PHL 932: When is a planetary nebula not a planetary nebula?

Abstract

The emission nebula around the subdwarf B (sdB) star PHL 932 is currently classified as a planetary nebula (PN) in the literature. Based on a large body of multi-wavelength data, both new and previously published, we show here that this low-excitation nebula is in fact a small Störmgren sphere (Hii region) in the interstellar medium around this star. We summarise the properties of the nebula and its ionizing star, and discuss its evolutionary status. We find no compelling evidence for close binarity, arguing that PHL 932 is an ordinary sdB star. We also find that the emission nebulae around the hot DO stars PG 0108 + 101 and PG 0109 + 111 are also Störmgren spheres in the ISM, and along with PHL 932, are probably associated with the same extensive region of high-latitude molecular gas in PiscesPegasus. © Astronomical Society of Australia 2010.