′′3. The HD169142 DCO+ radial intensity profile reveals a warm, inner component at radii <30 AU and a broad, ring-like structurefrom ∼50–230 AU with a peak at 100 AU just beyond the millimeter grain edge. We modeled DCO+ emission in HD169142 with a physical disk structure adapted from the literature, and employed a simple deuterium chemical networkto investigate the formation of DCO+ through the cold deuterium fractionation pathway via H2D

+. Contributionsfrom the warm deuterium fractionation pathway via CH2D

+ are approximated using a constant abundance in theintermediate disk layers. Parameterized models show that alterations to the midplane gas temperature and COabundance of the literature model are both needed to recover the observed DCO+ radial intensity profile. The best-fitmodel contains a shadowed, cold midplane in the region z/r < 0.1 with an 8 K decrease in gas temperature and a factorof five CO depletion just beyond the millimeter grain edge, and a 2 K decrease in gas temperature for r > 120 AU.The warm deuterium fractionation pathway is implemented as a constant DCO+ abundance of 2.0 × 10−12 between30–70 K. The DCO+ emission probes a reservoir of cold material in the HD 169142 outer disk that is not revealed bythe millimeter continuum, the SED, nor the emission from the 12CO, 13CO, or C18O J=2–1 lines.

Accepted by A&A

http://arxiv.org/pdf/1802.09280

Radio outburst from a massive (proto)star. When accretion turns into ejection

R. Cesaroni1, L. Moscadelli1, R. Neri2, A. Sanna3, A. Caratti o Garatti4, J. Eisloffel5, B. Stecklum5,

T. Ray4, and C.M. Walmsley

1 INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy; 2 Institut de RadioastronomieMillimetrique (IRAM), 300 rue de la Piscine, F-38406 Saint Martin d’Heres, France; 3 Max Planck Institut furRadioastronomie, Auf dem Hugel 69, D-53121 Bonn, Germany; 4 Dublin Institute for Advanced Studies, Astronomy& Astrophysics Section, 31 Fitzwilliam Place, Dublin 2, Ireland; 5 Thuringer Landessternwarte Tautenburg, Sternwarte5, D-07778 Tautenburg, Germany

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

Context. Recent observations of the massive young stellar object S255 NIRS 3 have revealed a large increase in bothmethanol maser flux density and IR emission, which have been interpreted as the result of an accretion outburst,

13

possibly due to instabilities in a circumstellar disk. This indicates that this type of accretion event could be commonin young/forming early-type stars and in their lower mass siblings, and supports the idea that accretion onto the starmay occur in a non-continuous way.Aims. As accretion and ejection are believed to be tightly associated phenomena, we wanted to confirm the accretioninterpretation of the outburst in S255 NIRS 3 by detecting the corresponding burst of the associated thermal jet.Methods. We monitored the radio continuum emission from S255 NIRS 3 at four bands using the Karl G. JanskyVery Large Array. The millimetre continuum emission was also observed with both the Northern Extended MillimeterArray of IRAM and the Atacama Large Millimeter/submillimeter Array.Results. We have detected an exponential increase in the radio flux density from 6 to 45 GHz starting right after July10, 2016, namely about 13 months after the estimated onset of the IR outburst. This is the first ever detection ofa radio burst associated with an IR accretion outburst from a young stellar object. The flux density at all observedcentimetre bands can be reproduced with a simple expanding jet model. At millimetre wavelengths we infer a marginalflux increase with respect to the literature values and we show this is due to free-free emission from the radio jet.

Accepted by A&A

http://arxiv.org/pdf/1802.04228

Nitrogen and hydrogen fractionation in high-mass star-forming cores from observationsof HCN and HNC

L. Colzi1,2, F. Fontani2, P. Caselli3, C. Ceccarelli4,5, P. Hily-Blant4,5 and L. Bizzocchi3

1 Universita degli studi di Firenze, Dipartimento di fisica e Astronomia, via Sansone, 1 50019 Sesto Fiorentino,Italy; 2 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy; 3 Max-Planck-Institutfr extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching bei Mnchen, Germany; 4 CNRS, IPAG, 38000Grenoble, France; 5 Univ. Grenoble Alpes, IPAG, 38000 Grenoble, France

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

The ratio between the two stable isotopes of nitrogen, 14N and 15N, is well measured in the terrestrial atmosphere(∼ 272), and for the pre-solar nebula (∼ 441, deduced from the solar wind). Interestingly, some pristine solar systemmaterials show enrichments in 15N with respect to the pre-solar nebula value. However, it is not yet clear if and howthese enrichments are linked to the past chemical history because we have only a limited number of measurements indense star-forming regions. In this respect, dense cores, which are believed to be the precursors of clusters and alsocontain intermediate- and high-mass stars, are important targets because the solar system was probably born withina rich stellar cluster, and such clusters are formed in high-mass star-forming regions. The number of observations insuch high-mass dense cores has remained limited so far. In this work, we show the results of IRAM-30m observationsof the J=1-0 rotational transition of the molecules HCN and HNC and their 15N-bearing counterparts towards 27intermediate- and high-mass dense cores that are divided almost equally into three evolutionary categories: high-massstarless cores, high-mass protostellar objects, and ultra-compact Hii regions. We have also observed the DNC(2-1)rotational transition in order to search for a relation between the isotopic ratios D/H and 14N/15N. We derive average14N/15N ratios of 359±16 in HCN and of 438±21 in HNC, with a dispersion of about 150-200. We find no trend of the14N/15N ratio with evolutionary stage. This result agrees with what has been found for N2H

+ and its isotopologuesin the same sources, although the 14N/15N ratios from N2H

+ show a higher dispersion than in HCN/HNC, and onaverage, their uncertainties are larger as well. Moreover, we have found no correlation between D/H and 14N/15Nin HNC. These findings indicate that (1) the chemical evolution does not seem to play a role in the fractionation ofnitrogen, and that (2) the fractionation of hydrogen and nitrogen in these objects is not related.

Accepted by A&A

https://www.aanda.org/articles/aa/pdf/2018/01/aa30576-17.pdf

arxiv.org/pdf/1709.04237

ALMA’s Polarized View of 10 Protostars in the Perseus Molecular Cloud

Erin G. Cox1, Robert J. Harris2,1, Leslie W. Looney1, Zhi-Yun Li3, Haifeng Yang3, John J. Tobin4,5

and Ian Stephens6

14

1 Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W. Green St., Urbana, IL 61801, USA;2 National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 1205 W Clark St,Urbana, IL 61801; 3 Department of Astronomy, University of Virginia, 530 McCormick Rd, Charlottesville, VA 22903,USA; 4 Homer L. Dodge Department of Physics and Astronomy, Oklahoma University, 440 W. Brooks St. Norman,OK 73019, USA; 5 Leiden Observatory, Leiden University, P.O. Box 9513, 2000-RA Leiden, The Netherlands; 6

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

E-mail contact: egcox2 at illinois.edu

We present 870 µm ALMA dust polarization observations of 10 young Class 0/I protostars in the Perseus MolecularCloud. At ∼0.′′35 (80 au) resolution, all of our sources show some degree of polarization, with most (9/10) showingsignificantly extended emission in the polarized continuum. Each source has incredibly intricate polarization signatures.In particular, all three disk-candidates have polarization vectors roughly along the minor axis, which is indicative ofpolarization produced by dust scattering. On ∼100 au scales, the polarization is at a relatively low level (<∼1%) andis quite ordered. In sources with significant envelope emission, the envelope is typically polarized at a much higher(>∼5%) level and has a far more disordered morphology. We compute the cumulative probability distributions forboth the small (disk-scale) and large (envelope-scale) polarization percentage. We find that the two are intrinsicallydifferent, even after accounting for the different detection thresholds in the high/low surface brightness regions. Weperform Kolmogorov-Smirnov and Anderson-Darling tests on the distributions of angle offsets of the polarization fromthe outflow axis. We find disk-candidate sources are different from the non-disk-candidate sources. We conclude thatthe polarization on the 100 au scale is consistent with the signature of dust scattering for disk-candidates and that thepolarization on the envelope-scale in all sources may come from another mechanism, most likely magnetically alignedgrains.

Accepted by ApJ

http://arxiv.org/pdf/1802.00449

Chemistry of a newly detected circumbinary disk in Ophiuchus

Elizabeth Artur de la Villarmois1, Lars E. Kristensen1, Jes K. Jørgensen1, Edwin A. Bergin2, Christian

Brinch3, Søren Frimann4, Daniel Harsono5, Nami Sakai6 and Satoshi Yamamoto7

1 Centre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, Universityof Copenhagen, Øster Voldgade 5 - 7, 1350 Copenhagen K., Denmark; 2 Department of Astronomy, University ofMichigan, 311 West Hall, 1085 S. University Ave, Ann Arbor, MI 48109, USA; 3 Niels Bohr International Academy,The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, DK-2100 Copenhagen Ø. Denmark; 4 ICREAand Institut de Ciencies del Cosmos, Universitat de Barcelona, IEEC-UB, Martı Franques 1, 08028 Barcelona, Spain; 5

Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands; 6 The Institute of Physicaland Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan; 7 Department of Physics, TheUniversity of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan

E-mail contact: elizabeth.artur at nbi.ku.dk

Context. Astronomers recently started discovering exoplanets around binary systems. Therefore, understanding theformation and evolution of circumbinary disks and their environment is crucial for a complete scenario of planetformation.Aims. The purpose of this paper is to present the detection of a circumbinary disk around the system Oph-IRS67 andanalyse its chemical and physical structure.Methods. We present high-angular-resolution (0.4′′, ∼60 AU) observations of C17O, H13CO+, C34S, SO2, C2H andc−C3H2 molecular transitions with the Atacama Large Millimeter/submillimeter Array (ALMA) at wavelengths of0.8 mm. The spectrally and spatially resolved maps reveal the kinematics of the circumbinary disk as well as itschemistry. Molecular abundances are estimated using the non-local thermodynamic equilibrium (LTE) radiative-transfer tool RADEX.Results. The continuum emission agrees with the position of Oph-IRS67 A and B, and reveals the presence of acircumbinary disk around the two sources. The circumbinary disk has a diameter of ∼620 AU and is well traced byC17O and H13CO+ emission. Two further molecular species, C2H and c−C3H2, trace a higher-density region which isspatially offset from the sources (∼430 AU). Finally, SO2 shows compact and broad emission around only one of thesources, Oph-IRS67 B. The molecular transitions which trace the circumbinary disk are consistent with a Keplerian

15

profile on smaller disk scales (<∼ 200 AU) and an infalling profile for larger envelope scales (>∼ 200 AU). The Keplerianfit leads to an enclosed mass of 2.2 M⊙. Inferred CO abundances with respect to H2 are comparable to the canonicalISM value of 2.7 × 10−4, reflecting that freeze-out of CO in the disk midplane is not significant.Conclusions. Molecular emission and kinematic studies prove the existence and first detection of the circumbinarydisk associated with the system Oph-IRS67. The high-density region shows a different chemistry than the disk, beingenriched in carbon chain molecules. The lack of methanol emission agrees with the scenario where the extended diskdominates the mass budget in the innermost regions of the protostellar envelope, generating a flat density profile whereless material is exposed to high temperatures, and thus, complex organic molecules would be associated with lowercolumn densities. Finally, Oph-IRS67 is a promising candidate for proper motion studies and the detection of bothcircumstellar disks with higher-angular-resolution observations.

