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

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.

Accepted to A&A

References in corpus (17)

• Standing on the shoulders of Dwarfs: the $Kepler$ asteroseismic LEGACY sample I - oscillation mode parameters
• Inferring the eccentricity distribution
• Asteroseismology of the solar analogs 16 Cyg A & B from Kepler observations
• Acoustic oscillations in rapidly rotating polytropic stars I. Effects of the centrifugal distortion
• Surface rotation of Kepler red giant stars
• Observing the Sun with the Atacama Large Millimeter-submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping
• Visibilities and bolometric corrections for stellar oscillation modes observed by Kepler
• Asteroseismic estimate of helium abundance of a solar analog binary system
• Oscillation mode linewidths and heights of 23 main-sequence stars observed by Kepler
• Model-independent measurement of internal stellar structure in 16 Cygni A and B
• Latitudinal differential rotation in the solar analogues 16 Cyg A and B
• Limits on radial differential rotation in Sun-like stars from parametric fits to oscillation power spectra
• Shape of a slowly rotating star measured by asteroseismology
• Anomalies in the Kepler Asteroseismic Legacy Project Data. A re-analysis of 16 Cyg A&B, KIC8379927 and 6 solar-like stars
• Testing abundance-age relations beyond solar analogues with Kepler LEGACY stars
• Thorough characterisation of the 16 Cygni system. Part II. Seismic inversions of the internal structure
• Asteroseismic Signature of a Large Active Region

Cited by in corpus (1)

• Les Trente Glorieuses: 29 years of helioseismic observations with the Luminosity Oscillations Imager