2025/09/30 by Gupta, Laksh, Choudhury, Samyaday, Calamida, Annalisa +2
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2509.26190
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 ≈ 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 ≈ 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.