The Motions of the Stars Within 20 Parsecs of the Sun.

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Abstract
The purpose of this investigation is to provide a representative sample of the motions of the stars in the neighborhood of the sun. The three components of the velocities of 444 stars within 20 parsecs from the sun have therefore been computed from their proper motions, radial velocities, and parallaxes. The constants for the velocity ellipsoids were determined for all the spectral types involved and are referred to the system of galactic co-ordinates. The velocities of the stars were then projected on the "dynamical axes" of the galaxy, the xi-axis being directed toward galactic longitude 339°, the y1-axis toward galactic longitude 69°, and the z1-axis toward the galactic pole. The x1-axis points approximately toward the center of the galaxy; the yi-axis is the axis of asymmetry in stellar motions. This asymmetry is very evident among the stars studied. Attempts were made to establish correlations between the motions of the stars and their masses, the bolometric magnitude Mb beiiig used as a measure of the masses of the stars. For all the velocity com- ponents studied a definite correlation was established, although the variation with mass is not very pro- nounced. The z1-components, referred to the galactic plane and taken without regard to sign, show a higher speed for the less massive stars than for the more massive. Both the si-components and the y1-compcrnents yield definite values for which the mass is a maximum. These values are Xi = +5 and = -9 km/sec, both referred to the sun. Values of v2 = (x1 + 17)2 + (yi + 300)2 + (z~ + 7)2 were computed and were assumed to represent the velocity of a star relative to the center of the galaxy in a nonrotating system of co-ordinates. These values show a maximum mass for a root-mean-square value of v equal to 295 km/sec. All these effects can be understood on the hypothesis that the more massive a star, the greater is the probability that it moves in an exact circle around the center of the galaxy and that its orbit lies in the galactic plane. The observed relationship between stellar motions and stellar masses has been interpreted as the effect of internal friction in a prestellar system of gas or dust, in accordance with theories previously advanced

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