Neon Abundances in the H II Regions of M33

Abstract

We present neon abundances for 25 H II regions of M33, measured from line profiles of the mid-infrared transitions of [Ne II] and [Ne III] taken with the Infrared Space Observatory Short-Wavelength Spectrometer. The distribution of neon abundances as a function of galactocentric radius is best described as a step, -0.15 dex relative to the solar neon abundance from 0.7 to 4.0 kpc and -0.35 dex from 4.0 to 6.7 kpc, with estimated intrinsic scatter of 0.07 dex. The nearly flat neon abundance distribution differs from the steep oxygen abundance gradient found by previous investigators. Unless the oxygen abundance determinations are wrong, the chemical evolution of the galaxy has been radially dependent.