This research was supported by grant KR 1053/3 from the DFG, Germany, grant 50OR90017 (Verbundforschung Astronomie) from the BMFT, Germany, and from CONACyT, Mexico. The ROSAT project is supported by the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/DARA) and the Max-Planck-Gesellschaft. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998