Dust absorption and scattering in the silicon K-edge^★

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
e-mail: S.T.Zeegers@sron.nl
² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³ Astrophysikalisches Institut und Universitäts-Sternwarte (AIU), Schillergäßchen 2-3, 07745 Jena, Germany
⁴ Anton Pannekoek Astronomical Institute, University of Amsterdam, PO Box 94249, 1090 GE Amsterdam, The Netherlands
⁵ Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands
⁶ Academia Sinica, Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, NTU/AS campus, No. 1, Section 4, Roosevelt Rd., Taipei 10617, Taiwan

Received: 11 January 2019
Accepted: 2 April 2019

Abstract

Context. 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.

Aims. 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.

Methods. 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.

Results. 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 ± 0.02 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.