PARALLAXES OF FIFTY-SEVEN STARS. 1 



By Mildred Booth and Frank Schlesinger. 



The determination of these parallaxes was carried out through the cooperation of several 

 institutions. The photographic plates were secured with the Thaw photographic refractor of 

 the Allegheny Observatory. They were measured and reduced at Yale Observatory under a 

 grant from the National Research Council (Division of Physical Sciences) to the committee on 

 stellar parallaxes of the American Astronomical Society. The measuring machine is one that 

 was purchased several years ago with a grant from the Draper fund of the National Academy 

 of Sciences. The authors desire to record their acknowledgments to all these agencies, espe- 

 cially to the National Research Council, without whose aid a long interval would have elapsed 

 before these results could have been made available. 



The measuring machine is an excellent one of the long screw type, made by William Gaertner 

 & Co. from specifications supplied by one of us. It was intended (and has been extensively 

 used) to measure 7 by 8 inch plates, somewhat smaller than the 8 by 10 inch parallax plates. 

 A modification in the plate-holding device sufficed to permit the measurement of the larger 

 plates. 



The measurements and computations were carried out by Miss Booth. The methods 

 employed are described in detail in the Publications of the Allegheny Observatory, volume 3, 

 pages 1 and following. Whenever possible four comparison stars were employed, otherwise 

 three. The average number for the present series is 3.8. The average number of plates for 

 each region is 15. 



A great many of the stars on the present list are double ; for this reason or for some other, 

 almost every object is one of more than average difficulty, the stars having in fact been selected 

 on that account from a long list awaiting attention at Allegheny. In view of these circum- 

 stances the average probable error for a parallax, ".0084, is very satisfactory. 



To preserve the continuity with the parallaxes previously determined from Allegheny 

 plates, the numbers 470 to 526 have been assigned to the present list. 



A summary of the results appears on page 6. The magnitudes and spectra are taken 

 from the Draper Catalogue. For the faint stars in the latter part of the list these were kindly 

 communicated by Prof. Bailey in advance of publication. The parallaxes in next to the last 

 column are relative. To get the absolute values, we should add ".003. This quantity was 

 determined with a probable error of about one-tenth of its value from a discussion of the proper 

 motions of several thousand comparison stars. 



The table following the summary gives information regarding the comparison stars. The 

 coordinates give the position of each one referred to the parallax star in its field as origin. 

 Positive coordinates correspond to large right ascensions and large north polar distances, 

 respectively. In the fourth, seventh, tenth, and thirteenth columns are the dependences used 

 in the solutions. In the last column appears a constant applied to the solution to obviate the 

 use of large numbers. In next to the last column is the mean photographic magnitude of the 

 three or four comparison stars in each field. This was determined from the photographic 

 magnitude of the parallax star, allowance being made for the opening of the sector used to 

 reduce the magnitude of the parallax star to apparent equality with the mean of the comparison 

 stars. 



Yale University Observatory, 



November, 1921. 



1 Read at the November, 1921, meeting of the National Academy. 



