2022ApJ...929...72L -
Astrophys. J., 929, 72-72 (2022/April-2)
Impact of the New 65As(p,γ)66Se Reaction Rate on the Two-proton Sequential Capture of 64Ge, Weak GeAs Cycles, and Type I X-Ray Bursts Such as the Clocked Burster GS 1826-24.
LAM Y.H., LIU Z.X., HEGER A., LU N., JACOBS A.M. and JOHNSTON Z.
Abstract (from CDS):
We reassess the 65As(p,γ)66Se reaction rates based on a set of proton thresholds of 66Se, Sp(66Se), estimated from the experimental mirror nuclear masses, theoretical mirror displacement energies, and full pf-model space shell-model calculation. The self-consistent relativistic Hartree-Bogoliubov theory is employed to obtain the mirror displacement energies with much reduced uncertainty, and thus reducing the proton-threshold uncertainty up to 161 keV compared to the AME2020 evaluation. Using the simulation instantiated by the one-dimensional multi-zone hydrodynamic code, KEPLER, which closely reproduces the observed GS 1826-24 clocked bursts, the present forward and reverse 65As(p,γ)66Se reaction rates based on a selected Sp(66Se) = 2.469 ± 0.054 MeV, and the latest 22Mg(α,p)25Al, 56Ni(p,γ)57Cu, 57Cu(p,γ)58Zn, 55Ni(p,γ)56Cu, and 64Ge(p,γ)65As reaction rates, we find that though the GeAs cycles are weakly established in the rapid-proton capture process path, the 65As(p,γ)66Se reaction still strongly characterizes the burst tail end due to the two-proton sequential capture on 64Ge, not found by the Cyburt et al. sensitivity study. The 65As(p,γ)66Se reaction influences the abundances of nuclei A = 64, 68, 72, 76, and 80 up to a factor of 1.4. The new Sp(66Se) and the inclusion of the updated 22Mg(α,p)25Al reaction rate increases the production of 12C up to a factor of 4.5, which is not observable and could be the main fuel for a superburst. The enhancement of the 12C mass fraction alleviates the discrepancy in explaining the origin of the superburst. The waiting point status of and two-proton sequential capture on 64Ge, the weak-cycle feature of GeAs at a region heavier than 64Ge, and the impact of other possible Sp(66Se) are also discussed.
Abstract Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.
Journal keyword(s):
Reaction rates - Computational methods - Neutron stars - Low-mass X-ray binary stars - X-ray bursts - X-ray bursters - X-ray binary stars
Simbad objects:
7
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