Distance and Proper Motion Measurement of the Red Supergiant, PZ Cas, in
  Very Long Baseline Interferometry H2O Maser Astrometry
  We present the very long baseline interferometry H2O maser monitoring
observations of the red supergiant, PZ Cas, at 12 epochs from 2006 April to
2008 May. We fitted maser motions to a simple model composed of a common annual
parallax and linear motions of the individual masers. The maser motions with
the parallax subtracted were well modeled by a combination of a common stellar
proper motion and a radial expansion motion of the circumstellar envelope. We
obtained an annual parallax of 0.356+/-0.026 mas and a stellar proper motion of
{\mu}*{\alpha}cos{\delta}=-3.7+/-0.2 and {\mu}*{\delta}=-2.0+/-0.3 mas/yr
eastward and northward, respectively. The annual parallax corresponds to a
trigonometric parallax of 2.81+0.22-0.19 kpc. By rescaling the luminosity of PZ
Cas in any previous studies using our trigonometric parallax, we estimated the
location of PZ Cas on a Hertzsprung-Russell diagram and found that it
approaches a theoretically evolutionary track around an initial mass of
~25M(sun). The sky position and the distance to PZ Cas are consistent with the
OB association, Cas OB5, which is located in a molecular gas super shell. The
proper motion of PZ Cas is close to that of the OB stars and other red
supergiants in Cas OB5 measured by the Hipparcos satellite. We derived the
peculiar motion of PZ Cas of Us = 22.8+/-1.5, Vs = 7.1+/-4.4, and Ws =
-5.7+/-4.4 km/s. This peculiar motion has rather a large Us component, unlike
those of near high-mass star-forming regions with negatively large Vs motions.
The uniform proper motions of the Cas OB5 member stars suggest random motions
of giant molecular clouds moving into local potential minima in a
time-dependent spiral arm, rather than a velocity field caused by the spiral
arm density wave.
