Photometric detection of non-transiting short-period low-mass companions through the beaming, ellipsoidal and reflection effects in Kepler and CoRoT light curves

Abstract

We present a simple algorithm, BEER, to search for a combination of the BEaming, Ellipsoidal and the Reflection/heating periodic modulations, induced by short-period non-transiting low-mass companions. The beaming effect is due to the increase (decrease) in the brightness of any light source approaching (receding from) the observer. To first order, the beaming and the reflection/heating effects modulate the stellar brightness at the orbital period, with phases separated by a quarter of a period, whereas the ellipsoidal effect is modulated with the orbital first harmonic. The phase and harmonic differences between the three modulations allow the algorithm to search for a combination of the three effects and identify stellar candidates for low-mass companions. The paper presents the algorithm, including an assignment of a likelihood factor to any possible detection, based on the expected ratio of the beaming and ellipsoidal effects, given an order-of-magnitude estimate of the three effects. As predicted by Loeb & Gaudi and by Zucker, Mazeh & Alexander, the Kepler and the CoRoT light curves are precise enough to allow detection of massive planets and brown-dwarf/low-mass-stellar companions with orbital period up to 10-30 days. To demonstrate the feasibility of the algorithm, we present two examples of candidates found in the first 33 days of the Q1 Kepler light curves. Although we used a relatively short time-span, the light curves were precise enough to enable the detection of periodic effects with amplitudes as small as one part in 104 of the stellar flux. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.