The ACS Survey of Galactic Globular Clusters. II. Stellar Evolution Tracks, Isochrones, Luminosity Functions, and Synthetic Horizontal-Branch Models

TL;DR

This paper provides a comprehensive set of stellar evolution models, isochrones, and synthetic horizontal-branch models tailored for analyzing high-quality photometric data of 65 galactic globular clusters from the ACS Survey, enhancing tools for stellar population studies.

Contribution

It introduces new stellar evolution tracks and isochrones across various metallicities, helium abundances, and ages, along with software for interpolation, luminosity functions, and synthetic horizontal-branch modeling.

Findings

Models cover a wide range of metallicities and ages.

Isochrones are converted to multiple observational filters.

Tools are provided for generating synthetic stellar populations.

Abstract

The ACS Survey of Galactic Globular Clusters, an HST Treasury Project, will deliver high quality, homogeneous photometry of 65 globular clusters. This paper introduces a new collection of stellar evolution tracks and isochrones suitable for analyzing the ACS Survey data. Stellar evolution models were computed at [Fe/H]= -2.5, -2.0, -1.5, -1.0, -0.5, and 0; [alpha/Fe]= -0.2, 0, 0.2, 0.4, 0.6, and 0.8; and three initial He abundances for masses from 0.1 to 1.8 Msun and ages from 2 to 15 Gyr. Each isochrone spans a wide range in luminosity from Mv~14 up to the tip of the red giant branch. These are complemented by a set of He-burning tracks that extend from the zero age horizontal branch to the onset of thermal pulsations on the asymptotic giant branch. In addition, a set of computer programs are provided that make it possible to interpolate the isochrones in [Fe/H], generate luminosity functions from the isochrones, and create synthetic horizontal branch models. The tracks and isochrones have been converted to the observational plane with two different color-Teff transformations, one synthetic and one semi-empirical, in ground-based B, V, and I, and F606W and F814W for both ACS-WFC and WFPC2 systems. All models and programs presented in this paper are available from http://stellar.dartmouth.edu/~models/