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

TL;DR

This study analyzes the residual velocity ellipsoid of hot subdwarfs from Gaia DR2 data, revealing how its parameters change with distance from the Galactic plane and providing insights into Galactic rotation and stellar kinematics.

Contribution

It presents a detailed analysis of the residual velocity ellipsoid of hot subdwarfs, including its size, shape, and inclination variations with respect to the Galactic plane, using Gaia DR2 data.

Findings

The residual velocity ellipsoid size increases with distance from the Galactic plane.

The inclination of the ellipsoid's first axis grows with height, reaching about 12 degrees at 0.9 kpc.

The Galactic rotation velocity gradient is estimated as -71 km/s per kpc with respect to |z|.

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, $V_0,$ versus $|z|,$ found to be $\Delta V_0/\Delta |z|=-71\pm7$ km s$^{-1}$ kpc$^{-1}$. The size of the residual velocity ellipsoid is $(\sigma_1,\sigma_2,\sigma_3)=(36.1,27.6,22.8)\pm(0.4,0.8,0.6)$ km/s for HSDs at $|z|<0.5$ kpc and $(\sigma_1,\sigma_2,\sigma_3)=(56.9,55.8,39.7)\pm(0.9,1.1,0.8)$ km/s for HSDs at $|z|\geq0.5$ 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, $z\sim\pm0.2$ kpc, and rises to $\mp12\pm4^\circ$ for $z\sim\pm0.9$ kpc.