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

TL;DR

The paper introduces the BEER algorithm to detect non-transiting low-mass companions by analyzing periodic brightness modulations in Kepler and CoRoT lightcurves, enabling identification of planets, brown dwarfs, or low-mass stars.

Contribution

It presents a novel, simple algorithm that combines beaming, ellipsoidal, and reflection effects to detect non-transiting companions in stellar lightcurves.

Findings

Successful detection of candidate companions in Kepler data

Algorithm can identify effects as small as 1 part in 10,000

Feasibility demonstrated with short-term lightcurve analysis

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) of 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 (2003) and Zucker, Mazeh & Alexander (2007), the Kepler and the CoRoT lightcurves 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 bring two examples of candidates found in the first 33 days of the Q1 Kepler lightcurves. Although we used relatively short timespan, the lightcurves were precise enough to enable the detection of periodic effects with amplitudes as small as one part in 10,000 of the stellar flux.