A New Look at the Dust Toward Omicron Persei and Sigma Scorpii With the International Ultraviolet Explorer

Abstract

The first IUE low dispersion spectra for Omicron Persei and Sigma Scorpii have been obtained and extinction curves from 1150 to 3250 A are presented. It is of interest to consider Omicron Persei and Sigma Scorpii dust in the context of the average extinction law of Cardelli et al (1989), here referred to as 'CCM', which depends on the R(v) parameter; this is defined as the ratio of total to selective extinction. Omicron Persei lies behind the edge of a dark cloud, and its dust shows a broad bump shifted to shorter wavelengths, similar to other dark cloud lines of sight, but shows no deviation from the CCM average curve in the far UV. Sigma Scorpii lies within the H II region near a dark cloud, and its dust shows a marked deviation from the CCM law in the far UV. These deviations are more typical of dark clouds or diffuse lines of sight, rather than of bright nebula lines of sight. The Omicron Persei and Sigma Scorpii dust characteristics exemplify a continuum of characteristics observed along various lines of sight, depending on the local dust environemnts.