The mosaic multiple stellar populations in $\omega$ Centauri : the Horizontal Branch and the Main Sequence

TL;DR

This study uses population synthesis to interpret the complex stellar populations of $mbda$ Centauri, successfully reproducing observed features and suggesting coeval populations with varying helium and CNO contents, shedding light on its evolutionary history.

Contribution

It presents a novel population synthesis model that explains multiple stellar populations in $mbda$ Centauri without requiring significant age spreads, incorporating helium and CNO variations.

Findings

No significant age spread needed; populations are coeval within 0.5 Gyr.

Successful reproduction of the horizontal branch and main sequence features.

Explains the split in the red HB with two distinct stellar populations.

Abstract

We interpret the stellar population of $\omega$ Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch data. The reproduction of the observed colour magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: 1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a $\sim 0.5$ Gyr time interval; in particular the most metal rich population can be coeval (in the above meaning) with the others, if its stars are very helium--rich (Y$\sim$0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = + 0.7); 2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub giant data. 3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars.