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Astron. Astrophys. 339, 537-544 (1998) AcknowledgementsSM acknowledges financial support from the DARA under grant 50 OR 96029-ZA. We want to thank the referee Dr. P. Dufton for his valuable advice. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: October 21, 1998 ![]() |