Photometric Analysis of Three Potential Red Nova Progenitors

We present photometric analysis of three bright red nova progenitor contact binary systems:ASAS J082151-0612.6,TYC 7281-269-1 and TYC 7275-1968-1.The primary components in all three systems are solar-type low mass stars with radii somewhat larger than their zero age main sequence counterparts.The secondaries,as in most contact binary systems,have radii and luminosities well above their main sequence counterparts.All three have extremely low mass ratios ranging from 0.075 to 0.097 and two have high degrees of contact,in excess of 75%.All three have mass ratios and separations below the theoretical values for orbital stability.Chromospheric activity,a hallmark of magnetic activity and magnetic braking,considered important in mediating angular momentum loss,is also explored.All three systems demonstrate the O’Connell effect,and all systems require the introduction of star spots for a better light curve solution.In addition,we show that ASAS J082151-0612.6 and TYC 7281-269-1 have a UV color excess in the range indicating high chromospheric activity.Another measure of potential significant magnetic activity is X-ray luminosity;TYC 7275-1968-1 and probably also TYC 7281-269-1 have X-ray luminosity well above other contact binary systems.We conclude that it is likely that all three are unstable and hence are potential merger candidates.