ox THE PERIOD OF THE VARIABLE STAR 

 S ARA£. 



By Alexander William Roberts, D.Sc, F.R.A.S., F.R.S.E. 



R.A. i7h. 51m. 27.3s. (1900). 

 Dec. 49° 25-3 



This remarkable variable star was discovered by Innes at the- 

 Cape in 1898. He also determined its period and light curve. 

 Observations were begun on the star at Lovedale in 1899, and 

 have been carried on until the present day. 



The period submitted by Innes in the " Revision of the Cape 

 Photographic Durchmusterony," page 128. B is : — 

 loh. 50m. 43.5secs. 



A discussion of the observations made at Lovedale from 

 1899 to 1909 yielded a period of : — - 



loh. 50m. 43.45s.ecs. 



Now the purpose of the present paper is to discover if this- 

 period is constant or variable, and if so to what nature and ex- 

 tent. 



This inquiry is important as it bears directly upon the genesis- 

 and evolution or devolution of the system S Arce. 



If the period of any binary system be constantly increasing 

 then the correspondent members of the system are slowly drifting 

 apart, a result due either to tidal action or to the loss of material' 

 from one or both components. 



If the period of any binary system is uniformly decreasing, 

 then the twQ components are slowly approaching one another, and" 

 will at some remote date coalesce. This approach may be due to- 

 a resisting medium retarding the movement of either one or botlv 

 components. 



Instead of taking maxima dates as a basis of our investiga- 

 tions, we take eight mean dates when the star passed througlii 

 10. o magnitude on its upward trend. 



These dates are in Julian days : — • 



