  We have analyzed the kinematics of 9750 OB2 stars with proper motions and
parallaxes selected by Xu et al. from the Gaia EDR3 catalogue. The relative
parallax errors for these stars do not exceed 10\%. Based on the entire sample
of stars, we have found the velocities $(U,V)_\odot=(7.17,7.37)\pm(0.16,0.24)$
km s$^{-1}$ and the components of the angular velocity of Galactic rotation:
$\Omega_0 =29.700\pm0.076$ km s$^{-1}$ kpc$^{-1}$, $\Omega^{'}_0
=-4.008\pm0.022$ km s$^{-1}$ kpc$^{-2}$, and $\Omega^{''}_0 = 0.671\pm0.011$ km
s$^{-1}$ kpc$^{-3}$, where the linear rotation velocity of the Galaxy at the
solar distance is $V_0=240.6\pm3.0$ km s$^{-1}$ for the adopted $R_0=8.1\pm0.1$
kpc. There are 1812 OB2 stars with measured line-of-sight velocities, and the
space velocities $V_R$ and $\Delta V_{circ}$ have been calculated from them.
Based on a spectral analysis independently for the radial and residual
tangential velocities, we have obtained the following estimates:
$f_R=4.8\pm0.7$ km s$^{-1}$, $f_\theta=4.1\pm0.9$ km s$^{-1}$,
$\lambda_R=2.1\pm0.2$ kpc, $\lambda_\theta=2.2\pm0.4$ kpc,
$(\chi_\odot)_R=-116\pm12^\circ$, and $(\chi_\odot)_\theta=-156\pm14^\circ$ for
the adopted four-armed ($m = 4$) spiral pattern. Thus, both velocity
perturbation amplitudes are nonzero at a high significance level.
