3 research outputs found
The effect of Ne diffusion in the evolution and pulsational properties of white dwarfs with solar metallicity progenitors
Because of the large neutron excess of Ne, this isotope rapidly
sediments in the interior of the white dwarfs. This process releases an
additional amount of energy, thus delaying the cooling times of the white
dwarf. This influences the ages of different stellar populations derived using
white dwarf cosmochronology. Furthermore, the overabundance of Ne in the
inner regions of the star, modifies the Brunt-V\"ais\"al\"a frequency, thus
altering the pulsational properties of these stars. In this work, we discuss
the impact of Ne sedimentation in white dwarfs resulting from Solar
metallicity progenitors (). We performed evolutionary calculations of
white dwarfs of masses , , and M_{\sun},
derived from full evolutionary computations of their progenitor stars, starting
at the Zero Age Main Sequence all the way through central hydrogen and helium
burning, thermally-pulsing AGB and post-AGB phases. Our computations show that
at low luminosities (\log(L/L_{\sun})\la -4.25), Ne sedimentation
delays the cooling of white dwarfs with Solar metallicity progenitors by about
1~Gyr. Additionally, we studied the consequences of Ne sedimentation on
the pulsational properties of ZZ~Ceti white dwarfs. We find that Ne
sedimentation induces differences in the periods of these stars larger than the
present observational uncertainties, particularly in more massive white dwarfs.Comment: Accepted for publication in ApJ. 8 pages, 6 figure
A consistency test of white dwarf and main sequence ages: NGC 6791
NGC 6791 is an open cluster that it is so close to us that can be imaged down to very faint luminosities. The main sequence turn-off age (âŒ8 Gyr) and the age derived from the cut-off of the white dwarf luminosity function (âŒ6 Gyr) were found to be significantly different. Here we demonstrate that the origin of this age discrepancy lies in an incorrect evaluation of the white dwarf cooling ages, and we show that when the relevant physical separation processes are included in the calculation of white dwarf sequences both ages are coincident