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Astron. Astrophys. 332, 314-324 (1998) AcknowledgementsI am grateful to the Alexander von Humboldt Foundation for support of this research and to Prof. M. Stix for valuable discussions and for reading the manuscript. I thank an anonymous referee for comments, which helped to improve the paper. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: March 10, 1998 ![]() |