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The Mount Wilson Ca HK survey revealed magnetic activity variations in alarge 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 therotational properties and the depths of the surface convection zones for starswith various masses and ages. In 2007 we initiated a long-term monitoringcampaign of Ca II H and K emission for a sample of 57 southern solar-type starsto measure their magnetic activity cycles and their rotational properties whenpossible. We report the discovery of a 1.6-year magnetic activity cycle in theexoplanet host star iota Horologii, and we obtain an estimate of the rotationperiod that is consistent with Hyades membership. This is the shortest activitycycle so far measured for a solar-type star, and may be related to theshort-timescale magnetic variations recently identified in the Sun and HD49933from helio- and asteroseismic measurements. Future asteroseismic observationscan be compared to those obtained near the magnetic minimum in 2006 to searchfor cycle-induced shifts in the oscillation frequencies. If such short activitycycles are common in F stars, then NASA's Kepler mission should observe theireffects in many of its long-term asteroseismic targets.

Discovery of a 1.6-year Magnetic Activity Cycle in the Exoplanet Host Star iota Horologii