Abstract
Spectrophotometric investigations of reddened B stars have determined the law of variation of the interstellar absorption with wave length, except for an additive constant. The uncertainty as to the order of magnitude of any possible non-selective absorption appears in the ratio of absorption to reddening, a quantity of great practical importance. It is shown that the ratio of the intensities, at two wave lengths, of the total light from stars of a given type depends on the intrinsic color of the stars and on the ratio of the interstellar absorption coefficients at those two wave lengths. The ratio of the interstellar absorption coefficients at the two effective wave lengths of the photoelectric color indices determined by Stebbins, Huffer, and Whitford is evaluated in Table i. The non-selective absorption is found to be small or zero. The ratio of photographic absorption to photoelectric color excess is found to be 8.i ± 0.4. I In recent years several observational investigations have been carried out with the purpose of determining the law of selective absorption by interstellar matter. In these investigations spectrophotometric methods have been used to compare, at various wave lengths, the light of reddened B stars with that of normal stars. Such comparisons are capable of determining total absorption to within an additive constant; that is, they de- termine a function, f(X), such that the absorption, A (X), is given by an expression of the form A(X) = f(X) + A0, (I
Published Version
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