The Triply Eclipsing Hierarchical Triple Star KIC002856960

Abstract

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 {\it Kepler} public data of KIC002856960 and proposed three possible hierarchical structures: (AB)b, (AB)C, and A(BC). We analyzed the {\it 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$\pm$2 d and 0.0021$\pm$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 M${}_{\odot }$ 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.

19 pages, including 5 figures and 3 tables, accepted for publication in ApJ

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• The Eclipsing System V404 Lyr: Light-Travel Times and Gamma Doradus Pulsations
• HD144548: A young triply eclipsing system in the Upper Scorpius OB association
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• Placing Limits On The Transit Timing Variations Of Circumbinary Exoplanets
• Fundamental Parameters of Kepler Eclipsing Binaries. I. KIC 5738698
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• Eclipse timing variation analysis of OGLE-IV eclipsing binaries toward the Galactic Bulge. II. Short periodic triple stellar systems
• KIC 2856960: the impossible triple star
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• On the RZ Draconis Sub-stellar Circumbinary Companions Stability Study of the Proposed Sub-stellar Circumbinary System
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• Three X-ray Flares Near Primary Eclipse of the RS CVn Binary XY UMa
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