Possible Astrometric Perturbation of LHS 288

A sample of 13 stars from the University of Virginia southern hemisphere parallax program has been tested for possible astrometric perturbations due to low-mass companions. The selected objects are primarily early to mid-M dwarfs with large parallaxes, all are within 25 parsecs, that are not known to be binaries. The data were collected from CCD parallax observations made between 1991 and 2002 with the 1-meter reflector at the Siding Spring Observatory, Coonabarabran, Australia. Following our standard central overlap solution for parallax and proper motion, the residuals were subjected to a time-series analysis using the Lomb-Scargle normalized periodogram method (Press et al. 1992).

Of these, LHS 288 displays a possible perturbation due to a very low mass companion; such a companion might be as small as 2.4 Jupiter masses. Because LHS 288 is a high proper-motion star in a rich field, the possibility that it passed over an undetected faint star during these observations cannot be eliminated; such a distorted point-spread function might mimic a perturbation. Additional observations from an independent data set could help determine whether the suggested perturbation is real.

The remaining stars demonstrate no indication of any companions greater than about 17 Jupiter masses with orbits between 1.5 and 10 years. The single stars are LHS 34 (white dwarf), LHS 271, LHS 337, LHS 532, LHS 1134, LHS 1565, LHS 2310, LHS 2739, LHS 2813, LHS 3064, LHS 3242, and LHS 3418.

We acknowledge support from NSF grants AST 98-20711 and 05-07711, Georgia State University, the Space Interferometry Mission (SIM), F. H. Levinson Fund of the Peninsula Community Foundation, UVa, and Hampden-Sydney College in addition to support and generous observing time allocations from the Research School of Astronomy and Astrophysics, Australian National University.