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SOPHIE velocimetry of Kepler transit candidates
I. Detection of the low-mass white dwarf KOI-74b

D. Ehrenreich, A.-M. Lagrange, F. Bouchy, C. Perrier, G. Hébrard, I. Boisse, X. Bonfils, L. Arnold, X. Delfosse, M. Desort, R. F. Díaz, A. Eggenberger, T. Forveille, C. Lovis, C. Moutou, F. Pepe, F. Pont, N. C. Santos, A. Santerne, D. Ségransan, S. Udry, A. Vidal-Madjar

Abstract
The Kepler mission has detected transits and occultations of a hot compact object around an early-type star, the Kepler Object of Interest KOI-74. The mass of this transiting object was photometrically assessed in a previous study using the presence of the relativistic beaming effect (so-called ‘Doppler boosting’) in the light curve. Our aim was to provide a spectroscopic validation of this pioneering approach. We measured the radial velocity variations of the A1V star KOI-74 with the SOPHIE spectrograph at the 1.93-m telescope of the Observatoire de Haute-Provence (France). Radial velocity measurements of this star are challenging to obtain because of the high level of stellar pulsations and the few available spectral lines. Using a technique dedicated to early-type main-sequence stars, we measure radial velocity variations compatible with a companion of mass 0.252 ± 0.025 M, in good agreement with the value derived from the Kepler light curve. This work strengthens the scenario suggesting that KOI-74 is a blue straggler orbited by a stellar core despoiled of its envelope, the low-mass white dwarf KOI-74b.

Keywords
techniques: radial velocities - stars: early-type - white dwarfs - blue stragglers - binaries: eclipsing - planets and satellites: general

Notes
Based on observations collected with the SOPHIE spectrograph on the 1.93-m telescope at Observatoire de Haute-Provence (CNRS), France, by the SOPHIE consortium (program 10A.PNP.CONS).

Astronomy and Astrophysics
Volume 525, Number of pages A85_1
2011 January

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia