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Session 5 - Accretion and Outflows in YSOs.
Display session, Wednesday, January 07
Exhibit Hall,
The far-infrared source in L483 numbers among the youngest protostars. We report high angular resolution images of the submillimeter emission obtained with SCUBA on the JCMT, and high spatial and spectral resolution images of the NH_3(1,1) and (2,2) lines obtained with the VLA. These images suggest that the disk currently accretes matter from the surrounding cloud. The highest optical depth line is the main hyperfine component of the (1,1) line, which is much weaker than the satellite line near the FIR source. The velocity of this component shifts significantly blueward within 2000 AU of the FIR source. Such a shift signifies that material between the observer and the optically thick envelope of the protostellar core is moving away from the observer, or falling toward the protostar.
The infall solution found by Shu (1977) was used to model the region interior to an expansion wave which propagates outward from the center of a singular isothermal sphere. Ammonia spectra were then synthesized and matched to the observations through adjustments to the model. The modeled profiles show enhanced linewidth in the (2,2) line relative to the (1,1) line, as well as a shift of emergent spectra towards lower line center velocity, though not so large as observed. We conclude that the ammonia images demonstrate that infall occurs within the central 5000 AU of the core centered on L483-FIR, but that more elaborate models will be necessary to fit the kinematics of the region in detail.
