Metal Abundances of 12 Dwarf Irregulars from the ADBS Survey
  We have analyzed long-slit spectra of 12 dwarf irregular galaxies from the
Arecibo Dual Beam Survey (ADBS). These galaxies represent a heterogeneous
sample of objects detected by ADBS, but on average are relatively gas-rich,
low-surface-brightness, and low-mass, thus represent a region of the galaxian
population that is not commonly included in optical surveys. The
metallicity-luminosity relationship for these galaxies is analyzed; the
galaxies discussed in this paper appear to be under-abundant at a given
luminosity when compared to a sample from the literature. We attempt to
identify a "second parameter" responsible for the intrinsic scatter and
apparent under-abundance of our galaxies. We do not find a definitive second
parameter but note the possible indication that infall or mixing of pristine
gas may be responsible. We derive oxygen abundances for multiple HII regions in
many of our galaxies but do not find any strong indications of metallicity
variation within the galaxies except in one case where we see variation between
an isolated HII region and the rest of the galaxy. Our data set includes the
galaxy with the largest known HI-to-optical size ratio, ADBS 113845+2008. Our
abundance analysis of this galaxy reveals that it is strongly over-enriched
compared to galaxies of similar luminosity, indicating it is not a young object
and confirming the result from Cannon et. al (2009) that this galaxy appears to
be intrinsically rare in the local universe.
