Publications of the Astronomical Society of Australia Publications of the Astronomical Society of Australia Society
Publications of the Astronomical Society of Australia
RESEARCH ARTICLE

PHL 932: When Is a Planetary Nebula Not a Planetary Nebula?

David J. Frew A B E , Greg J. Madsen C , Simon J. O’Toole D and Quentin A. Parker A D
+ Author Affiliations
- Author Affiliations

A Department of Physics, Macquarie University, NSW 2109

B Perth Observatory, Bickley, WA 6076

C Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006

D Anglo–Australian Observatory, PO Box 296, Epping, NSW 1710

E Corresponding author. Email: dfrew@physics.mq.edu.au

Publications of the Astronomical Society of Australia 27(2) 203-209 https://doi.org/10.1071/AS09043
Submitted: 20 July 2009  Accepted: 7 October 2009   Published: 31 May 2010

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 Strömgren 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 Strömgren spheres in the ISM, and along with PHL 932, are probably associated with the same extensive region of high-latitude molecular gas in Pisces–Pegasus.

Keywords: Hii regions — ISM: clouds — planetary nebulae: general — stars: horizontal-branch — stars: individual (PHL 932) — subdwarfs


Acknowledgments

D.J.F. gratefully acknowledges Macquarie University for a research scholarship, and also the Government of Western Australia for additional financial support. This study used data from the Wisconsin H-Alpha Mapper (WHAM), which was produced with support from the National Science Foundation through grant AST-0607512, and data from the Southern Hα Sky Survey Atlas (SHASSA), which was also produced with support from the National Science Foundation. This research has made use of the SIMBAD database, operated at the CDS, Strasbourg, France. Data products from the Two Micron All Sky Survey (2MASS) were also utilised, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. We also thank the support staff at the Anglo-Australian Observatory for assistance in observing with SPIRAL, and the anonymous referee for a careful reading of the manuscript.


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1 Méndez et al. (1988) classified the star as ‘late sdO’ (or sdOB) based on their detection of Heii λ4686 in absorption.

2 In the direction of PHL 932, vLSR = vhelio – 1.6 km s–1.

3 Deep Hα and [Nii] images taken by C.-T. Hua with the OHP 1.2-metre reflector show a non-limb brightened, irregular nebulosity with apparent dust lanes. The morphology is consistent with the nebula being a small Hii region. See http://www.oamp.fr/people/trung/phl932.html.

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