Authors are thankful to Drs. G.-L. Hildebrandt, M. Steffen, I. Hubeny and F. Herwig for kind assistance with the necessary software installation. Special thanks to Drs. F. Kupka and S.A. Korotin for the NLTE calculations and computation of the atmosphere models for helium deficient stars, to Dr. F. Kienzle for providing unpublished photometric data for one of the program stars, and to anonymous referee for several useful comments. SMA is also grateful to the Astrophysikalisches Institut of Potsdam (Germany) for the financial support and the opportunity to perform this work using its institutional facilities. The necessary information has been obtained through the SIMBAD and VALD data bases.
© European Southern Observatory (ESO) 2000
Online publication: April 10, 2000