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Neutrino cooling rates due to Fe for presupernova evolution of massive stars
Accurate estimate of neutrino energy loss rates are needed for the study of
the late stages of the stellar evolution, in particular for cooling of neutron
stars and white dwarfs. Proton-neutron quasi-particle random phase
approximation (pn-QRPA) theory has recently being used for a microscopic
calculation of stellar weak interaction rates of iron isotopes with success.
Here I present the detailed calculation of neutrino and antineutrino cooling
rates due to key iron isotopes in stellar matter using the pn-QRPA theory. The
rates are calculated on a fine grid of temperature-density scale suitable for
core-collapse simulators. The calculated rates are compared against earlier
calculations. The neutrino cooling rates due to isotopes of iron are in overall
good agreement with the rates calculated using the large-scale shell model.
During the presupernova evolution of massive stars, from oxygen shell burning
till around end of convective core silicon burning phases, the calculated
neutrino cooling rates due to Fe are three to four times larger than the
corresponding shell model rates. The Brink's hypothesis used in previous
calculations can at times lead to erroneous results. The Brink's hypothesis
assumes that the Gamow-Teller strength distributions for all excited states are
the same. It is, however, shown by the present calculation that both the
centroid and total strength for excited states differ appreciably from the
ground state distribution. These changes in the strength distributions of
thermally populated excited states can alter the total weak interaction rates
rather significantly. The calculated antineutrino cooling rates, due to
positron capture and -decay of iron isotopes, are orders of magnitude
smaller than the corresponding neutrino cooling rates and can safely be
neglected specially at low temperatures and high stellar densities.Comment: 25 pages, 9 figures, 6 table
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