Outflows from High Mass Protostars

Debra ShepherdNational Radio Astronomy Observatory

Cores, Disks, Jets & Outflows in Low & High Mass Star Forming Environments

Observations, Theory & Simulations

Banff, Alberta, Canada - July 12-16, 2004

Contents

• Motivation – why study outflows from Young Stellar Objects

• Review of Outflow Energetics• Observational summary:

• Outflows from Mid- to Early-B (Proto)stars• Outflows from young O Stars

• Impact of Luminosity on Outflows• Impact of Mass-loading and Disk Turbulence on

Outflows• Summary

Motivation

• Outflow & infall dynamics affect:– Energy input & turbulent support of molecular clouds– Dissipation of molecular clouds– Final mass of the central star– Disk (and planet) evolution

• Outflows provide a fossil record of mass-loss history of a protostar (or protostellar cluster).

• Outflow orientation establishes that a velocity gradient in circumstellar material (e.g. masers, dense gase) is due to a disk.

• Why massive protostellar outflows may differ from lower-mass flows:– OB stars usually form in clusters expect dynamical interactions – Expect massive YSO to evolve to ZAMS more rapidly:

O stars: tevolve ~ few x 104 yrs, G star: tevolve ~ few x 107 yrs– OB stars reach ZAMS while still embedded increased radiation

pressure may affect outflow dynamics

Massive vs Low-Mass Protostars

(Yorke 2003)

Kelvin-Helmholtz time scale (time to reach ZAMS):

KH = GM 2/RL

Accretion time scale:

acc = M*

/Macc

For M* ~ 8 M

acc = KH

And for M* > 8 M

the star reaches the ZAMS while still accreting – ionizing radiation affects outflow & infall

.

.

. Ae

Formation Mechanisms

Disk accretion: Sufficiently large, non-spherical accretion rates can overcome radiation pressure (Behrend & Maeder 2001, Yorke & Sonnhalter 2002, Tan & McKee 2002). Isolated and cluster formation possible.

Critical Macc at which all stellar UV

photons are absorbed by in-falling matter plotted against spectral type (Walmsley 1995, Churchwell 2002):

.

.

.Lo

g M

crit

(M

yr

-1)

Teff (1000 K)

5045403530-5.2

-5.0

-4.8

-4.6

-4.4

-4.2

-4.0B0 O9 O8 O7 O6 O5

Disk linked accretion & outflow may be similar to low mass protostars, e.g., x-winds (Shu et al. 2000) & disk winds (Konigl & Pudritz 2000).

..

Formation Mechanisms

Coalescence: coalescence of stars/protostars with masses below the critical value of 8 M (Bonnell & Bate 2002). Radiation pressure no longer a problem. Requires cluster formation only.

Mergers destroy accretion disks around lower mass components and disrupt their outflows. Resulting massive star will likely have rotating circumstellar material but accretion is not a necessary criteria for formation.

.

Outflow Energetics

Mf

.Pf

.Ef

.

Lacc LZAMS

Independent studies establish correlations like M Lbol0.6 for:

• The bipolar molecular outflow rate• The mass accretion rate• The ionized mass outflow rate

For Lbol = 0.3 to 105 Lsun strong link between accretion & outflow for most Lbol

e.g. Cabrit & Bertout 1992, Shepherd & Churchwell 1996, Henning et al. 2000

.

Outflow Energetics

More recently Beuther et al. (2002) added new massive outflows to correlations:

Pf

.

Mcore Lbol

Mechanical force, Pf vs Lbol correlation holds

Mf vs Lbol correlation may be an upper limit

May be a function of the entrainment efficiency?

Mout ~ 0.1 Mcore0.8 (derived from 1.2 mm dust emission)

Dust emission increases with protostar age.

(see also Sarceno et al. 1996, Chandler & Richer 2000, Richer et al. 2000)

.

.

Mf

.

Lacc LZAMSLbol

Mcore

Mou

t

Outflow Energetics

CO Outflows from low and high mass stars show a mass-velocity (MV) relation in the form of a power law dM(v)/dv ~ v with ranging from -1 to -8; steepens with age and energy in the flow (e.g. Rodriguez et al. 1982; Lada & Fich 1996; Shepherd et al. 1998; Richer et al. 2000; Beuther et al. 2002).

A similar relation of H2 Flux-velocity also exists with between -1.8 and -2.6 for low and high mass outflows (Salas & Cruz-Gonzalez 2002):

Vbreak differs but overlap where (H2 ) ~ (CO) association between CO & H2 in molecular outflows.

