Browsing by Author "Nabi, Jameel-Un"

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Nuclear inputs of key iron isotopes for core-collapse modeling and simulation
(IOP PUBLISHING LTD, 2014) Nabi, Jameel-Un; Tawfik, Abdel Nasser
From the modeling and simulation results of presupernova evolution of massive stars, it was found that isotopes of iron, Fe54-56, play a significant role inside the stellar cores, primarily decreasing the electron-to-baryon ratio (Y-e) mainly via electron capture processes thereby reducing the pressure support. The neutrinos produced as a result of these capture processes are transparent to the stellar matter and assist in cooling the core, thereby reducing the entropy. The structure of the presupernova star is altered both by the changes in Y-e and the entropy of the core material. Here we present the microscopic calculation of Gamow-Teller strength distributions for isotopes of iron. The calculation is also compared with other theoretical models and experimental data. Presented also are stellar electron capture rates and associated neutrino cooling rates, due to isotopes of iron, in a form suitable for simulation and modeling codes. It is hoped that the nuclear inputs presented here should assist core-collapse simulators in the process of fine-tuning of the Y-e parameter during various phases of presupernova evolution of massive stars. A reliable and accurate time evolution of this parameter is a possible key to generate a successful explosion in modeling of core-collapse supernovae.
Temperature-dependent nuclear partition functions and abundances in the stellar interior
(IOP PUBLISHING LTD, 2016-05) Khan, Ali Abas; Ezzelarab, Nada; Tawfik, Abdel Nasser; Nabi, Jameel-Un
We calculate the temperature-dependent nuclear partition functions (TDNPFs) and nuclear abundances for 728 nuclei, assuming nuclear statistical equilibrium (NSE). The theories of stellar evolution support NSE. Discrete nuclear energy levels have been calculated microscopically, using the pn-QRPA theory, up to an excitation energy of 10 MeV in the calculation of the TDNPFs. This feature of our paper distinguishes it from previous calculations. Experimental data is also incorporated wherever available to ensure the reliability of our results. Beyond 10 MeV, we employ a simple Fermi gas model and perform integration over the nuclear level densities to approximate the TDNPFs. We calculate nuclidic abundances, using the Saha equation, as a function of three parameters: stellar density, stellar temperature and the lepton-to-baryon content of stellar matter. All these physical parameters are considered to be extremely important in the stellar interior. The results obtained in this paper show that the equilibrium configuration of nuclei remains unaltered by increasing the stellar density (only the calculated nuclear abundances increase by roughly the same order of magnitude). Increasing the stellar temperature smoothes the equilibrium configuration showing peaks at the neutron-number magic nuclei.