We would like to thank our referee, Dr. R.O. Gray for his valuable comments. EP and WWW acknowledge support from the Fonds zur Förderung der wissenschaftlichen Forschung, project S7303-AST, Asteroseismology-AMS . Use was made of the Simbad, operated at CDS, Strasbourg, France.
© European Southern Observatory (ESO) 2000
Online publication: March 21, 2000