Galaxy Rotation Parameters from OB2 Stars with Proper Motions and
  Parallaxes from the Gaia EDR3 Catalog
  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,
$B_3=87.7\pm0.1^\circ.$
