An astronomer's dozen: spectroscopy of six double-lined binaries and constraints on detection limits*

Out of a group of 11 previously known binaries with |f(m) 0.1 M_| observed at red wavelengths centred near 6430 Å, seven have been found to be double-lined. Orbital elements and the mass ratio for six double-lined systems have been determined from the current and previously published radial-velocity observations. Spectrum addition was used to estimate the spectral types of the secondaries for the four solar-type systems but, because of the weakness of the secondary lines, only a limiting range of spectral types could be determined. HR 7038 appears to be metal rich relative to the spectral-type reference stars. On the basis of the detection or non-detection of the secondaries in these 11 main-sequence systems, it is estimated that secondaries with mass ratios as small as 0.6 can be detected at red wavelengths with solid-state detectors. Components with a red-magnitude difference slightly greater than 2.5 mag can be detected at wavelengths near 6430 Å. It appears that the secondary may be detected in a roughly solar-type main-sequence system if its mass function is greater than 0.05 |M_|⁠, provided that the inclination is not close to 90°. Eleven of the 12 components were determined to be synchronously or pseudo-synchronously rotating. The primary of HR 7038 appears to be rotating more slowly than its computed pseudo-synchronous velocity, unless it is a significantly evolved main-sequence star.