|
Description
The composition and properties of interstellar silicate dust are not well understood. Inthe X-rays, interstellar dust can be studied in detail, by making use of the fine structure features inthe Si K-edge. The features in the Si K-edge offer a range of possibilities to study silicon-bearingdust, such as investigating the crystallinity, abundance and the chemical composition along a given line of sight. We present newly acquired laboratory measurements of the silicon K-edge of several silicate-compounds which complement our measurements from our earlier pilot study. The resulting dust extinction profiles serve as templates for the interstellar extinction that we observe. The extinction profiles were used to model the interstellar dust in the dense environments of the Galaxy. The laboratory measurements, taken at the Soleil synchrotron facility in Paris, were adapted for astrophysical data analysis and implemented in the SPEX spectral fitting program. The models were used to fit the spectra of nine low-mass X-ray binaries located in the Galactic center neighborhood in order to determine the dust properties along those lines of sight. In most lines of sight can be well fitted by amorphous olivine. We also established upper limits on the amount of crystalline material that the modeling allows. We obtained values of the total silicon abundance, silicon dust abundance and depletion along each of the sightlines. We find a possible gradient of 0.06+/-0.02dex/kpc for the total silicon abundance versus the Galactocentric distance. We do not find a relation between the depletion and the extinction along the line of sight.
|
