Inferences on aspects of stellar evolution and the evolution of galaxies

Abstract

In this report we will try to summarize some key observations on isotopic abundances of radioactive nuclei in meteorites and their relationship to stellar sources. We will also cover the transition from the first generation of supermassive stars to the "normal" stellar population (including supernovae) in a galaxy. Two distinctive approaches are presented. The first is to utilize the observations on meteorites to infer the sources of radioactive nuclei in the solar system. We will show that some radioactive nuclides are clearly related to production in AGB stars, while others are produced in r-processes in SNII. We will show that there must be at least two distinct types of SNII sites with very different time scales for replenishing the ISM with different r-nuclides. This model leads us to a means of identifying the first generation of supernovae that contribute to the galactic inventory of r-process nuclei and of Fe. This is then related to observations of low metallicity stars and connects/disconnects more general r-process abundance patterns with/from Fe production and points to a first generation of stars having distinct characteristics. This approach is the view backward in time. The second approach uses the phenomenological model derived from the above considerations and applies it to the chronology evolving from Big Bang toward the present epoch. The latter approach proclaims an "absolute" time scale and what the evolutionary path of condensing, star-forming, baryonic matter should be. I am obviously going beyond my own capability in this approach, but it is at least interesting and may contain some seeds of truth. The assumption of a universal r-process that produces both Fe and r-nuclei in a coupled manner is in violation of the observations that the correlation of r-elements with Fe breaks down at [Fe/H] ≾ - 3 as observed in halo stars. Furthermore, the ab initio approaches to early star formation, chemical evolution, and the early universe, have not proven very successful so far. There has been no real success in establishing the relationship between the condensation of cold dark matter early in the universe (z ≳10?) with the aggregation of baryonic matter and the formation of the first generation of stars.

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