A Determination of Selective Absorption Based on the Spectrophotometry of Reddened B Stars
Abstract
An observational program has been carried out for the determination of the gradients of reddened B stars relative to normal B stars. Short-dispersion spectra, taken in series, were standardized on the tube photometer. The spectra were analyzed in the Moll self-recording microphotometer. The magnitude differences between reddened and nor- mal stars along the spectrum were used to determine the gradients and the change of gradient with wave length. The stars observed were taken from the Stebbins and Huffer catalogue of photo- electric color indices, which permits a discussion of the relation between the color in- dices, the present system of gradients, and the Greenwich system. The relative gradients were found to be substantially linear over a wide range of wave length. The photoelec- tric color index is found to be a representative measure of the reddening of the B stars. The curvature of the gradients is such that the selective absorption in interstellar space must vary nearly as i/X. Measures of the total photographic absorption in front of the reddened stars were obtained from star counts, and an independent estimate was made of the ratio of the color excess to the photographic absorption. The variation of selective absorption with wave length is again found to be nearly as i/X. The total photographic absorption is between four and six times the color excess on the International Scale. An interpretation on the basis of my theoretical discussion of the selective absorp- tion confirms the hypothesis there advanced, that the interstellar absorption is caused by small dust particles, with a frequency distribution close to that of hyperbolic meteors
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1938
- DOI:
- 10.1086/143914
- Bibcode:
- 1938ApJ....87..151G