KIC 5621294: an Algol Type Eclipsing Binary With a Circumbinary Brown Dwarf

The Kepler Eclipsing System KIC 5621294 and its Substellar Companion

Authors:

Lee et al

Abstract:

We present the physical properties of KIC 5621294 showing light and timing variations from the Kepler photometry. Its light curve displays partial eclipses and O'Connell effect with Max II fainter than Max I, which was fitted quite well by applying third-body and spot effects to the system. The results indicate that the eclipsing pair is a classical Algol-type system with parameters of q=0.22, i=76∘.8, and Δ(T1--T2)=4,235 K, in which the detached primary component fills about 77\% of its limiting lobe. Striking discrepancies exist between the primary and secondary eclipse times obtained with the method of Kwee \& van Woerden. These are mainly caused by surface inhomogeneities due to spot activity detected in our light-curve synthesis. The 1,253 light-curve timings from the Wilson-Devinney code were used for a period study. It was found that the orbital period of KIC 5621294 has varied due to a periodic variation overlaid on a downward parabola. The sinusoidal variation with a period of 961 d and a semi-amplitude of 22.5 s most likely arise from a light-time effect due to a third component with a mass of M3sini3=46.9 MJup, which is in good agreement with that calculated from the light curve itself. If its orbital inclination is larger than about 40∘, the mass of the circumbinary object would possibly match a brown dwarf. The parabolic variation could not be fully explained by either a mass transfer between the binary components or an angular momentum via magnetic braking. It is possible that the parabola may only be the observed part of a period modulation caused by the presence of another companion in a wider orbit.