H2 Vbreak versus outflow length, l, correlation: steepens and Vbreak increases for older flows - similar to molecular flows.

Vbreak ~ l 0.4

~ l 0.08

Jet Knot Spacing:

T Tauri stars: Knot spacing = 500-1000 AU, vjet ~ 300 km/s timescale = 10-20 yrs

HH 80-81: Knot spacing = 2000-3000 AU, vjet ~ 500-1400 km/s timescale = 10-30 yrs

Cautionary note: HH 30 knots are ejected every few years and knots appear to merge after a few years. (Stapelfeld et al. in prep). Thus, knot spacing at large distances from the central source may be more a function of the evolution of the jet structure and excitation rather than an intrinsic property of the star/disk system.

Ionized wind mass loss rates:

Determined from optical lines [SII] & [OI] for T Tauri stars and radio emission for massive protostars up to early B spectral type.

T Tauri jets Mwind (Msun/yr) Massive YSO Jet/wind

Mwind (Msun/yr)

HH 34 2 x 10-7 Ceph A HW2 8 x 10-7

HH 47 4 x 10-7 HH 80-81 6 x 10-6

HH 111 3 x 10-7 G192.16 1 x 10-6

Ionized Jet Energetics

. .

Cabrit (2002), Rodriguez et al. (1994), Marti et al. (1995), Shepherd & Kurtz (1999)

Ionization fraction in jets:

Collimated jets from low-mass sources appear to be mostly neutral (e.g. Bacciotti & Eisloffel 1999; Bacciotti, Eisloffel, & Ray 1999; Lavalley-Fouquet, Cabrit, & Dougados 2000). Ionization fraction xe ~ 0.01 to 0.1 within 50 AU from source.

Molecular jets from low-mass Class 0 sources have sufficient momentum to drive molecular flows (e.g. Richer et al. 1989; Bachiller et al. 1991; and discussion in Cabrit 2002)

The SiO jet from one early B protostar, IRAS 20126, may also have adequate momentum to power the larger-scale CO flow but uncertainties in assumed SiO abundance makes this difficult to prove (Cesaroni et al. 1999; Shepherd et al. 2000):

SiO: Pwind ~ 2 x 10 -1 2 x 10 -9 Msun km/s/yr [SiO/H2]

CO: Pwind ~ 6 x 10 -3 Msun km/s/yr

Ionized Jet Energetics

.

.

Young Early B StarsIRAS 18162-2048, GGD 27, HH 80-81

Yamashita et al. (1989)Aspin et al. (1991)Marti, Rodriguez, Reipurth (1993, 1995)Gomez et al. (1995, 2003)Stecklum et al. (1997)Benedettini et al. (2004)

B star cluster with Lbol ~ 2 x 10 4Lsun

Tdyn ~ 10 6 yrs

Mf ~ 570 Msun

Mf ~ 6 x 10 -4 Msun yr -1

GGD 27 ILL powers jet & illuminates reflection nebula, Sp. type < B1

CO opening angle > 40o

Collimated, ionized jet, no apparent UC HII region

.

HH 81

HH 80

HH 80 North

K band & 8.5 m K band & 6 cm

6 cm continuumCO red & blue-shifted emission

B2 star

GGD 27 ILL

K band reflection nebula

GGD 27 ILL

IR nebula

Later than B3?

POSTER J7: Gomez et al.

Young Early B Stars

G192.16-3.82

Indebetouw et al. (2003)Devine et al. (1999)Shepherd et al. (1998,1999,2001)

Lbol ~ 3 x 10 3Lsun

Tdyn ~ 2 x 10 5 yrs

M2.6mm ~ 10 Msun

Mf ~ 95 Msun

Mf ~ 6 x 10 -4 Msun yr -1

Pf ~ 4 x 10 -3 Msun km s -1 yr -1

..

[SII]

CO(1-0)

7 mm continuum

& model

K-band

YSO

B2 ZAMS star with UC HII region50o-90o-45o opening angle outflowCollimation consistent with wind-blown bubbleEvidence for 100AU accretion disk, 1000AU rotating torus

NH3 core not graviatationally bound – near end of accretion phase

Young Early B StarsW75 N B Star Cluster

Torrelles et al. (2004)Shepherd et al. (2003, 2004)Combined outflows:

Lbol ~ 4 x 10 4Lsun (combined)

Tdyn ~ 2 x 10 5 yrs

M2.6mm ~ 340 Msun

Mf ~ 165 Msun

Mf ~ 10 -3 Msun yr -1

Pf ~ 2 x 10 -2 Msun km s -1 yr -1

..

