Searching for OH maser emission towards the MIPSGAL compact Galactic bubbles

TL;DR

This study used radio observations to search for OH maser emission in 169 MIPSGAL compact Galactic bubbles, finding that such masers are rare, suggesting post-AGB stars are uncommon in this sample.

Contribution

First systematic search for OH maser emission in MIPSGAL bubbles, providing insights into their stellar evolution stages and rarity of post-AGB stars.

Findings

Only one confirmed OH maser detection among 169 sources.

OH maser emission is not common in MIPSGAL bubbles.

Post-AGB stars are likely very rare in this sample.

Abstract

We conducted radio observations searching for OH 18-cm maser emission from a sample of 169 unclassified MIPSGAL compact Galactic bubbles. These sources are thought to be the circumstellar envelopes of different kinds of evolved stars. Our observations were aimed at shedding light on the nature of MIPSGAL bubbles, since their characterisation is a fundamental aid for the development of accurate physical models of stellar and Galaxy evolution. The maser emission is observatively linked to the last stages of the life of low- and intermediate-mass stars, which may constitute a significant fraction of the MIPSGAL bubbles. In particular OH masers are usually observed towards post-AGB stars. Our observations were performed with the Green Bank Telescope and, for each source, produced spectra around the four OH 18-cm transitions. The observations were compared with archive interferometer data in order to exclude possible contamination from nearby sources. The main result is that the OH maser emission is not a common feature among the MIPSGAL bubbles, with only one certain detection. We conclude that among the MIPSGAL bubbles the post-AGB stars could be very rare.