BEER Analysis Finds two Brown Dwarfs in Tight Binaries

BEER analysis of Kepler and CoRoT light curves. III. Spectroscopic confirmation of seventy new beaming binaries discovered in CoRoT lightcurves

Authors:

Tal-Or et al

Abstract:

The BEER algorithm, introduced by Faigler & Mazeh (2011), searches stellar lightcurves for the BEaming, Ellipsoidal, and Reflection photometric modulations caused by a short-period companion. Applying the search to the first five long-run center CoRoT fields, we identified 481 non-eclipsing candidates with periodic flux amplitudes of 0.5−87 mmag. Optimizing the Anglo-Australian-Telescope pointing coordinates and the AAOmega fiber-allocations with dedicated softwares, we acquired 6−7 medium-resolution spectra of 281 candidates in a seven-night campaign. Analysis of the red-arm AAOmega spectra, which covered the range of 8342−8842 \AA{}, yielded a radial-velocity precision of ∼1 km/s. Spectra containing lines of more than one star were analyzed with TODCOR−the two-dimensional correlation algorithm. The measured radial velocities confirmed the binarity of seventy of the BEER candidates−45 single-line binaries, 18 double-line binaries, and 7 diluted binaries. We show that red giants introduce a major source of false candidates, and demonstrate a way to improve BEER's performance in extracting higher-fidelity samples from future searches of CoRoT lightcurves. The periods of the confirmed binaries span a range of 0.3−10 days, and show a rise in the number of binaries per ΔlogP towards longer periods. The estimated mass ratios of the double-line binaries and the mass-ratios assigned to the single-line binaries, assuming an isotropic inclination distribution, span a range of 0.03−1. On the low-mass end we have detected two brown-dwarf candidates on a ∼1 day period orbit. This is the first time non-eclipsing beaming binaries are detected in CoRoT data, and we estimate that ∼300 such binaries can be detected in the CoRoT long-run lightcurves.