1. 1)The importance of disks in massive (proto)stars 2)The search for disks: methods and tracers 3)The result: “real” disks found in B (proto)stars 4)The stability of disks  accretion rate onto star 5)The apparent lack of “real” disks in O stars: observational bias, short lifetime, or different star formation scenario? Disks around young O-B (proto)stars: Observations and theory R. Cesaroni, D. Galli, G. Lodato, C.M. Walmsley, Q. Zhang

2. Disks in young (proto)stars Disks seem natural outcome of star formation: collapse + angular momentum conservation   flattening + rotation speed up  disk Disks detected in low- & intermediate-mass (< 8 M O ) pre-main-sequence stars (Simon et al. 2000; Natta et al. 2000) Disks of a few AU found in young ZAMS B stars (Bik & Thi 2004) Disks disappear rapidly in intermediate-mass (2-8 M O ), pre-main-sequence stars (Fuente et al. 2003)

3. Disks and high-mass star formation Two relevant timescales in star formation: accretion: t acc = M star /(dM/dt) acc contraction: t KH = GM star /R star L star M > 8-14 M O  t acc > t KH (Palla & Stahler 1993) High-mass stars reach ZAMS still accreting! Spherical symmetry: radiation pressure > ram pressure  stars > 8-14 M O should not form!??

4. Disk + outflow may be the solution (Yorke & Sonnhalter, Kruhmolz et al.): Outflow  channels stellar photons   lowers radiation pressure Disk  focuses accretion   boosts ram pressure  Detection of accretion disks would support O-B star formation by accretion, otherwise other mechanisms are needed

5. The search for disks in massive YSOs Disks are likely associated with outflows: outflow detection rate = 40-90% in massive YSOs (Osterloh et al., Beuther et al., Zhang et al., …)  disks should be widespread! BUT… What to search for…?

6. outflow Theorist’s definition: Disk = long-lived, flat, rotating structure in centrifugal equilibrium Observer’s definition: Disk = elongated structure with velocity gradient perpendicular to outflow axis core disk

7. CH 3 OH masers5 mas 15 AU Norris et al., Phillips et al. Minier et al., Edris et al., Pestalozzi et al., … OH masers10 mas 30 AU Hutawarakorn & Cohen, Edris et al. SiO & H 2 O masers1 mas 3 AU Greenhill et al., Torrelles et al., Wright et al., Shepherd et al., … NIR, mm & cm continuum 100 mas 300 AU Gibb et al., Yao et al. Preibisch et al., Chini et al., Sridharan et al. Jiang et al., Puga et al., Shepherd et al., … Thermal lines: NH 3, C 18 O, CS, C 34 S, CH 3 CN, HCOOCH 3, … 500 mas 1500 AU Keto et al., Cesaroni et al., Zhang et al., Shepherd & Kurtz, Olmi et al., Sandell et al., Chini et al., Gibb et al., Beltràn et al., Beuther et al., … Which tracer…?

8. TRACERPROsCONTRAs Maser lines High angular & spectral resolution Unclear geometry & kinematics Continuum Sensitivity (and resolution) No velocity info Confusion with free- free and/or envelope Thermal lines Kinematics and geometry of outflow and disk Limited angular resolution and sensitivity (but see SMA and ALMA)

9. Results of disk search Two types of objects found: Toroids M > 100 M O R ~ 10000 AU L > 10 5 L O (dM/dt) star > 10 -3 M O /yr t rot ~ 10 5 yr t acc ~ M/(dM/dt) star ~ 10 4 yr  t acc << t rot  non-equilibrium, circum- cluster structures Disks M < 10 M O R ~ 1000 AU L ~ 10 4 L O (dM/dt) star ~ 10 -4 M O /yr t rot ~ 10 4 yr t acc ~ M/(dM/dt) star ~ 10 5 yr  t acc >> t rot  equilibrium, circumstellar structures

10. Examples of rotating toroids: G10.62-0.38 (Keto et al. 1988) G24.78+0.08 (Beltràn et al. 2004, 2005) G28.20-0.05 (Sollins et al. 2005) G29.96-0.02 (Olmi et al. 2003, Gibb et al. 2004) G31.41+0.31 (Beltràn et al. 2004, 2005) IRAS 18566+0404 (Zhang et al. 2005) NGC 7538 (Sandell et al. 2003)

11. Examples of rotating disks:

12. M17 Chini et al. (2004) 2.2 micron 0.01 pc 13 CO(1-0) 0.07 pc Sako et al. (2005) disk

13. IRAS 20126+4104 Cesaroni et al. Hofner et al. Moscadelli et al. M * =7 M O H 2 O masers prop. motions

14. IRAS 20126+4104 Edris et al. (2005) Sridharan et al. (2005) disk NIR & OH masers

15. 10 4 L O 1-15M O 6-25M O a few10 3 AU 10 -4 M O /yr 10 4 yr L tot M disk R disk M star (dM/dt) out t out  Disks do exist in B-type (proto)stars DISKS IN MASSIVE (PROTO)STARS

16. Open questions… 1.M disk ~ M star  Are disks stable? 2.Can disks sustain accretion rate onto star? 3.Are there disks in O-type stars?

