Research Note

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

Astronomy Unit, Queen Mary University of London, Mile End Road, London E1 4NS, UK
e-mail: I.W.Roxburgh@qmul.ac.uk

Received: 8 June 2014
Accepted: 1 September 2014

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%; it would therefore be inconsistent to impose the large separation 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. Using stellar models we show that the errors in estimating mass from the scaling relation between mass, radius and large separation can be up to 30%, and that the errors are not reduced on using the asymptotic value of the large separation estimated by extrapolation to high frequencies.