Models of Metal-Poor Stars with Different Initial Abundances of C, N, O, Mg, and Si. I. Bolometric Corrections Derived from New MARCS Synthetic Spectra and Their Implications for Observed Colour-Magnitude Diagrams

TL;DR

This paper presents new synthetic spectra and bolometric corrections for metal-poor stars with varied elemental abundances, improving stellar models and their fit to observed colour-magnitude diagrams, especially for HST data.

Contribution

It introduces updated MARCS synthetic spectra with detailed molecular treatments and computes stellar evolutionary grids for different metal mixtures, enhancing stellar modeling accuracy.

Findings

Significant differences in BCs for UV and blue passbands compared to previous models.

Improved fits of isochrones to HST photometry of globular cluster NGC 6496.

Enhanced understanding of the effects of elemental abundance variations on stellar colors.

Abstract

New, high-resolution MARCS synthetic spectra have been calculated for more than a dozen mixtures of the metals allowing, in turn, for variations in C:N:O, [CNO/Fe], and enhanced abundances of C, O, Mg, and Si. Bolometric Corrections (BCs) for many of the broad-band filters currently in use have been generated from these spectra. Due to improved treatments of molecules that involve atoms of C, N, and O, the BCs for UV and blue passbands, in particular, differ substantially from those derived from previous MARCS models. These differences, and the effects on BCs of varying the abundances of the metals, are shown in a number of instructive plots. Stellar evolutionary grids for -2.5 <= [Fe/H] <= -0.5 have also been computed for the different mixtures. Isochrones based on these tracks are intercompared on the theoretical H-R diagram and on a few of the colour-magnitude diagrams that can be constructed from HST Wide Field Camera 3 (WFC3) F336W, F438W, F606W, F814W, F110W, and F160W observations. For the first application of these models, isochrones have been fitted to WFC3 photometry of the globular cluster NGC 6496 from the HST UV Legacy Survey, with very encouraging results.