Detecting active latitudes of Sun-like stars using asteroseismic a-coefficients

TL;DR

This paper presents a new asteroseismic method to measure the latitudinal distribution of magnetic activity in Sun-like stars, validated with solar data and applied to Kepler stars, revealing activity patterns and potential activity phase transitions.

Contribution

It introduces a framework using asteroseismic a-coefficients to infer stellar activity latitudes and their variations, advancing stellar magnetic activity studies.

Findings

Successfully detected solar active latitude changes over solar cycle.

Identified equatorial activity band in 16 Cyg A with activity levels similar to the Sun.

Observed bi-modality in 16 Cyg B's a-coefficients, suggesting possible activity phase transition.

Abstract

We introduce a framework to measure the asphericity of Sun-like stars using $a_1$, $a_2$ and $a_4$ coefficients, and constrain their latitudes of magnetic activity. Systematic errors on the inferred coefficients are evaluated in function of key physical and seismic parameters (inclination of rotation axis, average rotation, height-to-noise ratio of peaks in power spectrum). The measured a-coefficients account for rotational oblateness and the effect of surface magnetic activity. We use a simple model that assumes a single latitudinal band of activity. Using solar SOHO/VIRGO/SPM data, we demonstrate the capability of the method to detect the mean active latitude and its intensity changes between 1999-2002 (maximum of activity) and 2006-2009 (minimum of activity). We further apply the method to study the solar-analogue stars 16 Cyg A and B using Kepler observations. An equatorial band of activity, exhibiting intensity that could be comparable to that of the Sun, is detected in 16 Cyg A. However, 16 Cyg B exhibits a bi-modality in $a_4$ that is challenging to explain. We suggest that this could be a manifestation of the transition between a quiet and an active phase of activity. Validating or invalidating this hypothesis may require new observations.