PI Total time #CoIs, team Silvia Leurini 24h (ALMA, extended and compact configurations, APEX?) Menten, Schilke, Stanke, Wyrowski Disk dynamics in very young stellar objects: the contribution from ALMA Two formation scenarios exist for massive stars: non spherical accretion and merging of lower mass stars. Discriminating between these two models represents a challenging observational goal. The high sensitivity and spatial resolution of ALMA will shed light on this topic.

How do massive stars form? coalescence of stars (M<8M  )? then we should detect high density of stars (10 8 pc -3 ) accretion? then we should be able to observe accretion disks and collimated molecular outflows as in the case of low mass stars. A conclusive evidence of accretion from high mass stars is the detection of an outflow-disk system from a single protostar. Only a few disk candidates in massive stars are known, and all are early B type stars. No circumstellar disk has been detected in O type YSOs, but rotating structures, very massive ( M  ) and extended (r d ~ AU), which are not in equilibrium.

Unambiguous probe of disks: Detection of continuum emission from a small (<0.1 pc) core located at the center of a bipolar outflow, AND of molecular emission with a velocity gradient PERPENDICULAR to the outflow. Potential molecular tracers of a disk are high-energy, optically thin lines of a low-abundance molecular species. color: Spitzer 8  m; red contours: N 2 H + (cold molecular gas); black contours: CH 3 OH (warm molecular gas)

ALMA Justification: high resolution, high sensitivity. Legacy Value: High statistics is needed. This will be part of a legacy project aimed at investigating circumstellar disks in high mass YSOs. Data Reduction: several lines will be observed simultaneously (large bandwidth correlator). There is a need for semi-automated tools for modelling the data, and better spectroscopic databases. source L~10 5 L  ~3kpc res.  v kms -1 GHz Trms mJy notes AG ” (40 AU) h1.2 CH 3 CN (disk) BG ~2” h CO, 12 CO (outflow) CG APEX? or compact array h87 12 CO, 13 CO