Asymmetry of line profiles of stellar oscillations measured by Kepler for ensembles of solar-like oscillators: impact on mode frequencies and dependence on effective temperature

TL;DR

This study analyzes the asymmetry of stellar oscillation line profiles in Kepler data, demonstrating its impact on frequency measurements and how asymmetry varies with stellar temperature, improving seismic inference accuracy.

Contribution

It provides the first large-scale measurement of mode asymmetries across diverse stars, highlighting their importance for precise stellar parameter estimation.

Findings

Neglecting asymmetry causes systematic errors exceeding 1σ in frequency estimates.

Asymmetry sign changes between cool and hot stars, constraining excitation source locations.

Asymmetric Lorentzian profiles improve the accuracy of seismic inferences.

Abstract

Oscillation properties are usually measured by fitting symmetric Lorentzian profiles to the power spectra of Sun-like stars. However the line profiles of solar oscillations have been observed to be asymmetrical for the Sun. The physical origin of this line asymmetry is not fully understood, although it should depend on the depth dependence of the source of wave excitation (convective turbulence) and details of the observable (velocity or intensity). For oscillations of the Sun, it has been shown that neglecting the asymmetry leads to systematic errors in the frequency determination. This could subsequently affects the results of seismic inferences of the solar internal structure. Using light curves from the {\it Kepler} spacecraft we have measured mode asymmetries in 43 stars. We confirm that neglecting the asymmetry leads to systematic errors that can exceed the $1\sigma$ confidence intervals for seismic observations longer than one year. Therefore, the application of an asymmetric Lorentzian profile is to be favoured to improve the accuracy of the internal stellar structure and stellar fundamental parameters. We also show that the asymmetry changes sign between cool Sun-like stars and hotter stars. This provides the best constraints to date on the location of the excitation sources across the Hertzsprung-Russel diagram.