Core-Collapse Supernovae And Neutrino-driven Wind

Supernovae and the related nucleosynthesis are one of the forefront topics for today astrophysics. In this thesis, the explosion process of core-collapse supernovae (C-C SNe) and the dynamic of neutrino-driven wind (NDW) are investigated. We summary the basic characters of SNe and the explosion mechanism of C-C SNe. In order to discuss the source of the powerful neutrinos flux, constituent quark mass model is adopted as a tentative one to study the phase transition between two-flavour quark matter and more stable three-flavour quark matter in the core of supernovae. We find that the constituent quark mass model is applicable to describing the transition in the supernova core. The transition has a significant influence on the increasing of the core temperature, the neutrino abundance and energy, which contributes to the enhancement of the successful probability of supernovae explosion. SN2006gy is an extraordinary C-C SNe, so we introduce the research progress of SN2006gy specially. NDW from Proto-Neutron Star (PNS) could be the main candidate site where the r- process occurs. In Chapter II, we summary the basic theory and progress of heavy element nucleosynthesis(including s-process, r-process and p-process), then we detailed introduce the history and recent progress of dynamics and nucleosynthesis of NDW.A new improved nuclear partition function developed by Rauscher et al. is employed to calculate the nuclear statistical equilibrium (NSE) in C-C SNe environment. The results show that nuclear partition function causes a slight change to nucleus abundance, which indicates that the effect of the nuclear partition function is not as important as shown in the previous estimation. By using a one-demension simulation, progenitor model WW15M⊙and our calculation method for the electron screening on electron capture (EC), the collapsing and bounce process of C-C SNe are investigated. The results show that, the effects of electron screening are significant. During the collapsing stage, the EC rate is decreased, the collapse time-scale is prolonged and collapse process in the outer core is changed. We make a detailed analysis for the energy of neutrino and bounce shock. A strict numerical simulation can not produce successful supernova explosion up to now. By adjusting the pressure grads at the stage of shock wave formation, a successful prompt explosion process has been obtained for progenitor model WW15M⊙. The various convections, including the Rayleigh-Taloy (R-T) convection, the lepton driven convection and the negative entropy grads driven convection, in the inner core of C-C SNe are analyzed. The simulation results show that the in the inner core region the powerful convections cause the energy transfer from the inner core to the shock wave rapidly.The steady equilibrium conditions for a mixed gas of neutrons, protons, electrons, positrons and radiation fields (abbreviated as npe^±gas) with or without external neutrino flux are investigated, and a general chemical potential equilibrium equationμn =μ_p + Cμe is obtained to describe the steady equilibrium at high temperatures (T > 10⁹ K). An analytic fitting formula of coefficient C is presented for the sake of simplicity, when neutrinos and antineutrinos are transparent. It is a simple method to estimate the electron fraction for the steady equilibrium npe^±gas adopting the corresponding equilibrium condition. As an example, we apply this method to the GRB accretion disk and confirm that the composition in the inner region is approximately in equilibrium when the accretion rate is low. For the case with external neutrino flux, we calculate the initial electron fraction of neutrino-driven wind from the proto-neutron star model M15-l1-r1. The results show that the improved equilibrium condition makes the electron fraction decrease significantly more than the caseμn =μp +μe when the time is less than 5s post bounce, which may be useful for r-process nucleosynthesis models.Based on Newtonian hydrodynamics equations, we discussed three different equation of state (EOS) (EOS I. strict; EOS II. ignoring the degenerate parameter; EOS III. ignoring the gas pressure) on the dynamics and nucleosynthesis of neutrino-driven wind. It is found, EOS ignoring the degenerate parameter is a good approximation; EOS ignoring the gas pressure will significantly decrease the density and temperature, but increase the speed and entropy per baryon, the electron fraction is almost not changed. Meanwhile, important nucleosynthesis parameters (e.g., outflow mass rate, dynamic time scale) will be changed dramatically. For a typical 1.4 M⊙PNS model, when the anti-neutrino luminosity is 8×10⁵¹erg s^-1, the wind material is neutron rich, and different EOSs can induce the average mass number of the r-element modification about 6; While when the anti-neutrino luminosity is 1×10⁵¹ erg s^-1, the wind is proton rich, the abundance of proton capture nuclei produced by EOSIII is almost one time less than other two cases. Therefore choosing an appropriate EOS is extremely important for final product of nucleosynthesis.