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Astron. Astrophys. 351, 701-706 (1999) AcknowledgementsThis work has been funded by the Swiss National Science Foundation under grant 7UKPJ048440. We thank A.S. Gadun for helpful discussions and R.J. Rutten for valuable comments on the manuscript.
© European Southern Observatory (ESO) 1999 Online publication: November 3, 1999 ![]() |