期刊
ASTROPHYSICAL JOURNAL
卷 767, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/767/2/111
关键词
binaries: eclipsing; binaries: spectroscopic; stars: abundances; stars: activity; stars: fundamental parameters; stars: individual (KOI-256); stars: late-type; stars: low-mass; stars: rotation
资金
- Alain Porter Memorial SURF Fellowship
- National Science Foundation [AST-1203023, AST0906060, AST-0960343]
- California Institute of Technology
- Inter-University Centre for Astronomy and Astrophysics
- Mt. Cuba Astronomical Foundation
- NASA Science Mission directorate
- NASA [NAS5-26555]
- NASA Office of Space Science [NNX09AF08G]
- W. M. Keck Foundation
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1203023] Funding Source: National Science Foundation
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 M-circle dot, R-* = 0.01345 +/- 0.00091 R-circle dot, T-eff = 7100 +/- 700 K) and an active M3 dwarf (M-* = 0.51 +/- 0.16 M-circle dot, R-* = 0.540 +/- 0.014 R similar to, T-eff = 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 synchronization 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 (R-Ein = 0.00473 +/- 0.00055 R-circle dot) 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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