Program: GN-2009B-Q-5

The galactocentric present-day abundance gradient of M33, the nearest and most extensively studied late-type spiral, should be known to high accuracy. Instead, values for the gradient slope found from different HII region samples in the literature span one order of magnitude. Moreover, recent work done at Keck on 61 HII regions has revealed an unexpectedly large intrinsic scatter in the gas metallicity at any given distance from the galaxy center. A scatter of the magnitude found has never been previously observed in this or any other galaxy, and is difficult to reconcile with our current knowledge of the chemical evolution of spiral galaxies. However, if real, the result might reflect a fundamental property of the chemical enrichment of spiral disks. New spectroscopy of HII regions in the central parts of M33, aimed at the detection of faint abundance diagnostic lines ([O III]4363), is proposed for a small subset (12 HII regions) of the Keck sample. The new data will be used to test the claim for the large abundance scatter, and to better constrain the slope and intercept of the metallicity gradient.