Research Note

Doppler-beaming in the Kepler light curve of LHS 6343 A

¹ Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, Facultat de Ciències, Torre C5 parell, 2a pl, 08193 Bellaterra, Spain
e-mail: eherrero@ice.cat; iribas@ice.cat; morales@ice.cat
² INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
e-mail: nuccio.lanza@oact.inaf.it
³ Dept. d’Astronomia i Meteorologia, Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Martí Franquès 1, 08028 Barcelona, Spain
e-mail: carme.jordi@ub.edu
⁴ SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh KY16 9SS, UK
e-mail: acc4@st-andrews.ac.uk
⁵ LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, 5 Pl. Jules Janssen, 92195 Meudon Cedex, France
e-mail: Juan-Carlos.Morales@obspm.fr

Received: 19 November 2013
Accepted: 18 February 2014

Abstract

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.