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arXiv · 2509.26190

An excess of luminous white dwarfs in the peculiar Galactic globular cluster NGC 2808

Laksh Gupta·Samyaday Choudhury·Annalisa Calamida·Christian I. Johnson·Domenico Nardiello
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Abstract

We study the white dwarf (WD) cooling sequence of the Galactic Globular Cluster (GGC) NGC 2808 by using deep near-UV data from the Hubble Space Telescope and theoretical models, to investigate if this cluster hosts an excess of WDs. Excess in WDs is a rare phenomenon that has been found to exist only in a few GGCs. We compared star counts from different evolutionary phases on the near-UV color-magnitude diagram to evolutionary times predicted by BaSTI models. The investigation was carried out over a region within a radii of 1.5 $\arcmin$ of the cluster center and a region of similar dimension located 5$\arcmin$ away. We find a WD excess of $\approx$ 60 - 70\% when comparing star counts and evolutionary models of the WD cooling sequence to the main-sequence turn-off, and by using different values and fractions of Helium enhancement. This excess decreases to $\approx$ 30 - 40\% when the WD cooling sequence is compared to the horizontal branch. The WD excess is slightly larger in the internal field that covers the cluster center; however, the difference with the external field is compatible within the uncertainties. We argue that this excess is possibly related to the existence of SCWDs and Helium-core WDs in NGC~2808, and might be directly associated to the extended blue horizontal branch of this GGC.

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Laksh Gupta, Samyaday Choudhury, Annalisa Calamida, Christian I. Johnson, Domenico Nardiello. 2025-10-03. An excess of luminous white dwarfs in the peculiar Galactic globular cluster NGC 2808. https://doi.org/10.3847/1538-4357%2Fae0ca6

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