284 research outputs found
Grids of white dwarf evolutionary models with masses from M= 0.1 to 1.2 Ms
We present detailed evolutionary calculations for carbon
- oxygen - and helium - core white dwarf (WD) models with masses ranging from
M= 0.1 to M= 1.2 solar masses and for metallicities Z= 0.001 and Z= 0. The
sequences cover a wide range of hydrogen envelopes as well. We employed a
detailed WD evolutionary code. In particular, the energy transport by
convectcion is treated within the formalism of the full spectrum turbulence
theory. The set of models presented here is very detailed and should be
valuable for the interpretation of the observational data on low - mass WDs
recently discovered in numerous binary configurations and also for the general
problem of determining the theoretical luminosity function for WDs. In this
context, we compare our cooling sequences with the observed WD luminosity
function recently improved by Leggett, Ruiz and Bergeron (1998) and we obtain
an age for the Galactic disc of approximately 8 Gyr. Finally, we applied the
results of this paper to derive stellar masses of a sample of low - mass white
dwarfs.Comment: 9 pages, 8 figures; accepted for publication in MNRAS; replaced with
minor corrections to tex
On the occurrence and detectability of Bose-Einstein condensation in helium white dwarfs
It has been recently proposed that helium white dwarfs may provide promising
conditions for the occurrence of the Bose-Einstein condensation. The argument
supporting this expectation is that in some conditions attained in the core of
these objects, the typical De Broglie wavelength associated with helium nuclei
is of the order of the mean distance between neighboring nuclei. In these
conditions the system should depart from classical behavior showing quantum
effects. As helium nuclei are bosons, they are expected to condense.
In order to explore the possibility of detecting the Bose-Einstein
condensation in the evolution of helium white dwarfs we have computed a set of
models for a variety of stellar masses and values of the condensation
temperature. We do not perform a detailed treatment of the condensation process
but mimic it by suppressing the nuclei contribution to the equation of state by
applying an adequate function. As the cooling of white dwarfs depends on
average properties of the whole stellar interior, this procedure should be
suitable for exploring the departure of the cooling process from that predicted
by the standard treatment.
We find that the Bose-Einstein condensation has noticeable, but not dramatic
effects on the cooling process only for the most massive white dwarfs
compatible with a helium dominated interior (\approx 0.50 M_\odot) and very low
luminosities (say, Log(L/L_\odot) < -4.0). These facts lead us to conclude that
it seems extremely difficult to find observable signals of the Bose-Einstein
condensation.
Recently, it has been suggested that the population of helium white dwarfs
detected in the globular cluster NGC 6397 is a good candidate for detecting
signals of the Bose-Einstein condensation. We find that these stars have masses
too low and are too bright to have an already condensed interior.Comment: 13 pages, 3 figures, 2 tables, accepted for publication in the
Journal of Cosmology and Astroparticle Physics (JCAP
Strangelet spectra from type II supernovae
We study in this work the fate of strangelets injected as a contamination in
the tail of a "strange matter-driven" supernova shock. A simple model for the
fragmentation and braking of the strangelets when they pass through the
expanding oxygen shell is presented and solved to understand the reprocessing
of this component. We find that the escaping spectrum is a scaled-down version
of the one injected at the base of the oxygen shell. The supernova source is
likely to produce low-energy particles of quite independently
of the initial conditions. However, it is difficult that ultrarrelativistic
strangelets (such as the hypothetical Centauro primaries) can have an origin in
those explosive events.Comment: RevTex file, 5 pp., no figure
Apsidal motion in massive close binary systems. I. HD 165052 an extreme case?
We present a new set of radial-velocity measurements of the spectroscopic
binary HD 165052 obtained by disentangling of high-resolution optical spectra.
The longitude of the periastron (60 +- 2 degrees) shows a variation with
respect to previous studies. We have determined the apsidal motion rate of the
system (12.1 +- 0.3 degree/yr), which was used to calculate the absolute masses
of the binary components: M_1 = 22.5 +- 1.0 and M_2 = 20.5 +- 0.9 solar masses.
Analysing the separated spectra we have re-classified the components as O7Vz
and O7.5Vz stars
Evolution of iron core white dwarfs
Recent measurements made by Hipparcos (Provencal et al. 1998) present
observational evidence supporting the existence of some white dwarf (WD) stars
with iron - rich, core composition. In this connection, the present paper is
aimed at exploring the structure and evolution of iron - core WDs by means of a
detailed and updated evolutionary code. In particular, we examine the evolution
of the central conditions, neutrino luminosity, surface gravity,
crystallization, internal luminosity profiles and ages. We find that the
evolution of iron - rich WDs is markedly different from that of their carbon -
oxygen counterparts. In particular, cooling is strongly accelerated as compared
with the standard case. Thus, if iron WDs were very numerous, some of them
would have had time enough to evolve at lower luminosities than that
corresponding to the fall - off in the observed WD luminosity function.Comment: 8 pages, 21 figures. Accepted for publication in MNRA
An evolutionary model for the gamma-ray system PSR J1311-3430 and its companion
The most recent member of the millisecond pulsar with very low-mass
companions and short orbital periods class, PSR J1311-3430 (Pletsch et al.
2012) is a remarkable object in various senses. Besides being the first
discovered in gamma-rays, its measured features include the very low or absent
hydrogen content. We show in this Letter that this important piece of
information leads to a very restricted range of initial periods for a given
donor mass. For that purpose, we calculate in detail the evolution of the
binary system self-consistently, including mass transfer and evaporation,
finding the features of the new evolutionary path leading to the observed
configuration. It is also important to remark that the detailed evolutionary
history of the system naturally leads to a high final pulsar mass, as it seems
to be demanded by observations.Comment: 5 pages, 5 figures, 1 table. Accepted for publication in MNRAS
Letter
- …