628 Tables 81 1 and 812 



TABLE 811.— Motions of the Stars 



The individual stars are moving in all directions, but, for the average of considerable 

 groups, there is evidence of a drift away from the point in the heavens towards which the 

 sun is moving (solar apex). The best determinations of the solar motion, relative to the 

 stars as a whole, are given in Table 804. In round numbers this motion of the sun may be 

 taken as 20 km/sec. towards the point R. A. 18 h. o. m., Dec. + 30. o°. 



After allowance is made for the solar motion, the motions of the stars in space, relative 

 to the general mean, present marked peculiarities. If from an arbitrary origin a series of 

 vectors are drawn, representing the velocities of the various stars, the ends of these vectors 

 do not form a spherical cluster (as would occur if the motions of the stars were at random), 

 but a decidedly elongated cluster, whose form can be approximately represented either by 

 the superposition of two intermingling spherical clusters with different centers (Kapteyn's 

 two-stream hypothesis) or by a single ellipsoidal cluster (Schwarzschild), the actual form, 

 however, being more complicated than is indicated by either of these hypotheses. The 

 direction of the longest axis of the cluster is known as that of preferential motion. The two 

 opposite points in the heavens at the extremities of this axis are called the vertices. The 

 components of velocity of the stars parallel to this axis average considerably larger than 

 those parallel to any axis perpendicular to it. 



The preferential motion varies greatly with spectral type, being practically absent in 

 Class B, very strong in Class A, and somewhat less conspicuous in Classes F to M, on 

 account of the greater mean velocities of these stars in all directions. The positions of the 

 vertices are nearly the same for all. 



Numerous investigators, from the more distant naked-eye stars, find substantially the 

 same position for the vertex, the mean being R. A. 6 h. 6 m., Dec. -f 9°. The nearer stars, 

 of large proper motion, give a mean of 6 h. 12 m., + 25 . (See Stromberg's discussion, cited 

 above.) 



In addition to these general phenomena, there are numerous clusters of stars whose 

 members possess almost exactly equal and parallel motions, — for example, the Pleiades, 

 the Hyades, and certain large groups in Ursa Major, Scorpius, and Orion. The vertices, 

 and the directions toward which these clusters are moving, are all in the plane of the galaxy. 



The greatest known p. m. star is Barnard's 9th m. in Ophiuchus, 10.3" per year, position 

 angle 356 , parallax 0.52", radial velocity about —117 km/sec. 



The average radial velocity of the globular clusters is 100 km/sec. The globular clusters 

 as a class are approaching the sun. The spiral nebulae are receding. 



A general card catalogue of radial velocities is kept at the Lick Observatory. See Camp- 

 bell, Radial velocities of 2600 stars, Lick Obs. Publ., vol. 16, 1928; of 741 stars, Adams, Joy, 

 Stromberg, Sanford — Astroph. Journ. 70, 1929. 



TABLE 812. — Known Stars of Radial Velocities Greater Than 100 km/sec. 



Star 



RZ Lyrae 



Washington 5583. . 

 Washington 5584. . 



S Carinae 



Kapteyn's star. . . . 

 Van Maanen No. 2. 



Cord. 5.243 



R Pictoris 



A G Wash. 3498. . . 

 41312 Boss 151 1 . . . 



03 Pavonis 



Luyten 680 



BD +34° 2476.... 

 V Urs. Min 



BD +35° 3659.... 



BD +6° 2932 



AGC 27600 



Barnard star 



n Columbae 



BD -3° 3746 



P GC 10404 br . . . . 



Cin. 2750 



172 G Puppis 



y 31 Aquilae 



Boss 4188 



8 Leporis 



— 61 4 



+ '5' 2 

 -45 59 

 -49 26 

 — 16 4 



— 26 17 

 —60 20 

 +32 17 

 +34 16 

 + 74 4i 

 +36 1 

 + 69 

 -36 21 



-32 21 



— 3 32 

 +21 27 

 +23 5i 

 -33 59 

 + 11 44 



— 7 22 

 -20 53 



Proper 

 motion 



3-68 

 3-68 



876 

 3.01 



•56 



•73 

 •54 



'•56 

 •93 



10.25 



•69 

 ■46 



Velocity 

 km/sec. 



+ 385 

 + 307 

 + 295 

 + 289 

 + 242 

 + 238 

 + 225 

 + 207 

 + 200 

 + 184 

 + l8l 

 -178 



— 164 

 -158 



— 172 



-139 

 -130 

 -117 

 + IIO 



— I06 



— 106 

 -103 

 4-I02 



— IOI 



4-101 

 + 100 



Smithsonian Tables 



