A selection of hot subluminous stars in the GALEX survey - I. Correlation with the Guide Star Catalog

• Published in: Monthly notices of the Royal Astronomical Society 2011-01, Vol.410 (3), p.2095-2112
• Main Authors: Vennes, S., Kawka, A., Németh, P.
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; stars: fundamental parameters; subdwarfs; ultraviolet: stars; white dwarfs
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2010.17584.x

We assembled a catalogue of bright, hot subdwarf and white dwarf stars extracted from a joint ultraviolet, optical and infrared source list. The selection is secured using colour criteria that correlate well with effective temperatures T eff≳ 12 000 K. We built a N UV− V versus V − J diagram for ≳60 000 bright sources using the Galaxy Evolution Explorer (GALEX) N UV magnitude (N UV < 14), the associated Guide Star Catalog (GSC2.3.2) photographic quick-V magnitude and the Two-Micron All-Sky Survey J and H magnitudes. This distillation process delivered a catalogue of ≈700 sources with N UV− V < 0.5 comprising ∼160 known hot subdwarf stars and another ∼60 known white dwarf stars. A reduced proper-motion diagram built using the proper-motion measurements extracted from the Naval Observatory Merged Astrometric Dataset allowed us to identify an additional ∼120 new hot subdwarf candidates and ∼10 hot white dwarf candidates. We present a spectroscopic study of a subset of 52 subdwarfs, 48 of them analysed here for the first time, and with nine objects brighter than V ∼ 12. Our sample of spectroscopically confirmed hot subdwarfs comprises 10 sdO-type stars and 42 sdB-type stars suitable for pulsation and binary studies. We also present a study of 50 known white dwarfs selected in the GALEX survey and six new white dwarfs from our catalogue of subluminous candidates. Ultraviolet, optical and infrared synthetic magnitudes employed in the selection and analysis of white dwarf stars are listed in appendix.