Radial distribution of the multiple stellar populations in omega Centauri

TL;DR

This study maps the radial distribution of multiple stellar populations in omega Centauri, revealing how different populations vary with distance from the core and their metallicity-related properties.

Contribution

It provides a detailed, multi-instrument analysis of the spatial distribution of stellar populations in omega Centauri, highlighting differences in their radial profiles and metallicity.

Findings

Blue main sequence stars are slightly more numerous than red main sequence stars in the core.

The ratio of blue to red main sequence stars decreases steeply with radius and then stabilizes.

The color dispersion of blue main sequence stars is greater than that of red main sequence stars.

Abstract

We present a detailed study of the radial distribution of the multiple populations identified in the Galactic globular cluster omega Cen. We used both space-based images (ACS/WFC and WFPC2) and ground-based images (FORS1@VLT and WFI@2.2m ESO telescopes) to map the cluster from the inner core to the outskirts (~20 arcmin). These data sets have been used to extract high-accuracy photometry for the construction of color-magnitude diagrams and astrometric positions of ~900 000 stars. We find that in the inner ~2 core radii the blue main sequence (bMS) stars slightly dominate the red main sequence (rMS) in number. At greater distances from the cluster center, the relative numbers of bMS stars with respect to rMS drop steeply, out to ~8 arcmin, and then remain constant out to the limit of our observations. We also find that the dispersion of the Gaussian that best fits the color distribution within the bMS is significantly greater than the dispersion of the Gaussian that best fits the color distribution within the rMS. In addition, the relative number of intermediate-metallicity red-giant-branch stars which includes the progeny of the bMS) with respect to the metal-poor component (the progeny of the rMS) follows a trend similar to that of the main-sequence star-count ratio N_bMS/N_rMS. The most metal-rich component of the red-giant branch follows the same distribution as the intermediate-metallicity component. We briefly discuss the possible implications of the observed radial distribution of the different stellar components in omega Cen.