A deep, unusual over-contact binary system with high rate of mass transfer: LP Ursa Major

Abstract

Abstract We observed the well-known unusual deep over-contact binary in 2012 and 2013. A new set of light curves and eight new observed times of light minima were derived. A total of 130 available CCD times of light minima were analyzed. The highest rate of long-term period increase in W UMa stars (+10.21 s century−1) was confirmed. The rapid period increase implies that the primary is accreting mass from the secondary at a high rate of $\skew4\dot{M} = 5.3 \times 10^{-6}\,M_{\odot }\:$yr−1. The asymmetric light curves (i.e., the O'Connell effect) were analyzed with the Wilson–Devinney Code. It was found that the spotted photometric solution with the third light is the best one for fitting the light curves. The main photometric results confirmed that LP UMa is an unusual W UMa system with a high mass ratio (q = 0.823 ± 0.003), deep-contact configuration (f = 66.6% ± 3.1%), and a temperature difference of Δ T = 700 K. The period increase in LP UMa may be a part of a long-period cyclic change because of the large third light contributions to the total system (61.52% in V, 61.39% in R, and 61.36% in I). All of these quite different properties make LP UMa a very interesting system to study. The possible evolutionary stage is also discussed.