SIMBAD references

To construct the rotation curve of the Galaxy, classical Cepheids with proper motions, parallaxes and line-of-sight velocities from the Gaia DR2 Catalogue are used in large part. Our working sample formed from literature data contains about 800 Cepheids with estimates of their age. We determined that the linear rotation velocity of the Galaxy at the solar distance is V₀ = 240 ± 3 km s^–1. In this case, the distance from the Sun to the axis of rotation of the Galaxy is found to be R₀ = 8.27 ± 0.10 kpc. A spectral analysis of radial and residual tangential velocities of Cepheids younger than 120 Myr showed close estimates of the parameters of the spiral density wave obtained from data both at the present time and in the past. Therefore, the value of the wavelength λ_R, θ_ is in the range [2.4-3.0] kpc, the pitch angle i_R, θ_ is in the range [-13^*, -10^*] for a four-arm pattern model, and the amplitudes of the radial and tangential perturbations are f_R ∼ 12 km s^–1 and f_θ ∼ 9 km s^–1, respectively. Velocities of Cepheids older than 120 Myr currently give a wavelength λ_R, θ_ ∼ 5 kpc. This value differs significantly from the one we obtained from samples of young Cepheids. An analysis of the positions and velocities of old Cepheids, calculated by integrating their orbits backward in time, made it possible to determine significantly more reliable values of the parameters of the spiral density wave: wavelength λ_R, θ_ = 2.7 kpc and amplitudes of radial and tangential perturbations f_R = 7.9 km s^–1 and f_θ = 5 km s^–1, respectively.