Interstellar absorption in the galactic plane

Abstract

UDC 524.5 We consider the distribution of interstellar absorption in the galactic plane using the classical Cepheids and main sequence stars of spectral classes B0-B3. In the method developed we use pairs of stars with the same absolute stellar magnitude, but with maximal difference of observed colors (B-V), The observed picture corresponds to the large-scale distribution of interstellar absorption in the local interstellar medium. 1. Introduction. The study of the interstellar medium as a function of galactic longitude and distance from the Sun is of considerable scientific interest. It is carried out using various methods {n a wide spectral range of wavelengths from X-rays to radio waves. The widely used method of color excess, based on studies of the dependence of color excess on direction and distance, requires high-precision photometric measurements, and in the majority of cases does not give the desired result, due to the wide dispersion of these quantities, while the averaged quantities smooth out the observed picture [1]. Because of this it ought to be reasonable to use other methods of processing the existing observational data. In the present article we develop and apply a new method [2] in order to determine the dependence of interstellar absorption on galactic longitude and distance from the Sun. We use observational data taken from the classical Cepheids [3] and stars of the spectral classes B0-B3 of the main sequence (luminosity class V) [4]. The essence of the method is the following: from a large number of stars for which the absolute ste!lar magnitudes are practically the same we choose pairs of stars with maximal difference of observed color indices (B-V). It is natural to assume that this difference is caused by a difference in the mass of absorbing matter in the respective directions and distances. Then in a given interval of galactic longitude or distance we determine the percent of stars that have maximum observed color index among all the stars constituting the pairs.