Detailed microscopic calculation of stellar electron and positron capture rates on²⁴Mg for O+Ne+Mg core simulations

Abstract

Abstract. Few white dwarfs, located in binary systems, may acquire sufficiently high mass accretion rates resulting in the burning of carbon and oxygen under nondegenerate conditions forming a O+Ne+Mg core. These O+Ne+Mg cores are gravitationally less bound than more massive progenitor stars and can release more energy due to the nuclear burning. They are also amongst the probable candidates for low entropy r-process sites. Recent observations of subluminous Type II-P supernovae (e.g., 2005cs, 2003gd, 1999br, 1997D) were able to rekindle the interest in 8 -10 M ⊙ which develop O+Ne+Mg cores. Microscopic calculations of capture rates on 24 Mg, which may contribute significantly to the collapse of O+Ne+Mg cores, using shell model and proton-neutron quasiparticle random phase approximation (pn-QRPA) theory, were performed earlier and comparisons made. Simulators, however, may require these capture rates on a fine scale. For the first time a detailed microscopic calculation of the electron and positron capture rates on 24 Mg on an extensive temperature-density scale is presented here. This type of scale is more appropriate for interpolation purposes and of greater utility for simulation codes. The calculations are done using the pn-QRPA theory using a separable interaction. The deformation parameter, believed to be a key parameter in QRPA calculations, is adopted from experimental data to further increase the reliability of the QRPA results. The resulting calculated rates are up to a factor of 14 or more enhanced as compared to shell model rates and may lead to some interesting scenario for core collapse simulators.

Stellar β±-decay rates of iron isotopes and its implications in astrophysics

“…The excited state GT strength distributions are also much different from the ground state distribution for the case of 55 Fe. The excited state GT distributions for 54,55,56 Fe are shown graphically in Figures 13,14 and 15, respectively. The ground state GT strength distributions were presented earlier in Ref.…”

Stellar neutrino energy loss rates due toMg24suitable forO+Ne+Nabi1 2008Phys. Rev. CSelf Cite

“…The ratio then starts decreasing with increasing T 9 . The enhancement of the QRPA rates around T 9 ∼ 1.5 − 2 may be traced back to the enhanced electron capture rates on 24 Mg [37] leading to an enhanced production of non-thermal neutrinos around these temperatures. It may also be seen from Table I that at high temperatures (T 9 ∼ 30) the ratios are in good agreement with previous calculations.…”