VLBI observations of H2O maser annual parallax and proper motion in IRAS 20143+3634: Reflection on the Galactic constants

We report the results of very long baseline interferometry (VLBI) observations of H2O masers in the IRAS 20143+3634 star-forming region (SFR) using VERA (VLBI Exploration of Radio Astrometry). By tracking masers for a period of over two years we measured a trigonometric parallax of pi = 0.367 +/- 0.037 mas, corresponding to a source distance of D = 2.72(-0.25)(+0.31) 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 +/- 0.16 mas yr(-1) and -4.37 +/- 0.43 mas yr(-1) in RA and Dec, respectively, which were used to estimate the peculiar motion of the source as (U-s, V-s, W-s)=(-0.9 +/- 2.9, -8.5 +/- 1.6, +8.0 +/- 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 +/- 2.9, -9.3 +/- 1.5, +8.0 +/- 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 +/- 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 International Astronomical Union 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.