Project P8: Temperature-dependent photostability and optical properties of realistic cometary ice composites

在升华距离之外，碎片盘中冰粒的主要侵蚀过程应该是UV光溅射，因为UV光子能够破坏水分子中的键，并且碎片可以从颗粒表面解吸。软X射线也可以被吸收并导致电离和键的断裂。在该项目中，我们将研究由水冰，天体物理学相关分子和耐火颗粒组成的混合物的异质颗粒的侵蚀和电阻率，以预测碎片盘宿主恒星的紫外线和X射线照射水平。H2O、分子和尘埃颗粒将同时沉积在可以保持在6至150 K温度的冷基底上。冰类似物将暴露于UV和X射线照射。将使用提供能量为10 eV的光子的氢放电灯来研究紫外范围内的冰的光溅射。在同步加速器设施中，可以为各种X射线线提供3x 108光子/秒/厘米2的天体物理相关X射线通量。将使用冰层的原位UV/维斯和IR光谱结合蒸发物质的质谱来研究脏水冰的光诱导处理。项目P1、P2和P4将利用冰粒对紫外线和X射线照射的抵抗力以及光谱特性和形态的变化来开发更真实的磁盘模型。

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 Xray 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 3x108 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, P2 and P4.