A Rare Low-mass Short-period Eclipsing Binary Candidate With A Close-in Non-coplanar Stellar Companion

Abstract

First multi-colour light curves (LCs) of the short-period contact eclipsing binary (CEB) 1SWASP J224747.20-351849.3 (hereafter J2247) are presented and analyzed by using the 2013 version of the Wilson-Devinney (W−D) code in this paper. We found that J2247 was a low-mass W-subtype medium CEB. Third light was detected and the average luminosity contribution (l3/Lall) was as high as 67.89%. Until now, it is the first reported CEB near the period cut-off with so strong third light. Using the O−C (observed-calculated) method, we analyzed its orbital period variations. We found that its O−C diagram shows a secular increase superimposed on a cyclic oscillation. The orbital period increases at a rate of dP/dt = +1.87 × 10−7 days yr−1, which can be explained by the mass transfer from the less massive component to the more massive one. Meanwhile, the O−C diagram also displays a cyclic oscillation with a period about 5.17 years and an amplitude of 0.0032 days, which may due to the light-travel time effect (LTTE) arising from the gravitational influence of a close-in tertiary component. The mass of the additional component is M3sin(i3)=0.24( ± 0.01)M⊙, and the orbital distance between the tertiary component and the central binary is about 2.82( ± 0.05) au. All of these suggest that the third body is not coplanar with the central system, at the same time, the orbital inclination is low. This close-in companion may helps to speed up the formation and evolution of J2247 by drawing angular momentum from the central system.