Session 70 - Searching for Other Planetary Systems.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center

[70.11] Mass Detection Limits for Planetary Companions to Barnard's Star and Proxima Centauri

G. F. Benedict, B. McArthur, A. Whipple, E. Nelan, D. Story, Q. Wang, W. H. Jefferys, H. Coleman, D. Chappell, P. D. Hemenway, P. J. Shelus (McDonald Obs., U. Texas), R. Duncombe (Aerospace Eng., U. Texas), W. F. van Altena (Yale U.), O. G. Franz (Lowell Obs.), L. W. Fredrick (Astronomy Dept., U. Virginia)

The Hubble Space Telescope Astrometry Science team has collected 52 sets of observations of a star field containing Proxima Centauri and 30 sets of a field containing Barnard's Star. These data are acquired with Fine Guidance Sensor 3 (FGS 3). Our primary goal is to determine upper limits for the masses of planetary companions. Our detection sensitivity is at or below one Jupiter mass for periods between 90 and 600 days for both Proxima Cen and Barnard's Star. Our results for Barnard's Star are consistent with those of Gatewood (1995, Ap&SS, 223, 91).

The twenty-eight observation sets of the field containing Barnard's Star have significant value, whether or not we detect perturbations associated with that star. Any systematics introduced by HST or FGS 3 should be present in the data for both Barnard's Star and Proxima Cen. We have identified at least one strong systematic effect in these data. We have not, as yet, identified the source. Our detection sensitivity should improve from future re-calibrations and re- reductions. Seven additional observation sets are yet to be obtained for both fields during the remainder of HST Cycle 5 (November 1995 - June 1996).


Planet Detection Limits for Proxima Centauri

In the absence of systematic error Monte Carlo simulations indicate that an 0.0015 arcsec amplitude perturbation would be found in the Proxima data at a 1% false positive level, with a 5% miss rate. Assuming MProx = 0.11M(solar) yields these detection limits.

 Freq (days^(-1))

 P (days)





 1.0 (0.4)


 1.0 (0.65)








Systematic effects present at the longer periods increase our detection limits from the values in parentheses. Once we eliminate those effects, we will achieve the lower limits.