Spiral density-wave structure parameters in the solar neighbourhood derived from longitudinal velocities of Gaia EDR3 OB stars: 3D approach

Distances and transverse along the Galactic longitude velocities v<SUB>l</SUB> of 2640 Gaia EDR3 O-B2 stars of Xu et al. within 2.5 kpc from the Sun and 250 pc from the Galactic plane with relative distance and velocity accuracies of <10 and <50 per cent are selected. Under the assumption of spiral density waves, both Galactic differential rotation parameters and parameters of the wave structure in this solar neighbourhood are derived from observed v<SUB>l</SUB>. In contrast to all preceding studies, we take into account the effect of small but finite thickness of the disc of the Galaxy on even parity ('sausage') gravity perturbations of the kind investigated by Lin and Shu. As previously predicted by the modified theory of 3D density waves, two scales of periodic rarefaction-compression irregularity of the v<SUB>l</SUB> velocity field with the radial λ<SUB>0</SUB> ≍ 1.5 kpc and vertical ξ<SUB>0</SUB> ≍ 1.0 kpc wavelengths in the form of a spiral wave propagating in the disc are revealed. The Gaia's DR2 line-of-sight and EDR3 longitudinal velocities analyses performed in the last papers of a series exhibit consistent findings, thus providing a further evidence to support the Lin-Shu density-wave proposal.