We thank A.N. Burenkov for his help during spectral observations with the 6m telescope. JAS, VHC and LKE were partially supported by the research grant No 95-02-04024 from the Russian Foundation for Basic Research. We are indebted to G. Kojoian and N. Andreasian for their help in preparing of this article.
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998