On the asymptotic acoustic-mode phase in red-giant stars and its dependence on evolutionary state

TL;DR

This paper analyzes how the asymptotic acoustic-mode phase in red giants varies with evolutionary state, revealing differences linked to the thermodynamic state of their convective envelopes and potential for stellar classification.

Contribution

It provides a detailed analysis of the relation between the asymptotic phase and stellar evolution, highlighting its dependence on the convective envelope's thermodynamic state and its use in stellar classification.

Findings

Phase differences distinguish red giants from helium-burning stars.

Potential to determine helium abundance via acoustic glitches.

Phase analysis can classify stars with short observational data.

Abstract

Asteroseismic investigations based on the wealth of data now available,in particular from the CoRoT and Kepler missions, require a good understanding of the relation between the observed quantities and the properties of the underlying stellar structure. Kallinger et al. 2012 found a relation between their determination of the asymptotic phase of radial oscillations in evolved stars and the evolutionary state, separating ascending-branch red giants from helium-burning stars in the `red clump'. Here we provide a detailed analysis of this relation, which is found to derive from differences between these two classes of stars in the thermodynamic state of the convective envelope. There is potential for distinguishing red giants and clump stars based on the phase determined from observations that are too short to allow distinction based on determination of the period spacing for mixed modes. The analysis of the phase may also point to a better understanding of the potential for using the helium-ionization-induced acoustic glitch to determine the helium abundance in the envelopes of these stars.