From AstronomyOutreach network
Benjamin Clark is a senior at Penn Manor High School in Millersville, PA, and the 2011 Astronomical League's National Young Astronomer Award First Place Winner.
Mr Clark used cross-correlation to determine radial velocities from 145,888 individual spectra of a magnitude limited sample of 39,543 M (spectral classes M0-L0) dwarf stars that were observed by the Sloan Digital Survey (SDSS). Bayesian anaylsis and Monte Carlo statistical simulations were then employed to determine the fraction of binary systems whose components were separated by <0.4 AU (i.e., the close binary fraction) of the sampled M dwarf stars.
While previous results on the close binary fraction were based upon very small samples and thus were unable to provide very precise values, the results that Mr Clark presented were developed from far larger samples, and thus were more precise and better fit to serve as a constraint on proposed theories of star formation. After adjusting for the detection efficiency, he found that the frequency of binary stars with a separation of less than 0.4 AU to be 3.0% (+0.6%/-0.9%). Mr Clark also demonstrated that the close binary fraction, like the total binary fraction, decreases with decreasing primary mass.