Publications (1)0 Total impact
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R. Silvotti,
R. H. Østensen,
S. Bloemen,
J. H. Telting,
U. Heber,
R. Oreiro,
M. D. Reed,
L. E. Farris,
S. J. O'Toole, L. Lanteri,
P. Degroote,
H. Hu,
A. S. Baran,
J. J. Hermes,
L. G. Althaus,
T. R. Marsh,
S. Charpinet,
J. Li,
R. L. Morris,
D. T. Sanderfer
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ABSTRACT: We have used 605 days of photometric data from the Kepler spacecraft to study
KIC 6614501, a close binary system with an orbital period of 0.15749747(25)
days (3.779939 hours), that consists of a low-mass subdwarf B (sdB) star and a
white dwarf. As seen in many other similar systems, the gravitational field of
the white dwarf produces an ellipsoidal deformation of the sdB which appears in
the light curve as a modulation at two times the orbital frequency. The
ellipsoidal deformation of the sdB implies that the system has a maximum
inclination of ~40 degrees, with i \approx 20 degrees being the most likely.
The orbital radial velocity of the sdB star is high enough to produce a Doppler
beaming effect with an amplitude of 432 \pm 5 ppm, clearly visible in the
folded light curve. The photometric amplitude that we obtain, K1 = 85.8 km/s,
is ~12 per cent less than the spectroscopic RV amplitude of 97.2 \pm 2.0 km/s.
The discrepancy is due to the photometric contamination from a close object at
about 5 arcsec North West of KIC 6614501, which is difficult to remove. The
atmospheric parameters of the sdB star, Teff = 23 700 \pm 500 K and log g =
5.70 \pm 0.10, imply that it is a rare object below the Extreme Horizontal
Branch (EHB), similar to HD 188112 (Heber et al. 2003). The comparison with
different evolutionary tracks suggests a mass between ~0.18 and ~0.25 Msun, too
low to sustain core helium burning. If the mass was close to 0.18-0.19 Msun,
the star could be already on the final He-core WD cooling track. A higher mass,
up to ~0.25 Msun, would be compatible with a He-core WD progenitor undergoing a
cooling phase in a H-shell flash loop. A third possibility, with a mass between
~0.32 and ~0.40 Msun, can not be excluded and would imply that the sdB is a
"normal" (but with an unusually low mass) EHB star burning He...
05/2012;
