Maser Properties of the Enigmatic IRAS Source 19312+1950

TL;DR

This study uses VLBI and MERLIN observations of SiO, H2O, and OH masers to investigate IRAS 19312+1950, revealing properties consistent with an evolved star but also showing peculiar features that challenge standard stellar evolution models.

Contribution

The paper provides detailed interferometric maser observations that support the evolved star nature of IRAS 19312+1950, while highlighting unusual features that suggest complex evolutionary status.

Findings

H2O maser emission shows bipolar flow characteristics.

SiO maser emission confirms evolved star properties.

OH maser profile indicates a spherically expanding shell.

Abstract

The IRAS source, 19312+1950, exhibits SiO maser emission, which is predominantly detected in evolved stars enshrouded by a cold molecular envelope. In fact, the mojority of the observational properties of IRAS 19312+1950 is consistent with the nature of an asymptotic giant branch (AGB) star or post-AGB star. Interestingly, however, some of the observational properties cannot be readily explained within the standard scheme of stellar evolution, and those are rather reminiscent of young stellar objects. In the present research we considered the evolutionary status of IRAS 19312+1950 as revealed by the VLBI and MERLIN observations in SiO, H2O and OH maser lines. The double-peaked profile of the 22 GHz H2O maser line is clearly detected, with the emission regions of its red and blue-shifted components separately located, leaving a space of about 10.9 mas between them. The kinematic properties of H2O maser emission region appear to be more consistent with a bipolar flow rather than other interpretations such as the Keplerian rotation of a disk. The red-shifted component of the SiO maser emission, which exhibits a double-peak profile in previous single-dish observations, is clearly detected in the present interferometry, while the 1612 MHz OH maser line exhibits a complicated line profile consisting of a single strong peak and many weak, high-velocity spikes. The structure of OH maser emission region is partially resolved, and the kinematic properties of the OH maser emission region are reminiscent observations of a spherically expanding shell, even though the evidence is scant. Collectively, the maser observations described here provide additional support for the evolved star hypothesis for IRAS 19312+1950.