Interstellar Highly Ionized Species toward Cygnus: A Closer Look

Abstract

Abstract We examine Hubble Space Telescope (HST)/STIS data, complemented with International Ultraviolet Explorer (IUE) data, to delineate interstellar absorption of highly ionized species, C iv, Si iv, and N v, and low ionization species toward four stars in Cygnus. Previous IUE studies indicate two major velocity complexes for C iv and Si iv extending across Cygnus. We see interstellar N v in HST/STIS data for HD 190918 and Cyg X-1. In both stars, the N v is at the velocities of interstellar C iv and Si iv. In HD 190918, the N v is weak, possibly due to enhanced X-ray ionization produced by this binary system. The Cyg X-1 data are of low signal-to-noise, but N v is quite strong with a small b-value, indicating N v arises in a cooler H ii region resulting from X-ray Auger ionization by Cyg X-1.