The Spiral Pattern Speed in the Milky Way Galaxy

Based on a sample of masers, we have solved the basic kinematic equations with the inclusion of the Galactic rotation parameters and the peculiar solar velocity as the sought-for unknowns. Based on a spectral analysis, we have obtained the following estimates: $$|f|_{R,\theta}=(7.0,5.1)\pm(1.2,1.4)$$ km s $${}^{-1}$$ , the corresponding wavelengths $$\lambda_{R,\theta}=(1.9,1.7)\pm(0.4,0.7)$$ kpc, and $$\chi_{\odot}={-}140^{\circ}\pm 15^{\circ}$$ . We have confirmed the presence of periodic perturbations in the vertical maser velocities with an amplitude $$|f|_{W}=3.1\pm 1.4$$ km s $${}^{-1}$$ and a wavelength $$\lambda=1.9\pm 0.8$$ kpc. We show that the velocity perturbations $$f_{R}$$ and $$f_{\theta}$$ can have both the same and opposite signs. Therefore, we have obtained a large spread of estimates. For example, if $$f_{R}$$ and $$f_{\theta}$$ have the same signs, then $$\Omega_{p}=25.8\pm 2.0$$ km s $${}^{-1}$$ kpc $${}^{-1}$$ and $$R_{\textrm{cor}}=9.1\pm 0.8$$ kpc, while if $$f_{R}$$ and $$f_{\theta}$$ have opposite signs, then $$\Omega_{p}=35.4\pm 2.0$$ km s $${}^{-1}$$ kpc $${}^{-1}$$ and $$R_{\textrm{cor}}=6.8\pm 0.8$$ kpc.