Features of the Residual Velocity Ellipsoid of Hot Subdwarfs from the Gaia DR2 Catalog

Abstract

The evolution of the parameters of the residual velocity ellipsoid of hot subdwarfs (HSDs) with their position relative to the Galactic plane is traced, using the HSDs selected by Geier et al. from the Gaia DR2 catalog. Parameters of the Galactic rotation are determined for two ∣z∣ zones. These are used to estimate the gradient of the circular rotation velocity, V0, versus ∣z∣, found to be ΔV0/Δ∣z∣ = −71 ± 7 kms−1kpc−1. The size of the residual velocity ellipsoid is (σ1, σ2, σ3) = (36.1, 27.6, 22.8) ± (0.4, 0.8, 0.6) km/s for HSDs at ∣z∣ < 0.5 kpc and (σ1, σ2, σ3) = (56.9, 55.8, 39.7) ± (0.9, 1.1, 0.8) km/s for HS Ds at ∣z∣≥ 0.5 kpc. When forming the HSD residual velocities, the Galactic rotation was taken into account using individual approaches for each z zone. Parameters of the residual velocity ellipsoids for HSDs located in four plane-parallel layers are also determined. The size of the ellipsoid increases with z, and the inclination of the first axis relative to the Galactic plane also increases. This inclination is close to zero in zones close to the Galactic plane, z ∼ ±0.2 kpc, and rises to ∓12° ± 4° for z ∼ ±0.9 kpc.