We are grateful to R. Beck for numerous helpful discussions and critical reading of the manuscript. A generous assistance of G. Breuer is gratefully acknowledged. We thank S. Sukumar for useful suggestions which improved the presentation of results. A.D.P., A.S. and D.D.S. acknowledge financial support of the Russian Foundation for Basic Research under grants No. 93-02-3638, 95-02-03724 and 96-02-16252 and the International Science Foundation under grant MNP000/300. A.D.P., A.S. and D.D.S. are grateful to R. Wielebinski for hospitality at the Max-Planck-Institut für Radioastronomie (Bonn). A.D.P., A.S., D.D.S., M.K., and N.N. thank the Deutsche Forschungsgemeinschaft and the Russian Academy of Sciences for financial support during mutual visits.
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998