We are grateful to J.-C. Hénoux for his illuminating suggestions and to G. Chambe and K.-L. Klein for critical discussions. We would like to thank the `Associazione Specola Solare Ticinese', Switzerland, for its hospitality during the observations. This present work was supported by FAPESP under grants No. 97/00243-6 and 93/03321-7, by the Swiss National Science Foundation under grant No. 20-42265.94 and by the French-Bresilian program of exchange of scientists (CNRS-CNPq contract 4130).
© European Southern Observatory (ESO) 2000
Online publication: April 17, 2000