Thursday, June 11, 2015

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.

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