Photometric studies of the short-period eclipsing binary V1094 Her and MT Cas

Abstract

We obtained three new full BVRI light curves for two eclipsing binaries V1094 Her and MT Cas on nine nights from 2015 to 2018 using two optical telescopes. We analysed the orbital period variations using all available light curve minima, seven of which were from our work. For V1094 Her, we found that there is a cyclic variation overlaying a continuous period decrease. The cyclic variation of V1094 Her may be caused by the light-time effect by a third body of $$P_{3}=13.2(\pm 1.2)$$ yr or magnetic activity cycle with $$T=15.1(\pm 0.8)$$ yr. The decreasing period of V1094 Her can be explained by either mass exchange $${\dot{M}}_{2}=-2.20\times 10^{-7}\; M_{\odot }$$ /yr for a third body or $${\dot{M}}_{2}=-2.03\times 10^{-7}\; M_{\odot }$$ /yr for magnetic activity cycle. We confirmed there exist a period increase for MT Cas. For MT Cas, the secular decrease of period can be explained by the mass exchange $${\dot{M}}_{1}=-1.09\times 10^{-8}\; M_{\odot }$$ /yr (including angular momentum loss of $${\dot{M}}=-5.99\times 10^{-11}\; M_{\odot }$$ /yr). We obtained the orbital parameters for V1094 Her using the Wilson & Devinney program for the first time. For MT Cas, we updated their orbital parameters, which are similar to the results from previous work. We concluded that V1094 Her and MT Cas are contact eclipsing binaries with low contact factors and period variations.