We present constraints on the progenitor metallicities of core-collapse
supernovae. To date, nearly all metallicity constraints have been inferred from
indirect methods such as metallicity gradients in host galaxies, luminosities
of host galaxies, or derived global galaxy metallicities. Here, progenitor
metallicities are derived from optical spectra taken at the sites of nearby
supernovae, from the ratio of strong emission lines found in their host HII
regions.We present results from the spectra of 74 host HII regions and discuss
the implications that these have on the nature of core-collapse supernova
progenitors. Overall, while we find that the mean metallicity of type Ibc
environments is higher than that of type II events, this difference is smaller
than observed in previous studies. There is only a 0.06 dex difference in the
mean metallicity values, at a statistical significance of ~1.5 sigma, while
using a KS-test we find that the two metallicity distributions are marginally
consistent with being drawn from the same parent population (probability >10%).
This argues that progenitor metallicity is not a dominant parameter in deciding
supernovae type, with progenitor mass and/or binarity playing a much more
significant role.Comment: ACCEPTED for publication in MNRA
