High-mass vs low-mass: the dividing line

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Outflow, infall, and rotation in high-mass star
forming regions
Riccardo Cesaroni Osservatorio Astrofisico di
Arcetri

1. High-mass vs low-mass the dividing line
2. The formation of high-mass stars accretion vs
   coalescence
3. Observations infall, outflows, and disks
4. Kinematical evidence supports accretion

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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/RL
• Low?mass (lt 8 MO) tacc lt tKH
• High?mass (gt 8 MO) tacc gt tKH ? accretion on
  ZAMS

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• PROBLEM
• High-mass stars switch on still accreting ?
• ? radiation pressure stops accretion ?
• ? stars gt 8 MO cannot form!?
• SOLUTIONS
• Yorke (2003) Kdustlt Kcrit ? M/L
• Reduce L non-spherical accretion
• Increase M large accretion rates
• Reduce Kdust large grains (coalescence of lower
  mass stars)

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Possible models

• (Non-spherical) accretion Behrend Maeder
  (2001) Yorke Sonnhalter (2002) Tan McKee
  (2003)
• ram pressure gt radiation pressure
• Coalescence Bonnell et al. (2004) many
• low-mass stars merge into one massive star

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Implications predictions

• Accretion
• infall ? disks ? outflows
• isolated star formation possible
• massive stars form at cluster centre
• (dM/dt) ? FWHM3 (Shu et al. 1987)
• massive stars form with lower mass stars
• t ? M1/4 (Tan Mc Kee 2003)

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Implications predictions

• Coalescence
• infall, low-mass disks, multiple outflows
• isolated star formation impossible
• massive stars form at cluster centre
• large n (108 /pc3 !) ? many collisions
• massive stars form after lower mass stars

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• best discriminant between models kinematics of
  molecular gas
• infall accretion ? large accretion rate
  coalescence ? small(?) accretion rate
• outflow accretion ? single massive flow
  coalescence ? multiple low-mass flows
• rotation infallang. mom. conservation ?
• ? rotating disks (only in accretion model)

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• best discriminant between models kinematics of
  molecular gas
• infall accretion ? large accretion rate
  coalescence ? small(?) accretion rate
• outflow accretion ? single massive flow
  coalescence ? multiple low-mass flows
• rotation infallang. mom. conservation ?
• ? rotating disks (only in accretion model)

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• best discriminant between models kinematics of
  molecular gas
• infall accretion ? large accretion rate
  coalescence ? small(?) accretion rate
• outflow accretion ? single massive flow
  coalescence ? multiple low-mass flows
• rotation infallang. mom. conservation ?
• ? rotating disks (only in accretion model)

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• best discriminant between models kinematics of
  molecular gas
• infall accretion ? large accretion rate
  coalescence ? small(?) accretion rate
• outflow accretion ? single massive flow
  coalescence ? multiple low-mass flows
• rotation infallang. mom. conservation ?
• ? rotating disks (only in accretion model)

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Discriminating between models observations

• Observational problems
• IMF ? high-mass stars are rare
• formation in clusters ? confusion
• rapid evolution tacc20 MO /10-3MOyr-12 104yr
• large distance gt300 pc, typically a few kpc
• parental environment profoundly altered
• Advantage
• very luminous (cont. line) and rich (molecules)!

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High-mass star forming region
0.5 pc
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G9.620.19
NIR JHK
10 pc
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G9.620.19 350 micron
0.5 pc
Hunter et al. (2000)
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Testi et al. Cesaroni et al.
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Infall

• Difficult to reveal Vff ? R-0.5
• direct evidence
• red-shifted (self)absorption ambiguous
• position-velocity plots/channel maps
• indirect evidence
• lack of support Mgas gt Mvir
• model fit to SED
• dM/dt10-310-2 MOyr-1 ? accretion possible
• insufficient resolution infall on single star?

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Infall

• Difficult to reveal Vff ? R-0.5
• direct evidence
• red-shifted (self)absorption ambiguous
• position-velocity plots/channel maps
• indirect evidence
• lack of support Mgas gt Mvir
• model fit to SED
• dM/dt10-310-2 MOyr-1 ? accretion possible
• insufficient resolution infall on single star?

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Infall

• Difficult to reveal Vff ? R-0.5
• direct evidence
• red-shifted (self)absorption ambiguous
• position-velocity plots/channel maps
• indirect evidence
• lack of support Mgas gt Mvir
• model fit to SED
• dM/dt10-310-2 MOyr-1 ? accretion possible
• insufficient resolution infall on single star?

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Outflow

• Easy to detect even with low angular resolution
• single-dish (gt10 i.e. gt0.5 pc) CO surveys of
  UCHIIs, IRAS sources, masers (Shepherd
  Churchwell 1996 Zhang et al. 2001 Beuther et
  al. 2002, etc.), H2 (shocked) 2.2?m emission
• outflows in high-mass stars do exist
• typical parameters 1 pc, 55000 MO ,
• 10-410-2 MO yr-1, dM/dt ? L0.7
• BUT are these from the most massive (proto)star?

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CO(2-1) outflow 1mm continuum Beuther et al.
(2002)
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Outflow

• Easy to detect even with low angular resolution
• single-dish (gt10 i.e. gt0.5 pc) CO surveys of
  UCHIIs, IRAS sources, masers (Shepherd
  Churchwell 1996 Zhang et al. 2001 Beuther et
  al. 2002, etc.), H2 (shocked) 2.2?m emission
• outflows in high-mass stars do exist
• typical parms. 1 pc, 5-5000 MO , 10-4-10-2 MO
  yr-1
• dM/dt ? L0.7 ? continuity from low- to high-mass
• BUT is outflow from one massive (proto)star?

