We introduce a framework to measure the asphericity of Sun-like stars using a1, a2 and a4 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 a4 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.
@article{arxiv.2308.08779,
title = {Detecting active latitudes of Sun-like stars using asteroseismic a-coefficients},
author = {Othman Benomar and Masao Takata and Michael Bazot and Takashi Sekii and Laurent Gizon and Yuting Lu},
journal= {arXiv preprint arXiv:2308.08779},
year = {2023}
}