Accepted by A&A

https://arxiv.org/pdf/1802.09286

The emergence of the galactic stellar mass function from a non-universal IMF in clusters

Sami Dib1,2 and Shantanu Basu3

1 Instituto de Astronomia y Ciencias Planetarias, Universidad de Atacama, Copiapo, Chile; 2 Niels Bohr InternationalAcademy, Niels Bohr Institute, Copenhagen, Denmark; 3 University of Western Ontario, London, Canada

E-mail contact: sami.dib at gmail.com

We investigate how a single generation galactic mass function (SGMF) depends on the existence of variations in theinitial stellar mass functions (IMF) of stellar clusters. We show that cluster-to-cluster variations of the IMF leadto a multicomponent SGMF where each component in a given mass range can be described by a distinct power-lawfunction. We also show that a dispersion of ≈ 0.3 M⊙ in the characteristic mass of the IMF, as observed for youngGalactic clusters, leads to a low mass slope of the SGMF that matches the observed Galactic stellar mass functioneven when the IMFs in the low mass end of individual clusters are much steeper.

Accepted by A&A

https://arxiv.org/pdf/1711.07487v2

The ALMA-PILS survey: The sulphur connection between protostars and comets:IRAS 16293−2422 B and 67P/Churyumov–Gerasimenko

Maria N. Drozdovskaya1, Ewine F. van Dishoeck2,3, Jes K. Jørgensen4, Ursina Calmonte5, Matthijs

H.D. van der Wiel6, Audrey Coutens7, Hannah Calcutt4, Holger S.P. Muller8, Per Bjerkeli9, Magnus

V. Persson9, Susanne F. Wampfler1, Kathrin Altwegg5

1 Center for Space and Habitability, Universitat Bern, Sidlerstrasse 5, 3012 Bern, Switzerland; 2 Leiden Observatory,Leiden University, P.O. Box 9513, 2300 RA, Leiden, The Netherlands; 3 Max-Planck-Institut fur ExtraterrestrischePhysik, Giessenbachstrasse 1, 85748 Garching, Germany; 4 Centre for Star and Planet Formation, Niels Bohr Institute& Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K., Den-mark; 5 Physikalisches Institut, Universitat Bern, Sidlerstrasse 5, 3012 Bern, Switzerland; 6 ASTRON, The NetherlandsInstitute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands; 7 Laboratoire d’Astrophysique deBordeaux, Univ. Bordeaux, CNRS, B18N, allee Geoffroy Saint-Hilaire, 33615 Pessac, France; 8 I. Physikalisches Insti-tut, Universitat zu Koln, Zulpicher Strasse 77, 50937 Koln, Germany; 9 Department of Space, Earth and Environment,Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden

E-mail contact: maria.drozdovskaya at csh.unibe.ch

The evolutionary past of our Solar System can be pieced together by comparing analogous low-mass protostars withremnants of our Protosolar Nebula — comets. Sulphur-bearing molecules may be unique tracers of the joint evolutionof the volatile and refractory components. ALMA Band 7 data from the large unbiased Protostellar InterferometricLine Survey (PILS) are used to search for S-bearing molecules in the outer disc-like structure, 60 au from IRAS16293−2422 B, and are compared with data on 67P/C–G stemming from the ROSINA instrument aboard Rosetta.Species such as SO2, SO, OCS, CS, H2CS, H2S and CH3SH are detected via at least one of their isotopologues towardsIRAS 16293−2422 B. The search reveals a first-time detection of OC33S towards this source and a tentative first-time

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detection of C36S towards a low-mass protostar. The data show that IRAS 16293−2422 B contains much more OCSthan H2S in comparison to 67P/C–G; meanwhile, the SO/SO2 ratio is in close agreement between the two targets.IRAS 16293−2422 B has a CH3SH/H2CS ratio in range of that of our Solar System (differences by a factor of 0.7–5.3).It is suggested that the levels of UV radiation during the initial collapse of the systems may have varied and havepotentially been higher for IRAS 16293−2422 B due to its binary nature; thereby, converting more H2S into OCS.It remains to be conclusively tested if this also promotes the formation of S-bearing complex organics. Elevated UVlevels of IRAS 16293−2422 B and a warmer birth cloud of our Solar System may jointly explain the variations betweenthe two low-mass systems.

Accepted by MNRAS

http://arxiv.org/pdf/1802.02977

A revised distance to IRAS 16293−2422 from VLBA astrometry of associated watermasers

S.A. Dzib1, G.N. Ortiz-Leon1,2, A. Hernandez-Gomez3,4, L. Loinard3,5, A.J. Mioduszewski6, M. Claussen6,

K.M. Menten1, E. Caux4, and A. Sanna1

1 Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, D-53121 Bonn, Germany; 2 Humboldt Fellow; 3

Instituto de Radioastronomıa y Astrofsica, Universidad Nacional Autonoma de Mexico, Morelia 58089, Mexico; 4

IRAP, Universite de Toulouse, CNRS, UPS, CNES, Toulouse, France; 5 Instituto de Astronomıa, Universidad NacionalAutonoma de Mexico, Apartado Postal 70-264, CdMx C.P. 04510, Mexico; 6 National Radio Astronomy Observatory,P.O. Box 0, Socorro, NM 87801, USA

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

IRAS 16293−2422 is a very well studied young stellar system seen in projection towards the L1689N cloud in theOphiuchus complex. However, its distance is still uncertain with a range of values from 120 pc to 180 pc. Our goalis to measure the trigonometric parallax of this young star by means of H2O maser emission. We use archival datafrom 15 epochs of VLBA observations of the 22.2 GHz water maser line. By modeling the displacement on the sky ofthe H2O maser spots, we derived a trigonometric parallax of 7.1±1.3 mas, corresponding to a distance of 141+30

−21 pc.This new distance is in good agreement with recent values obtained for other magnetically active young stars in theL1689 cloud. We relate the kinematics of these masers with the outflows and the recent ejections powered by sourceA in the system.

Accepted by A&A

http://arxiv.org/pdf/1802.03234

2MASS J13243553+6358281 is an Early T-Type Planetary-Mass Object in the AB Do-radus Moving Group

Jonathan Gagne1,2, Katelyn N. Allers3, Christopher A. Theissen4, Jacqueline K. Faherty5, Daniella

Bardalez Gagliuffi5 and Etienne Artigau6

1 Carnegie Institution of Washington DTM, 5241 Broad Branch Road NW, Washington, DC 20015, USA; 2 NASASagan Fellow; 3 Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837, USA; 4 Center forAstrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Dr., Mail Code 0424, La Jolla, CA92093, USA; 5 Department of Astrophysics, American Museum of Natural History, Central Park West at 79th St.,New York, NY 10024, USA; 6 Institute for Research on Exoplanets, Universite de Montreal, Departement de Physique,C.P. 6128 Succ. Centre-ville, Montreal, QC H3C 3J7, Canada

E-mail contact: jgagne at carnegiescience.edu

We present new radial velocity and trigonometric parallax measurements indicating that the unusually red and photo-metrically variable T2 dwarf 2MASS J13243553+6358281 is a member of the young (∼150 Myr) AB Doradus movinggroup based on its space velocity. We estimate its model-dependent mass in the range 11–12 MJup at the age of theAB Doradus moving group, and its trigonometric parallax distance of 12.7±1.5 pc makes it one of the nearest knownisolated planetary-mass objects. The unusually red continuum of 2MASS J13243553+6358281 in the near-infrared waspreviously suspected to be caused by an unresolved L+T brown dwarf binary, although it was never observed with

17

high-spatial resolution imaging. This new evidence of youth suggests that a low surface gravity may be sufficient toexplain this peculiar feature. Using the new parallax we find that its absolute J-band magnitude is ∼0.4 mag fainterthan equivalent-type field brown dwarfs, suggesting that the binary hypothesis is unlikely. The fundamental propertiesof 2MASS J13243553+6358281 follow the spectral type sequence of other known high-likelihood members of the ABDoradus moving group. The effective temperature of 2MASS J13243553+6358281 provides the first precise constrainton the L/T transition at a known young age, and indicates that it happens at a temperature of ∼1150 K at ∼150Myr, compared to ∼1250 K for field brown dwarfs.

Accepted by ApJL

http://arxiv.org/pdf/1802.00493

Three-dimensional structure of the Upper Scorpius association with the Gaia first datarelease

Phillip A.B. Galli1, Isabelle Joncour2,3 and Estelle Moraux2

1 Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao, 1226, CidadeUniversitaria, Sao Paulo-SP, Brazil; 2 Univ. Grenoble Alpes, CNRS, IPAG, 38000, Grenoble, France; 3 Departmentof Astronomy, University of Maryland, College Park, MD, 20742, USA

E-mail contact: phillip.galli at iag.usp.br

Using new proper motion data from recently published catalogs, we revisit the membership of previously identifiedmembers of the Upper Scorpius association. We confirmed 750 of them as cluster members based on the convergentpoint method, compute their kinematic parallaxes and combined them with Gaia parallaxes to investigate the 3Dstructure and geometry of the association using a robust covariance method. We find a mean distance of 146±3±6 pcand show that the morphology of the association defined by the brightest (and most massive) stars yields a prolateellipsoid with dimensions of 74 × 38 × 32 pc3, while the faintest cluster members define a more elongated structurewith dimensions of 98× 24× 18 pc3. We suggest that the different properties of both populations is an imprint of thestar formation history in this region.

Accepted by MNRAS (letters)

Velocity–Resolved [CII] Emission from Cold Diffuse Clouds in the Interstellar Medium

Paul F. Goldsmith1, Jorge L. Pineda1, David A. Neufeld2, Mark G. Wolfire3, Christophe Risacher4 and

Robert Simon5

1 Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena CA 91109, MS 169-506, USA; 2 Department of Physics &Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 20218, USA; 3 Department of Astronomy,University of Maryland, College Park, MD 20742-2421, USA; 4 Max Planck Institut fuer Radioastronomie, Bonn53121, Germany; 5 Cologne University, Koeln 50937, Germany

E-mail contact: paul.f.goldsmith at jpl.nasa.gov

We have combined emission from the 158 µm fine structure transition of C+ observed with the GREAT and upGREATinstruments on SOFIA with 21–cm absorption spectra and visual extinction to characterize the diffuse interstellarclouds found along the lines of sight. The weak [C ii] emission is consistent in velocity and line width with the strongestH i component produced by the Cold Neutral Medium (CNM). The H i column density and kinetic temperature areknown from the 21cm data, and assuming a fractional abundance of ionized carbon, we calculate the volume densityand thermal pressure of each source, which vary considerably, with 27 cm−3 ≤ n(H0) ≤ 210 cm−3 considering onlythe atomic hydrogen along the lines of sight to be responsible for the C+, while 13 cm−3 ≤ n(H0 + H2) ≤ 190 cm−3

including the hydrogen in both forms. The thermal pressure varies widely with 1970 cm−3K ≤ Pth/k ≤ 10440 cm−3Kfor H0 alone and 750 cm−3K ≤ Pth/k ≤ 9360 cm−3K including both H0 and H2. The molecular hydrogen fractionvaries between 0.10 and 0.67. Photoelectric heating is the dominant heating source, supplemented by a moderately–enhanced cosmic ray ionization rate, constrained by the relatively low 45 K to 73 K gas temperatures of the clouds.The resulting thermal balance for the two lower–density clouds is satisfactory, but for the two higher–density clouds,the combined heating rate is insufficient to balance the observed C+ cooling.

Accepted by The Astrophysical Journal

18

Massive, wide binaries as tracers of massive star formation

Daniel W. Griffiths1, Simon P. Goodwin1 and Saida M. Caballero-Nieves2,1

1 Dept. Physics & Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK; 2

Department of Physics and Space Sciences, Florida Institute of Technology, 150 W. University Boulevard, Melbourne,FL 32901, USA

E-mail contact: d.griffiths at sheffield.ac.uk

Massive stars can be found in wide (hundreds to thousands AU) binaries with other massive stars. We use N-body simulations to show that any bound cluster should always have approximately one massive wide binary: onewill probably form if none are present initially; and probably only one will survive if more than one are presentinitially. Therefore any region that contains many massive wide binaries must have been composed of many individualsubregions. Observations of Cyg OB2 show that the massive wide binary fraction is at least a half (38/74) whichsuggests that Cyg OB2 had at least 30 distinct massive star formation sites. This is further evidence that Cyg OB2 hasalways been a large, low-density association. That Cyg OB2 has a normal high-mass IMF for its total mass suggeststhat however massive stars form they ‘randomly sample’ the IMF (as the massive stars did not ‘know’ about eachother).

