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Post Info TOPIC: KIC 002856960
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KIC 2856960
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Title: KIC 2856960: the impossible triple star
Author: T.R. Marsh, D.J. Armstrong, P.J. Carter

KIC 2856960 is a star in the Kepler field which was observed by Kepler for 4 years. It shows the primary and secondary eclipses of a close binary of 0.258d as well as complex dipping events that last for about 1.5d at a time and recur on a 204d period. The dips are thought to result when the close binary passes across the face of a third star. In this paper we present an attempt to model the dips. Despite the apparent simplicity of the system and strenuous efforts to find a solution, we find that we cannot match the dips with a triple star while satisfying Kepler's laws. The problem is that to match the dips the separation of the close binary has to be larger than possible relative to the outer orbit given the orbital periods. Quadruple star models can get round this problem but require the addition of a so-far undetected intermediate period of order 5 -- 20d that has be a near-perfect integer divisor of the outer 204d period. Although we have no good explanation for KIC 2856960, using the full set of Kepler data we are able to update several of its parameters. We also present a spectrum showing that KIC 2856960 is dominated by light from a K3- or K4-type star.

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RE: KIC 002856960
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Title: The Triply Eclipsing Hierarchical Triple Star KIC002856960
Authors: Jae Woo Lee, Seung-Lee Kim, Chung-Uk Lee, Byeong-Cheol Lee, Byeong-Gon Park, Tobias Cornelius Hinse

In a recent study, Armstrong et al. presented an eclipsing binary star of about 6.2 h period with transit-like tertiary signals occurring every 204.2 d in the Kepler public data of KIC002856960 and proposed three possible hierarchical structures: (AB)b, (AB)C, and A(BC). We analysed the Kepler light curve by including a third light source and one starspot on each binary component. The results represent that the close eclipsing pair is in a low-mass eccentric-orbit, detached configuration. Based on 123 eclipse timings calculated from the Wilson-Devinney binary model, a period study of the close binary reveals that the orbital period has experienced a sinusoidal variation with a period and a semi-amplitude of 205±2 d and 0.0021±0.0002 d, respectively. The period variation would be produced by the light-travel-time effect due to a gravitationally-bound third body with a minimum mass of M_3 \sin i_3=0.76 solar masses in an eccentric orbit of e_3=0.61. This is consistent with the presence of third light found in our light-curve solution and the tertiary signal of 204.2 d period most likely arises from the K-type star crossed by the close eclipsing binary. Then, KIC002856960 is a triply eclipsing hierarchical system, A(BC), consisting of a close binary with two M-type dwarfs and a more massive K-type component. The presence of the third star may have played an important role in the formation and evolution of the close pair, which may ultimately evolve into a contact system by angular momentum loss.

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Title: A transiting companion to the eclipsing binary KIC002856960
Authors: D. Armstrong, D. Pollacco, C. A. Watson, F. Faedi, Y. Gómez Maqueo Chew, H. M. Cegla, P. McDaid, J. Burton, J. McCormac, I. Skillen

We present an early result from an automated search of Kepler eclipsing binary systems for circumbinary companions. An intriguing tertiary signal has been discovered in the short period eclipsing binary KIC002856960. This third body leads to transit-like features in the light curve occurring every 204.2 days, while the two other components of the system display eclipses on a 6.2 hour period. The variations due to the tertiary body last for a duration of \sim1.26 days, or 4.9 binary orbital periods. During each crossing of the binary orbit with the tertiary body, multiple individual transits are observed as the close binary stars repeatedly move in and out of alignment with the tertiary object. We are at this stage unable to distinguish between a planetary companion to a close eclipsing binary, or a hierarchical triply eclipsing system of three stars. Both possibilities are explored, and the light curves presented.

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