We present measurements of the dust attenuation of H\alpha-selected
emission-line galaxies at z=0.8 from the NewH\alpha\ narrowband survey. The
analysis is based on deep follow-up spectroscopy with Magellan/IMACS, which
captures the strong rest-frame optical emission lines from [OII] \lambda 3727
to [OIII] \lambda 5007. The spectroscopic sample used in this analysis consists
of 341 confirmed H\alpha\ emitters. We place constraints on the AGN fraction
using diagnostics which can be applied at intermediate redshift. We find that
at least 5% of the objects in our spectroscopic sample can be classified as AGN
and 2% are composite, i.e. powered by a combination of star-formation and AGN
activity. We measure the dust attenuation for individual objects from the
ratios of the higher order Balmer lines. The H\beta\ and H\gamma\ pair of lines
is detected with S/N>5 in 55 individual objects and the H\beta\ and H\delta\
pair is detected in 50 individual objects. We also create stacked spectra to
probe the attenuation in objects without individual detections. The median
attenuation at H\alpha\ based on the objects with individually detected lines
is A(H\alpha)=0.9+-1.0 magnitudes, in good agreement with the attenuation found
in local samples of star-forming galaxies. We find that the z=0.8 galaxies
occupy a similar locus of attenuation as a function of magnitude, mass and SFR
as a comparison sample drawn from the SDSS DR4. Both the results from the
individual z=0.8 galaxies and from the stacked spectra show consistency with
the mass -- attenuation and SFR -- attenuation relations found in the local
Universe, indicating that these relations are also applicable at intermediate
redshift.Comment: Submitted to AJ. Revised per referee's comment