Abstract
DEDUCTION OF STAR-DISTANCES FROM PROPER MOTIONS.—The proper motions are almost our sole guides in estimating the distances of the more remote stars. Hence any method that affords a check on the results is of value. Prof. H. N. Russell points out in the Astrophysical Journal for September last that we can estimate the distance either (I) by correlating the motion away from the solar apex with the sun's velocity, or (2) by correlating the cross-motion with the line-of-sight velocity. As a test he has divided the 180 stars of type B, to B5, the radial velocities of which were found by Campbell, into eighteen groups, the mean position of each group being nearly the same. He finds for the general mean parallax 0.0083“from (i) and 0.0058“from (2). One reason given for the smaller value from method (2) is that some of the stars may be undetected spectroscopic binaries, in which case the adopted line-of-sight velocity is presumably too great. The probable error of result (I) is o.ooio“, of (2) 0.0014“. In general, method (I) gives the best results for objects of small average velocity like the B stars, while (2) is better for quick movers like the planetary nebulae. The apparent close connection between period and absolute magnitude in the Cepheid variables was originally deduced from results obtained by method (I), and later obtained considerable confirmation from a study of the variables in the globular clusters, which appear to be mainly Cepheids.
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Our Astronomical Column. Nature 109, 121 (1922). https://doi.org/10.1038/109121a0
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DOI: https://doi.org/10.1038/109121a0