Context. Kepler observations revealed a brown dwarf eclipsing the M-type star LHS 6343 A with a period of 12.71 days. In addition, an out-of-eclipse light modulation with the same period and a relative semi-amplitude of ~2 × 10-4 was observed showing an almost constant phase lag to the eclipses produced by the brown dwarf. In a previous work, we concluded that this was due to the light modulation induced by photospheric active regions in LHS 6343 A.
Aims: In the present work, we prove that most of the out-of-eclipse light modulation is caused by the Doppler-beaming induced by the orbital motion of the primary star.
Methods: We introduce a model of the Doppler-beaming for an eccentric orbit and also considered the ellipsoidal effect. The data were fitted using a Bayesian approach implemented through a Markov chain Monte Carlo method. Model residuals were analysed by searching for periodicities using a Lomb-Scargle periodogram.
Results: For the first seven quarters of Kepler observations and the orbit previously derived from the radial velocity measurements, we show that the light modulation of the system outside eclipses is dominated by the Doppler-beaming effect. A period search performed on the residuals shows a significant periodicity of 42.5 ± 3.2 days with a false-alarm probability of 5 × 10-4, probably associated with the rotational modulation of the primary component.