Abundances in HII regions of M81

The aim is to derive plasma and abundance analysis for a sizable set of emission-line targets to study the galactic chemical contents in the framework of galactic metallicity gradients. We used the weak-line abundance approach by deriving electron density and temperatures for several HII regions in M81.

Gradient analysis is based on oxygen abundances. Together with a set of HII region abundances determined similarly by us with Multi-Mirror Telescope (MMT) spectra, the new data yield to a radial oxygen gradient of -0.088+/-0.013dex/kpc, which is steeper than the metallicity gradient obtained for planetary nebulae (-0.044+/-0.007dex/kpc). This result could be interpreted as gradient evolution with time: Models of galactic evolution with inside-out disk formation associated to pre-enriched gas infall would produce such difference of gradients, although stellar migration effects would also induce a difference in the metallicity gradients between the old and young populations.