Full evolution of low-mass white dwarfs with helium and oxygen cores

PANEI, J.; ALTHAUS, L. G.; CHEN, X.; HAN, Z.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Blackwell Publishing

Año: 2007 vol. 382 p. 779 - 792

0035-8711

We study the full evolution of low-mass white dwarfs with helium  and oxygen cores. We revisit the age dichotomy observed in many white dwarf companions to millisecond pulsar on the basis of white dwarf configurations derived from binary evolution computations. We evolve eleven dwarf sequences for helium cores with final masses of 0.1604, 0.1869, 0.2026, 0.2495, 0.3056, 0.3333, 0.3515, 0.3844, 0.3986, 0.4160, and 0.4481 M_sun. In addition, we compute the evolution of five sequences for oxygen cores with final masses of0.3515, 0.3844, 0.3986, 0.4160, and 0.4481 M_sun. A metallicity of Z=0.02 is assumed. Gravitational settling, chemical and thermal diffusion are accounted for during the white dwarf regime. Our study reinforces the result that diffusion processes are a key ingredient in explaining the observed age and envelope dichotomyin low-mass helium-core white dwarfs, a conclusion we arrived atearlier on the basis of a simplified treatment for the binaryevolution of progenitors stars. We determine the mass threshold where the age dichotomy occurs. For the oxygen white dwarf sequences, we report the occurrence of diffusion-induced, hydrogen shell flashes, which, as in the case of their helium counterparts, strongly influence the late stages of white dwarf cooling. Finally, we present our results as a set of white dwarf mass-radius relations for helium and oxygen cores.