Photometric Metallicities for 367,324 stars of Omega Centauri

TL;DR

This study develops a photometric method using HST data to estimate metallicities for stars in Omega Centauri, creating a large catalog that reveals well-mixed stellar populations without significant metallicity gradients.

Contribution

The paper introduces a new photometric metallicity estimation technique applied to a large star sample in Omega Centauri, extending previous metallicity catalogs and enabling analysis of stellar population mixing.

Findings

No significant metallicity gradient within the half-light radius.

The ring-like structure in metallicity is less pronounced, indicating well-mixed populations.

The catalog includes over 367,000 stars with estimated metallicities, enhancing previous data sets.

Abstract

Omega Centauri is the most massive and chemically complex multi-population globular cluster with a wide metallicity range that has been extensively studied photometrically and spectroscopically. Using the wide metallicity range of omega Cen, HST photometry (F275W, F336W, F435W, F625W), and MUSE spectroscopy ([M/H]), we derive [M/H]- and M_{F625W}-dependent stellar loci to estimate photometric metallicities from HST colors. Our tests yield metallicity precisions of 0.10\,dex for giants and 0.22\,dex for fainter dwarfs. We construct a photometric metallicity catalog from simultaneous F336W, F435W, and F625W observations (plus F275W where available), containing 20,778 giants and 346,546 dwarfs. A subsample of 20,533 giants is used to study the spatial metallicity distribution and gradient. We find no significant metallicity gradient within the half-light radius, consistent with previous work. Moreover, the previously reported ring-like structure is less pronounced in our data, and no physically significant, irregular two-dimensional metallicity pattern is detected, indicating that the stellar subpopulations are well mixed within the half-light radius. Our catalog significantly extends the metallicity sample of omega Cen, and this approach can be applied to other HST data to estimate photometric metallicities.