2019PASP..131l4201Y

In this study, new data concerning the EB-type eclipsing binary EG Cas are presented as observed using three telescopes in China. A spectral type of F0V was determined from the low-precision spectrum. By solving the radial velocity and BV light curves, the absolute parameters of this system are preliminarily deduced. The results imply that EG Cas is a semi-detached binary with the secondary star filling its Roche lobe. An unequal height between the light maxima (i.e., <=0.02 mag) of the light curves is modeled with the addition of a magnetic dark spot on the surface of the less-massive component. Analyzing the O - C curve a secular decrease at {dot}P=-1.94(±0.11)×10^–7daysyr^–1 is identified in the orbital period, which corresponds to a mass-loss rate of {dot}M∼-10^–7M_☉yr^–1 in the case of non-conserved evolution of the binary. From the spectral energy distribution, an excess in the infrared occurs in the WISE W4 band, which may be attributed to the circumstellar envelope due to mass loss via the stellar magnetic wind. With the ongoing mass transfer and loss, this kind of F-type near-contact binary will eventually evolve into an A-subtype contact binary, as predicted by the thermal relaxation oscillation theory.