A search for new emission nebulae from the SHASSA and VTSS surveys

Abstract

As an adjunct to the planetary nebula (PN) search from the AAO/UKST Ha survey, a visual search was conducted for new emission nebulae from the SHASSA and VTSS surveys, outside a Galactic latitude of \b| = 10°. Fifteen new objects were found from SHASSA and three from the available fields of VTSS. With one exception, all objects are >5′ across, as smaller nebulae are confused with large numbers of artifacts and compact emitters on these surveys. All previously known PNe larger than this size in the search area, as well as Hewett 1, PG 0108, and PG 0109 were recovered in this blind search. Candidates were selected as discrete, morphologically symmetric Ha enhancements, to differentiate them from the ubiquitous diffuse emission structure of the ISM. These criteria were relaxed for the VTSS survey due to its poorer inherent resolution. Most of the new discoveries are probable Stromgren spheres in the ISM. Some show unusual line ratios (e.g. strong [O III] or [N II] emission) based on slit spectroscopy and WHAM data (see Madsen et al. 2006, this volume), suggesting these are ionised by a hot subdwarf or white dwarf star, and may be possible PNe. Our most interesting discovery is a rare bowshock nebula around a bright, previously unnoticed, nova-like cataclysmic variable. © 2006 International Astronomical Union.