42 Transactions of the South African Philosophical Society. 



VAEIATION OF LACAILLE 5861 

 By Alex. W. Koberts. 



This star, the position of which is — 



B.A. 14 h. 8 m. 10-2 s. (1875) 

 Bee. — 57° 16' 12" 



is a variable of an extremely rare type. Only one other star of the 

 same nature of variations is known, namely, U Pegasi (Chandler 

 8598). 



The peculiarity about these two stars is that their decreasing 

 period is slightly shorter than the increasing period ; with all other 

 variable stars the rise to maximum brightness is much more rapid 

 than their fall to minimum. Both stars also vary in a remarkably 

 short time, the period of L 5861, being 7 h. 16 m., and of U Pegasi 

 5h. 22m. 



This is the shortest period known, and accordingly extreme rapid 

 variation might be claimed as a second characteristic of this type. 

 This may, however, be an accident, as the variation of some other 

 short period variables falls not very far short of this, notably the 

 southern variable, S. Antlice, period 7 h. 56 m. 



The slow rise to maximum is however so definite and unmis- 

 takeable a characteristic, that it must be taken as the main point of 

 difference between these two stars and all the other short period 

 variables, some 45 in number. 



U Pegasi was discovered by Chandler, of Harvard, towards the 

 close of last year ; L 5861 was discovered at Lovedale in April of 

 this year. Since then it has been regularly observed, the number 

 of observations made being considerably over 500. 



The range of variation is very slight, only 0-4 magnitudes — 

 an amount that to an untrained eye would be almost imper- 

 ceptible. 



As already said, the star goes through all its variations in seven 

 hours and a quarter, passing in this time from its maximum bright- 

 ness down to its minimum, and up again to its maximum. There is 

 no halt at any stage, variation is constantly going on. 



One naturally wonders as to the cause of such perplexing light 



