  PG 2131+066 is a composite-spectrum binary with a hot pulsating PG 1159-type
pre-white dwarf and an early M-type main sequence star. Analysis of Whole Earth
Telescope observations of the pulsating pre-white dwarf component provided an
asteroseismological determination of its mass, luminosity, and effective
temperature. These determinations allowed Kawaler et al. (1995) to determine
the distance to this star. In this paper, we refine the asteroseismological
distance determination, and confirm the distance by an independent measurement
to the system via the spectroscopic parallax of the M star. PG 2131+066 was
observed by the HST using the original PC in September 1993. Exposures with
filters F785LP and F555W both showed the companion at a distance of 0.3 arc
seconds. Photometry of the images provides an apparent magnitude for the main
sequence companion of v=18.97+/-0.15, from which we find a distance of 560
(+200 -134) pc. We also recalculated the asteroseismological distance to the
pre-white dwarf using updated models and new spectroscopic constraints from UV
spectra. The new seismological distance is 668 (+78 -83) pc, in satisfactory
agreement with the distance of the secondary star. These results suggest that
this is indeed a physical binary, and that seismological distance determination
may be the best way to determine the distance to the pulsating hot pre-white
dwarf stars.
