DEPARTMENT OF MERIDIAN ASTROMETRY.^ 



Benjamin Boss, Director. 



The efforts of the Department during the past year have been mainly 

 employed in completing the work on the San Luis observations and in 

 preparing them for catalogue form, though considerable work has been 

 devoted to the reduction of the Albany observations. Progress has 

 also been registered in the determination of the systematic corrections 

 to star catalogues in preparation for the general catalogue. In addi- 

 tion, a number of special researches have been carried on. Preparation 

 for the future work of the Department has also called for a careful 

 study of the problems involved. 



A brief summary of the most salient landmarks in our progress 

 follows. 



ABSOLUTE MAGNITUDE. 



A study of absolute stellar magnitudes is in progress. While defini- 

 tive results have not been attained, some conclusions seem to be fairly 

 well marked. When the frequency curves are drawm, the maximum 

 for the giant stars is placed at M = +0.75, the bulk of giant stars 

 lying between absolute magnitudes —1.5 to +3.0. But the elements 

 of distance play an important role in determining the frequency 

 curve, for with increase in the distance of the star it is evident that, 

 in the main, only the brighter stars have been observed. If the absolute 

 magnitudes of the giant stars are arranged in groups according to 

 increasing distance, it becomes evident that in order to obtain an 

 absolute magnitude of +2.0 for a star whose parallax is 0^006, the 

 apparent magnitude would have to be 8.1. As the parallaxes of but 

 few stars of this magnitude have been obtained, and those mostly 

 for dwarf stars, it would seem more probable that the mean absolute 

 magnitude for a giant star is in the vicinity of +1.2, instead of +0.75 

 as given by the frequency curve. A peculiarity in the distribution of 

 the observed giant stars among the types is the striking lack of such 

 stars in the A and F classes. The frequency curves of the dwarf stars 

 show well-defined maxima, increasingly positive, with progression in 

 type from the B to the M class, following the results previously ob- 

 tained by other investigators. It is interesting to note, however, 

 that the dwarf phenomenon is distinctly apparent among the A-type 

 stars. 



DIURNAL TERM IN CLOCK-RATE. 



In the preliminary reductions of the primary clock stars for clock 

 corrections and rate, preparatory to deducing the final places of the 

 primary clock stars, Mr. Varnum spared no efforts to insure the funda- 

 mental nature of the reductions. Where possible, the observations 

 have been combined to eliminate the known systematic errors. For 



^Address: Dudley Observatory, Albany, N. Y. 



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