Accepted by MNRAS

http://arxiv.org/pdf/1802.04560

Is the spiral morphology of the Elias 2-27 circumstellar disc due to gravitational insta-bility?

Cassandra Hall1,2, Ken Rice2,3, Giovanni Dipierro1, Duncan Forgan4,5, Tim Harries6 and Richard

Alexander1

1 Department of Physics & Astronomy, University of Leicester, Leicester, LE1 7RH, UK; 2 SUPA, Institute forAstronomy, University of Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK; 3 Centre for Exoplanet Science,University of Edinburgh, Edinburgh, UK; 4 SUPA, School of Physics & Astronomy, University of St Andrews, NorthHaugh, St Andrews, KY16 9SS, UK; 5 St Andrews Centre for Exoplanet Science, University of St Andrews, UK; 6

University of Exeter, Stocker Road, Exeter EX4 4QL, UK

E-mail contact: cassandra.hall at le.ac.uk

A recent ALMA observation of the Elias 2-27 system revealed a two-armed structure extending out to ∼300 au inradius. The protostellar disc surrounding the central star is unusually massive, raising the possibility that the system isgravitationally unstable. Recent work has shown that the observed morphology of the system can be explained by discself-gravity, so we examine the physical properties of the disc necessary to detect self-gravitating spiral waves. Usingthree-dimensional Smoothed Particle Hydrodynamics, coupled with radiative transfer and synthetic ALMA imaging,we find that observable spiral structure can only be explained by self-gravity if the disc has a low opacity (and thereforeefficient cooling), and is minimally supported by external irradiation. This corresponds to a very narrow region ofparameter space, suggesting that, although it is possible for the spiral structure to be due to disc self-gravity, otherexplanations, such as an external perturbation, may be preferred.

Accepted by MNRAS

http://arxiv.org/pdf/1802.09451

Discovery of New Dipper Stars with K2: A Window into the Inner Disk Region of TTauri Stars

Christina Hedges1, Simon Hodgkin1, Grant Kennedy2

1 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK; 2 Department ofPhysics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK

E-mail contact: chedges at ast.cam.ac.uk

In recent years a new class of Young Stellar Object has been defined, referred to as dippers, where large transient

19

drops in flux are observed. These dips are too large to be attributed to stellar variability, last from hours to days andcan reduce the flux of a star by 10–50%. This variability has been attributed to occultations by warps or accretioncolumns near the inner edge of circumstellar disks. Here we present 95 dippers in the Upper Scorpius association andρ Ophiuchus cloud complex found in K2 Campaign 2 data using supervised machine learning with a Random Forestclassifier. We also present 30 YSOs that exhibit brightening events on the order of days, known as bursters. Not alldippers and bursters are known members, but all exhibit infrared excesses and are consistent with belonging to eitherof the two young star forming regions. We find 21.0±5.5% of stars with disks are dippers for both regions combined.Our entire dipper sample consists only of late-type (KM) stars, but we show that biases limit dipper discovery forearlier spectral types. Using the dipper properties as a proxy, we find that the temperature at the inner disk edge isconsistent with interferometric results for similar and earlier type stars.

Accepted by MNRAS

http://arxiv.org/pdf/1802.00409

Inside-Out Planet Formation. IV. Pebble Evolution and Planet Formation Timescales

Xiao Hu1,2, Jonathan C. Tan1,3, Zhaohuan Zhu2, Sourav Chatterjee4, Tilman Birnstiel5, Andrew N.

Youdin6 and Subhanjoy Mohanty7

1 Department of Astronomy, University of Florida, Gainesville, FL 32611, USA; 2 Department of Physics and Astron-omy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154, USA; 3 Department ofPhysics, University of Florida, Gainesville, FL 32611, USA; 4 Center for Interdisciplinary Exploration and Researchin Astrophysics (CIERA), Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA; 5 UniversityObservatory, Faculty of Physics, LudwigMaximilians-Universitt Munchen, Scheinerstr. 1, 81679 Munich, Germany; 6

Department of Astronomy and Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ85721, USA; 7 Imperial College London, 1010 Blackett Lab, Prince Consort Rd., London SW7 2AZ, UK

E-mail contact: xiao.hu.astro at gmail.com

Systems with tightly-packed inner planets (STIPs) are very common. Chatterjee & Tan proposed Inside-Out PlanetFormation (IOPF), an in situ formation theory, to explain these planets. IOPF involves sequential planet formationfrom pebble-rich rings that are fed from the outer disk and trapped at the pressure maximum associated with thedead zone inner boundary (DZIB). Planet masses are set by their ability to open a gap and cause the DZIB to retreatoutwards. We present models for the disk density and temperature structures that are relevant to the conditions ofIOPF. For a wide range of DZIB conditions, we evaluate the gap opening masses of planets in these disks that areexpected to lead to truncation of pebble accretion onto the forming planet. We then consider the evolution of dustand pebbles in the disk, estimating that pebbles typically grow to sizes of a few cm during their radial drift fromseveral tens of AU to the inner, <∼1 AU-scale disk. A large fraction of the accretion flux of solids is expected to be insuch pebbles. This allows us to estimate the timescales for individual planet formation and entire planetary systemformation in the IOPF scenario. We find that to produce realistic STIPs within reasonable timescales similar to disklifetimes requires disk accretion rates of ∼ 10−9 M⊙ yr−1 and relatively low viscosity conditions in the DZIB region,i.e., Shakura-Sunyaev parameter of α ∼ 10−4.

Accepted by ApJ

https://arxiv.org/pdf/1709.10130

The Herschel-PACS legacy of low-mass protostars: Properties of warm and hot gas andits origin in far-UV illuminated shocks

Agata Karska1,2,3, Michael J. Kaufman4, Lars E. Kristensen5, Ewine F. van Dishoeck6,2, Gregory J.

Herczeg7, Joseph C. Mottram8, Lukasz Tychoniec6, Johan E. Lindberg9, Neal J. Evans II10 Joel D.

Green11,10, Yao-Lun Yang10, Antoine Gusdorf12, Dominika Itrich1 and Natasza Siodmiak13

1 Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka5, 87-100 Torun, Poland; 2 Max-Planck Institut f ur Extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748Garching, Germany; 3 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands; 4

Department of Physics and Astronomy, San Jose State University, One Washington Square, San Jose, CA 95192-

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0106, USA; 5 Centre for Star and Planet Formation, Niels Bohr Institute and Natural History Museum of Denmark,University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark; 6 Leiden Observatory, LeidenUniversity, Niels Bohrweg 2, NL-2333 CA Leiden, The Netherlands; 7 Kavli Institute for Astronomy and Astrophysics,Peking University, Yi He Yuan Lu 5, Haidian Qu, 100871 Beijing, Peoples Republic of China; 8 Max Planck Institutefor Astronomy, Knigstuhl 17, 69117 Heidelberg, Germany; 9 NASA Goddard Space Flight Center, AstrochemistryLaboratory, Mail Code 691, 8800 Greenbelt Road, Greenbelt, MD 20771, USA; 10 Department of Astronomy, TheUniversity of Texas at Austin, Austin, TX 78712, USA; 11 Space Telescope Science Institute, Baltimore, MD, USA;12 LERMA, Observatoire de Paris, Ecole normale superieure, PSL Research University, CNRS, Sorbonne Universits,UPMC Univ. Paris 06, F-75231, Paris, France; 13 N. Copernicus Astronomical Center, Rabianska 8, 87-100 Torun,Poland

E-mail contact: agata.karska at umk.pl

Recent observations from Herschel allow the identification of important mechanisms responsible for the heating of gassurrounding low-mass protostars and its subsequent cooling in the far-infrared (FIR). Shocks are routinely invokedto reproduce some properties of the far-IR spectra, but standard models fail to reproduce the emission from keymolecules, e.g. H2O. Here, we present the Herschel-PACS far-IR spectroscopy of 90 embedded low-mass protostars(Class 0/I). The Herschel-PACS spectral maps covering ∼55–210 µm with a field-of-view of ∼50′′ are used to quantifythe gas excitation conditions and spatial extent using rotational transitions of H2O, high-J CO, and OH, as well as [OI] and [C II]. We confirm that a warm (∼300 K) CO reservoir is ubiquitous and that a hotter component (760±170K) is frequently detected around protostars. The line emission is extended beyond ∼1000 AU spatial scales in 40/90objects, typically in molecular tracers in Class 0 and atomic tracers in Class I objects. High-velocity emission (>∼90km s−1) is detected in only 10 sources in the [O I] line, suggesting that the bulk of [O I] arises from gas that is movingslower than typical jets. Line flux ratios show an excellent agreement with models of C-shocks illuminated by UVphotons for pre-shock densities of ∼105 cm−3 and UV fields 0.1–10 times the interstellar value. The far-IR molecularand atomic lines are a unique diagnostic of feedback from UV emission and shocks in envelopes of deeply embeddedprotostars.

Accepted by ApJS

http://arxiv.org/pdf/1802.03379

Core Emergence in a Massive Infrared Dark Cloud: A Comparison Between Mid-IRExtinction and 1.3 mm Emission

Shuo Kong1, Jonathan C. Tan2,3, Hector G. Arce1, Paola Caselli4, Francesco Fontani5 and Michael J.

Butler6

1 Dept. of Astronomy, Yale University, New Haven, Connecticut 06511, USA; 2 Dept. of Space, Earth and Envi-ronment, Chalmers University of Technology, Gothenburg, Sweden; 3 Dept. of Astronomy, University of Virginia,Charlottesville, Virginia 22904, USA; 4 Max-Planck-Institute for Extraterrestrial Physics (MPE), Giessenbachstr. 1,D-85748 Garching, Germany; 5 INAF - Osservatorio Astrofisico di Arcetri, I-50125, Florence, Italy; 6 Max PlanckInstitute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany

E-mail contact: shuo.kong at yale.edu

Stars are born from dense cores in molecular clouds. Observationally, it is crucial to capture the formation of cores inorder to understand the necessary conditions and rate of the star formation process. The Atacama Large Mm/sub-mmArray (ALMA) is extremely powerful for identifying dense gas structures, including cores, at mm wavelengths via theirdust continuum emission. Here we use ALMA to carry out a survey of dense gas and cores in the central region of themassive (∼ 105 M⊙) Infrared Dark Cloud (IRDC) G28.37+0.07. The observation consists of a mosaic of 86 pointingsof the 12m-array and produces an unprecedented view of the densest structures of this IRDC. In this first paper aboutthis data set, we focus on a comparison between the 1.3 mm continuum emission and a mid-infrared (MIR) extinctionmap of the IRDC. This allows estimation of the “dense gas” detection probability function (DPF), i.e., as a functionof the local mass surface density, Σ, for various choices of thresholds of mm continuum emission to define “dense gas”.We then estimate the dense gas mass fraction, fdg, in the central region of the IRDC and, via extrapolation withthe DPF and the known Σ probability distribution function, to the larger-scale surrounding regions, finding values ofabout 5% to 15% for the fiducial choice of threshold. We argue that this observed dense gas is a good tracer of theprotostellar core population and, in this context, estimate a star formation efficiency per free-fall time in the central

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IRDC region of ǫff ∼10%, with approximately a factor of two systematic uncertainties.

