204 



KNOWLEDGE 



[September 1, 1890. 



connection. Possibly the fainter companion may be much 

 fartlier fi'om us than tlie brighter star. The colours are 

 orange, and emerald or bluish gi'een, and the spectrum is 

 a splendid specimen of the 3rd tj^pe. There seems to be 

 some little doubt as to which of the components fluctuates 

 in light : Sir W. Hersehel and Argelander considered the 

 brighter star to be the variable one, whereas Struve thought 

 the variation was due to the fluctuations of the fainter 

 component from the 5th to the 7th magnitude. It is not so 

 easy to decide a question of this kind as might at first be 

 supposed. Viewing a pair like this with a magnifving 

 power sufficiently high to satisfactorily separate the com- 

 ponents, they are seen in a small telescopic field of \ievr 

 completely isolated fi-om other neigbouring stars of nearly 

 equal lustre with which they might be compared. 

 Observations with a wedge photometer might perhaps 

 settle the question. .Judging from the colours and 

 spectrum, my own opinion is that the brighter star is the 

 variable, and that possibly the fainter star may have 

 merely an optical, and not a physical, connection with 

 its brighter companion. 



Another close double star which is almost certainly 

 variable is Y Virginis (near 68 (i) Virginis). It seems 

 to have no regular period, but, though usually of about the 

 6th magnitude, it was observed by Schmidt as bright as 

 4| magnitude on .Tune 6, 1866. The Cordoba observations 

 in subsequent years seem to confirm the variability, but 

 possibly the star may remain constant in its light for 

 lengthened periods. In 1879 Burnham found it to be a 

 very close double star, the components being nearly of 

 equal brightness and separated by only half a second of 

 arc. Observations in recent years do not give much 

 evidence in favour of orbital motion. The colour of the 

 star is yellowish white, and the spectrum of the Sirian type. 



Among variables with distant companions may be men- 

 tioned T Cygni, to which Burnham found a 12th magnitude 

 companion at 10 seconds ; the Algol variable u Ophiuchi, 

 which has a very faint companion at a distance of about 

 20| seconds ; r (" Nova ") Orionis, which has a 10| magni- 

 tude attendant at 30 seconds ; 8 Orionis, a 2nd magnitude 

 star with a very faint companion at about 34 seconds, 

 and a 7th magnitude at 53 seconds ; and the short period 

 variable 8 Cephii with a 7th magnitude companion at 48 

 seconds. " 



Among stars certainly binary there is one, 36 Andro- 

 medse (Struve 73), which is, according to Schmidt, 

 variable to a small extent in periods varying fi'om 40 to 125 

 days, but I am not aware that this variability has been 

 confirmed by other observers. The components are of 

 about the 6th and 7th magnitude, and the present distance 

 between them a little over one second of arc. Dr. Doberck 

 has computed an orbit for this pair, and finds a period of 

 about 349 years. 



Among the numerous stars which have been suspected of 

 variable light, but which have not yet been admitted into 

 the ranks of the regular variables, there are some interesting 

 cases. The components of the well-known binary star 

 y Virginis have been suspected of alternate variation in 

 brightness. In the years 1851 and 1852 Struve foimd the 

 components sometimes exactly equal and sometimes 

 differing by nearly three-fourths of a magnitude in favour 

 of the southern star. In the years 1825 to 1832 he found 

 the other component certainly the brighter. Franks 

 foimd the southern star half a magnitude the brighter on 

 March 28, 1885. Struve's susjiicion seems to be con- 

 firmed by the observations of Fletcher, and the point 

 seems deserving of more attention than it has hitherto 

 received. An estimate of relative brightness might easily 

 be made by those observers who measure at intervals the 



position of the components, and in this way interesting 



results might be obtained. 



The companion of the double star Struve 547 has been 

 suspected of variable hght. It was estimated as 11^ 

 magnitude by Struve in the years 1829 and 1832 ; but 

 Denibowski could not see it in 1865. Burnham, although 

 gifted with keen eye-sight, failed to find it in 1873 and 

 1876. Gledhill was equally unsuccessful in 1879. The 

 companion was, however, seen and measured by Miidler 

 in 1845, by Burnham in 1877, 1879, 1880, and 1881, and 

 by Gledhill in 1880. The latter observer foimd the dis- 

 tance between the components about 21 seconds, and his 

 measure of angle (15-8°) seems to show some angular 

 motion since its discovery by Struve in 1831. 



A similar case is found in Struve 1058, in which the lltli 

 magnitude companion to an 8i magnitude star was 

 measured by Burnham in 1879 and 1881, but could not be 

 foimd by Denibowski in 1865, nor by Burnham in 1874, 

 1875, and 1878. 



In the double star Struve 1517 the observations of 

 Struve, 0. Struve, and Secclii seem to point to some varia- 

 tion in the relative brightness of the components. The 

 measures of position since 1832 indicate a slow angular 

 motion in the pair, which have also a common proper 

 motion through space. 



Struve 1932 is a double star in Corona Borealis, of which 

 the components were estimated 5'6 and 6-1 magnitudes 

 by Struve, 6 and 6-5 by Secchi, and 6-9 and 7-2 by 

 Dembowski. Struve suspected variability, and my own 

 observations with a binocular in the years 1885-1887 

 apparently show a small variation of light. The measm-es 

 indicate a marked angular motion since its discovery in 

 1830, so that the pair is probably a binary. 



The components of 36 Ophiuchi were rated 4i and 6^ 

 magnitude by Smyth in 1831. Sir -J. Herschel estimated 

 them both as 6th magnitude in 1834 and 1837. Dawes 

 rated them both 5th magnitude in 1841, and so they were 

 seen by .Jacob in 1846. In 1854 Webb foimd them " nearly 

 equal, about 65, Smyth's smaller perhaps rather the 

 larger." In 1875 in India I noted them as " Both yellow, 

 and almost exactly equal. The following star (Smyth's 

 brighter component) if anything rather the brighter of the 

 two." The measures show a well-marked angular motion 

 of the pair, which is probably a bmary as the components 

 have a considerable common proper motion of about 1^ 

 seconds per annum. Curious to say, they are accompanied 

 in their flight through space by the star 30 Scorpii which 

 is distant no less than 13 minutes of arc from the binary 

 pan-. 



One of the components of the double star O. Struve 256 

 has been suspected of variable light. They were rated 7-2 

 and 7'6 in 1848 by 0. Struve, who made the jirireiliiii/ star 

 in the field his primary. In 1867 Dembowski seems to 

 have seen the folhiuiwi component the brighter, as his 

 measures of position angle show. Perrotin in 1885 

 agi-ees with O. Struve and measured the position angle 

 from the jiircediiiri star. On August 22, 1887 an occidta- 

 tion of the star was observed by Mr. J. Tebbutt at M'indsor 

 New South Wales. He had not at the time identified 

 the star and was not aware that it was double. About 

 thi-ee-fourths of the star's light at first suddenly disappeared, 

 and about two seconds later " the rest of its light, which 

 resembled a blun-ed star of the 9th magnitude, vanished 

 quite as suddenly." This observation seems to show that 

 on the date of Tebbutt's observation, the pivcfilimi star 

 was tonsidenihhj the brighter of the two components, and 

 compared with Dembowsld's measures, appears clearly to 

 indicate variable Ught in one or other of the component 

 stars. The pair is probably a binary. 



