BIMA Array Observations of the Highly Unusual SiO Maser Source with a Bipolar Nebulosity, IRAS 19312+1950

We report the results of mapping observations of the bipolar nebula with SiO maser emission, IRAS 19312+1950, in the CO (J = 1–0 and J = 2–1), CO (J = 1–0 and J = 2–1), CO (J = 1–0), CS (J = 2–1), SO (JK = 32– 21) and HCO + (J = 3–2) lines with the Berkeley-Illinois-Maryland Association array. Evolutional status of this source has been evoking a controversy since its discovery, though SiO maser sources are usually identified as late-type stars with active mass loss. In line profiles, two kinematical components are found: a broad pedestal component and a narrow component. Spatio-kinetic properties of a broad component region are roughly explained by a simple spherical outflow model with a typical expanding velocity of an AGB star, though some properties still conflict with those of a typical AGB spherical outflow. A narrow component region apparently exhibits a bipolar flow. The angular size of the narrow component region is spatially larger than that of a broad component region. Intensity Current Address: Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei