2002A&A...392..295Z

The interstellar reddening law is investigated along the Galactic equator near the Cam, Per and Cas border. We used seven-color photometry of O-B5 stars in the Vilnius photometric system in the optical range, photometry of the ANS orbiting observatory in the ultraviolet range and broad-band color indices V-K in the infrared. In the optical range (345-660nm) the interstellar reddening law is found to be nearly normal. In the ultraviolet wavelengths shorter than the 330nm ANS passband, the extinction is found to be slightly larger than the average. Some stars, for example HD 24432, exhibit much stronger ultraviolet extinction which is well seen already in the 345nm passband of the Vilnius system. However, such stars are rare. The ratio R=A_V/E_B–V is found to be 2.9, i.e., it is slightly smaller than the normal. This is confirmed by the study of the wavelength of maximum polarization of reddened stars in the area. Both the ultraviolet anomaly and the smaller R value are in good agreement with the Cardelli et al. (1988ApJ...329L..33C) prediction. We conclude that in the investigated area it is safe to use normal ratios of color excesses to calculate reddening-free Q-parameters for the classification of stars from photometric data in the optical spectral range.