On the use of the average large separation in surface layer independent model fitting

TL;DR

This paper investigates the impact of outer stellar layers on the large separation used in asteroseismic modeling, showing that surface layers significantly influence this parameter and should not be used as surface-layer independent constraints.

Contribution

It quantifies the contribution of outer stellar layers to the large separation and argues against using it as a surface-layer independent constraint in stellar modeling.

Findings

Outer 0.1% of the star's radius contributes about 6% to the large separation.

Outer 5% of the star's radius contributes about 30% to the large separation.

Mass derived from surface gravity aligns better with binary mass than that from large separation.

Abstract

The physics of the outer layers of a star are not well understood but these layers make a major contribution to the large separation. We quantify this using stellar models and show that the contribution ranges from 6\% from the outer 0.1\% of the radius to 30\% from the outer 5\%. and therefore argue that the large separation should not be used as a constraint on surface layer independent model fitting. The mass and luminosity are independent of the outer layers and can be used as constraints, the mass being determined from binarity or from surface gravity and radius. The radius can be used as a constraint but with enhanced error estimates. We briefly consider the determination of the large separation for $\alpha$ Cen A and find that mass derived from surface gravity is closer to the binary mass than that derived from the large separation.