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.