This research was partially supported by the Italian "Ministero per l'Università e la Ricerca Scientifica e Tecnologica" (MURST) and by the EU grant ERBFMMACT980343; by the Deutsche Forschungs Gemeinschaft under travel grant DR 281/8-1; by the Austrian Fonds zur Förderung der wissenschaftlichen Forschung under grant S7304-AST; and by the Chinese National Science Foundation. S.D. would like to thank Ralf Geckeler (University of Tübingen) for providing his excellent CCD-photometry analysis program package as well as Katja Potschmidt (University of Tübingen) for her introduction to the time series analysis package of M. König and for her fruitful discussions. R.S. would like to thank Steven Kawaler (Iowa State University, Ames), Thomas Strauss (Astronomical Observatory of Capodimonte, Naples), Pawel Moskalik (Copernicus Astronomy Center, Warsow) and Scot Kleinman (University of Texas at Austin) for interesting discussions, and Adalberto Piccioni (University of Bologna) for the availability of the Loiano photometer. R.S. and S.D. are grateful to the Vienna Delta Scuti Network Group for their kind hospitality during the short stay in April-May 1998, in which part of this work has been done. The same applies to G.H.'s stay at the University of Tübingen in December 1997.
© European Southern Observatory (ESO) 1999
Online publication: February 23, 1999