  We have been using the Keck I High Resolution Spectrograph (HIRES) to search
for planetary companions in the Hyades cluster. We selected four stars from
this sample which showed significant radial velocity variability on short
timescales to search for short-period planetary companions. The radial
velocities of these four stars were monitored regularly with the Hobby Eberly
Telescope (HET) for approximately two months, while sparse data were also taken
over ~4 months: we also obtained near-simultaneous photometric observations
with one of the automatic photoelectric telescopes at Fairborn Observatory. For
three of the stars, we detect photometric variability with the same period
present in the radial velocity (rv) measurements, compatible with the expected
rotation rates for Hyades members. The fourth star continues to show rv
variations and minimal photometric variability but with no significant
periodicity. This study shows that for the three stars with periodic behavior,
a significant portion of the rv fluctuations are likely due primarily to
magnetic activity modulated by stellar rotation rather than planetary
companions. Using simple models for the rv perturbations arising from spot and
plage, we demonstrate that both are likely to contribute to the observed rv
variations. Thus, simultaneous monitoring of photometric (photospheric) and
spectroscopic (chromospheric) variations is essential for identifying the cause
of Doppler shifted absorption lines in more active stars.
