IALP   13078
INSTITUTO DE ASTROFISICA LA PLATA
Unidad Ejecutora - UE
artículos
Título:
Evolution of White Dwarf Stars with High-metallicity Progenitors: The Role of 22Ne Diffusion
Autor/es:
ALTHAUS, L. G.; GARCIA-BERRO, E.; RENEDO, I.; ISERN, J.; CORSICO, A. H.; ROHRMANN, R. D.
Revista:
ASTROPHYSICAL JOURNAL
Editorial:
IOP PUBLISHING LTD
Referencias:
Año: 2010 vol. 719 p. 612 - 621
ISSN:
0004-637X
Resumen:
Motivated by the strong discrepancy between the main-sequence turnoff
age and the white dwarf cooling age in the metal-rich open cluster NGC
6791, we compute a grid of white dwarf evolutionary sequences that
incorporates for the first time the energy released by the processes of
22Ne sedimentation and of carbon/oxygen phase separation upon
crystallization. The grid covers the mass range from 0.52 to 1.0 M
sun, and is appropriate for the study of white dwarfs in
metal-rich clusters. The evolutionary calculations are based on a
detailed and self-consistent treatment of the energy released from these
two processes, as well as on the employment of realistic carbon/oxygen
profiles, of relevance for an accurate evaluation of the energy released
by carbon/oxygen phase separation. We find that 22Ne
sedimentation strongly delays the cooling rate of white dwarfs stemming
from progenitors with high metallicities at moderate luminosities, while
carbon/oxygen phase separation adds considerable delays at low
luminosities. Cooling times are sensitive to possible uncertainties in
the actual value of the diffusion coefficient of 22Ne.
Changing the diffusion coefficient by a factor of 2 leads to maximum age
differences of ≈8%-20% depending on the stellar mass. We find that
the magnitude of the delays resulting from chemical changes in the core
is consistent with the slowdown in the white dwarf cooling rate that is
required to solve the age discrepancy in NGC 6791.