[7.10] {\it HST} Fine Guidance Sensor Astrometry of the Extrasolar Planet Candidates $\epsilon$ Eri and $\upsilon$ And

DPS 35th Meeting, 1-6 September 2003
Session 7. Extra Solar Planets I
Oral, Chairs: R. V. Yelle and R. A. Brown, Tuesday, September 2, 2003, 3:30-5:30pm, DeAnza I-II

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[7.10] HST Fine Guidance Sensor Astrometry of the Extrasolar Planet Candidates \epsilon Eri and \upsilon And - A Progress Report

G. F. Benedict, B. E. McArthur (McDonald Observatory), A. Hatzes (Tautenburg Observatory), E. Nelan (STScI), W. D. Cochran (McDonald Observatory), G. Gatewood (Allegheny Observatory), G. Marcy (University of California, Berkeley), P. Butler (Department of Terrestrial Magnetism, Carnegie Institution of Washington), M. McGrath (STScI)

We offer a progress report regarding HST Fine Guidance Sensor (FGS) fringe tracking astrometry of two stars possibly hosting planetary mass companions, \epsilon Eri and \upsilon And. We have only two years and one year of observations, respectively. However, because of the high per-observation precision offered by FGS 1r (~1 millisecond of arc), we can test for the presence or absence of acceleration and offer upper limits on companion masses, even at this early stage in our investigation. Following the approach used to establish the mass of Gl 876b (Benedict et al. 2002, ApJL, 581, 115), we will eventually combine three years of FGS 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.

This research is supported by ongoing 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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