We thank our colleagues Drs. P. Hadrava, K. Pavlovski and S. K and Messrs. D. ikoti and J. Honsa who obtained some of the observations used here, and Dr. D. Holmgren for a careful proofreading and some interesting suggestions. The use of the computerized bibliography from the Strasbourg Astronomical Data Centre is also gratefully acknowledged. This research was supported from the grant 205/96/0162 of the Grant Agency of the Czech Republic to PH and from project K1-003-601/4 of the Academy of Sciences of the Czech Republic.
© European Southern Observatory (ESO) 1998
Online publication: January 8, 1998