# The State-of-the-Art HST Astro-Photometric Analysis of the core of \omega Centauri. III. The Main Sequence's Multiple Populations Galore

## TL;DR

This study uses advanced Hubble Space Telescope photometry to identify and analyze at least 15 distinct stellar populations within the main sequence of Omega Centauri, revealing unprecedented complexity in its star formation history.

## Contribution

The paper introduces a novel multi-filter analysis strategy to distinguish multiple stellar populations and subpopulations in Omega Centauri's main sequence, expanding understanding of its stellar diversity.

## Key findings

- Identified at least 15 sub-populations within the main sequence.
- Confirmed the split of MSa into two subcomponents.
- Discovered new MS groups with multiple subcomponents.

## Abstract

We take advantage of the exquisite quality of the Hubble Space Telescope 26-filter astro-photometric catalog of the core of Omega Cen presented in the first paper of this series and the empirical differential-reddening correction presented in the second paper in order to distill the main sequence into its constituent populations. To this end, we restrict ourselves to the five most useful filters: the magic "trio" of F275W, F336W, and F438W, along with F606W and F814W. We develop a strategy for identifying color systems where different populations stand out most distinctly, then we isolate those populations and examine them in other filters where their sub-populations also come to light. In this way, we have identified at least 15 sub-populations, each of which has a distinctive fiducial curve through our 5-dimensional photometric space. We confirm the MSa to be split into two subcomponents, and find that both the bMS and the rMS are split into three subcomponents. Moreover, we have discovered two additional MS groups: the MSd (which has three subcomponents) shares similar properties with the bMS, and the MSe (which has four subcomponents), has properties more similar to those of the rMS. We examine the fiducial curves together and use synthetic spectra to infer relative heavy-element, light-element, and Helium abundances for the populations. Our findings show that the stellar populations and star formation history of Omega Cen are even more complex than inferred previously. Finally, we provide as a supplement to the original catalog a list that identifies for each star which population it most likely is associated with.