We are thankful to M. Nalezyty for his cooperation in observations. Special thanks to Janusz Kaluzny and Krzysztof Stanek for their fruitful comments. We would like to thank the Warsaw University Observatory for the observing time allocation. This work was supported from the grants KBN 2 P03D 024 09 and 2 P03D 010 15.
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999