Signatures of magnetic activity in the p mode frequencies of solar-type stars observed by Kepler
Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany
Natural Sciences (Astrophysics and Astrononmy)
Several hundred stars were observed in the short cadence mode of the Kepler satellite during the nominal mission phase. This generated a large pool of data which can provide insight into the characteristics of stellar activity cycles of solar-type stars through the methods of asteroseismology. From helioseismology it is known that the frequencies of solar acoustic oscillations (p modes) are positively correlated with the solar magnetic activity cycle. Evidence for a similar behaviour in the p modes of a star, which was observed by the CoRoT satellite, was provided by . This showed that it is feasible to trace activity cycles of stars in their p mode frequencies.
We analyse the Kepler time series of a set of solar-type stars with the aim to find signatures of stellar magnetic activity. We divide the time series of each star into shorter sub-series in order to analyse the temporal evolution of the p mode frequencies. The sub-series’ periodograms are cross-correlated to retrieve the shift of p mode frequencies over time. The errors on the shifts are computed by a resampling approach of the periodogram. We find significant frequency shifts, indicating stellar magnetic activity, for all stars we investigated. For the most prominent example, KIC 8006161, we find that, not unlike in the solar case, frequency shifts are smallest for the lowest and largest for the highest p mode frequencies.
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