Astrometric and photometric initial mass functions from the UKIDSS
  Galactic Clusters Survey: II The Alpha Persei open cluster
  We present the results of a deep (J=19.1 mag) infrared (ZYJHK) survey over
the full Alpha Persei open cluster extracted from the Data Release 9 of the
UKIRT Infrared Deep Sky Survey Galactic Clusters Survey. We have selected ~700
cluster member candidates in ~56 square degrees in \APer{} by combining
photometry in five near-infrared passbands and proper motions derived from the
multiple epochs provided by the UKIDSS GCS DR9. We also provide revised
membership for all previously published APer low-mass stars and brown dwarfs
recovered in GCS based on the new photometry and astrometry provided by DR9. We
find no evidence of $K$-band variability in members of APer with dispersion
less than 0.06-0.09 mag. We employed two independent but complementary methods
to derive the cluster luminosity and mass functions: a probabilistic analysis
and a more standard approach consisting of stricter astrometric and photometric
cuts. We find that the resulting luminosity and mass functions obtained from
both methods are consistent. We find that the shape of the APer mass function
is similar to that of the Pleiades although the characteristic mass may be
higher after including higher mass data from earlier studies (the dispersion is
comparable). We conclude that the mass functions of APer, the Pleiades, and
Praesepe are best reproduced by a log-normal representation similar to the
system field mass function although with some variation in the characteristic
mass and dispersion values.
