New Period Investigation of Algol-like Near-Contact Binary EG Cephei

Abstract

Abstract The Algol-like Near Contact Binary EG Cephei was observed in 2008 October. One new observed time of the secondary minimum was derived in $BV(IR)_{\rm c}$ bands. It turns out that the times of minima at longer wavelengths occur earlier than the shorter ones. All of the available eclipse times, including 735 epochs, spanning more than 100 years were analyzed. A period oscillation with a period of 35.8($\pm$0.1)yr and an amplitude of about 0.0037($\pm$0.0002)d was found, while undergoing a secular increase at a rate of $dP/dt$$=$ 3.4 $\times$ 10$^{-8}$($\pm$0.1)dyr$^{-1}$. This continuous period increase may be caused by mass transfer from the secondary component to the primary one on a thermal timescale, which is consistent with the Algol-like semi-detached configuration of EG Cep. Combining with the spectroscopic and photometric results, we derived a conservative mass-transfer rate of this target, $dM/dt$$=$ 3.0($\pm$0.1) $\times$ 10$^{-8}M_{\odot}$yr$^{-1}$. The oscillation part of the period variation may be the result of a light-time effect due to the existence of a coplanar additional body with a mass of $M_{3}$$=$ 0.11$M_{\odot}$, and a corresponding radius of $a_{3}$$=$ 14AU. The presumed third body may play an important role in the evolution of this system.