394,228 research outputs found
Type Ia supernovae and the ^{12}C+^{12}C reaction rate
The experimental determination of the cross-section of the ^{12}C+^{12}C
reaction has never been made at astrophysically relevant energies (E<2 MeV).
The profusion of resonances throughout the measured energy range has led to
speculation that there is an unknown resonance at E\sim1.5 MeV possibly as
strong as the one measured for the resonance at 2.14 MeV. We study the
implications that such a resonance would have for the physics of SNIa, paying
special attention to the phases that go from the crossing of the ignition curve
to the dynamical event. We use one-dimensional hydrostatic and hydrodynamic
codes to follow the evolution of accreting white dwarfs until they grow close
to the Chandrasekhar mass and explode as SNIa. In our simulations, we account
for a low-energy resonance by exploring the parameter space allowed by
experimental data. A change in the ^{12}C+^{12}C rate similar to the one
explored here would have profound consequences for the physical conditions in
the SNIa explosion, namely the central density, neutronization, thermal
profile, mass of the convective core, location of the runaway hot spot, or time
elapsed since crossing the ignition curve. For instance, with the largest
resonance strength we use, the time elapsed since crossing the ignition curve
to the supernova event is shorter by a factor ten than for models using the
standard rate of ^{12}C+^{12}C, and the runaway temperature is reduced from
\sim8.14\times10^{8} K to \sim4.26\times10^{8} K. On the other hand, a
resonance at 1.5 MeV, with a strength ten thousand times smaller than the one
measured at 2.14 MeV, but with an {\alpha}/p yield ratio substantially
different from 1 would have a sizeable impact on the degree of neutronization
of matter during carbon simmering. We conclude that a robust understanding of
the links between SNIa properties and their progenitors will not be attained
until the ^{12}C+^{12}C reaction rate is measured at energies \sim1.5 MeV.Comment: 15 pages, 6 tables, 10 figures, accepted for Astronomy and
Astrophysic
On the mass of supernova progenitors: the role of the CC reaction
A precise knowledge of the masses of supernova progenitors is essential to
answer various questions of modern astrophysics, such as those related to the
dynamical and chemical evolution of Galaxies. In this paper we revise the upper
bound for the mass of the progenitors of CO white dwarfs (\mup) and the lower
bound for the mass of the progenitors of normal type II supernovae (\mups). In
particular, we present new stellar models with mass between 7 and 10 \msun,
discussing their final destiny and the impact of recent improvements in our
understanding of the low energy rate of the \c12c12 reaction.Comment: To be published on the proceedings of NIC 201
Upper Limit on the molecular resonance strengths in the C+C fusion reaction
Carbon burning is a crucial process for a number of important astrophysical
scenarios. The lowest measured energy is around E=2.1 MeV, only
partially overlapping with the energy range of astrophysical interest. The
currently adopted reaction rates are based on an extrapolation which is highly
uncertain because of potential resonances existing in the unmeasured energy
range and the complication of the effective nuclear potential. By comparing the
cross sections of the three carbon isotope fusion reactions,
C+C, C+C and C+C, we have
established an upper limit on the molecular resonance strengths in
C+C fusion reaction. The preliminary results are presented
and the impact on nuclear astrophysics is discussed.Comment: 4 pages, 3 figures, FUSION11 conference proceedin
Global Examination of the C+C Reaction Data at Low and Intermediate Energies
We examine the C+C elastic scattering over a wide energy range
from 32.0 to 70.7 MeV in the laboratory system within the framework of the
Optical model and the Coupled-Channels formalism. The C+C system
has been extensively studied within and over this energy range in the past.
These efforts have been futile in determining the shape of the nuclear
potential in the low energy region and in describing the individual angular
distributions, single-angle 50 to 90 excitation functions and
reaction cross-section data simultaneously. In order to address these problems
systematically, we propose a potential that belongs to a family other than the
one used to describe higher energy experimental data and show that it is
possible to use it over this wide energy range. This potential also predicts
the resonances at correct energies with reasonable widths.Comment: 30 pages with 13 eps figues and 3 tables, LaTeX-Revtex
Effect of Reaction & Convective Mixing on the Progenitor Mass of ONe White Dwarfs
Stars in the mass range ~8 - 12 are the most numerous massive
stars. This mass range is critical because it may lead to supernova (SN)
explosion, so it is important for the production of heavy elements and the
chemical evolution of the galaxy. We investigate the critical transition mass
(), which is the minimum initial stellar mass that attains the
conditions for hydrostatic carbon burning. Stars of masses < evolve to
the Asymptotic Giant Branch and then develop CO White Dwarfs, while stars of
masses ignite carbon in a partially degenerate CO core
and form electron degenerate ONe cores. These stars evolve to the Super AGB
(SAGB) phase and either become progenitors of ONe White Dwarfs or eventually
explode as electron-capture SN (EC-SN). We study the sensitivity of to
the C-burning reaction rate and to the treatment of convective mixing. In
particular, we show the effect of a recent determination of the
fusion rate, as well as the extension of the convective core during
hydrogen and helium burning on in solar metallicity stars. We choose
the 9 model to show the detailed characteristics of the evolution
with the new C-burning rate.Comment: Submitted to AIP Conference proceedings of Carpathian Summer School
of Physics-201
Microscopic theories of neutrino-^{12}C reactions
In view of the recent experiments on neutrino oscillations performed by the
LSND and KARMEN collaborations as well as of future experiments, we present new
theoretical results of the flux averaged and
cross sections. The approaches used are
charge-exchange RPA, charge-exchange RPA among quasi-particles (QRPA) and the
Shell Model. With a large-scale shell model calculation the exclusive cross
sections are in nice agreement with the experimental values for both reactions.
The inclusive cross section for coming from the decay-in-flight of
is to be compared to the experimental value
of , while the one due to
coming from the decay-at-rest of is which
agrees within experimental error bars with the measured values. The shell model
prediction for the decay-in-flight neutrino cross section is reduced compared
to the RPA one. This is mainly due to the different kind of correlations taken
into account in the calculation of the spin modes and partially due to the
shell-model configuration basis which is not large enough, as we show using
arguments based on sum-rules.Comment: 17 pages, latex, 5 figure
Neutrino and antineutrino cross sections in C
We extend the formalism of weak interaction processes, obtaining new
expressions for the transition rates, which greatly facilitate numerical
calculations, both for neutrino-nucleus reactions and muon capture. We have
done a thorough study of exclusive (ground state) properties of B and
N within the projected quasiparticle random phase approximation (PQRPA).
Good agreement with experimental data is achieved in this way. The inclusive
neutrino/antineutrino () reactions C(N
and C(B are calculated within both the PQRPA, and
the relativistic QRPA (RQRPA). It is found that the magnitudes of the resulting
cross-sections: i) are close to the sum-rule limit at low energy, but
significantly smaller than this limit at high energies both for and
, ii) they steadily increase when the size of the configuration
space is augmented, and particulary for energies MeV,
and iii) converge for sufficiently large configuration space and final state
spin.Comment: Proceedings of the International Nuclear Physics Conference 2010,
Vancouver, BC - Canada 4-9 Jul 201
Longitudinal and Transverse Form Factors from C
Electron scattering form factors from C have been studied in the
framework of the particle-hole shell model. Higher configurations are taken
into account by allowing particle-hole excitations from the 1 and 1
shells core orbits up to the 1 shell. The inclusion of the higher
configurations modifies the form factors markedly and describes the
experimental data very well in all momentum transfer regions.Comment: 5 pages, 5 figures, 3 tables, late
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