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 Ω at the galactocentric distance of the Sun, R0= 8 kpc. We have obtained the following solutions: Ω0=−31.0 ± 1.2 km s−1 kpc−1, Ω′0= 4.46 ± 0.21 km s−1 kpc−2, Ω″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 V0= 248 ± 14 km s−1. A Fourier analysis of the galactocentric radial velocities of masers VR has allowed us to estimate the wavelength λ= 2.0 ± 0.2 kpc and peak velocity fR= 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 χ⊙≈−130°± 10°. 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⊙, V⊙, W⊙)LSR= (5.5, 11, 8.5) ± (2.2, 1.7, 1.2) km s−1.