RR Lyrae variables in Galactic globular clusters: IV. Synthetic HB and RR Lyrae predictions

TL;DR

This paper provides theoretical predictions for RR Lyrae variables in globular clusters, linking pulsation properties with stellar evolution models across different metallicities and horizontal branch morphologies.

Contribution

It introduces synthetic models that connect evolutionary and pulsational constraints, offering new relations and predictions for RR Lyrae stars in globular clusters.

Findings

Good agreement with observed period-metallicity distribution

Period-K magnitude and Wesenheit relations are largely independent of HB morphology for Z ≥ 0.001

Predictions for the parameter R vary with assumed HB luminosity levels

Abstract

We present theoretical predictions concerning horizontal branch stars in globular clusters, including RR Lyrae variables, as derived from synthetic procedures collating evolutionary and pulsational constraints. On this basis, we explore the predicted behavior of the pulsators as a function of the horizontal branch morphology and over the metallicity range Z=0.0001 to 0.006, revealing an encouraging concordance with the observed distribution of fundamentalised periods with metallicity. Theoretical relations connecting periods to K magnitudes and BV or VI Wesenheit functions are presented, both appearing quite independent of the horizontal branch morphology only with Z greater or equal than 0.001. Predictions concerning the parameter R are also discussed and compared under various assumptions about the horizontal branch reference luminosity level.