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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.

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disks in high mass ysos
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
slide2

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*

  • Lowmass (< 8 MO): tacc < tKH
  • Highmass (> 8 MO): tacc > tKH  accretion onZAMS (Palla & Stahler 1993)
slide3
PROBLEM:

High-mass stars “switch on” still accreting

 radiation pressure stops accretion 

 stars > 8 MOcannot form!?

SOLUTIONS

Yorke (2003): Kdust<Kcrit M*/L*

  • “Increase’’ M*/L*: non-spherical accretion
  • Reduce Kdust: large grains (or coalescence of lower mass stars)
possible models
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
slide5

Infall+ angular momentum conservation   rotatingdisks: “only’’ in accretion model

  • discriminant between models: rotation of molecular cores
high mass star forming regions observations
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
    • rapidevolution: tacc=20 MO /10-3MOyr-1=2104yr
    • parental environment profoundly altered
  • Advantage:
    • very luminous (cont. & line) and rich (molecules)!
slide7

High-mass star

forming region

disk?

0.5 pc

the evidence for disks in massive ysos
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’’…

slide9

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’’…
slide11
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
slide12

CH3OH masers

NGC7538

Pestalozzi et al. (2004)

M*=30 MO ???

6 GHz

slide13

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
slide14

OH masers

IRAS 20126+4104

Edris et al. (subm.)

NIR & OH masers

disk

slide15

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
slide16

H2O masers

Cep A HW2

Torrelles et al. (1996)

slide17

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

disk

outflow

outflow

slide18

G192.16-3.82

Shepherd & Kurtz (1999)

2.6mm cont.

disk

CO outflow

slide19

G192.16-3.82

Shepherd & Kurtz (1999)

Shepherd et al. (2002)

3.6cm cont. & H2O masers

slide20

IRAS 20126+4104

Cesaroni et al.; Moscadelli et al.

M*=7 MO

H2O masers prop. motions

slide22

0.01 pc

M17

Chini et al. (2004)

2.2 micron

13CO(1-0)

0.07 pc

disks toroids
Disks & Toroids

B stars

O stars

slide24

Gibb et al. (2002)

Olmi et al. (2003)

Olmi et al. (1996)

Furuya et al. (2002)

Beltran et al. (2004)

slide25

Furuya et al. (2002)

Beltran et al. (2004)

slide26

Furuya et al. (2002)

Beltran et al. (2004)

slide27

Furuya et al. (2002)

Beltran et al. (2004)

slide28

CH3CN(12-11)

Gibb et al. (2002)

Olmi et al. (2003)

Beltran et al. (2005)

slide29

Olmi et al. (1996)

Beltran et al. (2004)

1200 AU

slide30

Beltran et al.

(in prep.)

Temperature

slide31

Disks &Toroids

B stars

O stars

slide32

12CO(1-0) & 3mm continuum

Furuya et al. (in prep.)

VCH3CN(km/s)

results
Results
  • “Circumcluster’’ (massive) toroids in O (proto)stars
  • Circumstellar (Keplerian) disks in early-B(proto)stars

Are disks in O (proto)stars short lived?

slide34

Disk life time

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

slide35

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
the case of g31 41 0 31
The case of G31.41+0.31
  • “Pseudo” toroidal structure in CH3CN
  • T increase towards center  embedded YSO(s)
  • Vrotnot Keplerian (const. or increasing with R)
  • Evidence for infall:
    • Mdyn << Mtoroid
    • line FWHM increasing towards centre
slide39

Beltran et al.

(in prep.)

1200 AU

1200 AU

Hofner pers. comm.

slide40

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
slide41

Beltran et al.

(in prep.)

Temperature

slide42

Beltran et al.

(in prep.)

Column density

slide43

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
slide44

V=const.

Beltran et al.

(in prep.)

P-V plots

along disk plane

Ω=const.

slide45

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
slide46

Beltran et al.

(in prep.)

line FWHM

a different viewpoint
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!

slide48

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!

slide50

CH3OH masers

W48

Minier et al. (2000)

M*=6 MO

6 GHz