WR 72: a born-again planetary nebula with hydrogen-poor knots

TL;DR

This paper reports the discovery of hydrogen-poor knots in a planetary nebula around WR 72, suggesting a rare evolutionary phase possibly caused by a late thermal pulse or white dwarf merger.

Contribution

First identification of hydrogen-poor knots in a planetary nebula around WR 72, expanding understanding of late stellar evolution.

Findings

Hydrogen-poor knots are present in the nebula around WR 72.

The nebula has a circular halo and bipolar inner shell.

WR 72 is a rare hydrogen-poor planetary nebula.

Abstract

We report the discovery of a handful of optical hydrogen-poor knots in the central part of an extended infrared nebula centred on the [WO1] star WR 72, obtained by spectroscopic and imaging observations with the Southern African Large Telescope (SALT). Wide-field Infrared Survey Explorer (WISE) images of the nebula show that it is composed of an extended almost circular halo (of $\approx6$ arcmin or $\approx2.4$ pc in diameter) and an elongated and apparently bipolar inner shell (of a factor of six smaller size), within which the knots are concentrated. Our findings indicate that WR 72 is a new member of the rare group of hydrogen-poor planetary nebulae, which may be explained through a very late thermal pulse of a post-AGB star, or by a merger of two white dwarfs.