A circular planetary nebula around the OH/IR star OH 354.88-0.54 (V1018 Sco)

Abstract

New deep, high-resolution Ha imagery from the UK Schmidt Telescope (UKST) Unit's Ha survey of the Southern Galactic Plane reveals the presence of a faint, highly circular, planetary nebula (PN) surrounding a very long-period variable star (now known as V1018 Sco), first discovered as a 1612-MHz OH maser, OH 354.88-0.54. The nebular phase-lag distance, diameter and radial velocity are 3.2 kpc, 0.3 pc and 13 km s -1, respectively. Combining the maser attributes with near-, mid- and far-infrared data and with our optical spectrum of the ring we conclude that the object was an intermediate-mass asymptotic giant branch (AGB) star (initial stellar mass ≥ 4M⊙) in which the fast wind has recently turned on, ionizing previously shed circumstellar material. Hence, we speculate that we may be witnessing a hitherto unobserved phase of PN evolution, in which a PN has only recently started to form around a star that is unequivocally still in its AGB phase. © 2005 RAS.