The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources – I. The Bright Source Catalogue

The first all-sky survey for cosmic sources of extreme-ultraviolet radiation has been carried out with the UK Wide Field Camera on ROSAT. A first reduction of the survey data has yielded a catalogue of 383 relatively bright EUV sources, forming the WFC Bright Source Catalogue. This represents a 30-fold increase in the number of astrophysical objects detected in the ~ 60–200 eV energy band and covers a flux range, in each of the two survey bands, of more than 2000. A search of the (typically ~ 1-arcmin) error circles of the WFC sources, using a variety of catalogues and the SIMBAD data base, has identified probable optical counterparts of ~ 73 per cent, including many active stars, white dwarf stars and a variety of other galactic and extragalactic objects. A follow-up programme of optical spectroscopy has since added further identifications, but some 13 per cent of the EUV sources remain unidentified.