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A. M. Juett (MIT and University of Virginia), N. S. Schulz, D. Chakrabarty (MIT)
We have used photoelectric absorption features in the Chandra/HETGS spectra of bright X-ray binaries to study the detailed spectroscopic structure of oxygen, iron, and neon absorption in the interstellar medium (ISM). This represents the highest-resolution X-ray spectral study of interstellar absorption ever performed, revealing previously undetected features and demonstrating the inadequacy of existing models for grating data. We find that the ISM absorption edges are well described by the neutral, atomic cross-section calculations and laboratory measurements, although requiring small (<50 mÅ) shifts to the wavelength scales. The high-resolution spectra allow us to make an independent determination of the relative abundances of the elements. These measurements are compared to optical and ultraviolet determinations of the ISM gas-phase and solar abundances. The K-shell edges of oxygen and neon also include absorption lines from singly and doubly ionized forms. From the relationship between the equivalent widths of the ionized lines and the column density of the neutral edges, we are able to measure the large-scale ionization fractions of oxygen and neon in the ISM. We also searched for spectral features attributable to molecular forms of oxygen and iron. These features would provide a direct measurement of the elemental abundances of the molecular phase of the ISM, including dust. This work is part of a program to produce a reliable high-resolution spectral model for interstellar absorption.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.