This work has been carried out as part of a DFG project (ref. Se 420/12-1). We are indebted to P.P. Eggleton (IoA Cambridge, UK) for his permission and help to use his evolutionary code in the most up-to-date version. The IoA supported that collaboration by additional travel money and their kind hospitality. The author also wishes to thank O. Pols (IAC, Tenerife), E. Novotny (IoA) and especially E. Sedlmayr (TU Berlin) for many valuable discussions on the topic of this paper and its motivation. The ease of accessing the Hipparcos data through the Strasbourg astronomical data centre (CDS) was very much appreciated.
© European Southern Observatory (ESO) 1998
Online publication: June 2, 1998