Water maser detections in southern candidates to post-AGB stars and Planetary Nebulae

TL;DR

This study investigates water maser emissions in post-AGB stars and planetary nebulae, discovering new masers and proposing an evolutionary scenario for maser development through these stellar stages.

Contribution

It reports the first detection of a water fountain maser in a planetary nebula candidate and develops a new evolutionary model for water masers in late stellar evolution.

Findings

Four new water masers detected, all in obscured sources.

Water fountain masers identified in a PN candidate, IRAS 15103-5754.

Obscured sources with massive envelopes favor water maser presence.

Abstract

We intended to study the incidence and characteristics of water masers in the envelopes of stars in the post-AGB and PN evolutionary stages. We have used the 64-m antenna in Parkes (Australia) to search for water maser emission at 22 GHz, towards a sample of 74 sources with IRAS colours characteristic of post-AGB stars and PNe, at declination $< -32 \deg$. In our sample, 39% of the sources are PNe or PNe candidates, and 50% are post-AGB stars or post-AGB candidates. We have detected four new water masers, all of them in optically obscured sources: three in PNe candidates (IRAS 12405-6219, IRAS 15103-5754, and IRAS 16333-4807); and one in a post-AGB candidate (IRAS 13500-6106). The PN candidate IRAS 15103-5754 has water fountain characteristics, and it could be the first PN of this class found. We confirm the tendency suggested in Paper I that the presence of water masers in the post-AGB phase is favoured in obscured sources with massive envelopes. We propose an evolutionary scenario for water masers in the post-AGB and PNe stages, in which ``water fountain'' masers could develop during post-AGB and early PN stages. Later PNe would show lower velocity maser emission, both along jets and close to the central objects, with only the central masers remaining in more evolved PNe.