IALP   13078
INSTITUTO DE ASTROFISICA LA PLATA
Unidad Ejecutora - UE
artículos
Título:
New evolutionary sequences for extremely low-mass white dwarfs. Homogeneous mass and age determinations and asteroseismic prospects
Autor/es:
ALTHAUS, L. G.; MILLER BERTOLAMI, M. M.; CÓRSICO, A. H.
Revista:
ASTRONOMY AND ASTROPHYSICS
Editorial:
EDP SCIENCES S A
Referencias:
Lugar: Paris; Año: 2013 vol. 557 p. 19 - 31
ISSN:
0004-6361
Resumen:
Context. The number of detected extremely low-mass (ELM) white
dwarf stars has increased drastically in recent years, thanks to the
results of many surveys. In addition, some of these stars have been
found to exhibit pulsations, making them potential targets for
asteroseismology.
Aims. We provide a fine and homogeneous grid of
evolutionary sequences for helium (He) core white dwarfs for the whole
range of their expected masses (0.15 ≲ M∗/M⊙ ≲ 0.45), including the mass range for ELM white dwarfs (M∗/M⊙ ≲ 0.20).
The grid is appropriate for mass and age determination of these stars,
as well as for studying their adiatabic pulsational properties.
Methods. White dwarf sequences have been computed by
performing full evolutionary calculations that consider the main energy
sources and processes of chemical abundance changes during white dwarf
evolution. Realistic initial models for the evolving white dwarfs have
been obtained by computing the nonconservative evolution of a binary
system consisting of an initially 1 M⊙ ZAMS star and a 1.4 M⊙
neutron star for various initial orbital periods. To derive cooling
ages and masses for He-core white dwarfs, we perform a least square
fitting of the M(Teff,g) and Age(Teff,g)
relations provided by our sequences by using a scheme that takes into
account the time spent by models in different regions of the Teff − g
plane. This is particularly useful when multiple solutions for cooling
age and mass determinations are possible in the case of CNO-flashing
sequences. We also explore in a preliminary way the adiabatic
pulsational properties of models near the critical mass for the
development of CNO flashes (~0.2 M⊙). This is motivated by the discovery of pulsating white dwarfs with stellar masses near this threshold value.
Results. We obtain reliable and homogeneous mass and
cooling age determinations for 58 very low-mass white dwarfs, including
three pulsating stars. Also, we find substantial differences in the
period spacing distributions of g-modes for models with stellar masses near ~ 0.2 M⊙,
which could be used as a seismic tool to distinguish stars that have
undergone CNO flashes in their early cooling phase from those that have
not. Finally, for an easy application of our results, we provide a
reduced grid of values useful to obtain the masses and ages of He-core
white dwarfs.