MOUNT WILSON OBSERVATORY. 245 



STELLAR SPECTROSCOPY. 



The stellar spectroscopic work throughout the year has been carried 

 on by Mr. Adams, Mr. Joy, and Mr. Stroraberg. Mr. Merrill, Mr. 

 Sanford, and Mr. Duncan shared in the observations during the sum- 

 mer of 1919. A considerable portion of the work had been planned 

 with a view to facihtating the determination of the absolute magni- 

 tudes of the highly luminous stars by the spectroscopic method. For 

 this purpose a large number of stars with apparent visual magnitudes 

 of 5.0 or brighter have been added to the observing list. Such stars 

 furnish material especially suitable for a comparison with results from 

 mean parallaxes obtained from parallactic motion. Spectrographic ob- 

 servations have also been continued on the stars listed in the American 

 Ephemeris and the selected groups of stars to which reference was made 

 in the last annual report. 



The number of photographs of spectra obtained during the year 

 with the Cassegrain spectrograph and the 60-inch reflector is 1,337. 

 These are distributed in magnitude as follows : 



Brighter than 5.0 visually 480 



5.0 to 6.0 408 



6.0 to 7.0 252 



7.0 to 8.0 119 



Fainter than 8.0 78 



The 7-inch camera has been used for 90 of the spectrograms of the 

 fainter stars. The observations include 20 photographs of Nova 

 Aquilse No. 3 and 100 photographs of variable stars. 



Radial Velocities. 



The radial velocities of 133 stars have been determined from measure- 

 ments of three or more spectrograms. Among the more interesting 

 results for individual stars the following may be mentioned : 



(1) The orbits of four spectroscopic binaries have been pubUshed. 

 These are Boss 593, Boss 2285, W Ursse Majoris, and Z Herculis. 

 In the case of the last two stars the presence of the spectra of both 

 components and the photometric data provide the means for a de- 

 termination of the absolute dimensions of the orbits. 



(2) A list of 14 spectroscopic binaries was pubhshed early in the 

 year. Five of these stars show composite spectra. 



(3) An investigation of the motions in space of 37 stars with radial 

 velocities exceeding 80 km. leads to the conclusion that stream-motion 

 is very marked for these stars. 



(4) The apices of these stars He almost wholly in one hemisphere, 

 their galactic longitudes all falling between 131° and 322°. 



(5) The components of velocity parallel to the plane of the Galaxy 

 are more than double that normal to this plane. The velocity of the 

 centroid of these stars is remarkably high, amounting to 74 km., even 



