On the Motion of Stars in the Pleiades according to Gaia DR2 Data
  We used Gaia DR2 data in order to estimate parameters of the Pleiades. With
the data on stars with m_G<=18 mag, we constructed the density maps and
profile, luminosity and mass functions, determined the cluster radius,
10.9+/-0.3 deg (26.3+/-0.7 pc), and the radius of its core, 2.62 deg (6.24 pc),
and obtained estimates for the number of stars in the cluster, 1542+/-121, and
their mass, 855+/-104 solar mass. Distribution of stars with m_G<16 mag at
distances r_s from the cluster center in three-dimensional space of r_s<1 pc
and at r_s~1.4-5 pc contains radial density waves. We determined the average
`prograde' rotation velocity of the core of the cluster v_c=0.56+/-0.07 km/s at
distances d in the sky plane d<=4.6 pc from its center. The rotation velocity
of the cluster core at a distance of d~5.5 pc from its center is close to zero:
v_c=0.1+/-0.3 km/s. The velocity of the `retrograde' rotation of the cluster at
a distance of d~7.1 pc from its center is v_c=0.48+/-0.20 km/s. The dependences
of moduli of the tangential and radial components of the cluster core star
velocities in the sky plane on the distance d to the cluster center contain the
periodic oscillations. The velocity dispersions of the cluster core stars
increase on average with an increase in r_s, which, like the radial density
waves and the waves of oscillations of the velocity field in the sky plane,
indicates the non-stationarity of the cluster in the regular field. The Jeans
wavelength in the cluster core decreases, and the velocity dispersion of the
core stars under the Jeans instability increases after taking into account the
Galactic gravitational field. The region of gravitational instability in the
Pleiades cluster is located in the interval r_s=2.2-5.7 pc and contains
39.4-60.5% of the total number of stars in the considered samples.
