  The Mount Wilson Ca HK survey revealed magnetic activity variations in a
large sample of solar-type stars with timescales ranging from 2.5 to 25 years.
This broad range of cycle periods is thought to reflect differences in the
rotational properties and the depths of the surface convection zones for stars
with various masses and ages. In 2007 we initiated a long-term monitoring
campaign of Ca II H and K emission for a sample of 57 southern solar-type stars
to measure their magnetic activity cycles and their rotational properties when
possible. We report the discovery of a 1.6-year magnetic activity cycle in the
exoplanet host star iota Horologii, and we obtain an estimate of the rotation
period that is consistent with Hyades membership. This is the shortest activity
cycle so far measured for a solar-type star, and may be related to the
short-timescale magnetic variations recently identified in the Sun and HD49933
from helio- and asteroseismic measurements. Future asteroseismic observations
can be compared to those obtained near the magnetic minimum in 2006 to search
for cycle-induced shifts in the oscillation frequencies. If such short activity
cycles are common in F stars, then NASA's Kepler mission should observe their
effects in many of its long-term asteroseismic targets.
