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Nuclear Weak Processes in Presupernova Stars

Published online by Cambridge University Press:  12 April 2016

A. Ray ,
T. Kar ,
S. Sarkar  and
S. Chakravarti
A. Ray
Affiliation:
Tata Institute of Fundamental Research, Bombay 400 005, India
T. Kar
Affiliation:
Saha Institute of Nuclear Physics , Calcutta 700 064, India
S. Sarkar
Affiliation:
Saha Institute of Nuclear Physics , Calcutta 700 064, India
S. Chakravarti
Affiliation:
California State Polytechnic University, Pomona, CA91768, USA

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The structure and the size of the core of massive presupernova stars are determined by the electron fraction and entropy of the core during its late stages of evolution; these in turn affect the subsequent evolution during gravitational collapse and supernova explosion phases. Beta decay and electron capture on a number of neutron rich nuclei can contribute substantially towards the reduction of the entropy and possibly the electron fraction in the core. Methods for calculating the weak transition rates for a number of nuclei for which no reliable rates exist (particularly for A > 60) are outlined. The calculations are particularly suited for presupernova matter density (p = 107 - 109 g/cc) and temperature (T = 2 - 6 × 109 °K). We include besides the contributions from the ground state and the known excited states, the Gamow-Teller (GT) resonance states (e.g. for beta decay rates, the GT+ states) in the mother nucleus which are populated thermally. For the GT strength function for transitions from the ground state (as well as excited states) we use a sum rule calculated by the spectral distribution method where the centroid of the distribution is obtained from experimental data on (p,n) reactions. The contribution of the excited levels and GT+ resonances turn out to be important at high temperatures which may prevail in presupernova stellar cores.

Type
Type lb and Type II Supernovae
Information
International Astronomical Union Colloquium , Volume 145: Supernovae and Supernova Remnants , 1996 , pp. 165 - 172
Copyright
Copyright © Cambridge University Press 1996

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