1SWASP J074658.62+224448.5: A LOW MASS-RATIO CONTACT BINARY AT THE PERIOD CUTOFF

The first sets of high-quality light curves of the extremely short period eclipsing binary 1SWASP J074658.62+224448.5 (hereafter J074658) were obtained in 2012 and 2014. The photometric solutions were derived using the 2013 version of the Wilson-Devinney code. Two different modes of overcontact binaries were used to analyze the light curves, and the adopted solutions show that J074658 is a shallow contact system (the degree of contact is f = 13.1 +/- 2.1%) with a mass ratio of q= 0.386 +/- 0.017. The two components have very close temperatures, which may indicate that J074658 is in thermal contact. The variation of the orbital period was studied using all the available times of minimum light. According to the O - C diagram, the orbital period of J074658 shows an increase at a rate of P = 5.39 10(-7) days yr(-1) in about an eight-year span. The reasons for the period increase compared with other well-studied contact binaries with extremely short periods are discussed. The period increase may be caused by mass transfer from the less massive component to the more massive one, or it could be only part of a long period cyclic variation that may reveal the presence of a third body. In this paper, the latter is suggested.