Journal
ASTROPHYSICAL JOURNAL
Volume 662, Issue 2, Pages 1188-1197Publisher
IOP PUBLISHING LTD
DOI: 10.1086/517869
Keywords
dense matter; nuclear reactions, nucleosynthesis; abundances; stars : neutron; X-rays : binaries; X-rays : bursts
Categories
Funding
- Division Of Physics
- Direct For Mathematical & Physical Scien [0822648] Funding Source: National Science Foundation
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We perform a self-consistent calculation of the thermal structure in the crust of a superbursting neutron star. In particular, we follow the nucleosynthetic evolution of an accreted fluid element from its deposition into the atmosphere down to a depth where the electron Fermi energy is 20 MeV. We include temperature-dependent continuum electron capture rates and realistic sources of heat loss by thermal neutrino emission from the crust and core. We show that, in contrast to previous calculations, electron captures to excited states and subsequent gamma-emission significantly reduce the local heat loss due to weak-interaction neutrinos. Depending on the initial composition, these reactions release up to a factor of 10 times more heat at densities < 10(11) g cm(-3) than obtained previously. This heating reduces the ignition depth of superbursts. In particular, it reduces the discrepancy noted by Cumming et al. between the temperatures needed for unstable C-12 ignition on timescales consistent with observations and the reduction in crust temperature from Cooper pair neutrino emission.
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