Galactic Rotation Curve and Spiral Density Wave Parameters from 73
  Masers
  Based on kinematic data on masers with known trigonometric parallaxes and
measurements of the velocities of HI clouds at tangential points in the inner
Galaxy, we have refined the parameters of the Allen-Santillan model Galactic
potential and constructed the Galactic rotation curve in a wide range of
Galactocentric distances, from 0 to 20 kpc. The circular rotation velocity of
the Sun for the adopted Galactocentric distance $R_0=8$ kpc is $V_0=239\pm16$
km s$^{-1}$. We have obtained the series of residual tangential, $\Delta
V_{\theta}$, and radial, $\Delta V_R,$ velocities for 73 masers. Based on these
series, we have determined the parameters of the Galactic spiral density wave
satisfying the linear Lin.Shu model using the method of periodogram analysis
that we proposed previously. The tangential and radial perturbation amplitudes
are $f_\theta=7.0\pm1.2$ km s$^{-1}$ and $f_R=7.8\pm0.7$ km s$^{-1}$,
respectively, the perturbation wavelength is $\lambda=2.3\pm0.4$ kpc, and the
pitch angle of the spiral pattern in a two-armed model is
$i=-5.2^\circ\pm0.7^\circ$. The phase of the Sun $\chi_\odot$ in the spiral
density wave is $-50^\circ\pm15^\circ$ and $-160^\circ\pm15^\circ$ from the
residual tangential and radial velocities, respectively.
