Transactions of The Royal Society of Canada 



SECTION III 

 Series III . MARCH 1915 Vol. VIII 



The Spectroscopic Binary 2 Tauri. 

 By Dr. J. S. Plaskett, F.R.S.C. 



The Star # 2 Tauri a, 4h 22m -9, 5, + 15° 39', magnitude 3-6, 

 spectral type A5, was announced as a spectroscopic binary by Moore 

 in the Lick Observatory Bulletin No. 62 and by Frost in the Astrophy- 

 sical Journal XXIX p.' 238. 



The published velocities from these observatories with the date, 

 Julian day, phase, and residual, the two latter being obtained from the 

 elements finally accepted, are given at the beginning of the table of 

 measures below. 



The star was placed under observation here on Dec. 11, 1909 

 and 66 plates were obtained between that date and March 1912 of which 

 52 were selected for measurement. From these measures preliminary 

 elements were obtained and presented to the Society under the above 

 title at the May meeting 1912. This was not published in the Trans- 

 actions owing to its preliminary character, although a. short account 

 of the work to date was given in the Journal R.A.S.C., VI, p. 231, July- 

 August 1912. A summary of this is given below but, owing to un- 

 certainty in some of the results obtained, further observations were 

 considered desirable. Hence 16 more plates were obtained making 

 a total of 68 plates on which the present determination is based. 



The spectrum is of type A5 containing numerous metallic lines, 

 but unfortunately all these lines are wide and diffuse, making the 

 measurements more or less uncertain. This is shown by the poor 

 agreement often present between different lines on the same plate 

 and by the comparatively high probable error ±3-6 km. per second 

 of a single plate derived from the plate residuals from the final orbit. 

 Four different dispersions were tried in the hope of getting more 

 satisfactory measures with this type of spectrum , but no one showed 

 very marked advantages over the others. This will be discussed more 

 fully later. 



The principal lines measured — all those used in the measures — 

 with their chosen wave lengths and source are given in the accom- 



Sec. Ill, 1914—12 



