[plaskett] THE SPECTROSCOPIC BINARY THETA 2 TAURI 



163 



There is very little difference in the accuracy of measurement 

 with the different dispersions the advantage seeming to lie with the 

 three-prism dispersion and short cameras. The advantage of increased 

 linear scale is offset evidently by increased diffuseness of the lines. 

 Considering the character of the spectrum and the presence of 

 some abnormal effect, the accuracy may be considered satisfactory. 



In the velocity curve drawn from these elements the normal 

 places are represented by circles. It will be seen that, considering the 

 diffuse character of the spectrum lines, the agreement is quite satis- 

 factory, excepting between phases 70 and 134, where there is a marked 

 double hump. As the five normal places in this region have on the 

 average four plates each, it is evident that this deviation must be 

 considered to have a probable objective existence. 



It is impossible to give a definite cause for this abnormal effect. 

 As its period is approximately half the main period and as there seems 

 to be a continuance of this effect farther along the velocity curve, one 

 apparent explanation would be a secondary disturbance of half the 

 period of the binary. Although such an effect does not admit of any 

 probable physical explanation, it was thought worth while to determine 

 the elements of the orbit on this supposition. 



Assuming suitable preliminary elements and carrying through a 

 least squares solution, adding terms for the amplitude and phase of a 

 simple sine curve superposed on the velocity curve, the following 

 elements were obtained. 



Periods 140-70 days and 70 • 35 days. 



Eccentricity e =0-711 



Long, of apse a) = 50° • 80 



Semi-ampl. primary K = 29 • 03 km 



Periastron passage T = J.D. 2,418, 054-641. 



Veolcity of system y = +42 • 63 km 



Semi-ampl. sec K = 3 • 57 km. 



Phase ascending node sec J.D. 2,418,067-42. 



Max. vel. primary 84-71 combined 81 • 1 



Min. " " 26-65 " 27-0 



