2013AJ....146...38Q

By analyzing multi-color light curves of the newly discovered W UMa-type binary, MR Com, we discovered that it is a shallow-contact binary with a degree of contact factor of f = 10.0%±2.1%. Photometric solutions reveal that MR Com is a W-type system with a mass ratio of q = 3.9 where the less massive component is about 90 K hotter than the more massive one. By investigating all of the available times of minimum light, we found that the general trend of the Observed-Calculated (O - C) curve shows a downward parabolic variation while it undergoes a cyclic variation with a small amplitude of 0.0031 days and a period of 10.1 yr. The downward parabolic change corresponds to a long-term decrease in the orbital period at a rate of {dot}P = -5.3 x 10^–7 days/yr that may be caused by a combination of a mass transfer and an angular momentum loss (AML) via magnetic braking. Among the 16 shallow-contact systems with a decreasing orbital period, MR Com has the lowest mass ratio (e.g., 1/q = 0.26). The shallow-contact configuration, the low-mass ratio, and the long-term period decrease all suggest that systems similar to MR Com are on the AML-controlled stage of the evolutionary scheme proposed by Qian. They will oscillate around a critical mass ratio and evolve into a deep contact with a higher mass ratio. The small-amplitude cyclic change in the O - C curve was analyzed for the light-travel time effect via the presence of an extremely cool stellar companion.