  We report our long-term spectroscopic monitoring of the Pleiades member
HII-2147, which has previously been spatially resolved at radio wavelengths in
VLBI observations. It has also been claimed to be a (presumably short-period)
double-lined spectroscopic binary with relatively sharp lines, although no
orbit has ever been published. Examination of our new spectroscopic material,
and of the historical radial velocities, shows that the current and previous
spectra are best interpreted as showing only a single set of lines of a
moderately rapidly rotating star with slowly variable radial velocity, which is
one of the sources detected by VLBI. We combine our own and other velocities
with the VLBI measurements and new adaptive optics observations to derive the
first astrometric-spectroscopic orbit of the G5 + G9 pair, with a period of
18.18 $\pm$ 0.11 years. We infer dynamical masses of 0.897 $\pm$ 0.022 MSun for
the spectroscopically visible star and 0.978 $\pm$ 0.024 MSun for the other,
along with a distance of 136.78 (+0.50/-0.46) pc. The lack of detection of the
lines of the more massive component in our spectra can be adequately explained
if it is rotating much more rapidly than the star we see. This is consistent
with the observation that the lines of the secondary are shallower than
expected for a star of its spectral type.
