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Astron. Astrophys. 331, 535-540 (1998) AcknowledgementsThe work was supported by the RFFI (95-02-6053) and the INTAS (93-3364) grants. The work of S.P. was also supported by the ISSEP. We thank Dr. I.E. Panchenko, the unknown referee and Dr. J. Lequeux, who made a lot of suggestions to improve the article (especially the quality of the language) and Prof. S.R. Pottasch for his help. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: February 16, 1998 ![]() |