Oxygen and iron in interstellar dust as seen by XMM-Newton and Chandra
Ioanna Psaradaki
University of Michigan
Understanding the chemistry of the interstellar medium (ISM) is fundamental for the comprehension of the Galaxy evolution. Some of the refractory interstellar elements, such as Si, Mg, O and Fe, are known to be locked up into dust grains. Iron is known to be highly depleted from the gas phase into solids, but the exact composition of the iron-bearing grains is not yet well understood. Oxygen is one of the most abundant elements in the Galaxy and important for life on Earth. Nevertheless, the exact reservoirs of oxygen in different interstellar environments still remain an open question. The X-ray energy band includes a plethora of transitions from atomic and solid species of elements from carbon to nickel. X-ray radiation from astronomical X-ray sources (such as X-ray binaries) can be absorbed by atoms and solids in the ISM, producing distinct absorption features. By studying these features, we can investigate the dust chemical composition, crystallinity and grain size in different density environments of the ISM. In this talk, I will present new X-ray dust extinction models in the O K and Fe L edges, calculated based on a series of laboratory experiments. I will show recent results on the dust properties using the new models and their application to the high-resolution X-ray absorption spectra of a sample of bright background sources along the galactic plane. Finally, I will discuss the prospects of studying the ISM abundances using joint information from the FUV and X-ray bands, using SPEX.