disks in high-mass ysos
DESCRIPTION
Disks in High-Mass YSOs. Riccardo Cesaroni Osservatorio Astrofisico di Arcetri. High-mass vs low-mass: the dividing line The formation of high-mass stars: accretion vs coalescence The importance of disks in massive YSOs The search for disks : results & implications. - PowerPoint PPT PresentationTRANSCRIPT
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