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Astron. Astrophys. 337, 39-42 (1998) AcknowledgementsThis project was supported partially by the grant A-02-049 of ESO C&EE Programme and the grant of the Bulgarian National Foundation. I am grateful to Dr. A. Aparicio and Dr. Yu. Efremov for their constructive suggestions which improved this paper. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: August 6, 1998 ![]() |