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Session 121 - Molecular Clouds/Star Formation.
Oral session, Saturday, January 10
We discuss the first evidence for the process of terminating accretion in protostellar disks through the interaction between infall and a very wide opening angle outflow in a Young Stellar Object (YSO) IRS1 in B5. IRS1 is a relatively young object with a dynamical age of 10^4 yr for its molecular outflow and pc scale optical jet. The OVRO-MMA interferometer maps obtained with 1^\prime\prime resolution at 1.3 mm in the continuum and in CO isotopes are presented. The C^18O(2-1) traces the dense infalling gas, while the line wings of ^12CO(2-1) trace the molecular outflow. The most remarkable feature revealed in these maps is the geometrical shapes and clear demarkation of the outflow and infall boundaries. The infall is confined to a narrow equatorial region perpendicular to the jet's outflow axis, while the high velocity outflow originates in bipolar cones which we trace deep down to within 0.4" (150 AU) from the star. The outflow cones are widest at the vertices indicating a significant widening of the outflow with time. We suggest that this widening of outflow marks the final stages of isolating the disk from further accretion. The widening of the outflow cones and the flattening of the infall must be coupled to each other through the processes involved in generating the molecular outflow near the star and provides a natural mechanism for the end of infall, and hence, the end of the accreting phase in YSOs. By tracing the time evolution in the outflow cones, we estimate that the infall will be shutdown in \sim 10^4 yr in IRS1 in B5. Therefore, once outflow begins, typically the entire accretion phase lasts only \sim 20,000 yr.
This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The Owens Valley Radio Observatory millimeter-wave array is supported by the NSF.
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