Accepted by ApJL

http://arxiv.org/pdf/1802.07376

Characterization of methanol as a magnetic field tracer in star-forming regions

Boy Lankhaar1, Wouter Vlemmings1, Gabriele Surcis2,3, Huib Jan van Langevelde3,4, Gerrit C. Groenenboom5

and Ad van der Avoird5

1 Department of Space, Earth and Environment, Onsala Space Observatory, Chalmers University of Technology,Onsala, Sweden; 2 INAF, Osservatorio Astronomico di Cagliari, Selargius, Italy; 3 Joint Institute for VLBI ERIC,Dwingeloo, Netherlands; 4 Sterrewacht Leiden, Leiden University, Leiden, Netherlands; 5 Theoretical Chemistry,Institute for Molecules and Materials, Radboud University, Nijmegen, Netherlands

E-mail contact: lankhaar at chalmers.se

Magnetic fields play an important role during star formation. Direct magnetic field strength observations have provenparticularly challenging in the extremely dynamic protostellar phase. Because of their occurrence in the densest partsof star-forming regions, masers, through polarization observations, are the main source of magnetic field strengthand morphology measurements around protostars. Of all maser species, methanol is one of the strongest and mostabundant tracers of gas around high-mass protostellar disks and in outflows. However, as experimental determinationof the magnetic characteristics of methanol has remained largely unsuccessful, a robust magnetic field strength analysisof these regions could hitherto not be performed. Here, we report a quantitative theoretical model of the magneticproperties of methanol, including the complicated hyperfine structure that results from its internal rotation. We showthat the large range in values of the Land g factors of the hyperfine components of each maser line lead to conclusionsthat differ substantially from the current interpretation based on a single effective g factor. These conclusions aremore consistent with other observations and confirm the presence of dynamically important magnetic fields aroundprotostars. Additionally, our calculations show that (nonlinear) Zeeman effects must be taken into account to furtherenhance the accuracy of cosmological electron-to-proton mass ratio determinations using methanol.

Accepted by Nature Astronomy

http://rdcu.be/FPeB

Near-infrared study of new embedded clusters in the Carina complex

R.A.P. Oliveira1, E. Bica1, and C. Bonatto1

1 Departamento de Astronomia, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500 Porto Alegre91501-970, RS, Brazil

E-mail contact: rap.oliveira at usp.br

We analyse the nature of a sample of stellar overdensities that we found projected on the Carina complex. This studyis based on 2MASS photometry and involves the photometry decontamination of field stars, elaboration of intrinsiccolour-magnitude diagrams J × (J −Ks), colour-colour diagrams (J −H)× (H −Ks) and radial density profiles, inorder to determine the structure and the main astrophysical parameters of the best candidates. The verification ofan overdensity as an embedded cluster requires a CMD consistent with a PMS content and MS stars, if any. Fromthese results, we are able to verify if they are, in fact, embedded clusters. The results were, in general, rewarding:in a sample of 101 overdensities, the analysis provided 15 candidates, of which three were previously catalogued asclusters (CCCP-Cl16, Treasure Chest and FSR1555), and the 12 remaining are discoveries that provided significantresults, with ages not above 4.5Myr and distances compatible with the studied complex. The resulting values for thedifferential reddening of most candidates were relatively high, confirming that these clusters are still (partially or fully)embedded in the surrounding gas and dust, as a rule within a shell. Histograms with the distribution of the masses,ages and distances were also produced, to give an overview of the results. We conclude that all the 12 newly foundembedded clusters are related to the Carina complex.

Accepted by MNRAS

http://arxiv.org/pdf/1802.02104

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The physical and chemical structure of Sagittarius B2. III. Radiative transfer simula-tions of the hot core SgrB2(M) for methyl cyanide

S. Pols1, A. Schworer1, P. Schilke1, A. Schmiedeke1,2, A. Sanchez-Monge1, and Th. Moller1

1 I. Physikalisches Institut, Universitat zu Koln, Zulpicher Str. 77, D-50937 Koln, Germany; 2 Max-Planck Institutefor Extraterrestrial Physics, Giessenbachstrasse 1, D-85748 Garching, Germany

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

We model the emission of methyl cyanide (CH3CN) lines towards the massive hot molecular core SgrB2(M). Weaim at reconstructing the CH3CN abundance field and investigating the gas temperature distribution as well as thevelocity field. SgrB2(M) was observed with the ALMA in a spectral line survey from 211 to 275 GHz. This frequencyrange includes several transitions of CH3CN (including isotopologues and vibrationally excited states). We employ thethree-dimensional radiative transfer toolbox Pandora in order to retrieve the velocity and abundance field by modelingdifferent CH3CN lines. For this purpose, we base our model on the results of a previous study that determined thephysical structure of SgrB2(M), i.e. the distribution of dust dense cores, ionized regions and heating sources. Themorphology of the CH3CN emission can be reproduced by a molecular density field that consists of a superpositionof cores with modified Plummer-like density profiles. The averaged relative abundance of CH3CN with respect to H2

ranges from 4×10−11 to 2×10−8 in the northern part of SgrB2(M) and from 2×10−10 to 5×10−7 in the southern part.In general, we find that the relative abundance of CH3CN is lower at the center of the very dense and hot cores, causingthe general morphology of the CH3CN emission to be shifted with respect to the dust continuum emission. The dusttemperature calculated by the radiative transfer simulation based on the available luminosity reaches values up to 900K. However, in some regions vibrationally excited transitions of CH3CN are underestimated by the model, indicatingthat the predicted gas temperature, which is assumed to be equal to the dust temperature, is partly underestimated.The determination of the velocity component along the line of sight reveals that a velocity gradient from the north tothe south exists in SgrB2(M).

Accepted by A&A

http://arxiv.org/pdf/1802.09231

Seeds of Life in Space (SOLIS). III. Zooming into the methanol peak of the pre-stellarcore L1544

Anna Punanova1,2, Paola Caselli1, Siyi Feng1, Ana Chacon-Tanarro1, Cecilia Ceccarelli3,4, Roberto

Neri5, Francesco Fontani6, Izaskun Jimenez-Serra7, Charlotte Vastel8,9, Luca Bizzocchi1, Andy Pon10,

Anton I. Vasyunin1,2, Silvia Spezzano1, Pierre Hily-Blant3,4, Leonardo Testi6,11, Serena Viti12, Satoshi

Yamamoto13,14, Felipe Alves1, Rafael Bachiller15, Nadia Balucani16, Eleonora Bianchi6,17, Sandrine

Bottinelli8,9, Emmanuel Caux8,9, Rumpa Choudhury1, Claudio Codella6, Francois Dulieu18, Cecile

Favre6, Jonathan Holdship12, Ali Jaber Al-Edhari3,4,19, Claudine Kahane3,4, Jake Laas1, Bertrand

LeFloch3,4, Ana Lopez-Sepulcre3,5, Juan Ospina-Zamudio3, Yoko Oya13, Jaime E. Pineda1, Linda

Podio6, Davide Quenard7, Albert Rimola20, Nami Sakai21, Ian R. Sims22, Vianney Taquet23, Patrice

Theule24 and Piero Ugliengo25

1 Max-Planck-Institut fur extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany; 2 Ural FederalUniversity, 620002, 19 Mira street, Yekaterinburg, Russia; 3 IPAG, Universite Grenoble Alpes, F-38000 Grenoble,France; 4 CNRS, IPAG, F-38000 Grenoble, France; 5 Institut de Radioastronomie Millimetrique, 300 rue de la Piscine,38406, Saint-Martin dHeres, France; 6 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Florence,Italy; 7 School of Physics and Astronomy, Queen Mary University of London, 327 Mile End Road, London, E1 4NS,UK; 8 Universite de Toulouse, UPS-OMP, IRAP, Toulouse, France; 9 CNRS, IRAP, 9 Av. Colonel Roche, BP 44346,F-31028 Toulouse Cedex 4, France; 10 Department of Physics and Astronomy, The University of Western Ontario,1151 Richmond Street, London, N6A 3K7, Canada; 11 European Southern Observatory, Karl-Schwarzschild-Str. 2,85748 Garching bei Munchen, Germany; 12 Department of Physics and Astronomy, University College London, GowerSt., London, WC1E 6BT, UK; 13 Department of Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033,Japan; 14 Research Center for the Early Universe, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; 15 Observatorio Astronomico Nacional (OAN, IGN), Calle Alfonso XII, 3, 28014 Madrid, Spain; 16

Dipartimento di Chimica, Biologia e Biotecnologie, Universita di Perugia, Via Elce di Sotto 8, I-06123 Perugia, Italy;17 Dipartimento di Fisica e Astronomia, Universita degli Studi di Firenze, Italy; 18 LERMA, Universite de Cergy

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Pontoise, Sorbonne Universites, UPMC Univ. Paris 6, PSL Research University, Observatoire de Paris, UMR 8112CNRS, 95000 Cergy Pontoise, France; 19 University of AL-Muthanna, College of Science, Physics Department, AL-Muthanna, Iraq; 20 Departament de Quımica, Universitat Autonoma de Barcelona, E-08193 Bellaterra, Spain; 21

The Institute of Physical and Chemical Research (RIKEN), 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan; 22

Institut de Physique de Rennes, UMR CNRS 6251, Universite de Rennes 1, 263 Avenue du General Leclerc, F-35042Rennes Cedex, France; 23 Leiden Observatory, Leiden University, P.O. Box 9513, 2300-RA Leiden, The Netherlands;24 Aix-Marseille Universite, PIIM UMR-CNRS 7345, 13397 Marseille, France; 25 Dipartimento di Chimica and NISCentre, Universita degli Studi di Torino, Via P. Giuria 7, I-10125 Torino, Italy

E-mail contact: punanovaanna at gmail.com

Towards the pre-stellar core L1544, the methanol (CH3OH) emission forms an asymmetric ring around the core centre,where CH3OH is mostly in solid form, with a clear peak 4000 au to the north-east of the dust continuum peak. Aspart of the NOEMA Large Project SOLIS (Seeds of Life in Space), the CH3OH peak has been spatially resolved tostudy its kinematics and physical structure and to investigate the cause behind the local enhancement. We find thatmethanol emission is distributed in a ridge parallel to the main axis of the dense core. The centroid velocity increasesby about 0.2 km s−1 and the velocity dispersion increases from subsonic to transonic towards the central zone of thecore, where the velocity field also shows complex structure. This could be indication of gentle accretion of materialonto the core or interaction of two filaments, producing a slow shock. We measure the rotational temperature andshow that methanol is in local thermodynamic equilibrium (LTE) only close to the dust peak, where it is significantlydepleted. The CH3OH column density, Ntot(CH3OH), profile has been derived with non-LTE radiative transfermodelling and compared with chemical models of a static core. The measured Ntot(CH3OH) profile is consistent withmodel predictions, but the total column densities are one order of magnitude lower than those predicted by models,suggesting that the efficiency of reactive desorption or atomic hydrogen tunnelling adopted in the model may beoverestimated; or that an evolutionary model is needed to better reproduce methanol abundance.

Accepted by ApJ

https://arxiv.org/pdf/1802.00859.pdf

Spiral density waves and vertical circulation in protoplanetary discs

A. Riols1,2, H. Latter1

1 Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for MathematicalSciences, Wilberforce Road, Cambridge CB3 0WA, UK; 2 Institut de Planetologie et d’Astrophysique de Grenoble,BP 53 38041 Grenoble, Cedex 9, France

E-mail contact: antoine.riols at univ-grenoble-alpes.fr

Spiral density waves dominate several facets of accretion disc dynamics — planet-disc interactions and gravitationalinstability (GI) most prominently. Though they have been examined thoroughly in two-dimensional simulations,their vertical structures in the non-linear regime are somewhat unexplored. This neglect is unwarranted given thatany strong vertical motions associated with these waves could profoundly impact dust dynamics, dust sedimentation,planet formation, and the emissivity of the disc surface. In this paper we combine linear calculations and shearingbox simulations in order to investigate the vertical structure of spiral waves for various polytropic stratifications andwave amplitudes. For sub-adiabatic profiles we find that spiral waves develop a pair of counter-rotating poloidalrolls. Particularly strong in the nonlinear regime, these vortical structures issue from the baroclinicity supported bythe background vertical entropy gradient. They are also intimately connected to the disk’s g-modes which appearto interact nonlinearly with the density waves. Furthermore, we demonstrate that the poloidal rolls are ubiquitousin gravitoturbulence, emerging in the vicinity of GI spiral wakes, and potentially transporting grains off the diskmidplane. Other than hindering sedimentation and planet formation, this phenomena may bear on observations ofthe disk’s scattered infrared luminosity. The vortical features could also impact on the turbulent dynamo operatingin young protoplanetary discs subject to GI, or possibly even galactic discs.

