Condensed Matter Astrophysics A Prescription for Determining the Species-Specific Composition and Quantity of Interstellar Dust using X-rays
Bruce D. Ravel, Julia C. Lee, Jingen Xiang, Jeffrey Kortright, Kathryn Flanagan
We present a new technique for determining the quantity and composition of dust in astrophysical environments using < 6 keV X-rays. We argue that high resolution X-ray spectra as enabled by the Chandra and XMM-Newton gratings should be considered a powerful and viable new resource for delving into a relatively unexplored regime for directly determining dust properties: composition, quantity, and distribution. We present initial cross-section measurements of astrophysically likely iron-based dust candidates taken at the Lawrence Berkeley National Laboratory Advanced Light Source synchrotron beamline, as an illustrative tool for the formulation of our technique for determining the quantify and composition of interstellar dust with X-rays. (Cross sections for the materials presented here will be made available for astrophysical modelling in the near future.) Focused at the 700 eV Fe LIII and LII photoelectric edges. we discuss a technique for modeling dust properties in the soft X-rays using L-edge data, to complement K-edge X-ray absorption fine structure analysis techniques discussed in Lee & Ravel (2005). The paper is intended to be a techniques paper of interest and usefulness to both condensed matter experimentalists and astrophysicists. For the experimentalists, we offer a new prescription for normalizing relatively low S/N L-edge cross section measurements. For astrophysics interests, we discuss the use of X-ray absorption spectra for determining dust composition in cold and ionized astrophysical environments, and a new method for determining species-specific gas and dust ratios. Possible astrophysical applications of interest, including relevance to Sagittarius A* are offered.