Metal-rich, Metal-poor: Updated Stellar Population Models for Old Stellar Systems

TL;DR

This paper introduces updated stellar population models for old stellar systems that cover a wide metallicity range, include detailed element abundance variations, and are validated against Galactic globular clusters using full spectrum fitting.

Contribution

The paper provides new comprehensive stellar population models with flexible element abundance variations and demonstrates their accuracy through fitting to globular cluster spectra.

Findings

Models accurately predict spectral variations with metallicity and age.

Full spectrum fitting yields smaller uncertainties than line index methods.

Good agreement with literature for metallicity and certain element abundance ratios.

Abstract

We present updated stellar population models appropriate for old ages (>1 Gyr) and covering a wide range in metallicities (-1.5<[Fe/H]<0.3). These models predict the full spectral variation associated with individual element abundance variation as a function of metallicity and age. The models span the optical-NIR wavelength range (0.37-2.4um), include a range of initial mass functions (IMFs) and contain the flexibility to vary 18 individual elements including C, N, O, Mg, Si, Ca, Ti, and Fe. To test the fidelity of the models we fit them to integrated light optical spectra of 41 Galactic globular clusters (GCs). The value of testing models against GCs is that their ages, metallicities, and detailed abundance patterns have been derived from the HR diagram in combination with high resolution spectroscopy of individual stars. We determine stellar population parameters from fits to all wavelengths simultaneously ("full spectrum fitting"), and demonstrate explicitly with mock tests that this approach produces smaller uncertainties at fixed S/N ratio than fitting a standard set of 14 line indices. Comparison of our integrated-light results to literature values reveals good agreement in metallicity, [Fe/H]. When restricting to GCs without prominent blue horizontal branch populations we also find good agreement with literature values for ages, [Mg/Fe], [Si/Fe], and [Ti/Fe].