Project P8: Ice-silicate-carbon mixtures in stellar UV fields (IFK/Jena)


Outside the sublimation distance, the dominant erosive process for ice grains in debris disks is supposed to be UV photosputtering since UV photons are able to break bonds in water molecules and fragments can be desorbed from the grain surfaces. Soft X-rays can also be absorbed and cause ionization and the breaking of bonds. In the project, we will study the erosion and resistivity of heterogeneous grains consisting of blends of water ice, astrophysically relevant molecules, and refractory grains to UV and X-ray irradiation at levels predicted for the debris disk host stars. H2O, molecules, and dust particles will be simultaneously deposited on cold substrates that can be kept at temperatures between 6 and 150 K. The ice analogs will be exposed to UV and X-ray irradiation. A hydrogen discharge lamp providing photons with an energy of 10 eV will be used to study the photosputtering of ices in the UV range. Astrophysically relevant X-ray fluxes of 3⨉108 photons/s/cm² can be provided for a variety of X-ray lines at synchrotron facilities. In-situ UV/VIS and IR spectroscopy of the ice layers in combination with mass spectrometry of evaporated species will be used to study the photo-induced processing of the dirty water ice. The resistivity of icy grains to UV and X-ray irradiation and changes in the spectral properties and morphology will be used to develop more realistic disk models in projects P1–P4.