VLBI Observations of H2O Maser Annual Parallax and Proper Motion in IRAS
  20143+3634: Reflection on the Galactic Constants
  We report the results of VLBI observations of H$_{2}$O masers in the IRAS
20143+3634 star forming region using VERA (VLBI Exploration of Radio
Astronomy). By tracking masers for a period of over two years we measured a
trigonometric parallax of $\pi = 0.367 \pm 0.037$ mas, corresponding to a
source distance of $D = 2.72 ^{+0.31}_{-0.25}$ kpc and placing it in the Local
spiral arm. Our trigonometric distance is just 60% of the previous estimation
based on radial velocity, significantly impacting the astrophysics of the
source. We measured proper motions of $-2.99 \pm 0.16$ mas yr$^{-1}$ and $-4.37
\pm 0.43$ mas yr$^{-1}$ in R.A. and Decl. respectively, which were used to
estimate the peculiar motion of the source as $(U_{s},V_{s},W_{s}) = (-0.9 \pm
2.9, -8.5 \pm 1.6, +8.0 \pm 4.3)$ km s$^{-1}$ for $R_0=8$ kpc and
$\Theta_0=221$ km s$^{-1}$, and $(U_{s},V_{s},W_{s}) = (-1.0 \pm 2.9, -9.3 \pm
1.5, +8.0 \pm 4.3)$ km s$^{-1}$ for $R_0=8.5$ kpc and $\Theta_0=235$ km
s$^{-1}$. IRAS 20143+3634 was found to be located near the tangent point in the
Cygnus direction. Using our observations we derived the angular velocity of
Galactic rotation of the local standard of rest (LSR), $\Omega_{0} = 27.3 \pm
1.6$ km s$^{-1}$ kpc$^{-1}$, which is consistent with previous values derived
using VLBI astrometry of SFRs at the tangent points and Solar circle. It is
higher than the value recommended by the IAU of $\Omega_{0} = 25.9$ km s$^{-1}$
kpc$^{-1}$ which was calculated using the Galactocentric distance of the Sun
and circular velocity of the LSR.
