First detection of the field star overdensity in the Perseus arm
  Aims. The main goal of this study is to detect the stellar overdensity
associated with the Perseus arm in the anticenter direction. Methods. We used
the physical parameters derived from Str\"omgren photometric data to compute
the surface density distribution as a function of galactocentric distance for
different samples of intermediate young stars. The radial distribution of the
interstellar absorption has also been derived. Results. We detected the Perseus
arm stellar overdensity at 1.6+-0.2 kpc from the Sun with a significance of
4-5{\sigma} and a surface density amplitude of around 10%, slightly depending
on the sample used. Values for the radial scale length of the Galactic disk
have been simultaneously fitted obtaining values in the range [2.9,3.5] kpc for
the population of the B4-A1 stars. Moreover, the interstellar visual absorption
distribution is congruent with a dust layer in front of the Perseus arm.
Conclusions. This is the first time that the presence of the Perseus arm
stellar overdensity has been detected through individual star counts, and its
location matches a variation in the dust distribution. The offset between the
dust lane and the overdensity indicates that the Perseus arm is placed inside
the co-rotation radius of the Milky Way spiral pattern.