6 cm 2 cmH2O masers

jet

VLBA H2O maser proper motions Wide-angle flow

B0.5 – B2 ZAMS stars

Jet seen in ionized gas & water masers from YSO (unknown spectral type)

Wide-angle outflow from B2 ZAMS star with UC HII region

Early B ProtostarsLebron et al. (in prep) Cesaroni et al. (1999,2004, in prep)Hofner et al (1999,2001, in prep)Moscadelli et al. (2000, in prep) Shepherd et al. (2000)Zhang et al. (1998, 1999)

Lbol ~ 10 4Lsun

Tdyn ~ 2x10 4 yrs

M2.6mm ~ 50 Msun

Mf ~ 50-60 Msun

Mf ~ 8 x 10 -4 Msun yr -1

Pf ~ 6 x 10 -3 Msun km s -1 yr -1

.

.

H & CO(1-0)

CO(2-1) & 1mm cont

B0.5 Protostar (not ZAMS but cm continuum detected)Precessing jet may create wider angle CO outflow

Evidence for 2000 AU rotating torus & 10,000 AU rotating NH3 core

IRAS 20126+4104

Estimated jet full opening angle ~ 40o (based on SiO emission) – wider than typically observed in low-mass systems ( ~ 1-2o)

POSTER J16: Lebron et al

POSTER J38: Rosen – rotating molecular jets

.

Early B Protostars

IRAS 05358+3543 B Star Cluster

Beuther et al. (2002, 2004)Sridharan et al. (2002)Combined outflows:

Lbol ~ 6 x 10 3Lsun (combined)

Tdyn ~ 3-4 x 10 4 yrs

M1.2mm ~ 75 - 100 Msun

(near each protostar)

Mf ~ 20 Msun (combined)

Mf ~ 6 x 10 -4 Msun yr -1

.

3 or 4 early B protostars (not on Main Sequence yet)

CO & SiO outflows are well collimated

No cm continuum emission detected – perhaps accretion is so large that UC HII region is quenched? Thus, effects of stellar UV radiation field absent or minimized.

Collimated flows are produced by early B

protostars.

Early B to Late O Protostars

M 17 new massive YSO

Chini et al. (2004)

Lbol ~ 6 x 10 4Lsun

(B0 – O9 star, 20 Msun)

Mdisk > 110 Msun

Rdisk ~ 20,000 AU (largest known)

Mf ~ unknown

Outflow opening angle > 120o based on reflection nebula (molecular outflow not mapped).

Spectra of central source (H, Ca II, and He I) ongoing accretion.

2.2 m image, 13CO contours trace disk.

Outflow

Disk seen in silhouette

Massive accretion disks

(Mdisk/M* > 5) exist around

stars as early as late O type turbulent disks, linked

accretion/outflow.

POSTER C22: Nuernberger on the M17 diskPOSTER D15: Yamashita et al. on the M17 disk

See also POSTER D2: Beltran et al. on massive disks

Early B to Late O Protostars

IRAS 16547-4247

Brooks et al. (2003)Garay et al. (2003)

Lbol ~ 6 x 10 4Lsun (B0 – O9 star assuming single central star)

Mcore ~ 900 Msun

Mf ~ unknown Centimeter continuum consistent with a thermal jet. Synchrotron emission farther out in jet strong B field collimating ionized gas.

Spectra show HV molecular gas (v ~ 20 km/s) but outflow not mapped yet.

Assuming v = 1000 km/s, inner synchrotron knots were ejected ~ 140 years ago.

2.12 m image1.2 mm continuum contours

8.4 GHz contours

HH 80-81 like jets may be possible in more massive stars (up to late O spectral type)

See also POSTER J5: Davis et al. - jets from massive YSOs (IRAS 18151-1208) and Poster J27: Wolf-Chase et al. - search for jets near HM YSOs

Outflows from Early B (proto)stars

(Yorke 2003)

Location of early B stars with outflow in M vs plot:

Not on ZAMS – little or no ionizing radiation from protostar, jet-like molecular outflows

ZAMS stars

No jet with UC HII regions (W75N, G192)

Jet (HH 80-81)

IRAS 20126

IRAS 05358

W75 N

G192.16

HH 80-81

POSTER C9: Forster – Infall/Outflow in massive cores

Poster C16: Klein et al. – Protostar Cores in outer Galaxy

Ae

Young O Stars

G5.89-0.39

Cesaroni et al. (1991)Acord et al. (1997, 1998)Faison et al. (1998)Feldt et al. (1999)

Lbol ~ 3 x 10 5Lsun

Tdyn ~ 3 x 10 3 yrs (very young)

Mf ~ 80 Msun

Mf ~ 3 x 10 -2 Msun yr -1

C34S(J=3-2)

3.6 cm HII region expansionO6 (proto)star

C34S outflow detected along axis of UC HII region expansion – outflow affecting the ionized gas?

