Chasing disks around massive stars with Malcolm Disks and the formation of OB stars How HMCs studies turned into quest for disks Before ALMA: disks versus toroids The ALMA era: disks around B stars The current & future challenge: disks around O stars

«First things first!» (Malcolm priv. comm.): Why are disks so important? Star formation: 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 on ZAMS  radiation pressure may halt accretion in spherical symmetry  disk may be solution! 2

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 3

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 protostars could not exist! 4

A little bit of history In the ’90s: Growing evidence of disks around low mass YSOs from HST (proplyds; O’Dell et al. 1993) and mm interferometry (GG Tau, etc.; Dutrey et al. 1994, Simon et al. 2000) Very little evidence of disks around OB stars (G10.6-0.4; Keto et al. 1987, 1988): too embedded, too far? But many studies of hot molecular cores! (see Friedrich’s talk)

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

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

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

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

IRAM PdBI observations: 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

PdBI in 1995: CH3CN(6-5) 3’’ resolution Plots of peak positions in different velocity channels: elongated perp. to outflow velocity gradient outflow axis 11

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

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

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 Image: H2 at 2µm CH3CN H2O masers 14

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 15

H2O, CH3OH, OH, SiO maser lines  mas resolution 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 16

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

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

Chasing disks with Malcolm in 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

Typical ALMA spectra 13CH3CN CH3CN 20

B-type YSOs

Keplerian rotation about 18 MO G35.20-0.74 N ALMA 350 GHz continuuum: Sanchez-Monge et al. (2013, 2014) Keplerian rotation about 18 MO ALMA 350 GHz continuuum: filament (~ 40 MO) perpendicolar to bipolar nebula ~ 6 cores along filament 22

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) 23

O-type YSOs

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

Detection rate depends more on L/M than on distance  age effect? Name dist. L/M CH3CN disk? kpc LO/MO Y/N/? G17.64 2.2 300 N G24.78 7.7 15 N? G29.96 6.2 < 300 Y G31.41 7.9 17 ? G345.49 2.4 22 G345.50 2.0 84 Y (2) AFGL4176 time Detection rate depends more on L/M than on distance  age effect? Too young  disk too embedded: difficult detection Too old  too few molecular gas

41 disks/toroids around OB-type stars 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 27

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

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

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

Io credo nulla! (I believe nothing!) 31