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Astron. Astrophys. 318, 687-699 (1997) AcknowledgementsWe thank Achim Weiss for carefully reading, and very useful comments on our manuscript and an anonymous referee for his very constructive comments which helped improving the presentation. This work was supported by the "Sonderforschungsbereich 375-95 für Astro-Teilchenphysik" der Deutschen Forschungsgemeinschaft. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1997 Online publication: July 3, 1998 ![]() |