RELATIVE ABUNDANCES IN THE LOW-METALLICITY DWARF IRREGULAR GALAXY UGC-4483

UGC 4483 is a dwarf irregular galaxy in the M 81 group. Narrow-band optical imaging has revealed an H II region in UGC 4483 with an H-alpha flux of almost-equal-to 2 x 10(-13) erg cm-2 angstrom-1 s-1. Optical, ultraviolet, and near-infrared spectroscopy of this H II region yield He, C, N, O, Ne, and S abundances for the ISM in this galaxy. With an oxygen abundance of 2.1 x 10(-5) (12 + log(O/H) = 7.3), this galaxy is among the most metal-poor dwarf irregulars known to date. A comparison of the S/O abundance ratio in this galaxy with that in I Zw 18 supports the claim by Garnett 1990 that the S/O ratio is consistent with the solar ratio for low-metallicity dwarf irregulars. The C/O ratio in UGC 4483 is lower than that derived for I Zw 18 and, therefore, more in line with the trend seen in higher metallicity H II regions. The derived helium abundance is He/H = 0.075, which converts to a helium mass fraction of 0.23, consistent with earlier determinations of the primordial helium abundance.