No accretion disk. Star located in a 10,000 AU dust-free cavity

But – new obse

rvations s

uggest a m

ore complicated pict

ure

.

Red-shifted

Blue-shifted

Young O StarsFeldt et al. (2003): ~ O5 star detected, no disk-like structure but small excess 3.5 m emission circumstellar material.

Sollins et al. (2004): SiO(5-4) outflow opening angle ~ 90o. Outflow axis does not match axis found in C34S or CO/HCO+. Dust continuum extension along SiO outflow axis.

Multiple flows?H, K, & L’ NIR image

Watson et al. (2002): CO outflow larger than SiO. Outflow roughly to UC HII region expansion.

G5.89-0.39 New Results

Lbol ~ 3 x 10 5Lsun

Tdyn = 7.5 x 10 3 yrs

Mf > 77 Msun

Mf > 10 -3 Msun yr -1

.

POSTER C51: Sollins on G5.89

POSTER J12: Klaassen et al.

O Protostars

Subaru J, H, K Images

Orion

H2 ‘fingers’

Explosive event forming fragmented stellar wind bubble (McCaughrean & Mac Low 1997)

Or a precessing flow (Rodriguez-Franco et al. 1999)

POSTER C2: Beuther – sub-

mm lines & continuum in

Orion

O Protostars

Orion

Snell et al. (1984)Plambeck, Wright, Carlstrom (1990)Dougados et al. (1993)Menten & Reid (1995)Chernin & Wright (1996)Greenhill et al. (1998, in prep)Doeleman et al. (2004)And many others

Lbol >10 4Lsun

Tdyn ~ 1.5 x 10 3 yrs (very young)

Mf ~ 8 Msun

Mf ~ 5 x 10 -3 Msun yr -1

.

Assuming a single source powers the outflow:

Outflow opening angle ~ 90o – 120o. Low collimation even at highest CO velocities.

Elongated emission seen in 7mm continuum within 25 AU of protostar (source I) disk or outflow?

SiO masers trace outflow opening angle and slow equitorial flow.

H2 and HV blue-shifted CO

SiO masers

?

POSTER J21: Satoko – SiO in Orion

O Protostars

DR21 outflow powered by mid-IR cluster of OB stars, most have no circumstellar material.

A newly discovered O star DR21:IRAC-4 appears to

have a hot, accreting envelope: Lacc > L*

POSTER S8: Smith et al. – Spitzer images of DR21

Blue: 3.6m green: 4.5m

orange: 5.8m red: 8m

DR21

Roelfsema et al. (1989) Lbol ~ 3 x 10 5Lsun

Garden et al. (1991) Tdyn > 5 x 10 4 yrs

Davis & Smith (1996) Mf ~ 3000 Msun

Smith et al. (2004, in prep) Mf < 6 x 10 -2 Msun yr -1

.

A few recent significant contributionsCharacteristics of OB outflows (and accretion disks).

A few references not already mentioned (there are MANY more):

• Billmeier, Jayawardhana, Marengo, Mardones, Alves (POSTER D3) – Mid-IR imaging of Massive Young Stars

• Forster (POSTER C9) – Infall & Outflow in Massive Cores

• Kim, Churchwell, Friedel, Sewilo (POSTER J11) – Molecular Outflows from Massive Stars

• Varricatt, Davis, Ramsay-Howat, Todd (POSTER J23) – A Near Infrared Imaging Survey of High Mass Young Stellar Candidates

• Beuther, Schilke, Sridharan, Menten, Walmsley, Wyrowski (2002) – Massive Molecular Outflows

• Beuther, Schilke, Gueth (2004) – Massive Molecular Outflows at High Spatial Resolution

• Henning, Schreyer, Launhardt, Burkert (2000) – Massive YSOs with Molecular Outflows

• Molinari, Testi, Rodriguez, Zhang (2002) – The Formation of Massive Stars. I. High-Resolution Millimeter and Radio Studies of High-Mass Protostellar Candidates.

