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

¹ Observatoire Astronomique, UMR 7550 CNRS, 11 rue de l'Université, F-67000 Strasbourg, France
² Max-Planck-Institut für extraterrestrische Physik, D-85740, Garching bei München, Germany
³ Landessternwarte, D-69117 Heidelberg-Königstuhl, Germany
⁴ Universitäts-Sternwarte, Geismarlandstrasse 11, D-37083, Göttingen, Germany

Send offprint request to: C. Motch

Received: 9 December 1997
Accepted: 30 April 1998

Abstract

We report on optical searches in the error circles of 93 ROSAT survey sources located at low galactic latitudes ( < 20° ). 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.