The absolute properties and evolutionary state for the shortest period field contact binary GSC 1387-0475

CCD photometric observations of the shortest period field contact binary, GSC 1387-0475, obtained in the observing season in 2008-2009, are presented. From new observations, eleven light minimum times were derived and the orbital period was revised. The light curves in BVR bands were analyzed using the W-D program. It is found that GSC 1387-0475 is an overcontact binary. The derived absolute physical parameters of this binary are: Mp=0.443(±0.004)M⊙, Ms=0.210(±0.003)M⊙,Rp=0.658(±0.008)R⊙,Rs=0.496(±0.011)R⊙,Lp=0.188(±0.005)L⊙, and Ls=0.090(±0.004)L⊙. From the LogL-LogM diagram, the primary component is found to be an evolved star. The additional component of GSC 1387-0475 may remove angular momentum from the central system. With the angular momentum decreasing, the separation between components may decrease, which will cause the inner and out critical Roche lobes to shrink, resulting in an increase degree of overcontact. Finally, GSC 1387-0475 with a deep overcontact degree (i.e., f=76.3±2.9%) may evolve into a rapid-rotating single star.