46 E. 0. Pickering — Spectrum of £ Ursoe Majoris. 



Art. YIIL — On the Spectrum of £ Ursce Majoris ;* by 

 Edward C. Pickering. 



In the Third Annual Report of the Henry Draper Me- 

 morial, attention is called to the fact that the K line in the 

 spectrum of f Ursse Majoris occasionally appears double. 

 The spectrum of this star has been photographed at the 

 Harvard College Observatory on seventy nights and a careful 

 study of the results has been made by Miss A. C. Maury, a 

 niece of Dr. Draper. The K line is clearly seen to be double 

 in the photographs taken on March 29, 1887, on May 17, 18S9 

 and on August 27 and 28, 1889. On many other dates the 

 line appeared hazy, as if the components were slightly sepa- 

 rated, while at other times the line appears to be well denned 

 and single. An examination of all the plates leads to the 

 belief that the line is double at intervals of 52 days, beginning 

 March 27, 1887, and that for several days before and after 

 these dates it presents a hazy appearance. The doubling of 

 the line was predicted for October 18, 1889, but only partialty 

 verified. The line appeared hazy or slightly widened on 

 several j)lates but was not certainly doubled. The star was 

 however low and only three prisms could be used, while the 

 usual number was four. The predicted times at which the 

 line should be again double are on December 9, 1889 and on 

 January 30, 1890. The hydrogen lines of £ Ursse Majoris are 

 so broad that it is difficult to decide whether they are also 

 separated into two or not. They appear, however, to be 

 broader when the K line is double than when it is single. 

 The other lines in the spectrum are much fainter, and although 

 well shown when the K line is clearly defined, are seen with 

 difficulty when it is hazy. Several of them are certainly 

 double when the K line is double. Measures of these plates 

 gave a mean separation of 0*246 million ths of a millimeter for 

 a line whose wave-length is 448*1, when the separation of the 

 K line, whose wave-length is 393*7, was 0*199. The only 

 satisfactory explanation of this phenomenon as yet proposed 

 is that the brighter component of this star is itself a double 

 star having components nearly equal in brightness and too 

 close to have been separated as yet visually. Also that the 

 time of revolution of the system is 104 days. When one com- 

 ponent is approaching the earth all the lines in its spectrum 

 will be moved toward the blue end, while all the lines in the 

 spectrum of the other component will be moved by an equal 

 amount in the opposite direction if their masses are equal. 

 Each line will thus be separated into two, When, the motion 



* Read at the Philadelphia meeting of the Nat. Acad, of Sciences, Nov. 13 r 

 1889. 



