Detection of periodic variations in vertical velocities of Galactic masers (1411.2246v1)

Abstract: We have collected literature data on Galactic masers with trigonometric parallaxes measured by means of VLBI. We have obtained series of residual tangential, \Delta V_{circ}, and radial, \Delta V_R, velocities for 107 masers. Based on these series, we have re-determined parameters of the Galactic spiral density wave using the method of spectral (periodogram) analysis. The tangential and radial perturbation amplitudes are f_\theta=6.0+/-2.6 km/s and f_R=7.2+/-2.2 km/s, respectively; the perturbation wavelengths are \lambda_\theta=3.2+/-0.5 kpc and \lambda_R=3.0+/-0.6 kpc for a four-armed spiral model, m=4. The phase of the Sun \chi_0 in the spiral density wave is -79^\circ+/-14^\circ and -199^\circ+/-16^\circ from the residual tangential and radial velocities, respectively. The most interesting result of this work is detecting a wave in vertical spatial velocities W versus distance R from the Galactic rotation axis. From the spectral analysis, we have found the following characteristics of this wave: the perturbation wavelength is \lambda_W=3.4+/-0.7 kpc and the amplitude f_W=4.3+/-1.2 km/s.