  Doppler spectroscopy of rho1 Cnc has detected evidence of a companion with an
orbital period of 14.65 days and a minimum mass of 0.88 Jupiter masses.
Astrometric observations performed with the Hubble Space Telescope Fine
Guidance Sensor 1r using a novel new observing technique have placed an upper
limit on the astrometric reflex motion of rho1 Cnc in a time period of only one
month. These observations detected no reflex motion induced by the 14.65 day
period radial velocity companion, allowing us to place a 3-sigma upper limit of
\~0.3 milliarcseconds on the semi-major axis of this motion, ruling out the
preliminary Hipparcos value of 1.15 milliarcseconds. The corresponding upper
limit on the true mass of the companion is ~30 Mj, confirming that it is a
sub-stellar object.
