  The potential existence of a giant planet orbiting within a few AU of a
stellar remnant has profound implications for both the survival and possible
regeneration of planets during post-main sequence stellar evolution. This paper
reports Hubble Space Telescope Fine Guidance Sensor and U.S. Naval Observatory
relative astrometry of GD 66, a white dwarf thought to harbor a giant planet
between 2 and 3 AU based on stellar pulsation arrival times. Combined with
existing infrared data, the precision measurements here rule out all
stellar-mass and brown dwarf companions, implying that only a planet remains
plausible, if orbital motion is indeed the cause of the variations in pulsation
timing.
