The HST Large Programme on Omega Centauri -- VII. The white dwarf cooling sequence

TL;DR

This study analyzes the white dwarf cooling sequence in Omega Centauri using Hubble data, revealing details about the cluster's age, composition, and the presence of massive helium-core white dwarfs, with implications for its star formation history.

Contribution

It provides the first detailed characterization of the white dwarf cooling sequence in Omega Centauri, including the luminosity function and implications for the cluster's age spread and stellar populations.

Findings

Peak at WD CS termination at m_F606W=30.1±0.2

Presence of massive He-core white dwarfs

Possible age spread up to 5 billion years

Abstract

We present a study of the white dwarf (WD) cooling sequence (CS) in the globular cluster (GC) Omega Centauri, the primary goal of a dedicated Hubble Space Telescope (HST) programme. Our analysis has revealed that the peak at the termination of the WD CS is located at $m_{\rm F606W}$=30.1$\pm$0.2 (equivalent to $V$$\sim$31). The brighter part of Omega Centauri'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) with theoretical counterparts have shown that a single-age population for the cluster is compatible with the data. However, an analysis of just 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, and with just a minority potentially as young as 8 Gyr. This underscores the need for global spectroscopic and photometric investigations that include simultaneously the WD populations together with the previous evolutionary phases to fully understand the cluster's diverse chemical compositions and ages.