Astron. Astrophys. 347, 583-589 (1999)

Acknowledgements

We would like to thank the referee Dr. Niemela for the very useful suggestions and comments which have helped us to improve the paper significantly. This work has been supported by UNAM/DGAPA grants IN 107094 and 109496, and CONACYT grant 3677P-A9607, ESO C&EE program grant A-05-95 and Bulgarian Science Fundation grant F704/97.

© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999
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