R.D. would like to thank I. Tuominen for his support, I. Ilyin for his advice during data reduction and S. Berdyugina for her help with the calculation of the model spectra. He thanks the staff of the Astronomical Institute in Sofia and at the Rozhen observatory for the pleasant atmosphere and their effort to make the observations a success under very difficult conditions. Finally, we would like to thank the referee, Barry Smalley, for his fast and careful reading of the manuscript and his valuable suggestions to improve the text. The observations were financially supported by the Academy of Finland and the Bulgarian Academy of Sciences.
© European Southern Observatory (ESO) 1997
Online publication: March 26, 1998