Astron. Astrophys. 324, 161-176 (1997)

Acknowledgements

This work has been supported by the Instituto de Astrofísica de Canarias (IAC) and by the Spanish DGES through project PB 95-0028. It has also been partly supported by the European Space Agency through an external fellowship at the Kiepenheuer-Institut für Sonnenphysik, and by the U.S. Department of Energy. We are also grateful to Dr. Oskar Steiner for useful discussions during the early stages of this investigation and to the referees, Drs. Petr Heinzel and Jiri Kubat, for their careful reading of the paper.

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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