Chasing disks around massive stars with Malcolm

1. Chasing disks around massive stars with Malcolm • Disks and the formation of OB stars • How HMCsstudiesturnedintoquest for disks • Before ALMA: disks versus toroids • The ALMA era: disks around B stars • The current & future challenge: disks around O stars

2. «First things first!»(Malcolm priv. comm.): Why are disks so important? Star formation: inside-out collapseontoprotostar Tworelevanttimescales: accretiontacc= M*/(dM/dt) contractiontKH= GM*/R*L* • Lowmass (< 8 MO): tacc< tKH • Highmass (> 8 MO): tacc> tKHaccretion on ZAMS radiation pressure mayhaltaccretionin sphericalsymmetrydisk may be solution!

3. Theory Different models of high-mass star formation (core accretion, competitive accretion, …), but all predict circumstellar disks of ~100-1000 AU See e.g. Bonnell 2005, Krumholz et al. 2007, Keto 2007, Kuiper et al. 2010, 2011 stars up to 140 MO may form by disk accretion

4. Existence of disks Disks are natural outcome of infall + angular momentum conservation, however: • B field  magnetic braking, pseudo disks? • Ionization by OB stars photoevaporation? • Tidal interaction with cluster truncation? • Merging of low-mass stars destruction?  Disks in OB protostarscould not exist!

5. A little bit of history In the ’90s: • Growingevidenceof disks aroundlow mass YSOsfrom HST (proplyds; O’Dell et al. 1993) and mm interferometry (GG Tau, etc.; Dutrey et al. 1994, Simon et al. 2000) • Verylittleevidenceof disks aroundOB stars(G10.6-0.4; Keto et al. 1987, 1988): tooembedded, too far? Butmanystudies of hot molecularcores! (seeFriedrich’s talk)

6. My collaboration with Malcolm: From HMCs to disks • HMCs are dense, hot, chemicallyrich: cradles of OB stars? • Surveys of UC HIIs, H2O masers, luminous IRAS sources, etc. to identifyHMCs • Tracers: NH3(4,4), CH3CN • Instruments: single-dish (IRAM, Effelsberg) interferometry (IRAM, VLA) of selectedobjects

7. The special case of the G31.41+0.31 HMC (106 LO O type) UCHII HMC

8. strong CH3CN(6-5) emission TB (K) frequency (GHz)

9. Elongated distribution of velocity peaks with velocity gradient! Rotation or outflow? Rotation  Mdyn = 900 MO~ Mcore 2’’ resolution

10. Velocity gradients found also in other luminous (O-type) HMCs, but too far  limited angular resolution & sensitivity closer HMCs needed B-type YSOs • Selected HMC: IRAS20126+4104 • distance 1.6 kpc  good spatial resolution • luminosity 104 LO massive enough • H2O masers  young and active • bipolar outflow  disk? • IRAM PdBI observations: • outflow tracer (HCO+) • High-density, high-temperature tracer (CH3CN) • 3 arcsec resolution

11. outflow axis PdBI in 1995: CH3CN(6-5) 3’’ resolution Plots of peak positions in differentvelocitychannels: • elongatedperp. to outflow • velocitygradient

12. jet disk PdBI in 1997: CH3CN(12-11) 0.7’’ resolution

13. Malcolm’s insight: Keplerian rotation  FWHMΘS-0.5

14. Image: H2 at 2µm CH3CN H2O masers IRAS 20126+4104 Cesaroni et al. (1997, 1999, 2005, 2013, 2014) Hofner et al. (1999, 2007) Moscadelli et al. (2005, 2010) Kepler+infall 8 MO star

15. The search for disks After year 2000, several groups engaged in search for disks around massive stars. Selection criteria for targets: • Bolometric (IRAS) luminosity > several 103 LOhigh-mass (proto)star • Association with outflowlikely disk? • Presence of massive (> 10 MO), compact (< 0.1 pc) molecular core deeply embedded (young) high-mass object • In some cases maser and/or UCHIIOB stars

16. Tools adopted: • Thermal lines of rare (low-abundance) molecules  trace high-density, high-temperature gas in disk • H2O, CH3OH, OH, SiO maser linesmas resolution • (sub)mm continuum  disk mass • IR continuum/lines  disk emission and absorption • cm continuum and RRLionised accretion flow Diagnostic: • Flattened (sub)mm core perpendicular to jet/outflow • Velocity gradient perpendicular to associated outflow • Peculiar (Keplerian) pattern in position-velocity plot • Dark silouhette in near-IR against bright background • Elongated emission in the mid-IR perpendicular to bipolar reflection nebula

17. Our choice: molecular lines kinematical signature of rotation & outflow core disk outflow outflow

18. Disks • M < a few 10 MO • R ~ 1000 AU L ~ 104 LOB (proto)stars • large tacc/trot circumstellarequilibrium structures Toroids • M > 100 MO • R ~ 10000 AU L > 105 LOO (proto)stars • small tacc/trot transientcircum-cluster structures Beltrán & de Wit (2017) Beltrán et al. (2010, 2014) Sánchez-Monge et al. (2014)

19. Chasing disks with Malcolmin the ALMA era • Is the Keplerian disk around the B-type protostar IRAS20126+4104 unique?  ALMA Cycle 0: 0.4’’ observations of 2 YSOs at ~2 kpc, with 104 LO • Are there disks around O-type YSOs?  ALMA Cycle 2: 0.2’’ observations of 6 YSOs with >105 LO

20. Typical ALMA spectra 13CH3CN CH3CN

21. B-type YSOs

22. Keplerian rotation about 18 MO G35.20-0.74 N Sanchez-Monge et al. (2013, 2014) ALMA350 GHz continuuum: • filament (~ 40 MO)perpendicolar to bipolar nebula • ~6 coresalong filament

23. G35.03+0.35 • Prominent core (~4 MO) at center of bipolar nebula • Position-velocity plots along cut perpendicular to bipolar nebula • White pattern: Keplerian rotation about about 6 MO Beltrán et al. (2014)

24. O-type YSOs

25. 97 K 778 K K=2 v8=1 G31.41+0.31 CH3CN(1211) Beltrán et al. (2018) 10 times better resolution than first observation in 1994! high V + small offset  small R + high T  rotation Vrot ~ R-a

26. AFGL4176 time Detectionrate depends more on L/Mthan on distanceage effect? • Too young disk too embedded: difficult detection • Tooold too few molecular gas

27. Current situation: Up do date review on disks around massive stars (Beltrán & de Wit 2017): 41 disks/toroids around OB-type stars Red: OB stars Blue: int. mass stars

28. Last paper with Malcolm (disk accretion and ejection): Radio follow-up of IR burst (Caratti o Garatti et al. 2017)

29. S255 NIRS3 disk from C34S Zinchenko et al. (2015) Keplerian PV plot map burst!

30. Conclusion • OK… disks, toroids, jets, bursts, etc., • all these may be very exciting, but… be scheptical and always keep in mind Malcolm’s warning:

31. Io credo nulla! (I believe nothing!)