The HST Large Programme on ω Centauri

VII. The white dwarf cooling sequence

¹ Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Giuseppe Saragat 1, Ferrara 44122, Italy
² Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova 35122, Italy
³ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁴ Istituto Nazionale di Astrofisica, Osservatorio Astronomico d’Abruzzo, Via Mentore Maggini, Teramo 64100, Italy
⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218, USA
⁶ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, Padova 35122, Italy
⁷ Department of Astronomy, Indiana University, Swain West, 727 E. 3rd Street, Bloomington IN 47405, USA
⁸ Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, Quebec H3C 3J7, Canada
⁹ Department of Astronomy & Astrophysics, University of California, San Diego, La Jolla, California 92093, USA
¹⁰ Department of Astronomy and Steward Observatory, The University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA
¹¹ Lunar and Planetary Laboratory, The University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, USA

^⋆ Corresponding author; michele.scalco@inaf.it

Received: 27 June 2024
Accepted: 5 September 2024

Abstract

We present a study of the white dwarf (WD) cooling sequence (CS) in the globular cluster (GC) Omega Centauri (or NGC 5139; hereafter, ω Cen), the primary goal of a dedicated Hubble Space Telescope (HST) programme. We find that the peak at the termination of the WD CS is located at m_F606W = 30.1 ± 0.2 (equivalent to V ∼ 31). The brighter part of ω Cen’s WD CS is consistent with the presence of massive He-core WDs, in agreement with previous HST analyses with ultraviolet and blue filters. Comparative analyses of the WD luminosity function (LF) and theoretical counterparts show that a single-age population for the cluster is compatible with the data. However, an analysis of only the WD LF cannot entirely exclude the possibility of an age range, due to uncertainties in the present-day WD mass function, with a star formation history potentially spanning up to 5 billion years, predominantly comprising stars about 13 Gyr old, with a minority potentially as young as 8 Gyr. This underscores the need for global spectroscopic and photometric investigations that simultaneously include both the WD populations and the previous evolutionary phases, in order to fully understand the cluster’s diverse chemical compositions and ages.