Halpha Imaging of the Herschel Reference Survey. The star formation
  properties of a volume-limited, K-band-selected sample of nearby late-type
  galaxies
  We present new Halpha+[NII] imaging data of late-type galaxies in the
Herschel Reference Survey aimed at studying the star formation properties of a
K-band-selected, volume-limited sample of nearby galaxies. The Halpha+[NII]
data are corrected for [NII] contamination and dust attenuation using different
recipes based on the Balmer decrement and the 24mic luminosities. We show that
the L(Halpha) derived with different corrections give consistent results only
whenever the uncertainty on the estimate of the Balmer decrement is <=0.1. We
use these data to derive the SFR of the late-type galaxies of the sample, and
compare these estimates to those determined using independent monochromatic
tracers (FUV, radio) or the output of SED fitting codes. This comparison
suggests that the 24mic based dust extinction correction for Halpha might be
non universal, and that it should be used with caution in all objects with a
SFA, where dust heating can be dominated by the old stellar population.
Furthermore, because of the sudden truncation of the SFA of cluster galaxies
occurring after their interaction with the surrounding environment, the
stationarity conditions required to transform monochromatic fluxes into SFR
might not always be satisfied in tracers other than L(Halpha). In a similar
way, the parametrisation of the SFH generally used in SED fitting codes might
not be adequate for these recently interacting systems. We then study the SFR
luminosity distribution and the typical scaling relations of late-type
galaxies. We observe a systematic decrease of the SSFR with increasing stellar
mass, stellar mass surface density, and metallicity. We also observe an
increase of the asymmetry and smoothness parameters measured in the Halpha-band
with increasing SSFR, probably induced by an increase of the contribution of
giant HII regions to the Halpha luminosity function in SF low-luminosity
galaxies.
