Cooling sequences and color-magnitude diagrams for cool white dwarfs with hydrogen-atmospheres

Jun, 2000
43 pages
Published in:
  • Astrophys.J. 543 (2000) 216
e-Print:

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Abstract: (arXiv)
We present new cooling sequences, color-magnitude diagrams, and color-color diagrams for cool white dwarfs with pure hydrogen atmospheres down to an effective temperature \te=1500 K. We include a more detailed treatment of the physics of the fully-ionized interior, particularly an improved discussion of the thermodynamics of the temperature-dependent ion-ion and ion-electron contributions of the quantum, relativistic electron-ion plasma. The present calculations also incorporate accurate boundary conditions between the degenerate core and the outermost layers as well as updated atmosphere models including the H2_2-H2_2 induced-dipole absorption. We examine the differences on the cooling time of the star arising from uncertainties in the initial carbon-oxygen profile and the core-envelope LL-TcT_c relation. The maximum time delay due to crystallization-induced chemical fractionation remains substantial, from 1.0\sim 1.0 Gyr for 0.5 and 1.2 \msol white dwarfs to 1.5\sim 1.5 Gyr for 0.6 to 0.8 \msol white dwarfs, even with initial stratified composition profiles, and cannot be ignored in detailed white dwarf cooling calculations. These cooling sequences provide theoretical support to search for or identify old disk or halo hydrogen-rich white dwarfs by characterizing their mass and age from their observational signatures.
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