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Astron. Astrophys. 317, 701-706 (1997) AcknowledgementsThis work has been supported by continuous grants from the Swiss National Science foundation. J.R.M. and J.D.N.Jr. acknowledge partial financial support from the CNPq Brazilian Agency. We are also grateful to the referee M.H. Pinsonneault for many constructive remarks and suggestions that helped us to improve the original manuscript. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1997 Online publication: July 8, 1998 ![]() |