Study of the Galactic Rotation Based on Masers and Radio Stars with VLBI
  Measurements of Their Parallaxes
  Based on published data, we have produced a sample of 256 radio sources whose
trigonometric parallaxes and proper motions were measured by VLBI. This sample
contains Galactic masers associated with massive protostars and stars in active
star-forming regions. It also includes young low-mass stars from the Gould Belt
region whose radio observations were performed in continuum. Based on this,
most complete sample of sources to date, we have estimated the velocities
$(U,V,W)_\odot$ and the parameters of the angular velocity of Galactic rotation
$\Omega_0, \Omega^{(1)}_0, ... , \Omega^{(4)}_0$ and obtained a new estimate of
the distance fromthe Sun to the Galactic center, $R_0=8.15^{+0.04}_{-0.20}$
kpc. The parameters of the Galactic spiral density wave have been found from
the series of radial, $V_R$, and residual tangential, $\Delta V_{circ}$,
velocities of stars. The amplitudes of the radial and tangential velocity
perturbations are $f_R=7.0\pm0.9$ km s$^{-1}$ and $f_\theta=3.8\pm1.1$ km
s$^{-1}$, the perturbation wavelengths are $\lambda_R=2.3\pm0.2$ kpc and
$\lambda_\theta=2.0\pm0.4$ kpc, and the Sun's phases in the spiral density wave
are $(\chi_\odot)_R=-163^\circ\pm9^\circ$ and
$(\chi_\odot)_\theta=-137^\circ\pm10^\circ$ for the adopted four-armed spiral
pattern.
