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

Abstract

ABSTRACT We report the discovery of a handful of optical hydrogen-poor (H-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 ≈6 arcmin or ≈2.4 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 H-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.