The parameters of the Galactic spiral wave are re-determined using a modified periodogram ( spectral ) analysis of the galactocentric radial velocities of 58 masers with known trigonometric parallaxes , proper motions , and line-of-site velocities .
The masers span a wide range of galactocentric distances , 3 < R < 14 kpc , which , combined with a large scatter of position angles \theta of these objects in the Galactic plane XY , required an accurate account of logarithmic dependence of spiral-wave perturbations on both galactocentric distance and position angle .
A periodic signal was detected corresponding to the spiral density wave with the wavelength \lambda = 2.4 \pm 0.4 kpc , peak velocity of wave perturbations f _ { R } = 7.5 \pm 1.5 km s ^ { -1 } , the phase of the Sun in the density wave \chi _ { \odot } = -160 \pm 15 ^ { \circ } , and the pitch angle of -5.5 \pm 1 ^ { \circ } .