Galaxy Rotation Parameters from OB2 Stars with Proper Motions and Parallaxes from the Gaia EDR3 Catalog

TL;DR

This study analyzes the kinematics of OB2 stars using Gaia EDR3 data to determine Galactic rotation parameters, residual velocity variances, and the orientation of the velocity ellipsoid, confirming the robustness of these measurements against systematic parallax corrections.

Contribution

The paper provides new precise measurements of Galactic rotation parameters and residual velocity ellipsoid orientations based on a large OB2 star sample from Gaia EDR3, with analysis of systematic parallax correction effects.

Findings

Galactic angular velocity parameters are precisely determined.

Residual velocity ellipsoid axes are oriented close to Galactic coordinates.

Systematic parallax correction has minimal impact on kinematic parameters.

Abstract

We have analyzed the kinematics of OB2 stars with proper motions and parallaxes selected by Xu et al. from the Gaia EDR3 catalog. The relative parallax errors for all the stars in this sample do not exceed 10\%. Based on a sample of 9750 stars, the group velocity components $(U,V,W)_\odot=(7.21,7.46,8.52)\pm(0.13,0.20,0.10)$~km/s were obtained and the parameters of the angular velocity of rotation of the Galaxy: $\Omega_0 =29.712\pm0.062$~km/s/kpc, $\Omega^{'}_0=-4.014\pm0.018$~km/s/kpc$^{2}$ and $\Omega^{''}_0=0.674\pm0.009$~km/s/kpc$^{3}$. The circular velocity of rotation of the solar neighborhood around the center of the Galaxy is $V_0=240.7\pm3.0$~km/s for the assumed distance of the Sun to the galactic center $R_0=8.1\pm0.1$~kpc. It is shown that the influence of the systematic correction to the trigonometric parallaxes of the Gaia EDR3 catalog with the value $\Delta\pi=-0.040$~mas does not exceed the $\sim1\sigma$ level of the errors of the sought-for kinematic parameters of the model. Based on the proper motions of OB stars, the following variances of the residual velocities were found: $(\sigma_1,\sigma_2,\sigma_3)=(11.79,9.66,7.21)\pm(0.06,0.05,0.04)$~km/s. It is shown that the first axis of this ellipsoid slightly deviates from the direction to the center of the Galaxy $L_1=12.4\pm0.1^\circ$, and the third axis is oriented almost exactly to the north pole of the Galaxy, $B_3=87.7\pm0.1^\circ.$