Redetermination of Galactic Spiral Density Wave Parameters Based on
  Spectral Analysis of Maser Radial Velocities
  To redetermine the Galactic spiral density wave parameters, we have performed
a spectral (Fourier) analysis of the radial velocities for 44 masers with known
trigonometric parallaxes, proper motions, and line-of-sight velocities. The
masers are distributed in a wide range of Galactocentric distances
$(3.5<R<13.2$ kpc) and are characterized by a wide scatter of position angles
$\theta$ in the Galactic XY plane. This has required an accurate allowance for
the dependence of the perturbation phase both on the logarithm of the
Galactocentric distances and on the position angles of the objects. To increase
the significance of the extraction of periodicities from data series with large
gaps, we have proposed and implemented a spectrum reconstruction method based
on a generalized maximum entropy method. As a result, we have extracted a
periodicity describing a spiral density wave with the following parameters from
the maser radial velocities: the perturbation amplitude $f_R =
7.7^{+1.7}_{-1.5}$ km s$^{-1}$, the perturbation wavelength
$\lambda=2.2^{+0.4}_{-0.1}$ kpc, the pitch angle of the spiral density wave
$i=-5^{+0.2^\circ}_{-0.9^\circ}$, and the phase of the Sun in the spiral
density wave $\chi_\odot= -147^{+3^\circ}_{-17^\circ}$.
