Kinematics of OB Stars with Data from the LAMOST and Gaia Catalogues

TL;DR

This study analyzes the kinematics of about 13,000 OB stars using Gaia and LAMOST data, deriving Galactic rotation parameters, velocity dispersions, and assessing distance scale accuracy.

Contribution

It provides new kinematic parameters for OB stars and evaluates the impact of different distance scales and velocity measurements on Galactic dynamics analysis.

Findings

Derived Galactic rotation parameters with high precision.

Found that line-of-sight velocities increase velocity dispersion estimates.

Suggested photometric distances should be increased by about 10%."

Abstract

We have analyzed the kinematics of OB stars from the list by Xiang et al. (2021) that contains $\sim$13 000 single OB stars. For these stars there are photometric distance estimates and proper motions from the Gaia catalogue and line-of-sight velocities from the LAMOST catalogue. Based on a sample of single OB stars and using the photometric distances and proper motions of stars from the Gaia EDR3 catalogue, we have found the group velocity components $(U_\odot,V_\odot,W_\odot)=(9.63,9.93,7.45)\pm(0.27,0.34,0.10)$ km s$^{-1}$, and the following parameters of the angular velocity of Galactic rotation: $\Omega_0=29.20\pm0.18$ km s$^{-1}$ kpc$^{-1}$, $\Omega^{'}_0=-4.150\pm0.046$ km s$^{-1}$ kpc$^{-2}$ and $\Omega^{''}_0=0.795\pm0.018$ km s$^{-1}$ kpc$^{-3}$, where the error per unit weight $\sigma_0$ is 9.56 km s$^{-1}$ and $V_0=236.5\pm3.3$ km s$^{-1}$ (for the adopted $R_0=8.1\pm0.1$ kpc). Based on the same OB stars, we have found the residual velocity dispersions $(\sigma_1,\sigma_2,\sigma_3)=(15.13,9.69,7.98)\pm(0.07,0.05,0.04)$ km s$^{-1}$. We show that using the line-of-sight velocities increases significantly the space velocity dispersion and leads to a biased estimate of the velocity $U_\odot$. A comparison of the distances scales used has shown that the photometric distances from Xiang et al. (2021) should be lengthened approximately by 10%.