Beat Cepheids as Probes of Stellar and Galactic Metallicity: The New AGS Abundances

TL;DR

This paper updates the use of Beat Cepheids as metallicity probes by incorporating recent solar abundance revisions and examines how envelope modeling affects period predictions, highlighting the importance of detailed stellar models.

Contribution

It revises previous metallicity constraints from Beat Cepheids using the latest AGS solar mixture and analyzes the impact of envelope depth on pulsation period accuracy.

Findings

Updated metallicity bounds using AGS solar mixture

Envelope depth significantly affects period calculations for low-period, high-Z Cepheids

Most observed Beat Cepheids are not in the regime requiring full stellar modeling

Abstract

It is well known that the mere location of a Beat Cepheid model in a Period Ratio \vs Period diagram (Petersen diagram) puts constraints on its metallicity Z. But these bounds are sensitive to the mixture of elements that are lumped into the parameter $Z$. In this short paper we update the previous results that were based on the Grevesse-Noels solar mixture to the recent, revised Asplund, Grevesse & Sauval (2005) (AGS) solar mixture. We also examine the effect of the envelope depth on the accuracy of the computed pulsation periods. We find that for low period Cepheids with high Z the customary approximation of envelope pulsation breaks down. It is necessary to compute stellar models that extend to the center and to include burning and composition inhomogeneities in the modeling. Fortunately, however, most Beat Cepheids that have been observed so far seem to avoid that regime.