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arXiv · 2308.08779

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

Othman Benomar·Masao Takata·Michael Bazot·Takashi Sekii·Laurent Gizon·Yuting Lu
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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.

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Othman Benomar, Masao Takata, Michael Bazot, Takashi Sekii, Laurent Gizon, Yuting Lu. 2023-08-17. Detecting active latitudes of Sun-like stars using asteroseismic a-coefficients. https://doi.org/10.1051/0004-6361/202347095

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