We are grateful to J. Trümper and W. Wamsteker for granting the numerous target of opportunity observations with ROSAT and IUE. We thank Janet A. Mattei for providing recent AAVSO observations of AG Dra, M. Friedjung for discussions on AG Dra properties and D. Schönberner and T. Blöcker for details on the expansion/contraction rate of small core-mass stars. We also thank the referee J. Mikolajewska for a careful reading of the manuscript and helpful comments. JG is supported by the Deutsche Agentur für Raumfahrtangelegenheiten (DARA) GmbH under contract FKZ 50 OR 9201. RV is partially supported by the Italian Space Agency under contract ASI 94-RS-59 and is grateful to Dr. Willem Wamsteker for hospitality at the IUE Observatory of ESA at Villafranca del Castillo (VILSPA). RES thanks NASA for partial support of this research through grants NAG5-2103 (IUE) and NAG5-2094 (ROSAT) to the University of Denver. The ROSAT project is supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/DARA) and the Max-Planck-Society.
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998