The Smallest Mass Ratio Young Star Spectroscopic Binaries

Using high-resolution near-infrared spectroscopy with the Keck Telescope, we have detected the radial velocity signatures of the cool secondary components in four optically identified pre-main-sequence, single-lined spectroscopic binaries. All are weak-lined T Tauri stars with well-defined center-of-mass velocities. The mass ratio for one young binary, NTTS 160905-1859, is M 2 / M 1 = 0.18 ± 0.01, the smallest yet measured dynamically for a pre-main-sequence spectroscopic binary. These new results demonstrate the power of infrared spectroscopy for the dynamical identification of cool secondaries. Visible-light spectroscopy, to date, has not revealed any pre-main-sequence secondary stars with masses <0.5 M ☉ , while two of the young systems reported here are in that range. We compare our targets with a compilation of the published young, double-lined spectroscopic binaries and discuss our unique contribution to this sample.