YY Geminorum. I - Photometry and absolute dimensions

Abstract

Over 2000 photoelectric observations in V, R, and I of YY Geminorum (dM1e+dM1e) from six nights in 1971 were analyzed. There is evidence of a period increase since 1950. Secondary variations were detected between phases 0.52 and 0.90. It is suggested that the secondary variations are the result of a starspot on the secondary rather than on the primary, as was reported by Kron (1952). A photometric solution was derived, and the absolute dimensions for both components were determined by combining the photometric solution and the spectroscopic solution of Bopp (1974). The effective temperature calculated from the luminosities derived from parallax and radii were higher by about 200 K than the value indicated by Johnson's (1966) infrared color-temperature calibration for lower-main-sequence stars.