1) High-mass vs low-mass: the dividing line

2) The formation of high-mass stars: accretion vs coalescence

3) The importance of disks in massive YSOs

4) The search for disks: results & implications

Disks in High-Mass YSOs

Riccardo CesaroniOsservatorio Astrofisico di Arcetri

Low-mass vs High-mass

Theory (Shu et al. 1987): star formation from inside-out collapse onto protostar

Two relevant timescales:

accretion tacc = M*/(dM/dt)

contraction tKH = GM*/R*L*

Lowmass (< 8 MO): tacc < tKH

Highmass (> 8 MO): tacc > tKH accretion on ZAMS (Palla & Stahler 1993)

PROBLEM:

High-mass stars “switch on” still accreting radiation pressure stops accretion

stars > 8 MO cannot form!?

SOLUTIONS

Yorke (2003): Kdust< Kcrit M*/L*

1) “Increase’’ M*/L*: non-spherical accretion

2) Reduce Kdust: large grains (or coalescence of lower mass stars)

Possible models

• (Non-spherical) accretion: Behrend & Maeder (2001); Yorke & Sonnhalter (2002); Tan & McKee (2003)ram pressure > radiation pressure

• Coalescence: Bonnell et al. (1998, 2004) many low-mass stars merge into one massive star

Infall + angular momentum conservation rotating disks: “only’’ in accretion model

discriminant between models: rotation of molecular cores

High-mass star forming regions: Observations

• Observational problems: IMF high-mass stars are rare large distance: >300 pc, typically a few kpc formation in clusters confusion rapid evolution: tacc=20 MO /10-3MOyr-1=2 104yr parental environment profoundly altered

• Advantage: very luminous (cont. & line) and rich (molecules)!

High-mass starforming region

0.5 pc

disk?

The evidence for disksin massive YSOs

• Large scale (1 pc)

rotating clumps seen e.g. in NH3 (G35.2-0.74; Little et al. 1985), CO (IRAS07427; Kumar et al. 2003)

• Small scale (<0.1 pc)

many claims of rotating “disks’’…

The evidence for disksin massive YSOs

• Large scale (1 pc)

rotating clumps seen e.g. in NH3 (G35.2-0.74; Little et al. 1985), CO (IRAS07427; Kumar et al. 2003)

• Small scale (<0.1 pc)many claims of rotating “disks’’…

CH3OH masers ATCA, EVN

Ellingsen et al., Walsh et al.

Minier et al., Edris et al., Pestalozzi et al.

OH masers Merlin outflow sources:

Cohen et al., Edris et al.

SiO & H2O masers

VLA, VLBA

e.g. Orion source I

Greenhill, Torrelles et al.

NIR, mm & cm continuum

BIMA, VLA

jets/outflows in massive stars Hoare et al., Gibb et al.

NH3, C18O, CS, C34S, CH3CN,…

PdBI, OVRO, BIMA, NMA

UC HIIs, Hot Cores

Keto et al., Cesaroni et al.,

Zhang et al., etc. etc….

• CH3OH masers: stellar mass too low; H2 jets parallel to CH3OH spots (De Buizer 2003)

• OH masers: very few examples

• SiO & H2O masers: outflow and/or disk

• NIR-cm cont.: confusion between disk and wind emission

• Molecular lines: kinematical signature of disk & outflow

CH3OH masersNGC7538

Pestalozzi et al. (2004)

6 GHz

M*=30 MO ???

• CH3OH masers: stellar mass too low; H2 jets parallel to CH3OH spots (De Buizer 2003)

• OH masers: very few examples

• SiO & H2O masers: outflow and/or disk

• NIR-cm cont.: confusion between disk and wind emission

• Molecular lines: kinematical signature of disk & outflow

OH masersIRAS 20126+4104

Edris et al. (subm.)

disk

NIR & OH masers

• CH3OH masers: stellar mass too low; H2 jets parallel to CH3OH spots (De Buizer 2003)

• OH masers: very few examples

• SiO & H2O masers: outflow and/or disk

• NIR-cm cont.: confusion between disk and wind emission

• Molecular lines: kinematical signature of disk & outflow

H2O masersCep A HW2

Torrelles et al. (1996)

• CH3OH masers: stellar mass too low; H2 jets parallel to CH3OH spots (De Buizer 2003)

• SiO & H2O masers: outflow or disk?

• NIR-cm cont.: confusion between disk and wind emission?

