﻿14. THE ANNUAL PARALLAX OF EIGHT STARS. 



By William E. Howard. 



Introduction. This work was begun in September, 1906, and 

 the last observations were made in August, 1907. The instrument 

 used was the 12-inch equatorial in the Kirkwood Observatory at 

 Indiana L^niversity.- 



The work as a whole was divided into three distinct divisions: 



(1) The history of parallax work from the earhest efforts to 1909; 



(2) The theory of the reductions in detail, arranged in a compact 

 and convenient form, together with a number of computed tables; 



(3) A catalogue of all the work in parallax, containing the name 

 of each star, the comparison stars, the results, the observer, the 

 instrument used, and a reference. This paper presents in condensed 

 form the author's own work, the second division above, without the 

 theory, or the tables. 



In selecting the observing list the magnitude or the proper 

 motion was not considered. The purpose in view w^as to select 

 spectrosopic binaries, but since it was not always possible to find 

 a binary coming just at the right time to distribute the observa- 

 tions properly, it became necessary in a few instances to select other 

 stars. The choice was limited to solar stars, because a solar star 

 is likely to be nearer than an Orion star. The selection was further 

 limited to stars that pass high above the horizon, in latitude of the 

 Kirkwood Observatory, so that refraction would affect the results 

 as little as possible. Spectroscopic binaries were selected, because 

 knowing the parallax of a spectroscopic binary, it is possible to 

 determine the relative mass of the bodies and thus to know con- 

 siderable about the system. In order to check the results 61 Cygni 

 was placed on the list; but unfortunately cloudy weather prevented 

 a good series of observations on it and thus it served as a poor check. 



The time of year at which to observe the maximum parallax 

 displacements was next determined. This is simply a matter, first, 

 of computing the longitude of the sun when it is 90 degrees from 

 the star, for the maximum displacement occurs at that time; then of 

 noting from the Nautical Almanac the time when the sun has the 

 computed longitude. The time of second maximum will be six 

 months later when the sun has moved 180 degrees. 



^ Accepted by the Graduate Council of Indiana University as a dissertation under the require- 

 ments for the degree of Doctor of Philosophy (June, 1909). 



- Acknowledgment should be made of the author's indebtedness to the skill of his wife, who 

 materially aided him in every computation, and without whose patience and encouragement he would 

 have failed in his task. 



(18c) 