• Ridge et al. (2002) – Massive Molecular Outflows

• Shepherd, Testi, Stark (2003) – Clustered Star Formation in W75N

• Su, Zhang, Lim (2004) – Bipolar Molecular Outflows from High-Mass Protostars

• Zhang, Hunter, Brand, Sriharan, Molinari, Kramer, Cesaroni (2001) – Search for CO Outflows toward a Sample of 69 High-Mass Protostellar Candidates: Frequency of Occurrence

Impact of Luminosity on Outflow Structure

Expect high luminosity of massive protostars to play an important role in • Dynamical Evolution • Outflow (& disk) thermal structure and morphology

Review by Konigl (1999) summarizes the issues: • Enhanced field-matter coupling near disk surface due to UV radiation may cause

higher accretion rates and mass outflow rates (e.g. Pudritz 1985).• Disk photo-evaporation could create a low-velocity disk outflow (e.g. Hollenbach

et al. 1994; Yorke & Welz 1996).• Radiation pressure higher for dusty gas (e.g. Wolfire & Cassinelli 1987), may

contribute to flow acceleration and also lead to the ‘opening up’ of the outflow streamlines (e.g. Konigl & Kartje 1994).

• Expect a strong, radiatively driven stellar wind (although momentum factor of 10-100 too low to power observed molecular outflow).

Consider an example of how radiatively-driven stellar winds could potentially affect outflow dynamics (Yorke & Sonnhalter 2002):

Frequency-dependent opacity calculations – 30Msun and 60Msun molecular cores which

collapse to produce a protostar (M* ~ 30Msun & 34Msun, respectively) with disk and radiatively-induced outflow.

Radiatively-Induced Outflows

Yorke & Sonnhalter 2002

F30: M* = 31 Msun in 2.4x104 yrs F60: M* = 34 Msun in 4.5x104 yrs104 yrs13 Msun

2x104 yrs28 Msun

2.5x104 yrs33 Msun

3x104 yrs34 Msun

3.5x104 yrs34 Msun

4.5x104 yrs34 Msun

104 yrs17 Msun

1.5x104 yrs24 Msun

1.9x104 yrs29 Msun

2.1x104 yrs31 Msun

2.2x104 yrs31 Msun

2.4x104 yrs31 Msun

Radiatively-induced outflow encased by shock fronts, relatively poorly collimated flow.

Stellar radiation softens at outflow-shock boundry cloud collapses along flow axis to produce well-collimated jet.

Density: gray scale & white

contours

Velocity: arrows

Carbon grain temperature: solid black contours

Silicate grain temperature:

dotted contours

Numbers: age &

M*

Mass loading impact on outflows

T Tauri star FU Ori Outburst

B9 Protostar (Low B field)

B9 protostar (High B field)

Bstar (G) 380 380 380 1500

R* (Rsun)2.5 2.5 4 4

M* (Msun)0.5 0.5 2.5 2.5

Macc (Msun yr-1) 10-8 10-5 8x10-5 8x10-5

Rx/R*5 0.7 0.45 1

Shu et al. (1994) – ‘X-point’ (outflow launching point) ~ 5 R* in a typical T Tauri star.

Hartmann & Kenyon (1996) – FU Ori stars in outburst have no hot UV continuum: magnetospheric accretion columns have been crushed onto stellar surface.

Even late B stars have high enough accretion rate to crush accretion columns.

Massive star outflows can not be due to X-winds from truncated disks. X-wind from rapidly rotating protostar (Shu et al. 1998) or pure disk-wind (Konigl & Pudritz 2001).

X-winds:

.

Mass loading impact on outflows

Ouyed & Pudritz (1999) – Magnetized Disk-Wind Simulations: For Mw ~ 10-8 Msun yr -1, disturbances appear to grow producing instabilities & shocks – outflows become episodic. As Mw increase 3 orders of magnitude, jet behavior goes from episodic to steady ejection. Ideal MHD assumed: all solutions re-collimate.

Anderson, Li, Krasnopolsky & Blandford (POSTER D17) – How mass loading from the disk affects structure and dynamics of the wind. Mw = 3 x 10 -5 to 3 x 10 -10 Msun yr -1 Degree of collimation increases with mass loading up to ~10 -5 Msun yr -1.

Re-collimation of the wind expected for ideal MHD where trecomb >> tdynamical and plasma and B fields are frozen-in. But, ideal MHD assumptions break down as:

• Plasma T and increase• Turbulence in the disk or wind increases• B field decreases

Not clear what the implications are, will this affect outflow?

