Globular Cluster UVIT Legacy Survey (GlobULeS). III. Omega Centauri in Far-ultraviolet
Abstract
We present the first comprehensive study of the most massive globular cluster, Omega Centauri, in the far-ultraviolet (FUV), extending from the center to ~28% of the tidal radius using the Ultraviolet Imaging Telescope on board AstroSat. A comparison of the FUV-optical color-magnitude diagrams with available canonical models reveals that horizontal branch (HB) stars bluer than the knee (hHBs) and the white dwarfs (WDs) are fainter in the FUV by ~0.5 mag than model predictions. They are also fainter than their counterparts in M13, another massive cluster. We simulated HB with at least five subpopulations, including three He-rich populations with a substantial He enrichment of Y up to 0.43 dex, to reproduce the observed FUV distribution. We find the He-rich younger subpopulations to be radially more segregated than the He-normal older ones, suggesting an in situ enrichment from older generations. The ω Cen hHBs span the same T eff range as their M13 counterparts, but some have smaller radii and lower luminosities. This may suggest that a fraction of ω Cen hHBs are less massive than those of M13, similar to the result derived from earlier spectroscopic studies of outer extreme HB stars. The WDs in ω Cen and M13 have similar luminosity-radius-T eff parameters, and 0.44-0.46 M ⊙ He-core WD model tracks evolving from progenitors with Y = 0.4 dex are found to fit the majority of these. This study provides constraints on the formation models of ω Cen based on the estimated range in age, [Fe/H], and Y (in particular) for the HB stars.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2022
- DOI:
- 10.3847/2041-8213/ac9901
- arXiv:
- arXiv:2210.05160
- Bibcode:
- 2022ApJ...939L..20P
- Keywords:
-
- Globular star clusters;
- Horizontal branch stars;
- Ultraviolet photometry;
- White dwarf stars;
- Hertzsprung Russell diagram;
- Extreme horizontal branch stars;
- Late stellar evolution;
- Helium-rich stars;
- 656;
- 746;
- 1740;
- 1799;
- 725;
- 513;
- 911;
- 715;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in ApJL