The peculiar molecular envelope around the post-AGB star IRAS 08544--4431

TL;DR

This study presents high-resolution observations of molecular emission around the binary post-AGB star IRAS 08544-4431, revealing a resolved envelope with a central component and bipolar outflow, contributing to understanding circumbinary disks.

Contribution

It provides detailed imaging and analysis of the molecular envelope structure around IRAS 08544-4431, highlighting the presence of a central component and bipolar outflow, advancing knowledge of post-AGB circumstellar environments.

Findings

Resolved molecular envelope with narrow linewidths

Detection of a bipolar outflow with expansion velocity up to 8 km/s

Estimated molecular gas mass of 0.0047 solar masses

Abstract

Circumbinary disks have been hypothesized to exist around a number of binary post-AGB stars. Although most of the circumbinary disks have been inferred through the near IR excess, a few of them are strong emitters of molecular emission. Here we present high angular resolution observations of the emission of $^{12}$CO and its isotopomer $^{13}$CO J=2--1 line from the circumstellar envelope around the binary post-AGB star IRAS 08544$-$4431, which is one of the most prominent members of this class of objects. We find that the envelope is resolved in our observations and two separate components can be identified: (a) a central extended and strong component with very narrow linewidth between 2 - 6 \kms; (b) a weak bipolar outflow with expansion velocity up to 8 \kms. The central compact component possesses low and variable $^{12}$CO/$^{13}$CO J=2--1 line ratio, indicating optically thick emission of the main isotope. We estimate a molecular gas mass of 0.0047 M$_\odot$ for this component based on the optically thinner $^{13}$CO J=2--1 line. We discuss the relation of the molecular envelope and the circumbinary disk inferred from near IR excess and compare with other known cases where the distribution of molecular gas has been imaged at high angular resolution.