12,582 research outputs found
Nucleosynthesis in Metal-Free and Metal-Poor Stars
There have been a number of important recent developments in theoretical and
observational studies of nucleosynthesis, especially regarding nucleosynthetic
sources at low metallicities. Those selected for discussion here include the
origin of Li6, the primary production of N, the s-process, and the supernova
sources for three groups of metals: (1) C to Zn with mass numbers A<70, (2) Sr
to Ag with A~90-110, and (3) r-process nuclei with A~130 and above.Comment: 8 pages, no figures, published in "Proceedings of First Stars III,"
Eds. Brian W. O'Shea, Alexander Heger & Tom Abe
Astrophysical Models of r-Process Nucleosynthesis: An Update
An update on astrophysical models for nucleosynthesis via rapid neutron
capture, the r process, is given. A neutrino-induced r process in supernova
helium shells may have operated up to metallicities of ~10^-3 times the solar
value. Another r-process source, possibly neutron star mergers, is required for
higher metallicities.Comment: 8 pages, invited talk given at 11th International Symposium on Origin
of Matter and Evolution of Galaxies (OMEG11), Wako, Japa
Recent Progress in Understanding Nucleosynthesis via Rapid Neutron Capture
I discuss the recent progress in our understanding of nucleosynthesis via
rapid neutron capture, the r-process, based on meteoritic data for the early
solar system and observations of stars at low metallicities. At present, all
data require that there be two distinct kinds of r-process events and suggest
that supernovae are associated with these events. The diversity of supernova
sources for the r-process may depend on whether a neutron star or black hole is
formed in an individual supernova. This dependence, if substantiated by future
observations discussed here, has important implications for properties of
nuclear matter.Comment: 7 pages including 2 figures, to appear in the Proceedings of the 7th
Conference on the Intersections of Particle and Nuclear Physic
Neutrino Processes in Strong Magnetic Fields
The processes of electron neutrino capture on neutron and electron
anti-neutrino capture on proton, and their reverse processes provide the
dominant mechanisms for heating and cooling the material below the stalled
shock in a core-collapse supernova. We summarize the major effects of strong
magnetic fields on the rates of the above reactions and illustrate these
effects with a simple supernova model. Due to parity violation of weak
interaction the heating rates are asymmetric even for a uniform magnetic field.
The cooling rates are also asymmetric for nonuniform fields. The most dramatic
effect of strong magnetic fields of 10^16 G is suppression of the cooling rates
by changing the equations of state through the phase space of electrons and
positrons.Comment: 10 pages, 4 figures, talk given at INT workshop "Open Issues in
Understanding Core Collapse Supernovae," Seattle, June 200
Neutrino Gravitational Redshift and the Electron Fraction Above Nascent Neutron Stars
Neutrinos emitted from near the surface of the hot proto-neutron star
produced by a supernova explosion may be subject to significant gravitational
redshift at late times. Electron antineutrinos decouple deeper in the
gravitational potential well of the neutron star than do the electron
neutrinos, so that the electron antineutrinos experience a larger redshift
effect than do the electron neutrinos. We show how this differential redshift
can increase the electron fraction Ye in the neutrino-heated ejecta from the
neutron star. Any r-process nucleosynthesis originating in the neutrino-heated
ejecta would require a low Ye, implying that the differential redshift effect
cannot be too large. In turn, this effect may allow nucleosynthesis to probe
the nuclear equation of state parameters which set the neutron star radius and
surface density scale height at times of order tpb = 10 to 25 s after core
bounce.Comment: 4 pages, uses espcrc2.sty, contribution to Festschrift for G. E.
Brown on the occasion of his 70th birthda
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