ON the Nature of the Local Spiral Arm of the Milky Way
  Trigonometric parallax measurements of nine water masers associated with the
Local arm of the Milky Way were carried out as part of the BeSSeL Survey using
the VLBA. When combined with 21 other parallax measurements from the
literature, the data allow us to study the distribution and 3-dimensional
motions of star forming regions in the spiral arm over the entire northern sky.
Our results suggest that the Local arm does not have the large pitch angle
characteristic of a short spur. Instead its active star formation, overall
length (>5 kpc), and shallow pitch angle (~10 degrees) suggest that it is more
like the adjacent Perseus and Sagittarius arms; perhaps it is a branch of one
of these arms. Contrary to previous results, we find the Local arm to be closer
to the Perseus than to the Sagittarius arm, suggesting that a branching from
the former may be more likely. An average peculiar motion of near-zero toward
both the Galactic center and north Galactic pole, and counter rotation of ~ 5
km/s were observed, indicating that the Local arm has similar kinematic
properties as found for other major spiral arms.