.

.

.

Expected for outflows & disks associated with luminous YSOs.

Gravitational instabilities induce spiral density waves; expected to be prevalent if

Mdisk > 0.3 M*, (Laughlin & Bodenheimer 1994). Toomre Q stability parameter (Yorke,

Bodenheimer & Laughlin 1995):

Q = cs / G = 56 (M*/Msun)1/2 (Rd /AU) -3/2 (Td /100K)1/2 (/103 g cm -3)

Where cs = local sound speed, = epicycle frequency of disk, = disk surface density, Rd = disk radius & Td = disk temperature.

For Q < 1 disk susceptible to local gravitational instability and axisymmertric fragmentation. Q = 1-2 disk susceptible to gravito-turbulence (Gammie 2001): Could be a significant angular momentum transport.

Early B (proto)stars appear to have Md /M* > 0.3 and can be as high as 1-10.

Example: Md ~ 3 Msun , M* ~ 8 Msun Assume Td = 100 K & Rd = 70 AU, then Q ~ 0.5

disk locally unstable, higher angular momentum transport through disk?

Will the outflow be less efficient for a given Macc ?

Disk turbulence - impact on outflows

TALK: Matzner – Low-mass star formation: initial conditions and disk instabilities. Irradiation quenches fragmentation due to local instability because disk temperature is raised above parent cloud temperature.

POSTER D18: Bodo et al. – Spiral density wave generation by vortices in accretion disks

..

Observations (Richer et al. 2000):

Outflow Force Fco vw Mw ------------------ = ------------- = f ---- where f = ------ Accretion Force Macc vkep vkep Macc

vw f ----- ~ 0.3 (1/1) for X-winds vkep

~ 0.03 (10/1) for Disk winds

Decrease in Mw / Macc

between Lbol = 1 and 104 Lsun ?

Errors are too large now to say.

Disk turbulence - impact on outflows

.

.

Log Lbol (Lsun )

0

-1

-2

1

2

-1 0 6 5 4 3 2 1

vw Log f --- vkep

Lbol = Lacc

Lbol = ZAMS

.

. .

POSTER:

Coffey et al – low mass jet can carry away

adequate angular momemtum.

Deflected Infall?

Moutflow ~ few x M* for T Tauri stars

Moutflow >> M* for OB protostars.

Churchwell (1999) points out that entrainment & swept-up mass do not appear to be able to account for large observed outflow masses. Circulation models: Moutflow > M*

easy (Richer et al. 2000). Most infalling material diverted magnetically at large radii into slow-moving outflow along the polar direction, infall proceeds along the equitorial plane (Fiege & Henriksen 1996: Lery, Henriksen, Fiege 1999; Aburihan et al 2001).

Summary

• Mid- to early-B protostars and late O protostars have accretion disks & outflows that can be well-collimated.

• Once UCHII region forms, associated ionized outflows have strong wide-angle winds. Jet component not detected? Must be verified.

- This would be unlike low-mass flows where there is evidence for a 2-component wind (jet+wide-angle) in older sources (e.g. Arce & Goodman 2002; Solf

2000).

• Mid to early O stars: Outflows appear to be poorly collimated. Explosive events coalescence a possibility in some cases.

• Expect changes in outflow dynamics due to increased:

- Luminosity (accretion & stellar)- Mass-loading onto the wind- Disk turbulence

Massive Star Formation & Outflow Reviews

1. Cesaroni 2004, in press “Outflow, Infall, and Rotation in High-Mass Star Forming Regions”

2. Churchwell 1998, in The Origin of Stars & Planetary Systems, NATO Science Series 540, p 515 “Massive Star Formation”

3. Churchwell 2002, ASP conf series, 267, 3 “The Formation and Early Evolution of Massive Stars”

4. Garay & Lizano, 1999, PASP, 111, 1049 “Massive Stars: Their Environment & Formation”

5. Konigl, 1999, New Astronomy Reviews, 43, 67 “Theory of Bipolar Outflows from High-Mass Young Stellar Objects”

6. Lizano, 2002, Nature, 416, 29L “Astronomy: How Big Stars are Made”

7. Richer, Shepherd, Cabrit, Bachiller, Churchwell, 2000, in Protostars & Planets IV, p 867 “Molecular Outflows from Young Stellar Objects”

8. Shepherd, 2003, ASP conf series, 287, 333 “The Energetics of Outflow and Infall from Low to High Mass YSOs”