Chemical evolution

Chemical evolution - Chemical evolution The stars are not...

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Chemical evolution . The stars are not evolving in a vacuum (well, not quite). They are marked by initial composition, and change the composition of the ISM and later-formed stars through winds, planetary nebulae, and supernovae; the relative abundances of heavy elements and dust increases with time. The best place to study this is our own galaxy, for which (in our little neighborhood) we can count stars in bins of age and metallicity. The simplest expectation is based on the one-zone closed-box model. This assumes a closed system with an initial complement of gas, in which star formation proceeds. It assumed instantaneous recycling of the elements under consideration; divide the stars into those that live longer than the time of interest and those with shorter lifetimes. In this case, the rate of recycling into the ISM depends only on SFR and IMF (at that time, if the IMF changes). This is justified as a first guess since so much nucleosynthesis goes on in the most massive, short-lived stars. Define some basic parameters: R returned fraction of gas y the yield, fraction of stellar mass turned into heavy elements This allows one to solve for the abundance as a function of gas content of the galaxy, not as a function of time. For this simple model, as described by Audouze and Tinsley 1976 (ARA&A 14,
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Chemical evolution - Chemical evolution The stars are not...

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