36 
ASTRONOMY: G. STROMBERG 
A DETERMINATION OF THE SOLAR MOTION AND THE STREAM 
MOTION BASED ON RADIAL VELOCITIES AND 
ABSOLUTE MAGNITUDES 
By Gustaf Stromberg 
Mount Wilson Solar Observatory, Carnegie Institution of Washington 
Communicated by W. S. Adams, December 14, 1917. Read before the Academy, 
November 21, 1917 
In previous determinations of the motion of the sun in space and of 
the star streams the stars have been divided for discussion according to spec- 
tral type or apparent magnitude. The recent investigations of Adams and 
Stromberg 1 have shown that the intrinsically faint stars have a higher average 
radial velocity than those that are intrinsically brighter, or in other words, 
that radial velocity is a function of absolute magnitude. Accordingly an 
investigation of the solar motion and the stream motion based upon a division 
of stars into groups of nearly equal absolute magnitude is of exceptional inter- 
est, since the dispersion of the radial velocities within each group is consid- 
erably less than in the usual case. A brief account of such an investigation 
is given in this communication. 
Of the 1300 stars of the spectral types F, G and K with measured radial 
velocities which have been used in the discussion, about 700 have absolute 
magnitudes determined spectroscopically by Adams. For the remainder, ob- 
served mainly at the Lick and Mills Observatories, mean parallaxes have 
been computed by the aid of the following formula connecting proper motion 
and apparent magnitude: 
Log 7T = log A + log (ju + c) + m log e, 
in which ir is the mean parallax, fx the proper motion, m the apparent magni- 
tude, and A , c and € constants determined by means of the spectroscopic paral- 
laxes. The formula differs from that of Kapteyn, 2 which for later type stars 
of very small proper motion gives parallaxes that are too small, in the addition 
of the constant c. 
Solar Motion. — The constants of the solar motion have been determined by 
a least squares solution of equations of condition of the form 
V = x 0 cos a cos 8 + y Q sin a cos 5 + z 0 sin 8 + K, 
in which V is the radial velocity, — x 0 , —yo, and — z Q the rectangular compo- 
nents of the sun's motion, and K Campbell's K-term, the quantity which must 
be- subtracted from each of the radial velocities, corrected for the sun's motion, 
in order to make their sum equal to zero. The results indicate that the K- 
term has a small positive value in the case of the very luminous stars, and 
probably a negative value in the case of the fainter stars. For K equal to 
