No abstract

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 Ñattened 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 outÑow, 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 outÑow on the inner region of the torus. Comparison with a kinematic radiative transfer model conÐrms that the torus is rotating and the rotation axis of the inner torus is aligned with the ionized outÑow. 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.

As part of an ongoing study of high-mass star formation regions, we have imaged the S255-2 triple H II region in near-infrared broadband wavelength bands J (1.23 km), H (1.65 km), K (2.23 km), and at 3.3 km. We have also obtained images in the Brc and Bra hydrogen recombination lines, in the H 2 , v \ 1 ] 0 S(1) line, and in the 3.29 km dust feature emission band. The region consists of a circular core of stars and young stellar objects, as well as nebulosity, and a more di †use stellar cluster. The Brackettline emission from the region is at least a factor of 10 greater than the value estimated from the radio continuum Ñux density, assuming case B recombination. The strongest Bra line emission object is IRS 1b, which appears to be an ionizing wind source. The central core region contains a narrow band of Brc and emission that we postulate is an ionized jet. The 3.29 km and the emission are found in a H 2 H 2 bubble-like region that overlaps and extends beyond the Bra and Brc emission into the photodissociation region. S255-2 appears to be a young cluster of stars still in the process of forming.