  The Hobby-Eberly Dark Energy Experiment pilot survey identified 284 [O II]
3727 emitting galaxies in a 169 square-arcminute field of sky in the redshift
range 0 < z < 0.57. This line flux limited sample provides a bridge between
studies in the local universe and higher-redshift [O II] surveys. We present an
analysis of the star formation rates (SFRs) of these galaxies as a function of
stellar mass as determined via spectral energy distribution fitting. The [O II]
emitters fall on the "main sequence" of star-forming galaxies with SFR
decreasing at lower masses and redshifts. However, the slope of our relation is
flatter than that found for most other samples, a result of the metallicity
dependence of the [O II] star formation rate indicator. The mass specific SFR
is higher for lower mass objects, supporting the idea that massive galaxies
formed more quickly and efficiently than their lower mass counterparts. This is
confirmed by the fact that the equivalent widths of the [O II] emission lines
trend smaller with larger stellar mass. Examination of the morphologies of the
[O II] emitters reveals that their star formation is not a result of mergers,
and the galaxies' half-light radii do not indicate evolution of physical sizes.
