Session 20 - Molecular Clouds, Dense Cores, and Protostars.
Display session, Monday, January 15
North Banquet Hall, Convention Center

## [20.11] The Dense Gas Toroid Surrounding the K3-50A Ionized Bipolar Outflow

E. M. Howard (U. Rochester), D. Koerner (JPL), J. L. Pipher (U. Rochester)

We present high spatial resolution, aperture synthesis images of K3-50A as part of an on-going study of high mass star formation regions. Maps in the HCO^+ (J = 1\rightarrow0), H^13CO^+ (J = 1\rightarrow0), and SiO (v = 0, J = 2\rightarrow1) emission lines at \sim 2.''5 resolution reveal a torus of dense molecular gas \sim 1.1pc in extent. The torus surrounds a bright continuum source, associated with the origin of a bipolar ionized gas outflow, and has HCO^+(1\rightarrow0) optical depth greater than 10. Comparison with a kinematic radiative transfer model confirms that the torus is rotating. 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 [HCO^+]/[H_2] = 3.9\times 10^-8, is enhanced, and falls in the upper range of typically measured values for star formation regions. SiO is likewise enhanced relative to both H_2 and to HCO^+. The ratio [SIO]/[H_2] = 3.9\times 10^-10 is consistent with that observed toward shock-excited regions. The cloud mass is estimated to be greater than 2500 M_ødot.