Title: : Nucleosynthesis Modes in the SN II High-Entropy-Wind Model
Author(s): Karl-Ludwig Kratz,K. Farouqi, J.J. Cowan, L.I. Mashonkina, B. Pfeiffer, C. Sneden, F.-K. Thielemann, and J.W. Truran
Abstract:Elemental abundances of neutron-capture elements beyond Ba in a number of ultra-metal-poor (UMP) halo stars in the early Galaxy accurately replicate the Solar-System (SS) rapid neutron-capture (r-porcess) pattern. In contrast, the abundances of the lighter elements show distinct differÂences from star to star, with yields varying by more than an order of magnitude. This appears to reÂquire different contributions from several primary nucleosynthesis modes, combining charged-particle and neutron-capture components.
In an attempt to explore the astrophysical implications of the above observations, we have performed large-scale theoretical nucleosynthesis calculations within the model of an adiabatically expanding high-entropy wind (HEW) of a core-collapse SN II. Using a grid of the three main model parameters (i) Yexp (expansion speed of the SN shock front), (ii) S (entropy of the HEW bubble), and (iii) Ye (neutron-to-proton ratio), we find that the above quantities are correlated and have to fulfill specific "r-process strength" conditions in order to obtain the necessary Yn/Yseed (neutron-to-seed) ratio for a complete r-process.
With this - still parameterized - HEW model, a superposition of several S-components with model inÂherent weightings (no longer an algebraic fit as in our earlier canonical model calculations!) results in an excellent reproduction of the overall heavy (A>100) SS r-process abundance pattern. Our model is also able to reproduce the observed elemental LEPP and r-process abundances of UMP halo stars.
For the heavy r-process elements beyond Sn, we obtain a very robust theoretical abundance pattern up to the Th, U r-chronometer region. This result confirms our earlier findings that the split between the classical "weak" and "main" r-processes must occur below Te at the onset of the N=82 rising wing of the A=130 r-abundance peak. For the lighter neutron-capture region, which could be produced by a Light Element Primary Process (LEPP), an S-dependent superposition of a primary alpha-component and a primary component from a neutron-rich alpha-freezeout followed by the recapture of beta-delayed neutrons emitted from the seed nuclei is indicated. The neutron densities obtained in this latter "Bdn-component" seem to mimic a primary s-like process, which has, however nothing to do with a classical, secÂondary s-process. In agreement with several recent observations of LEPP abundances in the Ge to Ag region, our HEW model confirms a Z-dependent non-correlation / partial correlation with the heavier "main" r-process elements.
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