# Dust absorption and scattering in the silicon K-edge

## TL;DR

This study uses laboratory X-ray measurements of silicon K-edge features in silicate dust to model interstellar dust properties along lines of sight in the Galactic center, revealing silicon abundance gradients and dust composition insights.

## Contribution

The paper introduces new laboratory measurements of silicate compounds' silicon K-edge and integrates them into astrophysical models to analyze interstellar dust in X-ray spectra.

## Key findings

- Most lines of sight are well fitted by amorphous olivine.
- Upper limits on crystalline silicate material were established.
- A potential silicon abundance gradient of 0.06±0.02 dex/kpc was identified.

## Abstract

The composition and properties of interstellar silicate dust are not well understood. In X-rays, interstellar dust can be studied in detail by making use of the fine structure features in the Si K-edge. The features in the Si K-edge offer a range of possibilities to study silicon-bearing dust, 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 that 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. Most lines of sight can be fit well 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 $0.06\pm0.02$ dex/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.