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Astron. Astrophys. 338, 599-611 (1998) AcknowledgementsThe author would like to express his thanks to Horst Drechsel for reading the manuscript and commenting on it and the referee, Hans Martin Schmid, for valuable comments. This research has been supported through the Alexander von Humboldt foundation. The author acknowledges the hospitality of the Astronomical Institute, University of Erlangen-Nürnberg, in Bamberg.
© European Southern Observatory (ESO) 1998 Online publication: September 14, 1998 ![]() |