The Optical Gravitational Lensing Experiment
OGLE #7: Binary Microlens or a New Unusual Variable?

Udalski A., Szymanski M., Mao, S., Di Stefano, R.,
Kaluzny J., Kubiak M., Mateo M., and Krzeminski W.

1994, Astrophys. J. Letters , 436, L103 (ADS).


We present the light curve of an unusual variable object, OGLE No. 7, detected during the OGLE search for microlensing events. After one season of being in a low, normal state, the star brightened by more than 2 mag with a characteristic double-maximum shape, and returned to normal brightness after 60 days. We consider possible explanations of the photometric behavior of OGLE No. 7. The binary microlens model seems to be the most likely explanation -- it reproduces well the observed light curve and explains the observed colors of OGLE No. 7. The characteristic timescale of the OGLE No. 7 event, t(sub E), is equal to 80 days, the longest observed to date. The binary microlens model predicts that the spectrum of the star should be composite, with roughly 50% of its light in the I-band coming from a nonlensed source.