VLBI observations of H2O maser annual parallax and proper motion in IRAS 20143+3634: Reflection on the Galactic constants
Nippon Tenmon Gakkai obun kenkyu hokoku
We report the results of VLBI observations of H_2O 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 π = 0.367 ± 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 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 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 ± 2.9, -8.5 ± 1.6, +8.0 ± 4.3) km s^-1 for R_0=8 kpc and Θ_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 Θ_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), Ω_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 IAU of Ω_0 = 25.9 km s^-1 kpc^-1 which was calculated using the Galactocentric distance of the Sun and circular velocity of the LSR.