Globular Cluster UVIT Legacy Survey (GlobULeS). III. Omega Centauri in Far-ultraviolet

Deepthi S. Prabhu, Annapurni Subramaniam, Snehalata Sahu, Chul Chung, Nathan W.C. Leigh, Emanuele Dalessandro, Sourav Chatterjee, N. Kameswara Rao, Michael Shara, Patrick Côté, Samyaday Choudhury, Gajendra Pandey, Aldo A.R. Valcarce, Gaurav Singh, Joesph E. Postma, Sharmila Rani, Avrajit Bandyopadhyay, Aaron M. Geller, John Hutchings, Thomas PuziaMirko Simunovic, Young Jong Sohn, Sivarani Thirupathi, Ramakant Singh Yadav

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Article numberL20
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Nov 1 2022

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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