Photometric properties of stellar populations in Galactic globular clusters: the role of the Mg-Al anticorrelation

TL;DR

This study models the impact of Mg-Al anticorrelations on stellar populations in globular clusters, finding negligible effects on stellar evolution but identifying spectral features useful for chemical analysis.

Contribution

It extends previous models by including Mg-Al anticorrelations, showing their minimal impact on stellar models and spectra, and proposes narrow-band filters to detect Mg variations.

Findings

Mg-Al anticorrelations have negligible effect on stellar models and isochrones.

A spectral feature at 490-520 nm is identified for MgH molecular bands.

Narrow-band filters can detect Mg abundance variations in stars.

Abstract

We have computed low-mass stellar models and synthetic spectra for an initial chemical composition that includes the full C-N, O-Na, and Mg-Al abundance anticorrelations observed in second generation stars belonging to a number of massive Galactic globular clusters. This investigation extends a previous study that has addressed the effect of only the C-N and O-Na anticorrelations, seen in all globulars observed to date. We find that the impact of Mg-Al abundance variations at fixed [Fe/H] and Helium abundance is negligible on stellar models and isochrones (from the main sequence to the tip of the red giant branch) and bolometric corrections, when compared to the effect of C-N and O-Na variations. We identify a spectral feature at 490-520 nm, for low-mass main sequence stars, caused by MgH molecular bands. This feature has a vanishingly small effect on bolometric corrections for Johnson and Stroemgren filters that cover that spectral range. However, specific narrow-band filters able to target this wavelength region can be powerful tools to investigate the Mg-poor unevolved stars and highlight possible splittings of the MS due to variations of Mg abundances.