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CO outflows in YSOs Churchwell (2002)
dM/dt ? L0.7
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Outflow

• Easy to detect even with low angular resolution
• single-dish (gt10 i.e. gt0.5 pc) CO surveys of
  UCHIIs, IRAS sources, masers (Shepherd
  Churchwell 1996 Zhang et al. 2001 Beuther et
  al. 2002, etc.), H2 (shocked) 2.2?m emission
• outflows in high-mass stars do exist
• typical parms. 1 pc, 5-5000 MO , 10-4-10-2 MO
  yr-1
• dM/dt ? L0.7 ? continuity from low- to high-mass
• BUT is outflow from one massive (proto)star?

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• interferometric (gt1 i.e. 0.05 pc) observations
  of selected targets in CO, HCO, SiO, etc. (PdBI,
  OVRO, BIMA, NMA)
• single-dish outflows resolved into (massive
  collimated) multiple outflows (Beuther et al.
  2002)
• precession of outflow complicate interpretation
  (Shepherd et al. 2000 Gibb et al. 2003)
• powering source difficult to identify
• ? infall/outflow insufficient to prove model

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CO(2-1) mm cont. Beuther et
al. (2002) single-dish (12 beam)
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053583543 Beuther et al. (2003) interferometer
(4 beam)
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• interferometric (gt1 i.e. 0.05 pc) observations
  of selected targets in CO, HCO, SiO, etc. (PdBI,
  OVRO, BIMA, NMA)
• single-dish outflows resolved into (massive
  collimated) multiple outflows (Beuther et al.
  2002)
• precession of outflow complicate interpretation
  (Shepherd et al. 2000 Gibb et al. 2003)
• powering source difficult to identify
• ? infall/outflow insufficient to prove model

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IRAS 201264104 Shepherd et al. (2000)
blue lobe
red lobe
H2 knots
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IRAS 201264104 jet in H2 line
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IRAS 201264104
Cesaroni et al. (in prep.)
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• interferometric (gt1 i.e. 0.05 pc) observations
  of selected targets in CO, HCO, SiO, etc. (PdBI,
  OVRO, BIMA, NMA)
• single-dish outflows resolved into (massive
  collimated) multiple outflows (Beuther et al.
  2002)
• precession of outflow complicate interpretation
  (Shepherd et al. 2000 Gibb et al. 2003)
• powering source difficult to identify
• ? infall/outflow insufficient to prove scenario

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Disks

• Circumstellar accretion disks predicted only by
  accretion model! Any evidence?
• Large scale (1 pc)
• rotating clumps seen in medium density tracers
  e.g. NH3 in G35.2-0.74 (Little et al. 1985)
• Small scale (lt0.1 pc)
• many claims of rotating disks

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Disks

• Circumstellar accretion disks predicted only by
  accretion model! Any evidence?
• Large scale (1 pc)
• rotating clumps seen in medium density tracers
  e.g. NH3 in G35.2-0.74 (Little et al. 1985)
• Small scale (lt0.1 pc)
• many claims of rotating disks

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CH3OH masers ATCA, EVN Ellingsen et al., Walsh et al. Minier et al.
OH masers Merlin outflow sources Cohen et al. (2003)
SiO H2O masers VLA, VLBA e.g. Orion source I Greenhill
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.,
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• 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 disk
  outflow

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CH3OH masers W48 Minier et al. (2000)
M6 MO
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H2O masers Cep A HW2 Torrelles et al. (1996)
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• 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 disk
  outflow

core
disk
outflow
outflow
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G192.16-3.82 Shepherd Kurtz (1999)
2.6mm cont. disk
CO outflow
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G192.16-3.82 Shepherd Kurtz (1999)
3.6cm cont. H2O masers
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NGC7538S Sandell et al. (2003)
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IRAS 201264104 Cesaroni et al. Moscadelli et al.
M7 MO
H2O masers prop. motions
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Disks Tori
L (LO) Mdisk (MO) Ddisk (AU) M (MO)
IRAS20126 104 4 1600 7
G192.16 3 103 15 1000 6-10
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
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Gibb et al. (2002) Olmi et al. (2003) Beltran et
al. (2004)
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Beltran et al. (2004)
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Beltran et al. (2004)
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Gibb et al. (2002) Olmi et al. (2003)
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Beltran et al. (2004)
1200 AU
Hofner priv comm.
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Disks Tori
L (LO) Mdisk (MO) Ddisk (AU) M (MO)
IRAS20126 104 4 1600 7
G192.16 3 103 15 1000 6-10
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
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Results

• Circumcluster (massive) tori in O (proto)stars
• Circumstellar (Keplerian) disks in early-B
  (proto)stars
• ? Are disks in O (proto)stars short lived?

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Assuming (dM/dt)acc ? (dM/dt)outflow and Mdisk ?
M
disk ioniz. accr. rates
disk life time
B stars
B stars
O stars
O stars
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Conclusions

• Circumstellar (Keplerian) disks in early-B
  (proto)stars ? disk accretion likely
• Circumcluster (unstable) tori in O (proto)stars ?
  large accretion rates make them long-lived
• ACCRETION SCENARIO MORE LIKELY

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G45.470.05 NH3(2,2) Hofner et al. (1999)
red-shifted absorption
systemic velocity
blue-shifted emission
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Fontani et al. (2001)
n ? R-2.6
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CO outflows in YSOs Beuther et al. (2002)
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