The Interstellar Medium toward Cyg X-1
Frederick Bruhweiler
Physicist-in-Residence
Integrated Space Science & Technology Institute
Department of Physics
American University (AU)
Wed, November 20, 2024 ~ 4:00 PM
Multi-wavelength observations have been key to providing a more complete picture of the interstellar medium of our Galaxy. These have been highly complementary to interpreting UV spectra obtained by HST and IUE. Coadded HST/E140M ultraviolet spectra(1200-1700 Angstroms) of the O-star/blackhole binary and x-ray source, HD 226868=Cyg X-1, is one example. More abundant neutral and low-ionization species require 4-6 velocity components to reproduce observed IS features. Spectral profile fitting reveals at least eight distinct interstellar velocity components toward Cyg X-1. Three velocity components clearly arise in H II regions. The presence of sharp, discrete N V λλ1238, 1242 IS-features at -8 km/s cannot be explained by either by a hot 106 oK substrate, or by normal O-star ionization, and requires x-ray ionization from Cyg X-1. Observed excited states in CO, C, O and Si II provide constraints on physical conditions in IS clouds.
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