Non-circular Motions in the Outer Perseus Spiral Arm
  We report measurements of parallax and proper motion for five 6.7-GHz
methanol maser sources in the outer regions of the Perseus arm as part of the
BeSSeL Survey of the Galaxy. By combining our results with previous astrometric
results, we determine an average spiral arm pitch angle of $9.2\pm1.5$ deg and
an arm width of 0.39 kpc for this spiral arm. For sources in the interior side
of the Perseus arm, we find on average a radial inward motion in the Galaxy of
$13.3\pm5.4$ km s$^{-1}$ and counter to Galactic rotation of $6.2\pm3.2$ km
s$^{-1}$. These characteristics are consistent with models for spiral arm
formation that involve gas entering an arm to be shocked and then forming
stars. However, similar data for other spiral arms do not show similar
characteristics.
