On the impact of the structural surface effect on global stellar properties and asteroseismic analyses

TL;DR

This paper investigates how improved modeling of stellar surface layers affects global stellar properties and asteroseismic inferences, revealing significant impacts on age estimates and frequency calculations crucial for space missions.

Contribution

It introduces a more realistic stellar surface modeling approach and assesses its effects on stellar properties and asteroseismic analyses across the Hertzsprung-Russell diagram.

Findings

Improved boundary conditions significantly alter stellar property predictions.

Asteroseismic age estimates can shift by more than 10%.

Gas Γ₁ approximation performs well for main-sequence stars.

Abstract

In a series of papers, we have recently demonstrated that it is possible to construct stellar structure models that robustly mimic the stratification of multi-dimensional radiative magneto-hydrodynamic simulations at every time-step of the computed evolution. The resulting models offer a more realistic depiction of the near-surface layers of stars with convective envelopes than parameterizations, such as mixing length theory, do. In this paper, we explore how this model improvement impacts on seismic and non-seismic properties of stellar models across the Hertzsprung-Russell diagram. We show that the improved description of the outer boundary layers alters the predicted global stellar properties at different evolutionary stages. In a hare and hound exercise, we show that this plays a key role for asteroseismic analyses, as it, for instance, often shifts the inferred stellar age estimates by more than 10 per cent. Improper boundary conditions may thus introduce systematic errors that exceed the required accuracy of the PLATO space mission. Moreover, we discuss different approximations for how to compute stellar oscillation frequencies. We demonstrate that the so-called gas $\Gamma_1$ approximation performs reasonably well for all main-sequence stars. Using a Monte Carlo approach, we show that the model frequencies of our hybrid solar models are consistent with observations within the uncertainties of the global solar parameters when using the so-called reduced $\Gamma_1$ approximation.