A Search for Astrometric Companions to Stars in the Southern Hemisphere

Thirteen nearby stars from the former University of Virginia Southern Parallax Program were tested for possible astrometric perturbations that might indicate very low mass companions. For 12 of these stars—LHS 34, 271, 337, 532, 1134, 1565, 2310, 2739, 2813, 3064, 3242, and 3418—no clear indication of any unseen companion was detected. One star, LHS 288, however, may have a perturbation meriting further investigation. These high proper motion stars are all members of the solar neighborhood, lying within 25 pc. Other than the white dwarf LHS 34, these stars are early M dwarfs (M0.5-M5.5 V). After a minimum of 50 observations spread over at least three years, the relative parallax solutions for these stars have errors less than 3 mas. Following the calculation of relative parallaxes and proper motions, time-series analyses using Lomb-Scargle periodograms tested the astrometric residuals for any additional periodic signals. An upper limit to the mass of companions that could remain undetected was estimated for each star individually.