Accepted by MNRAS

http://arxiv.org/pdf/1802.06620

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Study of the filamentary infrared dark cloud G192.76+00.10in the S254-S258 OB complex

Olga L. Ryabukhina1,2, Igor I. Zinchenko1,2, Manash R. Samal3, Peter M. Zemlyanukha1, Dmitriy A.

Ladeyschikov4, Andrei M. Sobolev4, Christian Henkel5,6 and Devendra K. Ojha7

1 Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia; 2 Lobachevsky StateUniversity of Nizhni Novgorod, Nizhny Novgorod, Russia; 3 Institute of Astronomy, National Central University,Taoyuan City, Taiwan (R.O.C.); 4 Kourovka Astronomical Observatory, Ural Federal University, Ekaterinburg, Russia;5 Max Planck Institute for Radio Astronomy, Bonn, Germany; 6 Astron. Dept., King Abdulaziz University, Jeddah,Saudi Arabia; 7 Tata Institute of Fundamental Research, Mumbai, India

E-mail contact: ryabukhina at ipfran.ru

We present results of a high resolution study of the filamentary dark cloud G192.76+00.10 in the S254-S258 OBcomplex in several molecular species tracing different physical conditions. These include three isotopologues of carbonmonoxide (CO), ammonia (NH3), carbon monosulfide (CS). The aim of this work is to study the general structureand kinematics of the filamentary cloud, its fragmentation and physical parameters. The gas temperature is derivedfrom the NH3 (J,K) = (1, 1), (2, 2) and 12CO(2–1) lines and the 13CO(1–0), 13CO(2–1) emission is used to investigatethe overall gas distribution and kinematics. Several dense clumps are identified from the CS(2–1) data. Values of thegas temperature lie in the ranges 10 − 35K, column density N(H2) reaches the value 5.1 1022 cm−2. The width ofthe filament is of order 1 pc. The masses of the dense clumps range from ∼ 30 M⊙ to ∼ 160 M⊙. They appear to begravitationally unstable. The molecular emission shows a gas dynamical coherence along the filament. The velocitypattern may indicate longitudinal collapse

Accepted by Research in Astronomy and Astrophysics

https://arxiv.org/pdf/1802.08030.pdf

Orbital Motion of Young Binaries in Ophiuchus and Upper Centaurus-Lupus

G. H. Schaefer1, L. Prato2 and M. Simon3

1 The CHARA Array of Georgia State University, Mount Wilson Observatory, Mount Wilson, CA 91023, USA; 2

Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA; 3 Department of Physics and Astronomy,Stony Brook University, Stony Brook, NY 11794, USA

E-mail contact: schaefer at chara-array.org

We present measurements of the orbital positions and flux ratios of 17 binary and triple systems in the Ophiuchus starforming region and the Upper Centaurus-Lupus cluster based on adaptive optics imaging at the Keck Observatory. Wereport the detection of visual companions in MML 50 and MML 53 for the first time, as well as the possible detectionof a third component in WSB 21. For six systems in our sample, our measurements provide a second orbital positionfollowing their initial discoveries over a decade ago. For eight systems with sufficient orbital coverage, we analyze therange of orbital solutions that fit the data. Ultimately, these observations will help provide the groundwork towardmeasuring precise masses for these pre-main sequence stars and understanding the distribution of orbital parametersin young multiple systems.

Accepted by Astronomical Journal, 155, 109 (2018)

http://adsabs.harvard.edu/pdf/2018AJ....155..109S

http://arxiv.org/pdf/1802.02747

Unlocking CO Depletion in Protoplanetary Disks I. The Warm Molecular Layer

Kamber R. Schwarz1, Edwin A. Bergin1, L. Ilsedore Cleeves2, Ke Zhang1, Karin I. Oberg2, Geoffrey

A. Blake3 and Dana Anderson3

1 Department of Astronomy, University of Michigan, 1085 South University Ave., Ann Arbor, MI 48109, USA; 2

Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA; 3 Division of Geological& Planetary Sciences, MC 150-21, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125,USA

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E-mail contact: kamberrs at umich.edu

CO is commonly used as a tracer of the total gas mass in both the interstellar medium and in protoplanetary disks.Recently there has been much debate about the utility of CO as a mass tracer in disks. Observations of CO inprotoplanetary disks reveal a range of CO abundances, with measurements of low CO to dust mass ratios in numeroussystems. One possibility is that carbon is removed from CO via chemistry. However, the full range of physicalconditions conducive to this chemical reprocessing is not well understood. We perform a systematic survey of the timedependent chemistry in protoplanetary disks for 198 models with a range of physical conditions. We varying dust grainsize distribution, temperature, comic ray and X-ray ionization rate, disk mass, and initial water abundance, detailingwhat physical conditions are necessary to activate the various CO depletion mechanisms in the warm molecular layer.We focus our analysis on the warm molecular layer in two regions: the outer disk (100 au) well outside the CO snowlineand the inner disk (19 au) just inside the midplane CO snow line. After 1 Myr, we find that the majority of modelshave a CO abundance relative to H2 less than 10−4 in the outer disk, while an abundance less than 10−5 requiresthe presence of cosmic rays. Inside the CO snow line, significant depletion of CO only occurs in models with a highcosmic ray rate. If cosmic rays are not present in young disks it is difficult to chemically remove carbon from CO.Additionally, removing water prior to CO depletion impedes the chemical processing of CO. Chemical processing alonecannot explain current observations of low CO abundances. Other mechanisms must also be involved.

Accepted by ApJ

http://arxiv.org/pdf/1802.02590

A Statistical Study of Massive Cluster-Forming Clumps

Tomomi Shimoikura1, Kazuhito Dobashi1, Fumitaka Nakamura2,3, Tomoaki Matsumoto4 and Tomoya

Hirota2,3

1 Tokyo Gakugei University, Japan; 2 National Astronomical Observatory of Japan; 3 SOKENDAI, Japan; 4 HoseiUniversity, Japan

E-mail contact: ikura at u-gakugei.ac.jp

We report results of the observations of 15 regions in several molecular lines for a statistical study of massive cluster-forming clumps. We identified 24 clumps based on the C18O (J = 1− 0) data obtained by the NRO 45 m telescope,and found that 16 of them are associated with young clusters. The clumps associated with clusters have a typical mass,radius, and molecular density of 1X103 Mo, 0.5 pc, 1X105 cm−3, respectively. We categorized the clumps and clustersinto four types according to the spatial coincidence of gas and star density, and discussed their evolutions: Clumpswithout clusters (Type 1), clumps showing good correlations with clusters (Type 2), clumps showing poor correlationswith clusters (Type 3), and clusters with no associated clumps (Type 4). Analyses of the velocity structures andthe chemical compositions imply that the clump + cluster systems should evolve from Type 1 to Type 4. We foundthat some of the Type 2 clumps are infalling on the clump-scale to form clusters at the clump center, which shouldcommonly occur in the beginning of cluster formation. Interestingly, all of the identified Type 1 clumps are likely tobe older than the Type 2 clumps in terms of chemical compositions, suggesting that they have been gravitationallystable for a long time possibly being supported by the strong magnetic field of >1 mG. Type 1 clumps younger thanthe observed Type 2 clumps should be very rare to find because of their short lifetime.

Accepted by ApJ

http://arxiv.org/pdf/1802.00589

Sun-Sized Water Vapor Masers in Cepheus A

A.M. Sobolev1, J.M. Moran2, M.D. Gray3, A. Alakoz4, H. Imai5, W.A. Baan6, A.M. Tolmachev4, V.A.

Samodurov4,7, and D.A. Ladeyshchikov1

1 Ural Federal University, Ekaterinburg, Russia; 2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street,Cambridge, MA 02138, USA; 3 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, Alan TuringBuilding, University of Manchester, M13 9PL, UK; 4 Astro Space Center of the Lebedev Physical Institute, Moscow,Russia; 5 Science and Engineering Area of the Research and Education Assembly, Kagoshima University, 1-21-35Korimoto, Kagoshima 890-0065, Japan; 6 ASTRON—Netherlands Foundation for Research in Astronomy, Dwingeloo,

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The Netherlands; 7 National Research University, Higher School of Economics, Moscow, Russia

E-mail contact: jmoran at cfa.harvard.edu

We present the first VLBI observations of a Galactic water maser (in Chepeus A) made with a very long baselineinterferometric array involving the RadioAstron Earth-orbiting satellite station as one of its elements. We detectedtwo distinct components at −16.9 and 0.6 km s−1 with a fringe spacing of 66 microarcseconds. In total power, the0.6 km s−1 component appears to be a single Gaussian component of strength 580 Jy and width of 0.7 km s−1.Single-telescope monitoring showed that its lifetime was only 8 months. The absence of a Zeeman pattern impliesthe longitudinal magnetic field component is weaker than 120 mG. The space-Earth cross power spectrum shows twounresolved components smaller than 15 microarcseconds, corresponding to a linear scale of 1.6 × 1011 cm, about thediameter of the Sun, for a distance of 700 pc, separated by 0.54 km s−1 in velocity and by 160±35 microarcsecondsin angle. This is the smallest angular structure ever observed in a Galactic maser. The brightness temperatures aregreater than 2 × 1014 K, and the line widths are 0.5 km s−1. Most of the flux (about 87%) is contained in a haloof angular size of 400±150 microarcseconds. This structure is associated with the compact HII region HW3diii. Wehave probably picked up the most prominent peaks in the angular size range of our interferometer. We discuss threedynamical models: (1) Keplerian motion around a central object, (2) two chance overlapping clouds, and (3) vorticescaused by flow around an obstacle (i.e., von Karman vortex street) with Strouhal number of about 0.3.

Accepted by ApJ

http://arxiv.org/pdf/1802.06756

Subsonic islands within a high-mass star-forming IRDC

Vlas Sokolov1, Ke Wang2, Jaime E. Pineda1, Paola Caselli1, Jonathan D. Henshaw3, Ashley T. Barnes1,4,

Jonathan C. Tan5,6, Francesco Fontani7, Izaskun Jimenez-Serra8 and Qizhou Zhang9

1 Max Planck Institute for Extraterrestrial Physics, Gießenbachstraßse 1, D-85748 Garching bei Munchen, Germany;2 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748, Garching bei Munchen, Germany; 3 MaxPlanck Institute for Astronomy, Konigstuhl 17, D-69117 Heidelberg, Germany; 4 Astrophysics Research Institute,Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK; 5 Department of Astronomy, Universityof Florida, Gainesville, FL, 32611, USA; 6 Department of Physics, University of Florida, Gainesville, FL, 32611,USA; 7 INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy; 8 School of Physics andAstronomy, Queen Mary University of London, Mile End Road, London E1 4NS, UK; 9 Harvard-Smithsonian Centerfor Astrophysics, 60 Garden Street, Cambridge MA 02138, USA

E-mail contact: vsokolov at mpe.mpg.de

High-mass star forming regions are typically thought to be dominated by supersonic motions. We present combinedVery Large Array and Green Bank Telescope (VLA+GBT) observations of NH3 (1,1) and (2,2) in the infrared darkcloud (IRDC) G035.39-00.33, tracing cold and dense gas down to scales of 0.07 pc. We find that, in contrast toprevious, similar studies of IRDCs, more than a third of the fitted ammonia spectra show subsonic non-thermalmotions (mean line width of 0.71 km s−1), and the sonic Mach number distribution peaks around M = 1. As possibleobservational and instrumental biases would only broaden the line profiles, our results provide strong upper limits tothe actual value of M, further strengthening our findings of narrow line widths. This finding calls for a reevaluationof the role of turbulent dissipation and subsonic regions in massive-star and cluster formation. Based on our findingsin G035.39, we further speculate that the coarser spectral resolution used in the previous VLA NH3 studies may haveinhibited the detection of subsonic turbulence in IRDCs. The reduced turbulent support suggests that dynamicallyimportant magnetic fields of the 1 mG order would be required to support against possible gravitational collapse. Ourresults offer valuable input into the theories and simulations that aim to recreate the initial conditions of high-massstar and cluster formation.

