Galactic parameters from masers with trigonometric parallaxes

The spatial velocities of all 28 currently known masers having trigonometric parallaxes, proper motion and line-of-site velocities are reanalysed using the Bottlinger equations. These masers are associated with 25 active star-forming regions and are located in the range of galactocentric distances 3 < R < 14 kpc. To determine the Galactic rotation parameters, we have used the first three Taylor expansion terms of angular rotation velocity at the galactocentric distance of the Sun, R(0) = 8 kpc. We have obtained the following solutions: (0) = -31.0 +/- 1.2 km s-1 kpc-1, '(0) = 4.46 +/- 0.21 km s-1 kpc-2, '(0) = -0.876 +/- 0.067 km s-1 kpc-3; Oort constants, A = 17.8 +/- 0.8 km s-1 kpc-1, B = -13.2 +/- 1.5 km s-1 kpc-1; the circular velocity of the solar neighbourhood rotation V(0) = 248 +/- 14 km s-1. A Fourier analysis of the galactocentric radial velocities of masers V(R) has allowed us to estimate the wavelength lambda = 2.0 +/- 0.2 kpc and peak velocity f(R) = 6.5 +/- 2 km s-1 of periodic perturbations from the density wave and velocity of the perturbations 4 +/- 1 km s-1 near the location of the Sun. The phase of the Sun in the density wave is estimated as chi(circle dot) approximate to -130 degrees +/- 10 degrees. Taking into account perturbations evoked by the spiral density wave, we have obtained the following non-perturbed components of the peculiar solar velocity with respect to the local standard of rest (LSR): (U(circle dot), V(circle dot), W(circle dot))(LSR) = (5.5, 11, 8.5) +/- (2.2, 1.7, 1.2) km s-1.