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Post Info TOPIC: KOI-256
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RE: KOI-256
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Title: Characterising the Cool KOIs. V. KOI-256: A Mutually Eclipsing Post-Common Envelope Binary
Authors: Philip S. Muirhead, Andrew Vanderburg, Avi Shporer, Juliette Becker, Jonathan J. Swift, James P. Lloyd, Jim Fuller, Ming Zhao, Sasha Hinkley, J. Sebastian Pineda, Michael Bottom, Andrew W. Howard, Kaspar von Braun, Tabetha S. Boyajian, Nicholas Law, Christoph Baranec, Reed Riddle, A. N. Ramaprakash, Shriharsh P. Tendulkar, Khanh Bui, Mahesh Burse, Pravin Chordia, Hillol Das, Richard Dekany, Sujit Punnadi, John Asher Johnson

We report that Kepler Object of Interest 256 (KOI-256) is a mutually eclipsing post-common envelope binary (ePCEB), consisting of a cool white dwarf (M = 0.592 ± 0.089 solar masses, R = 0.01345 ± 0.00091 solar radii, Teff = 7100 ± 700 K) and an active M3 dwarf (M = 0.51 ± 0.16 solar masses, R = 0.540 ± 0.014 solar radii, Teff = 3450 ± 50 K) with an orbital period of 1.37865 ± 0.00001 days. KOI-256 is listed as hosting a transiting planet-candidate by Borucki et al. and Batalha et al.; here we report that the planet-candidate transit signal is in fact the occultation of a white dwarf as it passes behind the M dwarf. We combine publicly-available long- and short-cadence Kepler light curves with ground-based measurements to robustly determine the system parameters. The occultation events are readily apparent in the Kepler light curve, as is spin-orbit synchronisation of the M dwarf, and we detect the transit of the white dwarf in front of the M dwarf halfway between the occultation events. The size of the white dwarf with respect to the Einstein ring during transit (REin = 0.00473 ± 0.00055 solar radii) causes the transit depth to be shallower than expected from pure geometry due to gravitational lensing. KOI-256 is an old, long-period ePCEB and serves as a benchmark object for studying the evolution of binary star systems as well as white dwarfs themselves, thanks largely to the availability of near-continuous, ultra-precise Kepler photometry.

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Blobrana


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Dead star warps its partner's light, astronomers say

The research team used Cornell-led ultraviolet measurements of the star called (Kepler Object of Interest) KOI-256 taken by the Galaxy Evolution Explorer (GALEX), a NASA space telescope operated by Caltech. The GALEX observations were conducted by Cornell researchers Jamie Lloyd, associate professor of astronomy and of mechanical and aerospace engineering; Kevin Covey, former postdoctoral associate now at Lowell Observatory; and Lucianne Walkowicz of Princeton University and Evgenya Shkolnik of Lowell Observatory.
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Gravity-Bending Find Leads to Kepler Meeting Einstein

NASA's Kepler space telescope has witnessed the effects of a dead star bending the light of its companion star. The findings are among the first detections of this phenomenon -- a result of Einstein's theory of general relativity -- in binary, or double, star systems.
The dead star, called a white dwarf, is the burnt-out core of what used to be a star like our sun. It is locked in an orbiting dance with its partner, a small "red dwarf" star. While the tiny white dwarf is physically smaller than the red dwarf, it is more massive.
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