Accepted by A&A Letters

https://arxiv.org/pdf/1802.07043.pdf

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Triggering the formation of the supergiant H II region NGC 604 in M33

Kengo Tachihara1, Pierre Gratier2, Hidetoshi Sano1,3, Kesetsu Tsuge1, Rie E. Miura4, Kazuyuki

Muraoka5 and Yasuo Fukui1,3

1 Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan; 2 Laboratoired’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, All’ee Geoffroy Saint-Hilaire, 33615 Pessac, France; 3

Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan; 4 Chile Obser-vatory, National Astronomical Observatory of Japan, National Institutes of Natural Sciences,2-21-1 Osawa, Mitaka,Tokyo 181-8588, Japan; 5 Department of Physical Science, Graduate School of Science, Osaka Prefecture University,1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan

E-mail contact: k.tachihara at a.phys.nagoya-u.ac.jp

Formation mechanism of a supergiant H II region NGC 604 is discussed in terms of collision of H I clouds in M33. Ananalysis of the archival H I data obtained with the Very Large Array (VLA) reveals complex velocity distributionsaround NGC 604. The H I clouds are composed of two velocity components separated by ∼ 20 km s−1 for an extent of∼ 700 pc, beyond the size of the the H II region. Although the H I clouds are not easily separated in velocity with somemixed component represented by merged line profiles, the atomic gas mass amounts to 6× 106 M⊙ and 9 × 106 M⊙

for each component. These characteristics of H I gas and the distributions of dense molecular gas in the overlappingregions of the two velocity components suggest that the formation of giant molecular clouds and the following massivecluster formation have been induced by the collision of H I clouds with different velocities. Referring to the existence ofgas bridging feature connecting M33 with M31 reported by large-scale H I surveys, the disturbed atomic gas possiblyrepresent the result of past tidal interaction between the two galaxies, which is analogous to the formation of the R136cluster in the LMC.

Accepted by PASJ

Helical Magnetic Fields in Molecular Clouds? A New Method to Determine the Line-of-Sight Magnetic Field Structure in Molecular Clouds

M. Tahani1, R. Plume1, J.C. Brown1and J. Kainulainen2,3

1 Physics & Astronomy, University of Calgary, Calgary, Alberta, Canada; 2 Dept. of Space, Earth and Environment,Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden; 3 Max-Planck-Institute forAstronomy, Konigstuhl 17, 69117 Heidelberg, Germany

E-mail contact: mtahani at ucalgary.ca

Magnetic fields pervade in the interstellar medium (ISM) and are believed to be important in the process of starformation, yet probing magnetic fields in star formation regions is challenging. We propose a new method to useFaraday rotation measurements in small scale star forming regions to find the direction and magnitude of the componentof magnetic field along the line-of-sight. We test the proposed method in four relatively nearby regions of Orion A,Orion B, Perseus, and California. We use rotation measure data from the literature. We adopt a simple approach basedon relative measurements to estimate the rotation measure due to the molecular clouds over the Galactic contribution.We then use a chemical evolution code along with extinction maps of each cloud to find the electron column density ofthe molecular cloud at the position of each rotation measure data point. Combining the rotation measures producedby the molecular clouds and the electron column density, we calculate the line-of-sight magnetic field strength anddirection. In California and Orion A, we find clear evidence that the magnetic fields at one side of these filamentarystructures are pointing towards us and are pointing away from us at the other side. Even though the magnetic fieldsin Perseus might seem to suggest the same behavior, not enough data points are available to draw such conclusions.In Orion B, as well, there are not enough data points available to detect such behavior. This behavior is consistentwith a helical magnetic field morphology. In the vicinity of available Zeeman measurements in OMC-1, OMC-B, andthe dark cloud Barnard 1, we find magnetic field values of −23± 38 µG, −129± 28 µG, and 32± 101 µG, respectively,which are in agreement with the Zeeman Measurements.

Accepted by A&A

http://arxiv.org/pdf/1802.07831

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The Envelope Kinematics and a Possible Disk Around the Class 0 Protostar withinBHR7

John J. Tobin1,2, Steven P. Bos2, Michael M. Dunham3,4, Tyler L. Bourke5, Nienke van der Marel6

1 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks Street, Norman,OK 73019, USA; 2 Leiden Observatory, Leiden University, P.O. Box 9513, 2300-RA Leiden, The Netherlands; 3 De-partment of Physics, State University of New York Fredonia, Fredonia, New York 14063, USA; 4 Harvard-SmithsonianCenter for Astrophysics, 60 Garden St., Cambridge, MA, USA; 5 SKA Organization, Jodrell Bank Observatory, LowerWithington, Macclesfield, Cheshire SK11 9DL, UK; 6 Institute for Astronomy, University of Hawaii, 2680 WoodlawnDrive, 96822 Honolulu, HI, USA; 7 Herzberg Astronomy & Astrophysics Programs, National Research Council ofCanada, 5017 West Saanich Road, Victoria, BC, Canada V9E 2E7

E-mail contact: jjtobin at gmail.com

We present a characterization of the protostar embedded within the BHR7 dark cloud, based on both photometricmeasurements from the near-infrared to millimeter and interferometric continuum and molecular line observations atmillimeter wavelengths. We find that this protostar is a Class 0 system, the youngest class of protostars, measuringits bolometric temperature to be 50.5 K, with a bolometric luminosity of 9.3 L⊙. The near-infrared and Spitzerimaging show a prominent dark lane from dust extinction separating clear bipolar outflow cavities. Observations of13CO (J=2–1), C18O (J=2–1), and other molecular lines with the Submillimeter Array (SMA) exhibit a clear rotationsignature on scales <1300 AU. The rotation can be traced to an inner radius of ∼170 AU and the rotation curve isconsistent with an R−1 profile, implying that angular momentum is being conserved. Observations of the 1.3 mm dustcontinuum with the SMA reveal a resolved continuum source, extended in the direction of the dark lane, orthogonalto the outflow. The deconvolved size of the continuum indicates a radius of ∼100 AU for the continuum source atthe assumed distance of 400 pc. The visibility amplitude profile of the continuum emission cannot be reproducedby an envelope alone and needs a compact component. Thus, we posit that the resolved continuum source could betracing a Keplerian disk in this very young system. If we assume that the continuum radius traces a Keplerian disk(R ∼ 120 AU) the observed rotation profile is consistent with a protostar mass of 1.0 M⊙.

Accepted by ApJ

http://arxiv.org/pdf/1802.08277

Dancing twins: stellar hierarchies that formed sequentially?

Andrei Tokovinin1

1 Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile

E-mail contact: atokovinin at ctio.noao.edu

This paper attracts attention to the class of resolved triple stars with moderate ratios of inner and outer periods(possibly in a mean motion resonance) and nearly circular, mutually aligned orbits. Moreover, stars in the inner pairare twins with almost identical masses, while the mass sum of the inner pair is comparable to the mass of the outercomponent. Such systems could be formed either sequentially (inside-out) by disk fragmentation with subsequentaccretion and migration or by a cascade hierarchical fragmentation of a rotating cloud. Orbits of the outer and innersubsystems are computed or updated in four such hierarchies: LHS 1070 (GJ 2005, periods 77.6 and 17.25 years), HIP9497 (80 and 14.4 years), HIP 25240 (1200 and 47.0 years), and HIP 78842 (131 and 10.5 years).

Accepted by AJ

http://arxiv.org/pdf/1802.06445

The Massive Star-Forming Regions Omnibus X-Ray Catalog, Second Installment

Leisa K. Townsley1, Patrick S. Broos1, Gordon P. Garmire2, Gemma E. Anderson3, Eric D. Feigelson1,

Tim Naylor4 and Matthew S. Povich5

1 Department of Astronomy & Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park,PA 16802, USA; 2 Huntingdon Institute for X-ray Astronomy, LLC, 10677 Franks Road, Huntingdon, PA 16652,USA; 3 International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth, WA 6845,

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Australia; 4 School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK; 5 Department of Physicsand Astronomy, California State Polytechnic University, 3801 West Temple Ave, Pomona, CA 91768, USA

E-mail contact: townsley at astro.psu.edu

We present the second installment of the Massive Star-forming Regions (MSFRs) Omnibus X-ray Catalog (MOXC2),a compilation of X-ray point sources detected in Chandra/ACIS observations of 16 Galactic MSFRs and surroundingfields. MOXC2 includes 13 ACIS mosaics, three containing a pair of unrelated MSFRs at different distances, with atotal catalog of 18,396 point sources. The MSFRs sampled range over distances of 1.3 kpc to 6 kpc and populationsvarying from single massive protostars to the most massive Young Massive Cluster known in the Galaxy. By carefullydetecting and removing X-ray point sources down to the faintest statistically-significant limit, we facilitate the study ofthe remaining unresolved X-ray emission. Through comparison with mid-infrared images that trace photon-dominatedregions and ionization fronts, we see that the unresolved X-ray emission is due primarily to hot plasmas threadingthese MSFRs, the result of feedback from the winds and supernovae of massive stars. The 16 MSFRs studied inMOXC2 more than double the MOXC1 sample, broadening the parameter space of ACIS MSFR explorations andexpanding Chandra’s substantial contribution to contemporary star formation science.

Accepted by ApJ Supplements

https://arxiv.org/pdf/1802.04902

data available at https://doi.org/10.5281/zenodo.1067748

Inward Migration of the TRAPPIST-1 Planets as Inferred From Their Water-RichCompositions

Cayman T. Unterborn1, Steven J. Desch1, Natalie R. Hinkel2 and Alejandro Lorenzo Jr.1

1 School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA; 2 Department of Physics& Astronomy, Vanderbilt University, Nashville, TN 37235, USA

E-mail contact: cayman.unterborn at asu.edu

Multiple planet systems provide an ideal laboratory for probing exoplanet composition, formation history and potentialhabitability. For the TRAPPIST-1 planets, the planetary radii are well established from transits (Gillon et al., 2016,Gillon et al., 2017), with reasonable mass estimates coming from transit timing variations (Gillon et al., 2017, Wanget al., 2017) and dynamical modeling (Quarles et al., 2017). The low bulk densities of the TRAPPIST-1 planetsdemand significant volatile content. Here we show using mass-radius-composition models, that TRAPPIST-1f and glikely contain substantial (> 50 wt%) water/ice, with b and c being significantly drier (< 15 wt%). We propose thisgradient of water mass fractions implies planets f and g formed outside the primordial snow line whereas b and c formedinside. We find that compared to planets in our solar system that also formed within the snow line, TRAPPIST-1band c contain hundreds more oceans worth of water. We demonstrate the extent and timescale of migration in theTRAPPIST-1 system depends on how rapidly the planets formed and the relative location of the primordial snowline. This work provides a framework for understanding the differences between the protoplanetary disks of our solarsystem versus M dwarfs. Our results provide key insights into the volatile budgets, timescales of planet formation,and migration history of likely the most common planetary host in the Galaxy.

