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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.

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Disks in High-Mass YSOs

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  1. 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

  2. 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)

  3. 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)

  4. 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

  5. Infall+ angular momentum conservation   rotatingdisks: “only’’ in accretion model • discriminant between models: rotation of molecular cores

  6. 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)!

  7. High-mass star forming region disk? 0.5 pc

  8. 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’’…

  9. 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’’…

  10. 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

  11. CH3OH masers NGC7538 Pestalozzi et al. (2004) M*=30 MO ??? 6 GHz

  12. 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

  13. OH masers IRAS 20126+4104 Edris et al. (subm.) NIR & OH masers disk

  14. 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

  15. H2O masers Cep A HW2 Torrelles et al. (1996)

  16. 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

  17. G192.16-3.82 Shepherd & Kurtz (1999) 2.6mm cont. disk CO outflow

  18. G192.16-3.82 Shepherd & Kurtz (1999) Shepherd et al. (2002) 3.6cm cont. & H2O masers

  19. IRAS 20126+4104 Cesaroni et al.; Moscadelli et al. M*=7 MO H2O masers prop. motions

  20. NGC7538S Sandell et al. (2003) HCN(1-0)

  21. 0.01 pc M17 Chini et al. (2004) 2.2 micron 13CO(1-0) 0.07 pc

  22. Disks & Toroids B stars O stars

  23. Gibb et al. (2002) Olmi et al. (2003) Olmi et al. (1996) Furuya et al. (2002) Beltran et al. (2004)

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

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

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

  27. CH3CN(12-11) Gibb et al. (2002) Olmi et al. (2003) Beltran et al. (2005)

  28. Olmi et al. (1996) Beltran et al. (2004) 1200 AU

  29. Beltran et al. (in prep.) Temperature

  30. Disks &Toroids B stars O stars

  31. 12CO(1-0) & 3mm continuum Furuya et al. (in prep.) VCH3CN(km/s)

  32. Results • “Circumcluster’’ (massive) toroids in O (proto)stars • Circumstellar (Keplerian) disks in early-B(proto)stars Are disks in O (proto)stars short lived?

  33. Disk life time Assuming (dM/dt)acc (dM/dt)outflow and Mdisk M*

  34. 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

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

  36. END

  37. 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

  38. Beltran et al. (in prep.) 1200 AU 1200 AU Hofner pers. comm.

  39. 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

  40. Beltran et al. (in prep.) Temperature

  41. Beltran et al. (in prep.) Column density

  42. 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

  43. V=const. Beltran et al. (in prep.) P-V plots along disk plane Ω=const.

  44. 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

  45. Beltran et al. (in prep.) line FWHM

  46. 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!

  47. 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!

  48. CH3OH masers W48 Minier et al. (2000) M*=6 MO 6 GHz

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