Tests of the asymptotic large frequency separation of acoustic oscillations in solar-type and red giant stars

TL;DR

This study evaluates the validity of asymptotic scaling relations in asteroseismology for solar-type and red giant stars, finding that atmospheric modeling significantly impacts the accuracy of these relations.

Contribution

The paper investigates the differences between observable oscillation parameters and their asymptotic estimates using stellar models, highlighting the importance of atmospheric extension in these calculations.

Findings

Larger atmospheric extension reduces discrepancies between observed and asymptotic large frequency separations.

Current discrepancies in scaling relations may have been overestimated due to atmospheric modeling.

Asymptotic approximations remain valid when atmospheric effects are properly considered.

Abstract

Asteroseismology, i.e. the study of the internal structures of stars via their global oscillations, is a valuable tool to obtain stellar parameters such as mass, radius, surface gravity and mean density. These parameters can be obtained using certain scaling relations which are based on an asymptotic approximation. Usually the observed oscillation parameters are assumed to follow these scaling relations. Recently, it has been questioned whether this is a valid approach, i.e., whether the order of the observed oscillation modes are high enough to be approximated with an asymptotic theory. In this work we use stellar models to investigate whether the differences between observable oscillation parameters and their asymptotic estimates are indeed significant. We compute the asymptotic values directly from the stellar models and derive the observable values from adiabatic pulsation calculations of the same models. We find that the extent to which the atmosphere is included in the models is a key parameter. Considering a larger extension of the atmosphere beyond the photosphere reduces the difference between the asymptotic and observable values of the large frequency separation. Therefore, we conclude that the currently suggested discrepancies in the scaling relations might have been overestimated. Hence, based on the results presented here we believe that the suggestions of Mosser et al. (2013) should not be followed without careful consideration.