Identification of selected sources from the ROSAT Galactic Plane Survey. I.

We report on optical searches in the error circles of 93 \ ROSAT survey sources located at low galactic latitudes (|b| < 20°e ). These sources were extracted from the ROSAT Galactic Plane Survey using various selection criteria on hardness ratio, X-ray and optical brightness and integrated galactic absorption in the direction of the source. We find optical identifications in 76 \ cases, among which are 25 new AGN, 6 new CVs and a new Be/X-ray binary. In order to illustrate the relevance of the source selections applied here, we cross-correlated the ROSAT all-sky survey bright source list with SIMBAD. Different classes of X-ray emitters populate distinct regions of a multi dimensional parameter space involving flux ratios, galactic latitude and N_H. This relatively good segregation offers the possibility to build source samples with enhanced probability of identification with a given class. Complete optical identification of such subsamples could eventually be used to compute meaningful probabilities of identification for all sources using as basis a restricted set of multi-wavelength information. Partly based on observations obtained at the European Southern Observatory, La Silla (Chile) with the 2.2~m telescope of the Max-Planck-Society, with the ESO 1.5~m telescope and at the Observatoire de Haute-Provence, CNRS, France.}\fnmsep\thanks{Figures 8, 9 and 10 are only available in the electronic version. Tables 4 and 5 are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html