17. Disk stability Stability: Toomre’s parameter Q > 1 Q(H/R,M disk /M tot ) with H=disk thickness and M tot = M disk+ M star Fiducial values (e.g. IRAS 20126+4104): H/R = 0.4 M disk /M tot = 4 M O /11 M O = 0.4  Q=2  the disk is stable to axisymmetric perturbations, but…

19. Disk stability Stability: Toomre’s parameter Q > 1 Q(H/R,M disk /M tot ) with H=disk thickness and M tot = M disk+ M star Fiducial values (e.g. IRAS 20126+4104): H/R = 0.4 M disk /M tot = 4 M O /11 M O = 0.4  Q=2  the disk is stable to axisymmetric perturbations, but…

20. Lodato and Rice (2004): thick (H ~ R/2) and massive (M disk ~ M star /2) disks with Q > 1 develop non-axisymmetric instabilities (over t rot ~ 10 4 yr) towards Q ~ 1  marginal stability Lodato, Rice, and Armitage (2005): disk cooling  development of spiral structure or disk fragmentation upper limit to the transport of matter through the disk by viscosity  maximum accretion rate through the disk onto the star, for disk surface density ~ R -1 : (dM/dt) star = 0.38 (H/R) 2 M disk /t rot ~ 10 -5 M O /yr

21. Disk accretion rate Problem: (dM/dt) star =10 -5 M O /yr too small Estimated mass accretion rate on star much smaller than accretion on disk: (dM/dt) disk = M cloud /t free-fall = 10 -4 -10 -3 M O /yr Star formation timescale too long: t star = M star /(dM/dt) star = 10 6 -10 7 yr >> 10 5 yr (e.g. Tan & McKee 2004).

22. Possible solutions: For surface density ~ R -p (dM/dt) star = 0.38/(2-p) (H/R) 2 M disk /t rot may be very large for p ~ 2 Massive disks (M disk ~ M star )  strong episodes of spiral activity  (dM/dt) star enhanced by 10 times over t rot ~ 10 4 yr (Lodato & Rice 2005) Magnetised disks also develop enhancements of accretion rate (Fromang et al. 2004)

23. Are there disks in O stars? In L star ~ 10 4 L O (B stars) true disks found In L star > 10 5 L O (O stars) no true disk (only toroids) found - but distance is large (few kpc) Orion I (450 pc) does have disk, but luminosity is unclear (< 10 5 L O ???)  Difficult to detect massive disks in O (proto)stars. Why?

24. Observational bias? For M disk = M star /2, a Keplerian disk in a 50 M O star can be detected up to:  continuum sensitivity: d < 1.7 [M star (M O )] 0.5 ~ 12 kpc  line sensitivity: d < 6.2 M star (M O ) sin 2 i/W 2 (km/s) ~ 8 kpc  spectral + angular resolution: d < 14 M star (M O ) sin 2 i/[D(’’)W 2 (km/s)] ~ ~ 19 kpc

25.  all disks detectable up to galactic center Caveats!!! One should consider also: rarity of O stars confusion with envelope chemistry confusion with outflow/infall non-keplerian rotation disk flaring inclination angle …

26. On the other hand, if O protostars do not have disks, a physical explanation is required: O-star disks “hidden” inside toroids O-star disk lifetime too short, i.e. less than rotation period:  photo-evaporation by O star (Hollenbach et al. 1994)  tidal destruction by stellar companions (Hollenbach et al. 2000) In both cases we assume M disk =M star /2 and disk surface density ~ R -1, i.e. M disk  R disk :

27. tidal destruction rotational period photo-evaporation

28. Disks in O (proto)stars might be shorter lived, and/or more deeply embedded than those detected in B (proto)stars Photoionosation: inefficient disk destruction mechanism, for all spectral types (if M disk comparable to M star ) Tidal interaction with the stellar companions: more effective to destroy outer regions of disks in O stars than in B-stars

29. Conclusions Found about ~10 disks in B (proto)stars  star formation by accretion as in low-mass stars No disk found yet (only massive, rotating toroids) in O (proto)stars  –observational bias (confusion, distance, rarity,…) –disks hidden inside toroids and/or destroyed by tidal interactions with stellar companions –disks do not exist; alternative formation scenarios for O stars needed: coalescence of lower mass stars, competitive accretion (see Bonnell, Bate et al.)

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

32. G192.16-3.82 Shepherd & Kurtz (1999) Shepherd et al. (2001) 3.6cm cont. & H 2 O masers

33. Simon et al. (2000): TTau stars Velocity maps (CO J=2  1)

34. Fuente et al. (2003): mm continuum in Herbig Ae/Be stars (age ~ 10 6 yr) M disk (B) << M disk (A)

35. Bik & Thi (2005): CO first overtone in four B5-O6 stars fitted with Keplerian disk

36. Cep A HW2 Torrelles et al. (1998) … but see Comito & Schilke for a different interpretation Patel et al. (2005)

37. IRAS 18089-1732 Beuther et al. (2004, 2005)

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

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

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

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

42. Gibb et al. (2002) Olmi et al. (2003) Beltran et al. (2005) CH 3 CN(12-11)

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

44. Disks & Toroids L (L O ) M disk (M O ) D disk (AU) M * (M O ) IRAS2012610 4 416007 G192.163 10 3 1510006-10 M17?>1102000015-20 NGC7538S10 4 100-4003000040 G24.78 (3)7 10 5 80-2504000-800020… G29.969 10 4 30014000- G31.413 10 5 49016000- O stars B stars