Measuring mean densities of delta Scuti stars with asteroseismology. Theoretical properties of large separations using TOUCAN

TL;DR

This paper investigates the theoretical relationship between large frequency separations and mean densities in delta Scuti stars using a new VO tool, TOUCAN, revealing a linear relation applicable under certain conditions.

Contribution

It introduces a new method for estimating delta Scuti stars' mean densities through asteroseismology, validated with observational data, and discusses the method's accuracy and limitations.

Findings

Linear relation between large separation and mean density in delta Scuti stars.

Method's accuracy within 20% when applied to observed stars.

Applicability limited to stars rotating up to 40% of break-up velocity.

Abstract

We aim at studying the theoretical properties of the regular spacings found in the oscillation spectra of delta Scuti stars. We performed a multi-variable analysis covering a wide range of stellar structure and seismic properties and model parameters representative of intermediate-mass, main sequence stars. The work-flow is entirely done using a new Virtual Observatory tool: TOUCAN (the VO gateway for asteroseismic models), which is presented in this paper. A linear relation between the large separation and the mean density is predicted to be found in the low frequency frequency domain (i.e. radial orders spanning from 1 to 8, approximately) of the main-sequence, delta Scuti stars' oscillation spectrum. We found that such a linear behavior stands whatever the mass, metallicity, mixing length, and overshooting parameters considered in this work. The intrinsic error of the method is discussed. This includes the uncertainty in the large separation determination and the role of rotation. The validity of the relation found is only guaranteed for stars rotating up to 40 percent of their break-up velocity. Finally, we applied the diagnostic method presented in this work to five stars for which regular patterns have been found. Our estimates for the mean density and the frequency of the fundamental radial mode match with those given in the literature within a 20 percent of deviation. Asteroseismology has thus revealed an independent direct measure of the average density of delta Scuti stars, analogous to that of the Sun. This places tight constraints on the mode identification and hence on the stellar internal structure and dynamics, and allows a determination the radius of planets orbiting around delta Scuti stars with unprecedented precision. This opens the way for studying the evolution of regular patterns in pulsating stars, and its relation with stellar structure and evolution.