THE ROTATING GAS TOROID SURROUNDING THE K3-50A IONIZED BIPOLAR OUTFLOW

We present high spatial resolution, aperture synthesis images of K3-50 A as part of an ongoing study of high-mass star formation regions. Map s in the HCO+ (J = 1 --> 0), (HCO+)-C-13 (J = 1, 0), and SiO (upsilon = 0, J = 2 --> 1) emission lines at similar to 2.5 '' resolution revea l both a flattened cloud of dense molecular gas similar to 1.1 pc in e xtent and a newly discovered inner torus similar to 0.5 pc in extent. The axis of the inner torus is tilted similar to 20 degrees with respe ct to the outer cloud. The inner torus surrounds a bright continuum so urce, associated with the origin of a bipolar ionized gas outflow, and has HCO+(J = 1-->0) optical depth greater than 14. Chemical abundance s in the inner torus are azimuthally asymmetric, possibly due to diffe rential impact of the ionized outflow on the inner region of the torus . Comparison with a kinematic radiative transfer model confirms that t he torus is rotating and the rotation axis of the inner torus is align ed with the ionized outflow. While the cloud is not in solid body rota tion, 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 spati al resolution. The abundance ratio [HCO+]/[H-2] = 3.9 x 10(-8) is enha nced and falls in the upper range of typically measured values for sta r formation regions. SiO is likewise enhanced relative to both H-2 and to HCO+. The ratio [SiO]/[H-2] = 3.9 x 10(-10) is within the range ob served toward shock-excited regions. The cloud mass is estimated to be greater than or similar to 22600 M(.).