The mass ratio distribution in main-sequence spectroscopic binaries measured by infrared spectroscopy

We report infrared spectroscopic observations of a large well-defined sample of main-sequence, single-lined spectroscopic binaries to detect the secondaries and derive the mass ratio distribution of short-period binaries. The sample consists of 51 Galactic disk spectroscopic binaries found in the Carney and Latham high proper motion survey, with primary masses in the range 0.6-0.85 M.. Our infrared observations detect the secondaries in 32 systems, two of which have mass ratios, q = M-2/M-1, as low as similar to0.20. Together with 11 systems previously identified as double-lined binaries by visible light spectroscopy, we have a complete sample of 62 binaries, of which 43 are double lined. The mass ratio distribution is approximately constant over the range q = 1.0-0.3. The distribution appears to rise at lower q values, but the uncertainties are sufficiently large that we cannot rule out a distribution that remains constant. The mass distribution derived for the secondaries in our sample and that of the extrasolar planets apparently represent two distinct populations.