Discovery of a 26.5-day optical periodicity of LSI + 61°303

Abstract

Observations obtained between December 1984 and February 1987 reveal an optical periodic modulation of the highly variable radio binary star LSI+61 deg 303. The modulation has a period of about 26.5 d, an amplitude of about 0.05 mag, and includes 'high' and 'low' states. The optical period and light curve are found to be similar to those observed in the radio regime. The binary is modeled under the assumption that the excess luminosity of the 'high' state is produced by some periodic mechanism. Two mechanisms for the 'high' state are considered, synchrotron radiation and the heating of the inner part of the accretion disk around a compact object.