Accepted by Nature Astronomy

https://arxiv.org/pdf/1706.02689

Nitrogen isotope fractionation in protoplanetary disks

Ruud Visser1, Simon Bruderer2, Paolo Cazzoletti2, Stefano Facchini2, Alan N. Heays3 and Ewine F.

van Dishoeck4,2

1 European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748, Garching, Germany; 2 Max-Planck-Institutfur extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany; 3 Observatoire de Paris, LERMA, UMR8112 du CNRS, 92195 Meudon, France; 4 Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden,The Netherlands

E-mail contact: ruudvisser at gmail.com

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Aims: The two stable isotopes of nitrogen, 14N and 15N, exhibit a range of abundance ratios both inside and outside thesolar system. The elemental ratio in the solar neighborhood is 440. Recent ALMA observations showed HCN/HC15Nratios from 83 to 156 in six T Tauri and Herbig disks and a CN/C15 N ratio of 323 30 in one T Tauri star. We aim todetermine the dominant mechanism responsible for these enhancements of 15N: low-temperature exchange reactionsor isotope-selective photodissociation of N2.Methods: Using the thermochemical code DALI, we model the nitrogen isotope chemistry in circumstellar disks witha 2D axisymmetric geometry. Our chemical network is the first to include both fractionation mechanisms for nitrogen.The model produces abundance profiles and isotope ratios for several key N-bearing species. We study how theseisotope ratios depend on various disk parameters.Results: The formation of CN and HCN is closely coupled to the vibrational excitation of H2 in the UV-irradiatedsurface layers of the disk. Isotope fractionation is completely dominated by isotope-selective photodissociation of N2.The column density ratio of HCN over HC15N in the disk’s inner 100 au does not depend strongly on the disk mass, theflaring angle or the stellar spectrum, but it is sensitive to the grain size distribution. For larger grains, self-shielding ofN2 becomes more important relative to dust extinction, leading to stronger isotope fractionation. Between disk radiiof 50 and 200 au, the models predict HCN/HC15N and CN/C15N abundance ratios consistent with observations ofdisks and comets. The HCN/HC15N and CN/C15N column density ratios in the models are a factor of 2-3 higherthan those inferred from the ALMA observations.

Accepted by A&A

https://arxiv.org/pdf/1802.02841

The Intricate Structure of HH 508, the Brightest Microjet in the Orion Nebula

Ya-Lin Wu1, Laird M. Close1, Jinyoung Serena Kim1, Jared R. Males1, and Katie M. Morzinski1

1 Steward Observatory, University of Arizona, Tucson, AZ 85721, USA

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

We present Magellan adaptive optics Hα imaging of HH 508, which has the highest surface brightness among proto-stellar jets in the Orion Nebula. We find that HH 508 actually has a shorter component to the west, and a longerand knotty component to the east. The east component has a kink at 0.|′′3 from the jet-driving star θ1 Ori B2, soit may have been deflected by the wind/radiation from the nearby θ1 Ori B1B5. The origin of both components isunclear, but if each of them is a separate jet, then θ1 Ori B2 may be a tight binary. Alternatively, HH 508 may bea slow-moving outflow, and each component represents an illuminated cavity wall. The ionization front surroundingθ1 Ori B2B3 does not directly face θ1 Ori B1B5, suggesting that the EUV radiation from θ1 Ori C plays a dominantrole in affecting the morphology of proplyds even in the vicinity of θ1 Ori B1B5. Finally, we report an Hα blob thatmight be ejected by the binary proplyd LV 1.

Accepted by ApJ

http://arxiv.org/pdf/1802.07911

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Dissertation Abstracts

Inner disk dynamics of classical T Tauri stars in NGC 2264

Pauline McGinnis

Thesis work conducted at: Departamento de Fısica - Universidade Federal de Minas Gerais (UFMG), Brazil, withone semester as a visiting PhD student at Institut de Planetologie et d’Astrophysique de Grenoble (IPAG), France

Current address: IPAG, Universite Grenoble Alpes, CS 40700, 38058 Grenoble Cedex 9, France

Electronic mail: Pauline.Mc-Ginnis@univ-grenoble-alpes.fr

Ph.D dissertation directed by: Sılvia Helena Paixao Alencar

Ph.D degree awarded: July 2017

The young open cluster NGC 2264 is a rich site of star formation, containing hundreds of young, accreting, low-massstars known as classical T Tauri stars (CTTS). In December 2011, this cluster was observed simultaneously by theCoRoT and Spitzer satellites, as well as quasi-simultaneously by a number of ground-based telescopes, such as theCFHT and the VLT with the FLAMES multi-object spectrograph in a spectral range covering the Hα line (a strongindicator of accretion). NGC 2264 had also been observed previously by CoRoT in March 2008, and it became thetarget of a new FLAMES campaign in 2014 centered on the forbidden [OI] 6300A line, a well-known tracer of jetsand winds in young stars. The goal of this thesis is to explore the richness of data available for NGC 2264 in order toinvestigate the dynamics of inner circumstellar disks of CTTSs and, with this, to better understand the processes ofmass accretion and mass ejection that occur therein.

In the first part of this work, we investigate a group of CTTSs that present photometric variability indicative ofextinction from inner disk material. These systems are viewed at high inclinations and represent an opportunity tostudy the interaction between the stellar magnetosphere and the inner accretion disk through indirect measurements.We analyze their CoRoT light curves alongside their simultaneous Spitzer light curves in order to better understandthe dust distribution in the inner disk region, and in this way find indications of the presence of grains larger thantypical interstellar grains. We investigate veiling variability in their FLAMES spectra and u− r color variations, andin many cases find evidence of hot spots that are spatially associated with occultations of the stellar photosphere bycircumstellar material, indicating that the occulting structures may be located at the base of accretion columns. Wefind that an occultation model of an inner disk warp, initially proposed to explain the photometric behavior of theCTTS AA Tau, is successful at reproducing the general aspects of most of the quasi-periodic light curves in our sample,finding warps of similar maximum height and azimuthal extension as had been found for AA Tau. We ascribe thisAA Tau-like variability to a stable accretion regime and similar but non-periodic variability to an unstable accretionregime. We see indications that a transition, and even certain coexistence, between the two regimes may be common.

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In the second part of this work we investigate ejection processes through the forbidden [OI] 6300A emission line. Weseparate the [OI] line profiles into three distinct features: a high-velocity component (HVC), a broad low-velocitycomponent (BLVC), and a narrow low-velocity component (NLVC). The HVC is believed to originate in bipolar,colimated jets, while the origin of the low-velocity components (LVC) is still under debate. The luminosities of allcomponents correlate positively with the stellar and accretion luminosity. We confirm earlier findings in Taurus whichfavor an inner MHD disk wind as the origin of the BLVC. The NLVC has been suggested to arise in X-ray or EUVdriven photoevaporative disk winds, which is consistent with some of our findings, but we have insufficient evidenceto confirm this. The HVC is only detected among systems with optically thick inner disks, while the BLVC is foundin a few systems with an anemic disk and the NLVC is common among systems with all types of disks, includingtransition disks. This points to an evolution of the [OI]λ6300 line profile as the disk disperses. We also find thatCTTSs accreting in the unstable regime tend to present HVCs more often than stars accreting in the stable regime.Stellar properties such as effective temperature, mass, and stellar rotation, do not seem to influence in a significantway the propagation velocity or luminosity of the protostellar jets from which the HVC originates.

https://www.dropbox.com/s/e99mm5922xmssfz/thesis-pauline-mcginnis.pdf?dl=0

Moving ... ??

If you move or your e-mail address changes, pleasesend the editor your new address. If the Newsletterbounces back from an address for three consecutivemonths, the address is deleted from the mailing list.

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New Jobs

Postdoctoral Research Fellow - Eruptive YSOs and Time-domainSurveys (University of Hertfordshire)

We seek to appoint a postdoctoral researcher to work on the project ”Eruptive YSOs and the Milky Way Timedomain surveys: VVV and VVVX” at the University of Hertfordshire’s Centre for Astrophysics Research (CAR). Theresearcher will work with Dr Philip Lucas (and the Star Formation group), and will also collaborate with the VVVconsortium in Chile and elsewhere.

Deadline: 11th March 2018Job Ref: 015976Salary: Starting at 32,548 pa to 35,550 pa, with appointment at the higher starting grades being dependent on sub-stantial proven post-doctoral experience.Grade: UH7FTE: Full time position working 37 hours per week (1.0 FTE)Duration of Contract: Fixed Term Contract for up to Three Years

The post holder will be required to carry out and regularly publish research, will present at research conferences,prepare telescope time proposals, supervise students and support CARs outreach programmes.

Experience in working with photometric datasets is essential together with a record of publishing scientific papersand of work on Young Stellar Objects or a related field; experience with spectroscopic and time-domain data and ofsupervising students is desirable. Abilities to complete research tasks in an effective and timely way and to work wellas part of a research team are essential.

The post will support research in the following main areas:

Identification of eruptive YSO candidates in the VVV and VVVX surveys; detailed analysis of variable YSO lightcurves, including exploration of new methods of time-domain analysis to characterise the variability and test theoreticalpredictions; spectroscopy of variable YSOs from VVV and UKIDSS; adaptive optics imaging and imaging polarimetryof variable YSOs; modelling of spectroscopic and imaging data; variability-based selection of samples of normal YSOsfrom the surveys.

The post also supports development and delivery of advanced public survey products such as PSF photometry andproper motions, in collaboration with other members of the VVV and VVVX consortia.

The post is funded by the Science and Technology Facilities Council as part of CAR’s Consolidated Grant and isavailable for up to 3 years with a start date of 1st April 2018 or soon thereafter.

Applicants must hold a PhD in a relevant area or must have been approved for the award of a PhD degree beforetaking up the position’.

Applications should be submitted online via the recruitment website http://www.herts.ac.uk/contact-us/jobs-and-vacanciesand should be accompanied by PDF versions of a CV, a list of publications, a summary of previous research (notexceeding two sides of A4 paper), and the contact details of two referees willing to write on your behalf.

Contact Details/Informal Enquiries: Informal enquiries may be directed to Dr Philip Lucas +44 (0)1707 286070,P.W.Lucas@herts.ac.uk

The University offers a range of benefits including a pension scheme, professional development, family friendly policies,child care vouchers, a fee waiver of 50% for all children of staff under the age of 21 at the start of the course, discountedmemberships at the Hertfordshire Sports Village and generous annual leave.

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Chalmers Cosmic Origins Ph.D. Fellowships(Galaxy, Star & Planet Formation)

Applications are invited for a Ph.D. position or positions at Chalmers University of Technology, Gothenburg, Sweden,as part of Prof. Jonathan C. Tan’s research group within the Astronomy and Plasma Physics Division, hosted withinthe Department of Space, Earth and Environment.

Tan’s group has a broad range of research activities in galaxy, star and planet formation, including both theoreticaland observational programs. Thus, a wide scope of possible Ph.D. projects are available, depending on the interestsof the candidate. See http://cosmicorigins.space/tan for more information about the research group. There arealso close connections to the Onsala Space Observatory, which is the Swedish national facility for Radio Astronomy.The observatory operates telescopes in Sweden, shares in the APEX telescope in Chile, and hosts the Nordic ALMARegional Center (ARC). In addition, Tan has established the Chalmers Initiative on Cosmic Origins (CICO) andits partnership with the Virginia Initiative on Cosmic Origins (VICO), hosted by the University of Virginia. Seehttp://cosmicorigins.space/ for more details. Ph.D. students will be expected to have active involvement in theseinitiatives, including opportunities of exchange visits to Univ. of Virginia.

