Abstract
DETERMINATION OF STAR CoLouRs.An expeditious photographic method of investigating the colour-indices of stars has been tested by Mr. F. H. Seares at Mt. Wilson (Proc. Nat. Acad. Sci., vol. iii., p. 29). The method consists of making a series of exposures with graduated exposure-times, first through a yellow filter and then without filter. In this way the ratio of exposure.times necessary to give images of the same size in yellow and blue light is determined. The colour-indices are then derived by reference to a curve showing similar ratios for standard polar stars, the colours of which have already been ascertained by a comparison of their photographic and visual magnitudes. In general, the method of exposure-ratios gives excellent results, showing no systematic errors of any importance which depend upon stellar magnitude. The probable error of a colour-index derived from a single exposure-ratio is 0.07 magnitude. The method would appear to be of special value on account of its independence of stellar magnitude, and because it gives a direct measure of the colour. The results obviously include that part of the colour which is a function of the star's intrinsic luminosity, and also such colour effect as may be due to the scattering of light in space. An interesting outcome of the new observations is the oonfirmation of the previously reported conclusion that there are no faint white stars in the vicinity of the pole, though this is apparently not true of all parts of the sky.
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Our Astronomical Column . Nature 99, 16 (1917). https://doi.org/10.1038/099016a0
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DOI: https://doi.org/10.1038/099016a0