2016ApJ...825...16N

We report the results of wide field CO mapping in the region of IRAS 19312+1950. This Infrared Astronomical Satellite (IRAS) object exhibits SiO/H₂O/OH maser emission, and is embedded in a chemically rich molecular component, the origin of which is still unknown. In order to reveal the entire structure and gas mass of the surrounding molecular component for the first time, we have mapped a wide region around IRAS 19312+1950 in the ¹²CO J=1-0, ¹³CO J=1-0 and C¹⁸O J=1-0 lines using the Nobeyama 45 m telescope. In conjunction with archival CO maps, we investigated a region up to 20' x 20' in size around this IRAS object. We calculated the CO gas mass assuming local thermal equilibrium, the stellar velocity through the interstellar medium assuming an analytic model of bow shock, and the absolute luminosity, using the latest archival data and trigonometric parallax distance. The derived gas mass (225 M_☉-478 M_☉) of the molecular component and the relatively large luminosity (2.63 x 10⁴ L) suggest that the central SiO/H₂O/OH maser source is a red supergiant rather than an asymptotic giant branch (AGB) star or post-AGB star.