We present the first results of a systematic identification programme of ROSAT all-sky survey sources in the galactic plane. The test region analyzed in this paper was chosen to be typical of deep plane conditions. Centered at l = b = it contains 128 sources above a maximum likelihood of 8 in a area. The overall log N( S)-log S function is fully consistent with that derived from the Einstein galactic plane surveys having similar X-ray sensitivity (Hertz & Grindlay 1984) and with the results of deep ROSAT pointings (Morley et al. 1996). Thanks to a high completeness of optical identifications we are in a position to discuss the relative contributions of various kinds of X-ray sources. An overwhelming fraction of X-ray sources are identified with late type active coronae. Our identified sample exhibits the X-ray luminosity distribution expected in a flux limited survey and we detect F-G stars up to 300 pc while M stars are not found beyond 100 pc. X-ray count models account satisfactorily both for the observed log N( S)-log S relation and for the distribution in spectral types and suggest that most of the stars detected by ROSAT in this low latitude region are probably younger than 1 Gyr. We also put strong constraints on the possible contributions of old neutron stars accreting from the interstellar medium and discuss the possible implications of our results.
© European Southern Observatory (ESO) 1997
Online publication: July 8, 1998