234 research outputs found
Nucleosynthesis as a result of multiple delayed detonations in Type Ia Supernovae
The explosion of a white dwarf of mass 1.36 M has been simulated in
three dimensions with the aid of a SPH code. The explosion follows the delayed
detonation paradigma. In this case the deflagration-detonation transition is
induced by the large corrugation of the flame front resulting from
Rayleigh-Taylor instability and turbulence. The nucleosynthetic yields have
been calculated, showing that some neutronized isotopes such as 54^Fe or 58^Ni
are not overproduced with respect to the solar system ratios. The distribution
of intermediate-mass elements is also compatible with the spectra of normal
SNIa. The excepcion is, however, the abundance of carbon and oxygen, which are
overproduced.Comment: 3 pages, 2 figures. Proceedings "Nuclei in the Cosmos VII" 2002. To
appear in Nucl. Phys.
Axisymmetric magneto-hydrodynamics with SPH
Many interesting terrestrial and astrophysical scenarios involving magnetic fields can be approached in axial geometry. Even though the Lagrangian smoothed particle hydrodynamics (SPH) technique has been successfully extended to handle magneto-hydrodynamic (MHD) problems, a well-verified, axisymmetric MHD scheme based on the SPH technique does not exist. In this work, we propose and check a new axisymmetric MHD hydrodynamic code that can be applied to astrophysical and engineering problems which display an adequate geometry. We show that a hydrodynamic code built on these axisymmetric premises is able to produce similar results to standard 3D-SPHMHD codes but with much lesser computational effort.Peer ReviewedPostprint (published version
Explosion models for thermonuclear supernovae resulting from different ignition conditions
We have explored in three dimensions the fate of a massive white dwarf as a
function of different initial locations of carbon ignition, with the aid of a
SPH code. The calculated models cover a variety of possibilities ranging from
the simultaneous ignition of the central volume of the star to the off-center
ignition in multiple scattered spots. In the former case, there are discussed
the possibility of a transition to a detonation when the mean density of the
nuclear flame decreases below 2x10**7 g cm**-3, and its consequences. In the
last case, the dependence of the results on the number of initial igniting
spots and the chance of some of these models to evolve to the pulsating delayed
detonation scenario are also outlined.Comment: 5 pages, 1 figure, proceedings of IAU Colloquium 192, 'Supernovae (10
years of SN1993J)', 22-26 April 2003, Valencia, Spai
Building initial models of rotating white dwarfs with SPH
A general procedure to build self-gravitational, rotating equilibrium structures with the Smoothed Particle Hydrodynamics (SPH) technique does not exist. In particular, obtaining
stable rotating configurations for white dwarf (WD) stars is
currently a major drawback of many astrophysical simulations.
Rotating WDs with low internal temperatures are connected with
both, explosive and implosive scenarios such as type Ia supernova
explosions or neutron stars formation. Simulations of these events
with SPH codes demand stable enough particle configurations as
initial models. In this work we have developed and tested a relaxation method to obtain equilibrium configurations of rotating
WDs. This method is straightforward and takes advantage of the
excellent mass and angular momentum conservation properties
of the SPH technique. Although we focus on rigid rotation and
its potential applications to several Type Ia supernova scenarios,
we also show that our proposal is also able to provide good initial
models in differential rotation, which has the potential to benefit
many other types of simulations where rotation plays a capital
role, like disk evolution and stellar formation.Peer ReviewedPostprint (published version
Coulomb corrections to the equation of state of nuclear statistical equilibrium matter: implications for SNIa nucleosynthesis and the accretion-induced collapse of white dwarfs
Coulomb corrections to the equation of state of degenerate matter are usually neglected in high-temperature regimes, owing to the inverse dependence of the plasma coupling constant, G, on temperature. However, nuclear statistical equilibrium matter is characterized by a large abundance by mass of large-Z (iron group) nuclei. It is found that Coulomb corrections to the ion ideal gas equation of state of matter in nuclear statistical equilibrium are important at temperatures TâČ5â10Ă109 K and densities Ïâł108 g cmâ3. At a temperature T=8.5Ă109 K and a density Ï=8Ă109 g cmâ3, the neutronization rate is larger by âł28 per cent when Coulomb corrections are included. However, the conductive velocity of a thermonuclear deflagration wave in C-O drops by âŒ16 per cent when Coulomb corrections to the heat capacity are taken into account. The implications for SNIa models and nucleosynthesis, and also for the accretion-induced collapse of white dwarfs, are discussed. Particularly relevant is the result that the minimum density for collapse of a white dwarf to a neutron star is shifted down to 5.5â6Ă109 g cmâ3, a value substantially lower than previously thought.Peer ReviewedPostprint (published version