A successful candidate will have a M.Sc. in physics or astronomy. Research and computing experience is desirable.Expected duration of the Ph.D. is 4 years, but may vary, up to 5 years, depending on circumstances of the candidate.A starting date of late August 2018 is anticipated, but there is some flexibility.

Included Benefits:

Competitive salary (∼30,000 SEK / month) is offered. Funds and opportunities for dissemination, networking, andinternational collaboration will be available. Ph.D. students are eligible for social security benefits including healthinsurance, paid leave, retirement benefits, etc.

Apply through this web page:

https://www.chalmers.se/en/about-chalmers/Working-at-Chalmers/Vacancies/Pages/default.aspx?rmpage=job&rmjob=6

Abstract submission deadline

The deadline for submitting abstracts and othersubmissions is the first day of the month.

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Meetings

4th CRISM conference

Cosmic Rays and the Inter Stellar Medium25 - 29 June 2018 Grenoble (France)

Science case

The main objective of the CRISM international workshop is to review the most recent achievements in topics relatedto the interplay between cosmic rays and the chemical and physical state of the Interstellar Medium. The followingtopics will be addressed:

1. CR sources: acceleration mechanisms, multi-wavelength observations, possible sources (supernova remnants,pulsar winds, stellar clusters, young stellar objects);

2. CR transport (theory, observation, phenomenology): role of self-generated turbulence, large-scale injected tur-bulence; direct and indirect observations, modelling and phenomenology, link to dark matter detection;

3. Local ISM: MeV CRs, Voyager data, gas and turbulence;

4. Impact of GCRs: dynamics of the ISM, physics and chemistry of molecular clouds, role in the formation of starsand planets, composition of cosmomaterials;

5. Future of CR studies: experiments, observations, simulations.

Conference website https://crism2018.sciencesconf.org/

Invited speakers

P. Blasi (Italy) D. Caprioli (USA)A. Cummings (USA) L. Derome (France)G. Dubner (Argentina) E. Hays (USA)M. Haverkorn (The Netherlands) N. Indriolo (USA)P. Mertsch (Germany) M. Padovani (Italy)C. Pfrommer (Germany) O. Reimer (Austria)A. Shukurov (UK)

Important deadlines:

Call for abstracts: 16 April, submission deadlineFees payment: 16 April, deadline for reduced fees18 May: deadline for payment

SOC:

Edwin Bergin; Bruna Bertucci; Andrei Bykov; Paola Caselli; Rosine Lallement; Marianne Lemoine-Goumard; Alexan-dre Marcowith Coordination with LOC; Marius Potgieter; Pierre Salati.

On behalf the LOC, Pierre Hily-Blant (IPAG), David Maurin (LPSC), Gilles Maurin (LAPP), Alexandre Marcowith(LUPM), Richard Taillet (LAPTh), Johana Paquien (LPSC), Marie-Helene Sztefek (IPAG)

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Astrophysical Frontiers in the Next Decade and Beyond:Planets, Galaxies, Black Holes, and the Transient Universe

We are pleased to announce that registration (http://go.nrao.edu/ngVLA18) is now open for the conference ”Astro-physical Frontiers in the Next Decade and Beyond: Planets, Galaxies, Black Holes, and the Transient Universe” to beheld in Portland, Oregon from 26-29 June 2018. This ambitious conference will bring together a large cross-section ofthe multi-wavelength astronomical community to discuss how best to tackle the most pressing astrophysical questionsin the near-future.

Over the past decade, many areas of astrophysics and cosmology have seen rapid progress, revealing numerable excitingdiscoveries. Highlights include the first detailed pictures of the complex nature of planet formation in a solar systemanalog; the discovery of rapidly star-forming galaxies and supermassive black hole growth detected well into theepoch of re-ionization; the direct detection of gravitational radiation from merging black holes; and the existence ofunexplained transient phenomena like Fast Radio Bursts. Building on this heterogeneous list, we can look beyondthe scientific frontier outlined by New Worlds, New Horizons now better informed, into an uncharted realm of newdiscovery space.

This conference will consist of plenary sessions of invited speakers and three parallel sessions that will include in-vited and contributed presentations covering Origins of Exoplanets and Protoplanetary Disks; Mechanisms of GalaxyEvolution; and Black Holes and Transient Phenomena.

Each session will highlight recent advances in observations and theory, unanswered questions, and future research direc-tions, in the context of the suite of next-generation facilities across the electromagnetic spectrum such as the includinga next-generation Very Large Array, the Large Synoptic Survey Telescope, 30m-class optical-infrared telescopes, theAdvanced Laser Interferometer Gravitational-Wave Observatory, and the Square Kilometre Array.

While this meeting is sponsored by NRAO, the science areas explored are truly multi-wavelength/messenger, and thescience program has strong representation from communities across the electromagnetic spectrum.

Registration is only $250 through May 1, 2018. Student registration has been discounted to $100 plus free hotelaccommodations with double occupancy. Travel assistance is available. See the website http://go.nrao.edu/ngVLA18for more details.

We hope to see you in Portland in June!

Cosmic Cycle of Dust and Gas in the Galaxy: from Old to Young Stars.

The registration for the conference is now open. The conference will take place, from July 9 to 13 2018, at theInternational Center for Interdisciplinary Science and Education (ICISE) which is located in the beautiful coastal cityof Quy Nhon, Vietnam. You are invited to register and submit contributed talks and posters.

https://cosmiccycle2018.sciencesconf.org/

Organized in the framework of the ”Rencontres du Vietnam”, the conference focuses on the evolution of dust andgas from evolved to young stars. The aim of the conference is to bring astronomers working on the circumstellarenvironment of evolved stars and star forming regions and planetologists working on the origin of the solar systemtogether to discuss about science in a friendly and relaxed environment at ICISE. In July 2016, in the same cycleof conferences, Blowing In the Wind addressed issues of dynamics of gas and dust in the Galaxy. In July 2017,another conference Star Formation in Different Environments focused on how stars form. This year’s conference willbe dedicated to the physico-chemistry and evolution of gas and dust. It will review state-of-the-art knowledge ofthe molecular and dust components of envelopes and shells surrounding AGB stars, planetary nebulae, diffuse giantmolecular clouds as well as Supernovae. Special sessions will be dedicated to the origin and evolution of matter in thesolar system: meteorites, comets, etc. Recent observations, in particular with ALMA, are the source of major progressin the study of the cosmic cycle of gas and dust in the Galaxy making such a conference very timely.

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The list of invited speakers can be found at: https://cosmiccycle2018.sciencesconf.org/resource/page/id/6

There is some funding from the Rencontres du Vietnam to pay the hotel for a few participants. Grants will be givenin priority to those giving a talk at the conference. If you need support, please fill in a form in the following link(Financial Support section):

https://cosmiccycle2018.sciencesconf.org/resource/page/id/2

Bootcamp:

During the weekend before the conference, we organize a series of tutorials and lectures introducing the topics of theconference to senior undergraduates, PhD students and young postdocs. If you are interested in attending it, pleasecontact Tuan-Anh Pham (ptanh@vnsc.org.vn).

Triple Evolution and DynamicsLorentz Centre, Leiden, The Netherlands, September 10th-14th, 2018

In this meeting we aim to explore the various observational and theoretical aspects of triple evolution, and the uniquerole triples play in the formation of stellar and planetary systems. The workshop aims to serve as a focal point forresearchers working on triple systems on all scales, from asteroids to stars to massive black holes. We aim to connecttheorists and observers as well as link together and share knowledge and tools between groups working on similarquestions, both on same scales as well as completely different scales. We will discuss the current state-of-the-art,identify open questions and find a way forward to answer them.

The workshop will consist of a few selected invited and contributed talks, poster presentation, as well as ample timefor discussion. There is no conference fee.

Please see the website for more details:http://www.lorentzcenter.nl/lc/web/2018/1016/info.php3?wsid=1016&venue=Oort

Registration is not possible yet, but will follow soon.

Hope to see you in Leiden!

Silvia Toonen, Hagai Perets, Andrei Tokovinin, Daniel Fabrycky

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Summary of Upcoming Meetings

Circumplanetary Disks and Satellite Formation

26 - 30 March 2018https://cpdsf2018.wixsite.com/home

Complex Organic Molecules in the Universe: Current Understanding and Perspective

4 April 2018, Liverpool, UKhttp://eas.unige.ch/EWASS2018/session.jsp?id=SS5

Cosmic Rays: the salt of the star formation recipe

2 - 4 May 2018, Florence, Italyhttp://www.arcetri.astro.it/cosmicrays

EPoS 2018 The Early Phase of Star Formation - Archetypes

13 - 18 May 2018, Ringberg Castle, Tegernsee, Germanyhttp://www.mpia.de/homes/stein/EPoS/epos.php

Interstellar: The Matter

14 - 18 May 2018, Cozumel, Mexicohttp://bigbang.nucleares.unam.mx/astroplasmas/interstellar-the-matter

Cloudy workshop

14 - 25 May 2018, Chiang Mai, Thailandhttp://www.narit.or.th/en/index.php/cloudy

From Prestellar Cores to Solar Nebulae

14 May - 22 June 2018, Paris-Saclay, Francehttps://www.ias.u-psud.fr/core2disk/

Formation of substellar objects: theory and observation

21-23 May 2018, ESAC, Madrid, Spainhttp://www.laeff.cab.inta-csic.es/projects/ws18/main/index.php

The Olympian Symposium 2018: Gas and stars from milli- to mega- parsecs

28 May - 1 June 2018, Mt. Olympus, Greecehttp://www.olympiansymposium.org

Cosmic Rays and the Inter Stellar Medium

25 - 29 June 2018, Grenoble, Francehttps://crism2008.sciencesconf.org/

Tracing the Flow: Galactic Environments and the Formation of Massive Stars

2 - 6 July 2018, Lake Windermere, UKhttp://almaost.jb.man.ac.uk/meetings/TtF

The Laws of Star Formation: from the Cosmic Dawn to the Present Universe

2 - 6 July 2018, Cambridge, UKhttp://www.ast.cam.ac.uk/meetings/2018/sf.law2018.cambridge

The Cosmic Cycle of Dust and Gas in the Galaxy: from Old to Young Stars

9 - 13 July 2018, Quy Nhon, Vietnamhttps://cosmiccycle2018.sciencesconf.org

Astrochemistry: Past, Present, and Future

10 - 13 July, 2018, Pasadena, USAhttp://www.cfa.harvard.edu/events/2018/astrochem18

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COSPAR 2018 sessions on Planet Formation and Exoplanets

14 - 22 July 2018, Pasadena, USAhttps://www.cospar-assembly.org/admin/sessioninfo.php?session=744

Cool Stars 20: Cambridge Workshop on Cool Stars, Stellar Systems and the Sun

29 July - 3 August 2018, Cambridge/Boston, USAhttp://www.coolstars20.com

Origins: From the Protosun to the First Steps of Life

20 - 23 August 2018, Vienna, Austriahttp://ninlil.elte.hu/IAUS345/

Magnetic fields along the star-formation sequence: bridging polarization-sensitive views

30-31 August 2018, Vienna, Austriahttp://escience.aip.de/iau30-fm4/

The Wonders of Star Formation

3 - 7 September 2018, Edinburgh, Scotlandhttp://events.ph.ed.ac.uk/star-formation

Triple Evolution and Dynamics

10 - 14 September 2018, Leiden, The Netherlandshttp://www.lorentzcenter.nl/lc/web/2018/1016/info.php3?wsid=1016&venue=Oort

Take a Closer Look - The Innermost Region of Protoplanetary Discs and its Connection to the Origin

of Planets

15 - 19 October 2018, ESO Headquarters, Garching, Germanyhttp://www.eso.org/sci/publications/announcements/sciann17072.html

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