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