The Lin–Shu type density–wave structure of the Galaxy: Line-of-sight velocities of selected 37354 RAVE DR5 stars

Abstract

We exploit information, including velocities from the fifth data release of the RAdial Velocity Experiment (RAVE), to find evidence of the Lin–Shu type tightly wound spiral density waves in the nearby Galactic disk. The Kunder et al. (2017) catalogue of 471117 stars with derived spectrophotometric distances and line-of-sight velocities are explored to find the geometry and parameters of the velocity field in the extended solar neighborhood. Possible existence of noncircular systematic motions of selected 37,354 disk objects within 2 kpc from the Sun and 500 pc from the Galactic mid-plane together with the ordinary differential rotation are assumed. Both the pitch angle of spiral arms and the spatial location of the Sun within the density–wave pattern and the deviations of the motion of objects from the circular motion are calculated by fitting the stellar line-of-sight velocities in RAVE DR5 with the simplest linear perturbation density–wave model. Two radial wavelengths of the wave pattern of about 0.5 kpc and 1.5 kpc in the solar vicinity are found. We argue that the spiral structure of the Galaxy has an oscillating nature corresponding to a concept of the fairly unstable, low amplitude, tightly wound, and rigidly rotating density waves.