H$_2$O maser emission associated with the planetary nebula IRAS 16333$-$4807

TL;DR

This study confirms IRAS 16333-4807 as a rare planetary nebula with associated H$_2$O maser emission, supporting the idea that such masers occur during a brief bipolar phase in nebula evolution.

Contribution

First unambiguous spatial association of H$_2$O masers with a planetary nebula, confirming IRAS 16333-4807 as the fifth known H$_2$O maser-emitting PN and highlighting its bipolar nature.

Findings

IRAS 16333-4807 is confirmed as a H$_2$O maser-emitting planetary nebula.

H$_2$O masers are spatially associated with IRAS 16333-4807's radio emission.

IRAS 12405$-$6219 is identified as an H II region, not a PN.

Abstract

We present simultaneous observations of H$_2$O maser emission and radio continuum at 1.3 cm carried out with the Australia Telescope Compact Array towards two sources, IRAS 16333$-$4807 and IRAS 12405$-$6219, catalogued as planetary nebula (PN) candidates, and where single-dish detections of H$_2$O masers have been previously reported. Our goal was to unambiguously confirm the spatial association of the H$_2$O masers with these two PN candidates. We detected and mapped H$_2$O maser emission in both fields, but only in IRAS 16333$-$4807 the maser emission is spatially associated with the radio continuum emission. The properties of IRAS 16333$-$4807 provide strong support for the PN nature of the object, hereby confirming it as the fifth known case of a H$_2$O maser-emitting PN. This source is bipolar, like the other four known H$_2$O maser-emitting PNe, indicating that these sources might pertain to a usual, but short phase in the evolution of bipolar PNe. In IRAS 12405$-$6219, the H$_2$O maser and radio continuum emission are not associated with each other and, in addition, the available data indicate that this source is an H II region rather than a PN.