The interstellar reddening law in the ultraviolet deduced from filter photometry obtained by the OAO-2 satellite

Filter photometry has been obtained of 16 BO stars at 10 effective wavelengths in the range AA42501430 A. The wavelength dependence of the interstellar reddening law, deduced from a least-squares fit of the observed values to the reddening line at each band, is found in satisfactory agreement with that derived by Bless and Savage. Toward the shorter wavelengths the increase of the computed probable error of the slope of the mean reddening line suggests that large fluctuations in the law may occur from star to star. Similar computations, separating main-sequence stars and supergiants, indicate that the large fluctuations of the law appear to be well related to the luminosity of the stars; the supergiants show systematically less extinction, this deficiency becoming large toward the far-ultraviolet. The small number in the sample, however, does not allow a general conclusion to be drawn. At 1550 A supergiants are found to be 0.9 mag fainter and giants about 0.3 mag fainter than main-sequence stars relative to their V-magnitude. Subject headings: early-type stars - interstellar reddening - spectrophotometry