Abstract

The diffuse interstellar medium (ISM) is an integral part of the evolution of the entire Galaxy. Metals are produced by stars and their abundances are the direct testimony of the history of stellar evolution. The interstellar dust composition and hence the total abundances are yet to be accurately determined. In this talk I will show how to probe ISM dust composition, total abundances, and their Galactic gradients through the study of interstellar absorption features in the X-ray spectra of Galactic low-mass X-ray binaries taken with XMM -Newton. I measured the column densities of O, Ne, Mg, and Fe with an empirical model and estimate the Galactic abundance gradients. Solids are a significant reservoir of metals like oxygen and iron. Respectively, 15-25 and 65-95 of the total amount of O I and Fe I is found in dust. The dust amount and mixture seem to be consistent along all the lines-of-sight (LOS). Abundance gradients and predictions of local interstellar abundances are in agreement with those measured at longer wavelengths. On a large scale the ISM appears to be chemically homogeneous showing similar gas ionization ratios and dust composition. The agreement between the abundances of the ISM and the young, stellar objects suggests that the young, local Galaxy is also chemically homogeneous.