1,297 research outputs found
Nucleosynthesis in 2D Core-Collapse Supernovae of 11.2 and 17.0 M Progenitors: Implications for Mo and Ru Production
Core-collapse supernovae are the first polluters of heavy elements in the
galactic history. As such, it is important to study the nuclear compositions of
their ejecta, and understand their dependence on the progenitor structure
(e.g., mass, compactness, metallicity). Here, we present a detailed
nucleosynthesis study based on two long-term, two-dimensional core-collapse
supernova simulations of a 11.2 M and a 17.0 M star. We
find that in both models nuclei well beyond the iron group (up to ) can be produced, and discuss in detail also the nucleosynthesis of the
p-nuclei Mo and Ru. While we observe the production of
Mo and Mo in slightly neutron-rich conditions in both
simulations, Ru can only be produced efficiently via the
p-process. Furthermore, the production of Ru in the p-process heavily
depends on the presence of very proton-rich material in the ejecta. This
disentanglement of production mechanisms has interesting consequences when
comparing to the abundance ratios between these isotopes in the solar system
and in presolar grains.Comment: 48 pages, 19 figures, accepted for publication in: J. Phys. G: Nucl.
Part. Phy
Gravitational waves from supernova matter
We have performed a set of 11 three-dimensional magnetohydrodynamical core
collapse supernova simulations in order to investigate the dependencies of the
gravitational wave signal on the progenitor's initial conditions. We study the
effects of the initial central angular velocity and different variants of
neutrino transport. Our models are started up from a 15 solar mass progenitor
and incorporate an effective general relativistic gravitational potential and a
finite temperature nuclear equation of state. Furthermore, the electron flavour
neutrino transport is tracked by efficient algorithms for the radiative
transfer of massless fermions. We find that non- and slowly rotating models
show gravitational wave emission due to prompt- and lepton driven convection
that reveals details about the hydrodynamical state of the fluid inside the
protoneutron stars. Furthermore we show that protoneutron stars can become
dynamically unstable to rotational instabilities at T/|W| values as low as ~2 %
at core bounce. We point out that the inclusion of deleptonization during the
postbounce phase is very important for the quantitative GW prediction, as it
enhances the absolute values of the gravitational wave trains up to a factor of
ten with respect to a lepton-conserving treatment.Comment: 10 pages, 6 figures, accepted, to be published in a Classical and
Quantum Gravity special issue for MICRA200
R-Process Nucleosynthesis in MHD Jet Explosions of Core-Collapse Supernovae
We investigate -process nucleosynthesis during the magnetohydrodynamical
(MHD) explosion of supernova in a massive star of 13 . Contrary to
the case of the spherical explosion, jet-like explosion due to the combined
effects of the rotation and magnetic field lowers the electron fraction
significantly inside the layers above the iron core. We find that the ejected
material of low electron fraction responsible for the -process comes out
from the silicon rich layer of the presupernova model. This leads to the
production up to the third peak in the solar -process elements. We examine
whether the fission affects the -process paths by using the full nuclear
reaction network with both the spontaneous and -delayed fission
included. Moreover, we pay particular attention how the mass formula affects
the -process peaks with use of two mass formulae. It is found that both
formulae can reproduce the global abundance pattern up to the third peak though
detailed distributions are rather different. We point out that there are
variations in the -process nucleosynthesis if the MHD effects play an
important role in the supernova explosion.Comment: 19 pages with 7 figures, submitted to Ap
Neutrino oscillations in magnetically driven supernova explosions
We investigate neutrino oscillations from core-collapse supernovae that
produce magnetohydrodynamic (MHD) explosions. By calculating numerically the
flavor conversion of neutrinos in the highly non-spherical envelope, we study
how the explosion anisotropy has impacts on the emergent neutrino spectra
through the Mikheyev-Smirnov-Wolfenstein effect. In the case of the inverted
mass hierarchy with a relatively large theta_(13), we show that survival
probabilities of electron type neutrinos and antineutrinos seen from the
rotational axis of the MHD supernovae (i.e., polar direction), can be
significantly different from those along the equatorial direction. The event
numbers of electron type antineutrinos observed from the polar direction are
predicted to show steepest decrease, reflecting the passage of the
magneto-driven shock to the so-called high-resonance regions. Furthermore we
point out that such a shock effect, depending on the original neutrino spectra,
appears also for the low-resonance regions, which leads to a noticeable
decrease in the electron type neutrino signals. This reflects a unique nature
of the magnetic explosion featuring a very early shock-arrival to the resonance
regions, which is in sharp contrast to the neutrino-driven delayed supernova
models. Our results suggest that the two features in the electron type
antineutrinos and neutrinos signals, if visible to the Super-Kamiokande for a
Galactic supernova, could mark an observational signature of the magnetically
driven explosions, presumably linked to the formation of magnetars and/or
long-duration gamma-ray bursts.Comment: 25 pages, 21 figures, JCAP in pres
Approaching the dynamics of hot nucleons in supernovae
All recent numerical simulations agree that stars in the main sequence mass
range of 9-40 solar masses do not produce a prompt hydrodynamic ejection of the
outer layers after core collapse and bounce. Rather they suggest that stellar
core collapse and supernova explosion are dynamically distinct astrophysical
events, separated by an unspectacular accretion phase of at least ~40 ms
duration. As long as the neutrinospheres remain convectively stable, the
explosion dynamics is determined by the neutrons, protons, electrons and
neutrinos in the layer of impact-heated matter piling up on the protoneutron
star. The crucial role of neutrino transport in this regime has been emphasized
in many previous investigations. Here, we search for efficient means to address
the role of magnetic fields and fluid instabilities in stellar core collapse
and the postbounce phase.Comment: 4 pages, contribution to Nuclei in the Cosmos VIII, Jul. 19-23,
submitted to Nucl. Phys.
Biermann Mechanism in Primordial Supernova Remnant and Seed Magnetic Fields
We study generation of magnetic fields by the Biermann mechanism in the
pair-instability supernovae explosions of first stars. The Biermann mechanism
produces magnetic fields in the shocked region between the bubble and
interstellar medium (ISM), even if magnetic fields are absent initially. We
perform a series of two-dimensional magnetohydrodynamic simulations with the
Biermann term and estimate the amplitude and total energy of the produced
magnetic fields. We find that magnetic fields with amplitude
G are generated inside the bubble, though the amount of
magnetic fields generated depend on specific values of initial conditions. This
corresponds to magnetic fields of erg per each supernova
remnant, which is strong enough to be the seed magnetic field for galactic
and/or interstellar dynamo.Comment: 12 pages, 3 figure
Gravitational Waves from Core Collapse Supernovae
We present the gravitational wave signatures for a suite of axisymmetric core
collapse supernova models with progenitors masses between 12 and 25 solar
masses. These models are distinguished by the fact they explode and contain
essential physics (in particular, multi-frequency neutrino transport and
general relativity) needed for a more realistic description. Thus, we are able
to compute complete waveforms (i.e., through explosion) based on
non-parameterized, first-principles models. This is essential if the waveform
amplitudes and time scales are to be computed more precisely. Fourier
decomposition shows that the gravitational wave signals we predict should be
observable by AdvLIGO across the range of progenitors considered here. The
fundamental limitation of these models is in their imposition of axisymmetry.
Further progress will require counterpart three-dimensional models.Comment: 10 pages, 5 figure
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