University of Cambridge > > Exoplanet Seminars > Spectral Binaries: An Approach for Measuring the True Binary Fraction of Very Low Mass Stars and Brown Dwarfs

Spectral Binaries: An Approach for Measuring the True Binary Fraction of Very Low Mass Stars and Brown Dwarfs

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The multiplicative properties of stars and brown dwarfs are fundamentally tied to their formation mechanisms, while multiple systems provide opportunities for direct mass measurements and tests of evolutionary theories and atmosphere models. The prevailing wisdom in the community is that the binary fraction of stars declines with mass, reaching 10-20% in the very-low-mass (VLM: M < 0.1 solar masses) regime. However, results for VLM dwarfs are based almost entirely on resolved imaging programs, which are limited in both projected separation and detectable mass ratios; alternate approaches suggest VLM binary fractions up to 3x higher. Capitalizing on the distinct spectral morphologies of late-M, L and T dwarfs, we have developed a robust approach for identifying VLM spectral binaries, systems identified by their blended-light spectra. Over 50 spectral binary candidates have been identified to date, and over a dozen systems confirmed through a combination of high resolution imaging, radial velocity monitoring and astrometric monitoring, including some of the shortest-period VLM binaries currently known. In this talk, I discuss our spectral binary methodology; review our follow-up program; and describe several of our key discoveries, including systems straddling the hydrogen burning mass limit with full orbit determinations. Examining the currently confirmed sample, I then critically analyze the VLM separation distribution and overall binary fraction, and discuss its possible impact on current star and brown dwarf formation models.

This talk is part of the Exoplanet Seminars series.

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