• Molecular lines: kinematical signature of rotation & outflow

core outflowoutflow disk

G192.16-3.82Shepherd & Kurtz (1999)

CO outflow

2.6mm cont.disk

G192.16-3.82Shepherd & Kurtz (1999)

Shepherd et al. (2002)

3.6cm cont. & H2O masers

IRAS 20126+4104Cesaroni et al.; Moscadelli et al.M*=7 MO

H2O masers prop. motions

NGC7538S Sandell et al. (2003)

HCN(1-0)

M17

Chini et al. (2004)

2.2 micron

0.01 pc

13CO(1-0)

0.07 pc

Disks & Toroids

L

(LO)

Mdisk

(MO)

Ddisk

(AU)

M*

(MO)

IRAS20126

104 4 1600 7

G192.16 3 103 15 1000 6-10

M17 ? >110 20000 15-20

NGC7538S 104 100-400

30000 40?

G24.78 (3) 7 105 80-250 4000-8000

20…

G29.96 9 104 300 14000 -

G31.41 3 105 490 16000 -

B stars

O stars

Gibb et al. (2002)Olmi et al. (2003)

Olmi et al. (1996)Furuya et al. (2002)Beltran et al. (2004)

Furuya et al. (2002)Beltran et al. (2004)

Furuya et al. (2002)

Beltran et al. (2004)

Furuya et al. (2002)

Beltran et al. (2004)

Gibb et al. (2002)Olmi et al. (2003)

Beltran et al. (2005)

CH3CN(12-11)

Olmi et al. (1996)Beltran et al. (2004)

1200 AU

Beltran et al.(in prep.)

Temperature

Disks & Toroids

L

(LO)

Mdisk

(MO)

Ddisk

(AU)

M*

(MO)

IRAS20126

104 4 1600 7

G192.16 3 103 15 1000 6-10

M17 ? >110 20000 15-20

NGC7538S 104 100-400

30000 40

G24.78 (3) 7 105 80-250 4000-8000

20…

G29.96 9 104 300 14000 -

G31.41 3 105 490 16000 -

O stars

B stars

12CO(1-0) & 3mm continuum

Furuya et al. (in prep.)

VCH3CN(km/s)

Results

• “Circumcluster’’ (massive) toroids in O (proto)stars

• Circumstellar (Keplerian) disks in early-B (proto)stars

Are disks in O (proto)stars short lived?

Assuming (dM/dt)acc (dM/dt)outflow and Mdisk M*

Disk life time

Conclusions

• Circumstellar (Keplerian) disks in early-B (proto)stars disk accretion likely

• Circumcluster (unstable) toroids in O (proto)stars large accretion rates make them long-lived

ACCRETION SCENARIO MORE LIKELY

http://www.arcetri.astro.it/iaus227

END

The case of G31.41+0.31

• “Pseudo” toroidal structure in CH3CN

• T increase towards center embedded YSO(s)

• Vrot not Keplerian (const. or increasing with R)

• Evidence for infall:– Mdyn << Mtoroid

– line FWHM increasing towards centre

Beltran et al.(in prep.)

1200 AU

Hofner pers. comm.

1200 AU

The case of G31.41+0.31

• “Pseudo” toroidal structure in CH3CN

• T increase towards center embedded YSO(s)

• Vrot const. or increasing with R

• Evidence for infall:– Mdyn << Mtoroid

– line FWHM increasing towards centre

Beltran et al.(in prep.)

Temperature

Beltran et al.(in prep.)

Column density

The case of G31.41+0.31

• “Pseudo” toroidal structure in CH3CN

• T increase towards center embedded YSO(s)

• Vrot const. or increasing with R

• Evidence for infall:– Mdyn << Mtoroid

– line FWHM increasing towards centre

Ω=const.

V=const.

Beltran et al.(in prep.)

P-V plotsalong disk plane

The case of G31.41+0.31

• “Pseudo” toroidal structure in CH3CN

• T increase towards center embedded YSO(s)

• Vrot const. or increasing with R

• Evidence for infall:– Mdyn << Mtoroid

– line FWHM increasing towards centre

Beltran et al.(in prep.)

line FWHM

A different viewpoint…Gibb et al. (2004) observed 2 “toroids” in C18O & H2S,

with 1” resol. opposite interpretation: H2S and CH3CN from outflow, C18O from disk

We need reliable outflow tracer! 12CO

Recent observations of 12CO & CH3CN in other high mass YSOs (Furuya et al. in prep.) seem to confirm that CH3CN traces rotation.

Whatever the interpretation, there is common agreement that cores are rotating!

A different viewpoint…Gibb et al. (2004) observed 2 “toroids” in C18O & H2S,

with 1” resol. opposite interpretation: H2S and CH3CN from outflow, C18O from disk

We need reliable outflow tracer! 12CO

Recent observations of 12CO & CH3CN in other high mass YSOs (Furuya et al. in prep.) seem to confirm that CH3CN traces rotation.

Whatever the interpretation, there is common agreement that cores are rotating!

CH3OH masersW48

Minier et al. (2000)

M*=6 MO

6 GHz