We present high spatial resolution, aperture synthesis images of K3-50A as part of an ongoing study of high-mass star formation regions.Maps in the HCO`(J \ 1 ] 0), H13CO`(J \ 1 ] 0), and SiO (v \ 0, J \ 2 ] 1) emission lines at resolution reveal both a attened cloud of dense molecular gas D2A .5 D1.1 pc in extent and a newly discovered inner torus D0.5 pc in extent.The axis of the inner torus is tilted D20 with respect to the outer cloud.The inner torus surrounds a bright continuum source, associated with the origin of a bipolar ionized gas outow, and has HCO`(J \ 1 ] 0) optical depth greater than 14.Chemical abundances in the inner torus are azimuthally asymmetric, possibly due to di erential impact of the ionized outow on the inner region of the torus.Comparison with a kinematic radiative transfer model conrms that the torus is rotating and the rotation axis of the inner torus is aligned with the ionized outow.While the cloud is not in solid body rotation, the rotational velocity of material in the cloud increases with radius.We estimate molecular abundance ratios by comparison with high-resolution dust extinction maps previously obtained at the same spatial resolution.The abundance ratio is [HCO`]/[H 2 ] \ 3.9 ] 10~8 enhanced and falls in the upper range of typically measured values for star formation regions.SiO is likewise enhanced relative to both and to HCO`.The ratio is within the H 2 [SiO]/[H 2 ] \ 3.9 ] 10~10 range observed toward shock-excited regions.The cloud mass is estimated to be Z2600 M _ .
Authors: Eric Howard, D. W. Koerner, J. L. Pipher
DOI: https://doi.org/10.1086/303750
Publish Year: 1997
