Signatures of magnetic activity in the seismic data of solar-type stars observed by Kepler

TL;DR

This study uses Kepler data to detect and analyze magnetic activity cycles in 87 solar-type stars through seismic frequency shifts, revealing diverse activity patterns and their relation to stellar interior changes.

Contribution

First comprehensive asteroseismic analysis of magnetic activity cycles in a large sample of solar-type stars using Kepler data, employing Bayesian peak-bagging and multi-proxy comparisons.

Findings

Over 60% of stars show quasi-periodic frequency shift variations.

Approximately 20% exhibit in-phase frequency and mode height variations.

Most activity-related variations are accompanied by changes in other proxies.

Abstract

In the Sun, the frequencies of the acoustic modes are observed to vary in phase with the magnetic activity level. These frequency variations are expected to be common in solar-type stars and contain information about the activity-related changes that take place in their interiors. The unprecedented duration of Kepler photometric time-series provides a unique opportunity to detect and characterize stellar magnetic cycles through asteroseismology. In this work, we analyze a sample of 87 solar-type stars, measuring their temporal frequency shifts over segments of length 90 days. For each segment, the individual frequencies are obtained through a Bayesian peak-bagging tool. The mean frequency shifts are then computed and compared with: 1) those obtained from a cross-correlation method; 2) the variation in the mode heights; 3) a photometric activity proxy; and 4) the characteristic timescale of the granulation. For each star and 90-d sub-series, we provide mean frequency shifts, mode heights, and characteristic timescales of the granulation. Interestingly, more than 60% of the stars show evidence for (quasi-)periodic variations in the frequency shifts. In the majority of the cases, these variations are accompanied by variations in other activity proxies. About 20% of the stars show mode frequencies and heights varying approximately in phase, in opposition to what is observed for the Sun.