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

TL;DR

This paper reports the discovery of the shortest known magnetic activity cycle of 1.6 years in the star iota Horologii, providing insights into stellar magnetic variability and its potential effects on asteroseismic observations.

Contribution

It presents the first detection of a 1.6-year magnetic activity cycle in an exoplanet host star, expanding understanding of stellar magnetic behavior and cycle diversity.

Findings

Shortest activity cycle measured for a solar-type star

Cycle duration consistent with star's Hyades membership

Potential link between short cycles and magnetic variations in Sun and other stars

Abstract

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.