J. Kerp thanks the Deutsche Forschungsgemeinschaft for support under grant No. ME 745/17-2. J. Pietz thanks the Deutsche Argentur für Raumfahrtangelegenheiten for support under grant No. 40012. The ROSAT project has been supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) and by the Max-Planck-Gesellschaft. We thank K.S. de Boer and the anonymous referee for comments based on careful readings of the manuscript.
© European Southern Observatory (ESO) 1999
Online publication: December 22, 1998