The PGPUC horizontal branch evolutionary tracks

¹ Departamento de Física, FACI, Universidad de Tarapacá, Casilla 7D, Arica, Chile
² Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
³ Millennium Institute of Astrophysics, Nuncio Monseñor Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile
⁴ Centro de Astro-Ingeniería, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile

^⋆ Corresponding author.

Received: 10 April 2025
Accepted: 1 June 2025

Abstract

Context. The horizontal branch (HB) phase of stellar evolution plays a critical role in understanding the life cycle of stars, particularly in the context of low-mass stars. However, generating theoretical evolutionary tracks for HB stars is computationally intensive, especially when attempting to match a wide range of observational data.

Aims. This work presents an extensive grid of HB evolutionary tracks computed using the PGPUC code, covering a broad range of chemical compositions, progenitor masses, and alpha-element distributions. The aim is to provide a robust tool for interpreting HB stellar populations and advancing our understanding of their diverse properties. The evolutionary tracks are made publicly available through the PGPUC Online database for easy access and interpolation.

Methods. We computed over 19 000 HB evolutionary tracks encompassing a wide range in terms of mass, metallicity, helium abundance, and alpha-element enhancement, along with different progenitor masses. Using these tracks, we calculated zero-age, middle-age, and terminal-age loci.

Results. The PGPUC database now includes a fine grid of HB evolutionary tracks, allowing for precise interpolation. Key findings include the dependence of HB morphology on progenitor mass, metallicity, and helium abundance.