We thank N. Fourniol, P. Guillout and the night assistants at Observatoire de Haute-Provence for carrying out some of the observations at the 1.2 m and 1.93 m telescope. We also thank S.A. Golçalves and R.D.A. da Costa for carrying out some of the observations at the 1.6 m of L.N.A. The ROSAT project is supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/DARA) and the Max-Planck-Gesellschaft. C.M. acknowledges support from a CNRS-MPG cooperation contract and thanks Prof. J. Trümper and the ROSAT group for their hospitality and fruitful discussions. We acknowledge detailed and useful comments from an anonymous referee. GSC data were extracted from the STARCAT facility at ESO (Pirenne et al. 1993) and later from the SIMBAD catalogue GSC browser (Preite-Martinez & Ochsenbein 1993). This research has made large use of the SIMBAD database operated at CDS, Strasbourg, France.
© European Southern Observatory (ESO) 1997
Online publication: May 26, 1998