Sascha Zeegers (ASIAA); Ciska Kemper (ESO/ASIAA); Stefan Bromley (Universitat de Barcelona); Joan Mariñoso Guiu (Universitat de Barcelona); Elisa Costantini (SRON); Daniele Rogantini (SRON); Irene Abril Cabezas (Universidad Complutense de Madrid); Cor de Vries (SRON); Ioanna Psaradaki (SRON); Missagh Mehdipour (SRON)
The size distribution of interstellar dust particles plays an important role in many astronomical models. However, we can only infer the sizes of the grains with indirect methods. This has resulted in many different size distribution models and it is difficult to discriminate between them. Infrared and X-ray spectroscopy offer important tools to solve this problem. The infrared provides the possibility to study the small-end of the size distributions of silicate grains (a major component of interstellar dust). Here we can observe the effect of silicate nano-grains on the spectra of infrared sources. Small silicate nano-grains may provide insight in the formation of grains in the interstellar medium (ISM), since the observation of these small clusters may point to active grain formation in the ISM. They may also explain the absence of crystalline dust in ISM, since many atoms are near the surface of the grain, distorting the lattice structure, which may make the grains appear amorphous while they are still in their lowest energy configuration. In the X-rays, bright low mass X-ray binaries are particularly useful to study dust in the interstellar medium of the Galaxy. We can use them as background sources to probe the intervening dust along the line of sight. Features in the spectra of these sources reveal information about the composition and size of the dust particles. The X-ray absorption edges of silicon and magnesium are particularly useful. These edges contain scattering features caused by dust grains, which can be directly linked to the particle size of the dust grains. In this talk, I will show the possibilities of studying the X-ray binaries in the Galaxy in order to constrain the dust size distribution. I will focus on the upcoming Athena X-ray Observatory (expected launch date 2030), which will be capable of discriminating between different dust models thanks to the high spectral resolution of the X-IFU instrument. From the infrared side I will discuss the properties of small silicate grains making use of archival Spitzer spectra and the possibilities to observe them with JWST and SPICA.