# Galactic Rotation Based on OB Stars from the Gaia DR2 Catalogue

## TL;DR

This study analyzes Gaia DR2 data of about 6000 OB stars to determine Galactic rotation parameters, spiral density wave effects, and the Sun's position within the spiral pattern.

## Contribution

It provides new measurements of Galactic rotation parameters and spiral wave characteristics using a large OB star sample from Gaia DR2.

## Key findings

- Galactic angular velocity parameters are precisely determined.
- The spiral density wave amplitudes and wavelengths are quantified.
- The Sun's phase in the spiral pattern is estimated.

## Abstract

We have studied a sample containing about 6000 OB stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The following parameters of the angular velocity of Galactic rotation have been found: $\Omega_0=29.70\pm0.11$ km s$^{-1}$ kpc$^{-1}$, $\Omega'_0=-4.035\pm0.031$ km s$^{-1}$ kpc$^{-2}$, and $\Omega''_0= 0.620\pm0.014$ km s$^{-1}$ kpc$^{-3}$. The circular rotation velocity of the solar neighborhood around the Galactic center is $V_0=238\pm5$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.0\pm0.15$ kpc. The amplitudes of the tangential and radial velocity perturbations produced by the spiral density wave are $f_\theta=4.4\pm1.4$ km s$^{-1}$ and $f_R=5.1\pm1.2$ km s$^{-1}$, respectively; the perturbation wavelengths are $\lambda_\theta=1.9\pm0.5$ kpc and $\lambda_R=2.1\pm0.5$ kpc for the adopted four-armed spiral pattern. The Sun's phase in the spiral density wave is $\chi_\odot=-178^\circ\pm12^\circ$.