Interstellar extinction law near the Galactic equator along the Camelopardalis, Perseus and Cassiopeia border

¹ Institute of Theoretical Physics and Astronomy, Goštauto 12, Vilnius 2600, Lithuania e-mail: justas@itpa.lt; straizys@itpa.lt
² Vatican Observatory Research Group, Steward Observatory, Tucson, Arizona 85721, USA e-mail: corbally@as.arizona.edu

Corresponding author: V. Straižys, straizys@itpa.lt

Received: 23 May 2002
Accepted: 19 June 2002

Abstract

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 in the infrared. In the optical range (345–660 nm) the interstellar reddening law is found to be nearly normal. In the ultraviolet wavelengths shorter than the 330 nm 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 345 nm passband of the Vilnius system. However, such stars are rare. The ratio 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. ([CITE]) 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.