The Onset of Convective Coupling and Freezing in the White Dwarfs of 47 Tucanae

Abstract

Using images from the Hubble Space Telescope Advanced Camera for Surveys, we measure the rate of cooling of white dwarfs in the globular cluster 47 Tucanae and compare it to modelled cooling curves. We examine the effects of the outer convective envelope reaching the nearly isothermal degenerate core and the release of latent heat during core crystallisation on the white dwarf cooling rates. For white dwarfs typical of 47 Tuc, the onset of these effects occur at similar times. The latent heat released during crystallisation is a small heat source. In contrast, the heat reservoir of the degenerate core is substantially larger. When the convective envelope reaches the nearly isothermal interior of the white dwarf, the star becomes brighter than it would be in the absence of this effect. Our modelled cooling curves that include this convective coupling closely match the observed luminosity function of the white dwarfs in 47 Tuc.

arXiv comment6 pages, 5 figures. Submitted to MNRAS

References in corpus (22)

• Modules for Experiments in Stellar Astrophysics (MESA)
• The Photometric Performance and Calibration of the HST Advanced Camera For Surveys
• An Improved Spectroscopic Analysis of DA White Dwarfs from the Sloan Digital Sky Survey Data Release 4
• Found: The missing blue opacity in atmosphere models of cool hydrogen white dwarfs
• Thermodynamic functions of dense plasmas: analytic approximations for astrophysical applications
• The Ages of the Thin Disk, Thick Disk, and the Halo from Nearby White Dwarfs
• The Masses of Population II White Dwarfs
• An Age Difference of 2 Gyr between a Metal-Rich and a Metal-Poor Globular Cluster
• Testing White Dwarf Crystallization Theory with Asteroseismology of the Massive Pulsating DA Star BPM 37093
• A Dynamical Signature of Multiple Stellar Populations in 47 Tucanae
• The Physics of Crystallization from Globular Cluster White Dwarf Stars in NGC 6397
• Calibration of the Mixing-Length Theory for Convective White Dwarf Envelopes
• The Spectral Energy Distributions of White Dwarfs in 47 Tucanae: The Distance to the Cluster
• Spectral Types and Masses of White Dwarfs in Globular Clusters
• A Deep, Wide-Field, and Panchromatic View of 47 Tuc and the SMC with HST: Observations and Data Analysis Methods
• A Deep Proper Motion Catalog Within the Sloan Digital Sky Survey Footprint. II. The White Dwarf Luminosity Function
• Deep HST Imaging in NGC 6397: Stellar Dynamics
• Comparing the White Dwarf Cooling Sequences in 47 Tuc and NGC 6397
• An Empirical Measure of the Rate of White Dwarf Cooling in 47 Tucanae
• When do stars in 47 Tucanae lose their mass?
• The Spectral Types of White Dwarfs in Messier 4
• Constraining white dwarf structure and neutrino physics in 47 Tucanae

Cited by in corpus (2)

• Core crystallization and pile-up in the cooling sequence of evolving white dwarfs
• The Cooling of Old White Dwarfs in 47 Tucanae