AAS 203rd Meeting, January 2004
Session 67 Nearby Star II
Special Session, Tuesday, January 6, 2004, 2:00-3:30pm, Centennial I/II

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[67.05] Looking for and Characterizing Planets Around Nearby Stars

G. F. Benedict, B. E. McArthur (McDonald Observatory), E. P. Nelan (STScI), Space Telescope Astrometry Team, `Are These Planets or Not?' Team

Using FGS 3 a white-light interferometer on HST, the Space Telescope Astrometry Team monitored Proxima Centauri and Barnard’s Star for 2000 and 1200 days, respectively, to search for planetary mass companions (Benedict et al. 1999, AJ, 118, 1086). Our null results are consistent with contemporaneous and more recent radial velocity studies of these objects.

The ‘Are These Planets or Not?’ Team has determined that the companion to Gl 876 has a planetary mass ~1.9 MJup (Benedict et al. 2002, ApJL, 581, 115). The Team is currently carrying out FGS astrometry of two stars possibly hosting planetary mass companions, \epsilon Eri and \upsilon And. For these targets we have only 2.5 and 1.5 years of observations, respectively. However, because of the per-observation precision offered by FGS 1r (~1 millisecond of arc), we can search for acceleration and offer upper limits on companion masses. Following the approach used to establish the mass of Gl 876b, we will eventually combine three years of HST astrometric observations with ground-based primary star radial velocities spanning more than one companion period to determine companion masses. Unlike our previous approach, this study will include ground-based, lower-precision astrometry, considerably extending our time span.

The Space Telescope Astrometry Team consisted of the authors and W. Jefferys, W. van Altena, O. Franz, L. Fredrick, R. Duncombe, P. Shelus, P. Hemenway, D. Story, A. Whipple, L. Wasserman, and A. Bradley. The ‘Are These Planets or Not?’ Team consists of the authors and combinations of A. Hatzes, W. Cochran, T. Forveille, G. Marcy, P. Butler, X. Delfosse, C. Perrier, B. Goldman, W. Spiesman, M. Mayor, G. Gatewood, W. Jefferys, and M. McGrath. This research is supported by grants GO-9969 and GO-9971 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

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