Mixing Sinc kernels to improve interpolations in smoothed particle hydrodynamics without pairing instability
The smoothed particle hydrodynamics technique strongly relies on the proper
choice of interpolating functions. In this work, we revisit and extend the main
properties of a family of interpolators called and compare them
with those of the widely used family of Wendland kernels. We show that a linear
combination of low and high-order Sinc kernels generates good quality
interpolators, which are resistant to the pairing instability while keeping
good sampling properties in a wide range of neighbor interpolating points,
. We show that a particular case of this linear mix of Sincs
produces a well-balanced and robust kernel, that improves previous results in
the Gresho-Chan vortex experiment even when the number of neighbors is not
large, while yielding a good convergence rate. Although such a mixing technique
is ideally suited for Sinc kernels owing to their excellent flexibility, it can
be easily applied to other interpolating families such as the B-splines and
Wendland kernels.Comment: 13 pages, 14 figures, 4 tables, submitted to MNRA
High resolution simulations of the head-on collision of white dwarfs
The direct impact of white dwarfs has been suggested as a plausible channel
for type Ia supernovae. In spite of their (a priori) rareness, in highly
populated globular clusters and in galactic centers, where the amount of white
dwarfs is considerable, the rate of violent collisions between two of them
might be non-negligible. Even more, there are indications that binary white
dwarf systems orbited by a third stellar-mass body have an important chance to
induce a clean head-on collision. Therefore, this scenario represents a source
of contamination for the supernova light-curves sample that it is used as
standard candles in cosmology, and it deserves further investigation. Some
groups have conducted numerical simulations of this scenario, but their results
show several differences. In this paper we address some of the possible sources
of these differences, presenting the results of high resolution hydrodynamical
simulations jointly with a detailed nuclear post-processing of the nuclear
abundances, to check the viability of white dwarf collisions to produce
significant amounts of 56Ni. To that purpose, we use a 2D-axial symmetric
smoothed particle hydrodynamic code to obtain a resolution considerably higher
than in previous studies. In this work, we also study how the initial mass and
nuclear composition affect the results. The gravitational wave emission is also
calculated, as this is a unique signature of this kind of events. All
calculated models produce a significant amount of 56Ni, ranging from 0.1 Msun
to 1.1 Msun, compatible not only with normal-Branch type Ia supernova but also
with the subluminous and super-Chandrasekhar subset. Nevertheless, the
distribution mass-function of white dwarfs favors collisions among 0.6-0.7 Msun
objects, leading to subluminous events.Comment: 24 pages, 12 figures, accepted for publication in MNRA
Integral SPH: Connecting the partition of unit to accurate gradient estimation
AYA2017-86274-P Del enfriamiento a las explosiones: la fĂsica de los objetos compactosPostprint (published version
Surface and core detonations in rotating white dwarfs
The feasibility of the double detonation mechanismâsurface helium detonation followed by complete carbon
detonation of the coreâin a rotating white dwarf with mass ;1Me is studied using three-dimensional
hydrodynamic simulations. A rapid rigid rotation of the white dwarf was assumed, so that its initial spherical
geometry is considerably distorted. Unlike spherically symmetric models, we found that when helium ignition is
located far from the spinning axis, the detonation fronts converge asynchronically at the antipodes of the ignition
point. Nevertheless, the detonation of the carbon core still remains as the most probable outcome. The detonation
of the core gives rise to a strong explosion, matching many of the basic observational constraints of Type Ia
supernovae (SNe Ia). We conclude that the double detonation mechanism also works when the white dwarf is
rapidly rotating. These results provide further evidence for the viability of sub-Chandrasekhar-mass models as well
as some double degenerate models (those having some helium fuel at the merging moment), making them
appealing channels for the production of SN Ia events.Peer ReviewedPostprint (published version
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