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. PI Silvia Leurini Total time 24 h (ALMA, extended and compact #Co. Is, team configurations, APEX? ) Menten, Schilke, Stanke, Wyrowski
How do massive stars form? • coalescence of stars (M<8 M )? then we should detect high density of stars (108 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 (60 -500 M ) and extended (rd~4000 -30000 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~105 L ~3 kpc res. v kms-1 GHz T rms m. Jy A G 327. 3 -0. 6 0. 02” (40 AU) 0. 5 230 8 h 1. 2 CH 3 CN 12 -11 (disk) B G 327. 3 -0. 6 ~2” 1. 0 230 8 h 1. 2 13 CO, 12 CO notes (outflow) C G 327. 3 -0. 6 APEX? or compact array 1. 0 230 14 h 87 12 CO, 13 CO
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