INVESTIGADORES
MILLER BERTOLAMI Marcelo Miguel
artículos
Título:
Outer boundary conditions for evolving cool white dwarfs
Autor/es:
ROHRMANN, R. D.; ALTHAUS, L. G.; GARCIA-BERRO, E.; CORSICO, A.; M. M. MILLER BERTOLAMI
Revista:
ASTRONOMY AND ASTROPHYSICS
Editorial:
EDP SCIENCES S A
Referencias:
Lugar: Paris; Año: 2012 vol. 546 p. 119 - 125
ISSN:
0004-6361
Resumen:
Context. White dwarf evolution is essentially a gravothermal cooling
process, which, for cool white dwarfs, depends on the treatment of the
outer boundary conditions. Aims: We provide detailed outer
boundary conditions that are appropriate to computing the evolution of
cool white dwarfs by employing detailed nongray model atmospheres for
pure hydrogen composition. We also explore the impact on the white dwarf
cooling times of different assumptions for energy transfer in the
atmosphere of cool white dwarfs. Methods: Detailed nongray model
atmospheres were computed by considering nonideal effects in the gas
equation of state and chemical equilibrium, collision-induced absorption
from molecules, and the Lyman α quasi-molecular opacity. We
explored the impact of outer boundary conditions provided by updated
model atmospheres on the cooling times of 0.60 and 0.90
M⊙ white dwarf sequences. Results: Our results
show that the use of detailed outer boundary conditions becomes relevant
for effective temperatures lower than 5800 K for sequences with 0.60
M⊙ and 6100 K with 0.90 M⊙. Detailed model
atmospheres predict ages that are up to ≈10% shorter at log
(L/L⊙) = -4 when compared with the ages derived using
Eddington-like approximations at τRoss = 2/3. We also
analyze the effects of various assumptions and physical processes that
are relevant in the calculation of outer boundary conditions. In
particular, we find that the Lyα red wing absorption does not
substantially affect the evolution of white dwarfs. Conclusions:
White dwarf cooling timescales are sensitive to the surface boundary
conditions for Teff ≲ 6000 K. Interestingly enough,
nongray effects have few consequences on these cooling times at
observable luminosities. In fact, collision-induced absorption
processes, which significantly affect the spectra and colors of old
white dwarfs with hydrogen-rich atmospheres, have no noticeable effects
on their cooling rates, except throughout the Rosseland mean opacity.