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

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

2000-06-26

arxiv.org/abs/astro-ph/0006363v1

Astronomy and Astrophysics

Astrophysics

43 pages, Latex file, uses aasms4.sty, accepted for publication in ApJ (November 10 issue)

Scientific paper

10.1086/317092

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 H$_2$-H$_2$ 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 $L$-$T_c$ relation. The maximum time delay due to crystallization-induced chemical fractionation remains substantial, from $\sim 1.0$ Gyr for 0.5 and 1.2 $\msol$ white dwarfs to $\sim 1.5$ 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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