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J. C. Wheeler (University of Texas at Austin)
While we have a decent understanding of the nucleosynthetic yields of supernovae at the current epoch, there is much to be done to understand the yields from the first epochs of star formation and how the resulting age-metallicity relations will vary with place and time. While some work has been done on zero-metallicity stars, there is very little systematic understanding of the evolution and hence yields of such stars. These are the supernovae that should be seen as the Universe emerges from the Dark Ages. They should be massive stars, but we do not know how massive. These stars may be shy of r-process elements, but their yields may be reflected in the abundances of the lowest metallicity stars on a one-to-one basis as the first supernovae seeded their region of the ISM. At low metallicities, it is likely that all supernovae exploded as blue supergiants reminiscent of SN 1987A and hence may have been dimmer than models at this epoch based on current Type II plateau supernovae. If the seeding of the ISM by individual supernovae is patchy, then subsequent cooling and star formation should also be. Computation of a mean metallicity versus age or redshift must take these deviations, perhaps very strong, into account. Epochs of strong star formation may happen at later epochs due to galaxy collisions, but could be delayed due to global effects of intermittancy. Our Galaxy might have undergone a burst of star formation 5-6 Gyr ago that would make it look like a faint blue galaxy at redshifts of around 1. Due to the still unknown binary evolution "fuse," Type Ia supernovae should come in at a later epoch than the first massive-star explosions. The very first Type Ia are likely to have more massive, shorter-lived progenitors than the mean at the current epoch. The change in the nucleosynthesis may be small, but the affect on the brightness that determines estimates of cosmological distances may not be. Understanding how growing, spotty, metallicity in turn affects the nature of Type Ia evolution is important for their accurate use as cosmological probes.
This research is supported by NSF, NASA, and the Texas Advanced Research Program.
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