CHemical Abundances of Spirals (CHAOS) II. M51

Using the Multi Object Double Spectrographs on the Large Binocular Telescope we are able to measure one or more of the temperature-sensitive auroral lines ([OIII]{lambda}4363, [NII]{lambda}5755, [SIII]{lambda}6312) and thus measure "direct" gas-phase abundances in 29 individual HII regions. [OIII]{lambda}4363 is only detected in two HII regions, both of which show indications of excitation by shocks.

We compare our data to previous direct abundances measured in NGC 5194 and find excellent agreement ({Delta}[log(O/H)]~0.05) for all but one region. We find no evidence of trends in Ar/O, Ne/O, or S/O within NGC 5194 or compared to other galaxies. We find modest negative gradients in both O/H and N/O with very little scatter ({sigma}<=0.08dex), most of which can be attributed to random error and not to intrinsic dispersion.