• S. Kalita

      Articles written in Journal of Astrophysics and Astronomy

    • A Comparative Study on SN II Progenitors for the Synthesis of Li7 and B11 with the help of Neutrinos

      N. Lahkar S. Kalita H. L. Duorah K. Duorah

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      The synthesis of Li7 and B11 confronts astrophysicists. Type II (SN II) and Type Ic (SN Ic) supernovae are supposed to be the producers of these two elements. In this study we calculate the yields of these two elements for SN II progenitors with 8, 10 and 20 solar masses. The process considered here is the neutral current interaction of heavy flavour neutrinos (𝜈𝜇 or 𝜈𝜏) with He4 nuclei of the helium zone. The low mass progenitors are considered because the helium zone lies much closer to the core and hence experiences large neutrino flux. The starting point of the helium zone depends on detail stellar model. However, the shell radius at which it begins is available for these stars. 20 solar mass is considered for comparison of our production ratio Li/B with that of an earlier work. It is contrasted with the shock heating yields in the hydrogen envelope. The Li/B ratio has been found to be about 0.96. In the three model stars, the Li7 and B11 yields are found to be in the range 6.61×10−6 −2.63×10−6 𝑀Sun and 6.92×10−6 −2.75×10−6 𝑀Sun respectively as we go from 8 to 20 𝑀Sun. Some equivalence is found with shock induced nucleosynthesis model for SN II. The SN II yield is found to be compatible with that of hypernovae produced by C–O core collapse but higher than the yields obtained by neutrino processes in SNIc.

    • Abundances of La138 and Ta180 Through ν-Nucleosynthesis in $20 M_\odot$ Type II Supernova Progenitor, Guided by Stellar Models for Seeds

      N. Lahkar S. Kalita H. L. Duorah K. Duorah

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      Yields of nature’s rarest isotopes La^{138} and Ta^{180} are calculated by neutrino processes in the Ne-shell of density $\rho ≈ 10^4 g/cc$ in a type II supernova (SN II) progenitor of mass 20 $M_\odot$. Two extended sets of neutrino temperature $- T_{\nue}$ = 3, 4, 5, 6 MeV and $T_{\nu(\mu/\tau)}$= 4, 6, 8, 10, 12 MeV respectively for charged and neutral current processes are taken. Solar mass fractions of the seeds La139, Ta181, Ba138 and Hf180 are taken for calculation. They are assumed to be produced in some s-processing events of earlier generation massive ‘seed stars’ with average interior density range $\langleρ\rangle \approx 10^3−10^6 g/cc$. The abundances of these two elements are calculated relative to O16 and are found to be sensitive to the neutrino temperature. For neutral current processes with the neutron emission branching ratio, $b_n = 3.81 \times 10^{-4}$ and $b_n = 9.61 \times 10^{−1}$, the relative abundances of La138 lie in the ranges $4.48 \times 10^{−14}−2.94 \times 10^{−13}$ and $1.13 \times 10^{−10} − 7.43 \times 10^{−10}$ respectively. Similarly, the relative abundances of Ta180 lie in the ranges $1.80 \times 10^{−15} − 1.17 \times 10^{−14}$ and 4.53 \times 10^{−12}−2.96 × 10^{−11} respectively for the lower and higher values of the neutron emission branching ratio. For charged current processes, the relative abundances of La138 and Ta180 are found to be in the ranges $1.38 \times 10^{−9} − 7.62 \times 10^{−9}$ and $2.09 \times 10^{-11} − 1.10 \times 10^{−10}$ respectively. Parametrized by density of the ‘seed stars’, the yields are found to be consistent with recent supernova simulation results throughout the range of neutrino temperatures. La138 and Ta180 are found to be efficiently produced in charged current interaction.

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      Posted on January 27, 2016

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