Dwarf Spheroidals and the Evolution of Not-Too-Old Population II Stars

TL;DR

This paper extends stellar evolutionary models to lower metallicities, providing new isochrones for young clusters and identifying potential anomalous helium-burning variables in low-metallicity environments.

Contribution

It presents extended evolutionary computations and isochrones for stars with very low metallicities and ages down to 1 billion years, highlighting features of helium burning phases.

Findings

Clusters with Z ≈ 1E-4 and ages 1-2 billion years may host anomalous He burning variables.

Isochrones for metallicities Z=10E-4 and 4E-4 are provided for ages down to 1 billion years.

Structural features during H and He burning phases are characterized for low-metallicity stars.

Abstract

Previous evolutionary computations concerning stars with masses in the range of the ``Red Giants Transition Phase'' are extended to lower metallicities. Clusters isochrones for two values of the metallicity Z (Z=10E-4, 4E-4) and for ages down to 1 billion years are presented, discussing selected evolutionary features characterizing the structure of the stars during both H or He burning phases. One finds that clusters with Z about equal to 1E-4 an age around 1-2 billion years could be characterized by the occurrence of anomalous He burning variables at a luminosity of the order of LogL= 2.0-2.2 (in solar units).