Maser and Infrared Studies of Oxygen-Rich Late/Post-AGB Stars and Water Fountains: Development of a New Identification Method

TL;DR

This study develops a new method combining maser spectra and infrared colours to efficiently identify oxygen-rich late/post-AGB stars and water fountains, leading to the discovery of new sources and improved classification techniques.

Contribution

The paper introduces a novel identification approach using maser and infrared data, enhancing detection of evolved oxygen-rich stars and water fountains compared to previous methods.

Findings

Discovery of a new water fountain candidate IRAS19356+0754.

Detection of high velocity OH maser emission in several objects.

Demonstration that infrared properties can distinguish aspherical from spherical objects.

Abstract

We explored an efficient method to identify evolved stars with oxygen-rich envelopes in the late AGB or post-AGB phase of stellar evolution, which include a rare class of objects - the "water fountains". Our method considers the OH and H2O maser spectra, the near infrared Q-parameters (these are colour indices accounting for the effect of extinction), and far-infrared AKARI colours. Here we first present the results of a new survey on OH and H2O masers. There were 108 colour-selected objects: 53 of them were observed in the three OH maser lines (1612, 1665, and 1667 MHz), with 24 detections (16 new for 1612 MHz); and 106 of them were observed in the H2O maser line (22 GHz) with 24 detections (12 new). We identify a new potential water fountain source, IRAS19356+0754, with large velocity coverages of both OH and H2O maser emission. In addition, several objects with high velocity OH maser emission are reported for the first time. The Q-parameters as well as the infrared [09]-[18] and [18]-[65] AKARI colours of the surveyed objects are then calculated. We suggest that these infrared properties are effective in isolating aspherical from spherical objects, but the morphology may not necessarily be related to the evolutionary status. Nonetheless, by considering altogether the maser and infrared properties, the efficiency of identifying oxygen-rich late/post-AGB stars could be improved.