Astron. Astrophys. 345, 521-530 (1999)

Acknowledgements

EF, GM and SS acknowledge financial support from MURST (Ministero della Università e della Ricerca Scientifica e Tecnologica). EF thanks the "Università degli Studi di Palermo" for awarding a fellowship. We thank the referee D. Raboud for his useful comments that helped to improve this work.

© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999
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