IP Lyn: A Totally Eclipsing Contact Binary with an Extremely Low Mass Ratio

Abstract

Abstract We present the first photometric and orbital period investigations for a neglected totally eclipsing contact binary IP Lyn. The photometric solutions derived from both ground-based and several surveys’ observations suggest that it is a shallow contact binary with an extremely low mass ratio of 0.055. The weak asymmetry observed in our multiple band light curves can be interpreted as a result of an active cool spot on the primary. The absolute physical parameters were determined with the Gaia-distance-based method and checked by an empirical relation. Combining the eclipse timings collected from the literature and those derived from our and variable surveys’ observations, we find that IP Lyn has been undergoing a secular orbital period increase for the past two decades, implying a mass transfer from the less massive secondary to the primary. By comparing the current parameters with the critical instability ones, we infer that IP Lyn is currently stable in spite of its relatively low mass ratio and orbital angular momentum. Finally, from a catalog of 117 extremely low mass ratio contact binaries, we find that their orbital angular momenta are significantly lower than those of the contact binaries with a relatively high mass ratio, suggesting they should be at the late evolutionary stage of a contact binary.