Type II-Plateau supernovae as metallicity probes of the Universe
  We explore a method for metallicity determinations based on quantitative
spectroscopy of type II-Plateau (II-P) supernovae (SNe). For consistency, we
first evolve a set of 15Msun main sequence stars at 0.1, 0.4, 1, and 2 x the
solar metallicity. At the onset of core collapse, we trigger a piston-driven
explosion and model the resulting ejecta and radiation. Our theoretical models
of such red-supergiant-star explosions at different metallicity show that
synthetic spectra of SNe II-P possess optical signatures during the
recombination phase that are sensitive to metallicity variations. This
sensitivity can be quantified and the metallicity inferred from the strength of
metal-line absorptions. Furthermore, these signatures are not limited to O, but
also include Na, Ca, Sc, Ti, or Fe. When compared to a sample of SNe II-P from
the Carnegie SN Project and previous SN followup programs, we find that most
events lie at a metallicity between 0.4 and 2 x solar, with a marked scarcity
of SN II-P events at SMC metallicity. This most likely reflects the paucity of
low metallicity star forming regions in the local Universe.
  SNe II-P have high plateau luminosities that make them observable
spectroscopically at large distances. Because they exhibit signatures of
diverse metal species, in the future they may offer a means to constrain the
evolution of the composition (e.g., the O/Fe ratio) in the Universe out to a
redshift of one and beyond.
