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

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.

arXiv comment21 pages, 10 figures, 11 tables, Accepted for publication in The Astrophysical Journal

References in corpus (61)

• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• A Triple Main Sequence in the Globular Cluster NGC 2808
• Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way
• A catalogue of masses, structural parameters and velocity dispersion profiles of 112 Milky Way globular clusters
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. I. Overview of the Project and Detection of Multiple Stellar Populations
• Gaia EDR3 view on Galactic globular clusters
• Age and Metallicity Distribution of the Galactic Bulge from Extensive Optical and Near-IR Stellar Photometry
• Ultraviolet Radiation from Evolved Stellar Populations -- I. Models
• A Catalog of Spectroscopically Confirmed White Dwarfs from the Sloan Digital Sky Survey Data Release 4
• SDSS DR7 White Dwarf Catalog
• White Dwarf Mass Distribution in the SDSS
• A helium spread among the main sequence stars in NGC 2808
• The early evolution of Globular Clusters: the case of NGC 2808
• New cooling sequences for old white dwarfs
• Super Helium-Rich Population and the Origin of Extreme Horizontal-Branch Stars in Globular Clusters
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. III. A quintuple stellar population in NGC2808
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters - XVII. Public Catalogue Release
• High-resolution UVES/VLT spectra of white dwarfs observed for the ESO SN Ia Progenitor Survey. III. DA white dwarfs
• New Asymptotic Giant Branch models for a range of metallicities
• The State-of-the-Art HST Astro-Photometric Analysis of the core of $\omega$ Centauri. I. The Catalog
• Stellar Evolution in NGC 6791: Mass Loss on the Red Giant Branch and the Formation of Low Mass White Dwarfs
• White dwarf evolutionary sequences for low-metallicity progenitors: The impact of third dredge-up
• The ELM Survey. IV. 24 White Dwarf Merger Systems
• Post-common envelope binaries from SDSS-X: The origin of low-mass white dwarfs
• The peculiar Horizontal Branch of NGC 2808
• Photometry of four binary subdwarf B stars and the nature of their unseen companion stars
• Discovery of another peculiar radial distribution of Blue Stragglers in Globular Clusters: The case of 47 Tuc
• The Lowest Mass White Dwarf
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XXIII. Proper-motion catalogs and internal kinematics
• White Dwarf Cosmochronology in the Solar Neighborhood
• Spectroscopic Analyses of the Blue Hook Stars in NGC 2808: A More Stringent Test of the Late Hot Flasher Scenario
• A possible solution for the lack of EHB binaries in globular clusters
• The infrared eye of the Wide-Field Camera 3 on the Hubble Space Telescope reveals multiple main sequences of very low-mass stars in NGC 2808
• The Na-O anticorrelation in horizontal branch stars. I. NGC 2808
• Peculiar Multimodality on the Horizontal Branch of the Globular Cluster NGC 2808
• The updated BaSTI stellar evolution models and isochrones. III. White Dwarfs
• Helium-Core White Dwarfs in the Globular Cluster NGC 6397
• The Helium White Dwarf orbiting the Millisecond Pulsar in the halo of the Globular Cluster NGC 6752
• Star Counts in the Globular Cluster Omega Centauri. I. Bright Stellar Components
• GeMS MCAO observations of the Galactic globular cluster NGC 2808: the absolute age
• On the Horizontal Branch of the Galactic Globular NGC2808
• On the white dwarf cooling sequence of the globular cluster Omega Centauri
• A Double White-Dwarf Cooling Sequence in ω Centauri
• The connection between missing AGB stars and extended horizontal branches
• First Detection of the White-Dwarf Cooling Sequence of the Galactic Bulge
• Absolute Magnitudes and Colors of RR Lyrae stars in DECam Passbands from Photometry of the Globular Cluster M5
• Discovery of more than two thousand white dwarfs in the globular cluster Omega Centauri
• Flash Mixing on the White Dwarf Cooling Curve: Spectroscopic Confirmation in NGC 2808
• Slowly cooling white dwarfs in M13 from stable hydrogen burning
• Hot subdwarfs in the Galactic Bulge
• High-precision abundances of first population stars in NGC 2808: confirmation of a metallicity spread
• A Robust Test of Evolution near the Tip of the Red Giant Branch and Missing Giants in NGC 2808
• The First Extensive Exploration of UV-bright Stars in the Globular Cluster NGC 2808
• Slowly cooling white dwarfs in NGC 6752
• A stellar census in globular clusters with MUSE. Metallicity spread and dispersion among first-population stars
• Comparison between Observed and Theoretical Red Giant Branch Luminosity Functions of Galactic Globular Clusters
• The internal kinematics of NGC 2808 and its multiple populations
• The "canonical" White Dwarf Cooling Sequence of M5
• A Wide View of the Galactic Globular Cluster NGC 2808: Red Giant and Horizontal Branch Star Spatial Distributions
• Globular Cluster UVIT Legacy Survey (GlobULeS) $-$ II. Evolutionary status of hot stars in M3 and M13