3.6.2.2 Velocity Ellipsoids of Nearby Stars
On the asymmetry of stellar motion, Karl Schwarzschild showed that an asymmetric
distribution could be represented by an ellipsoidal distribution, instead of the
two-stream hypothesis, that is, by a normal frequency function with unequal dispersions in different directions. The center of the ellipsoid indicates the mean motion of
the stars relative to the Sun (Schwarzschild 1907).
Kaburagi adopted the ellipsoidal hypothesis of Schwarzschild and derived the
velocity ellipsoids of nearby stars for different radial velocity steps. He derived the
velocity ellipsoids in six steps for low-velocity stars (0–15, 15–30, . . .,
65–70 km s
À1 ) and four steps for high-velocity stars (70–100, 100–150, . . .,
200–250 km s
À1 ), and the projections of ellipsoids on the galactic plane are
delineated in Fig. 3.13, where the horizontal direction corresponds to the galactic
longitude l ¼ 0
and 180
, and vertical direction to l ¼ 90
and 270
(in the old
system of galactic coordinates).
He noticed that the velocity ellipsoids represented different forms for different
velocity steps. The major and intermediate axes of the ellipsoid lie nearly in the
galactic plane, and the minor axis is perpendicular to it. The directions of the major
Fig. 3.13 Projection on galactic plane of velocity ellipsoids in relation to stars in solar neighborhood. The dots represent the centers of the ellipsoids (Kaburaki 1933)
3.6 Kaburaki Masaki and Stellar Astronomy
67
On the asymmetry of stellar motion, Karl Schwarzschild showed that an asymmetric
distribution could be represented by an ellipsoidal distribution, instead of the
two-stream hypothesis, that is, by a normal frequency function with unequal dispersions in different directions. The center of the ellipsoid indicates the mean motion of
the stars relative to the Sun (Schwarzschild 1907).
Kaburagi adopted the ellipsoidal hypothesis of Schwarzschild and derived the
velocity ellipsoids of nearby stars for different radial velocity steps. He derived the
velocity ellipsoids in six steps for low-velocity stars (0–15, 15–30, . . .,
65–70 km s
À1 ) and four steps for high-velocity stars (70–100, 100–150, . . .,
200–250 km s
À1 ), and the projections of ellipsoids on the galactic plane are
delineated in Fig. 3.13, where the horizontal direction corresponds to the galactic
longitude l ¼ 0
and 180
, and vertical direction to l ¼ 90
and 270
(in the old
system of galactic coordinates).
He noticed that the velocity ellipsoids represented different forms for different
velocity steps. The major and intermediate axes of the ellipsoid lie nearly in the
galactic plane, and the minor axis is perpendicular to it. The directions of the major
Fig. 3.13 Projection on galactic plane of velocity ellipsoids in relation to stars in solar neighborhood. The dots represent the centers of the ellipsoids (Kaburaki 1933)
3.6 Kaburaki Masaki and Stellar Astronomy
67