Oxygen Abundance Measurements of SHIELD Galaxies
  We have derived oxygen abundances for 8 galaxies from the Survey of HI in
Extremely Low-mass Dwarfs (SHIELD). The SHIELD survey is an ongoing study of
very low-mass galaxies, with M$_{\rm HI}$ between 10$^{6.5}$ and 10$^{7.5}$
M$_{\odot}$, that were detected by the Arecibo Legacy Fast ALFA (ALFALFA)
survey. H$\alpha$ images from the WIYN 3.5m telescope show that these 8 SHIELD
galaxies each possess one or two active star-forming regions which were
targeted with long-slit spectral observations using the Mayall 4m telescope at
KPNO. We obtained a direct measurement of the electron temperature by detection
of the weak [O III] $\lambda$4363 line in 2 of the HII regions. Oxygen
abundances for the other HII regions were estimated using a strong-line method.
When the SHIELD galaxies are plotted on a B-band luminosity-metallicity diagram
they appear to suggest a slightly shallower slope to the relationship than
normally seen. However, that offset is systematically reduced when the
near-infrared luminosity is used instead. This indicates a different
mass-to-light ratio for the galaxies in this sample and we suggest this may be
indicative of differing star-formation histories in the lowest luminosity and
surface brightness dwarf irregulars.
