Abstract
The accretion of heavy material from debris disk on the surface of hydrogen-rich white dwarfs induces a double diffusivity instability known as the fingering convection. It leads to an efficient extra mixing which brings the accreted material deeper in the star than by considering only mixing in the surface dynamical convection zone, in a time scale much shorter than that of gravitational settling. We performed numerical simulations of a continuous accretion of heavy material having a bulk Earth composition on the two well studied DAZ and ZZ Ceti pulsators GD 133 and G 29-38. We find that the existence of fingering convection implies much larger accretion rates to explain the observed abundances than previous estimates based on the standard mixing length theory and gravitational settling only.
Highlights
The fate of planetary systemsWhat happens to planetary systems when their central star reaches the final evolutionary stage as a white dwarf? The study of the white dwarfs that exhibit debris disks and photospheric composition polluted by heavy elements may provide crucial informations on their formation, evolution and final fate
These estimates did not take into account the extra-mixing induced by the fingering convection resulting from the building of an inverse μ-gradient
We show here on the cases of the two well studied DAZ G29-38 and GD 133 how important is the extra-mixing induced by fingering convection and estimate new accretion rates
Summary
What happens to planetary systems when their central star reaches the final evolutionary stage as a white dwarf? The study of the white dwarfs that exhibit debris disks and photospheric composition polluted by heavy elements may provide crucial informations on their formation, evolution and final fate. Facultad de Ciencias Astronomicas y Geofısicas, Universidad Nacional de La Plata, Argentina
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