Detection of bipolar flow toward the unusual SiO maser source IRAS 19312+1950

Abstract

We report results of an interferometric observation toward an SiO maser source, IRAS 19312+1950, in the HCO + J = 1-0 line with the Berkeley-Illinois-Maryland Association millimeter array. In the spatially integrated spectrum of HCO +, two kinematic components were seen: a strong line with a narrow width (∼2 km s -1, narrow component) and a weak symmetric line with a broad width (∼60 km s -1, broad component). The line profile of HCO + is reminiscent of that of CO. In the integrated intensity map, we found a pronounced bipolar shape consisting of the lower velocity part of the broad component. The higher velocity part of the broad component originated in a relatively small region (≲3″). The spatial structure of the narrow component clearly correlates with near-infrared structure. The position-velocity diagrams indicate the presence of a bipolar outflow with an expansion velocity of about 10 km s -1. On the basis of the present results, we suggest that the nature of the bipolar flow seen in IRAS 19312+1950 is explained by the hydrodynamical interaction between an asymptotic giant branch wind and ambient material with axial symmetric structure.