JWST imaging of omega Centauri

II. Evidence of a split white dwarf cooling sequence in the near-infrared

¹ Department of Astronomy, Indiana University, Swain West, 727 E. 3rd Street, Bloomington, IN 47405, USA
² Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
³ Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Abruzzo, via M. Maggini sn, I-64100 Teramo, Italy
⁴ Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova I-35122, Italy
⁵ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 2Y2, Canada
⁶ Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, Quebec H3C 3J7, Canada
⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁸ Department of Astronomy & Astrophysics, University of California, San Diego, La Jolla, California 92093, USA
⁹ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, Padova I-35122, Italy
¹⁰ Department of Physics and Astronomy, University of Notre Dame, Nieuwland Science Hall, Notre Dame, Indiana 46556, USA
¹¹ Department of Astronomy and Steward Observatory, The University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA
¹² Lunar and Planetary Laboratory, The University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, USA

^⋆ Corresponding author: mscalco@iu.edu

Received: 2 September 2025
Accepted: 9 October 2025

Abstract

We present a detailed analysis of the white dwarf (WD) cooling sequence (CS) in omega Centauri based on combined Hubble Space Telescope (HST) and JWST observations. Our analysis confirms the previously reported split –based on HST observations in ultraviolet filters – in the upper part of the WD CS, which is consistent with the presence of two distinct WD populations. We extend its study to a significantly fainter and cooler limit (down to ∼8000 K), which corresponds to cooling ages of about 1 Gyr. We used artificial star tests and cooling models to confirm that the split is evidence of two WD populations with different masses and progenitors: one sequence of ‘canonical’ WDs produced by the He-normal progenitors and one sequence of low-mass WDs that originated from the cluster He-rich component. We show that the fraction of WDs from the He-rich component in the outer regions is smaller than that found in the innermost regions. We also studied the kinematics of WDs and show that in the outer regions, the velocity distribution of WDs from He-rich progenitors is slightly radially anisotropic, while that of canonical WDs is slightly tangentially anisotropic. Both the radial variation in the fraction of WDs from the He-rich population and the difference between their velocity distribution and that of canonical WDs are consistent with spatial and kinematic differences previously found for He-rich and He-normal main-sequence stars and are in general agreement with models that predict that He-rich stars form more centrally concentrated than He-normal stars.