Direct Oxygen Abundances for Low Luminosity LVL Galaxies
  We present MMT spectroscopic observations of HII regions in 42 low luminosity
galaxies in the LVL. For 31 galaxies, we measured the temperature sensitive [O
III] line at a strength of 4 sigma or greater, and thus determine direct oxygen
abundances. Our results provide the first direct estimates of oxygen abundance
for 19 galaxies. Oxygen abundances were compared to B-band and 4.5 micron
luminosities and stellar masses in order to characterize the
luminosity-metallicity (L-Z) and mass-metallicity (M-Z) relationships at
low-luminosity.
  We present and analyze a "Combined Select" sample composed of 38 objects
(drawn from our parent sample and the literature) with direct oxygen abundances
and reliable distance determinations (TRGB or Ceph). Consistent with previous
studies, the B-band and 4.5 micron L-Z relationships were found to be
12+log(O/H)=(6.27+/-0.21)+(-0.11+/-0.01)M_B and
12+log(O/H)=(6.10+/-0.21)+(-0.10+/-0.01)M_[4.5] (sigma=0.15 and 0.14). For this
sample, we derive a M-Z relationship of
12+log(O/H)=(5.61+/-0.24)+(0.29+/-0.03)log(M*), which agrees with previous
studies; however, the dispersion (sigma=0.15) is not significantly lower than
that of the L-Z relationships. Because of the low dispersions in these
relationships, if an accurate distance is available, the luminosity of a
low-luminosity galaxy is often a better indicator of metallicity than that
derived using certain strong-line methods, so significant departures from the
L-Z relationships may indicate that caution is prudent in such cases. We also
revisit the 70/160 micron color metallicity relationship.
  Additionally, we examine N/O abundance trends with respect to oxygen
abundance and B-V color. We find a positive correlation between N/O ratio and
B-V color for 0.05\lesssimB-V\lesssim0.75:
log(N/O)=(1.18+/-0.9)x(B-V)+(-1.92+/-0.08), with a dispersion of sigma=0.14,
that is in agreement with previous studies.
