Infrared emission spectroscopy of nanograins in the laboratory for understanding hot exozodiacal dust

该项目的主要目标是获得将导致或有助于确定构成热外生尘星盘和太阳F-日冕的物质的信息。Exozodis经常被观察到，并被认为是由亚微米颗粒组成，温度可能高达2000K，因为它们离恒星非常近。这些颗粒的成分和来源目前尚不确定。同样的问题也涉及F-日冕的尘埃颗粒。考虑到热的虫体颗粒的存在是通过它们在近红外和中红外波长的热发射来揭示的，我们旨在获得的信息包括相关物质在红外波长范围内高温下的光学常数。这些数据将使我们能够计算不同颗粒几何形状和大小的热发射光谱，我们将把这些光谱与现有的或正在获得的天文观测数据进行比较，以确定或限制热外耳石和F日冕的组成。项目材料的选择考虑了热外生尘埃颗粒表现出的或预期的特性，如化学成分和升华温度。因此，我们选择了碳同素异形体，Fe，Fe2O3，Fe3O4，Fe3C和SIC，这是一个我们一直开放的名单。它们的光学常数将通过傅里叶变换红外(FTIR)热发射光谱的分析和FTIR反射光谱的分析得到。从发射光谱的室温到1800K，到反射光谱的1000K，分步骤加热材料，将使我们能够表征光学常数的温度依赖关系。为了进行FTIR热发射测量，该项目的一个目标是将这项技术引入我们的实验室。现有的FTIR光谱仪将配备一个可在1800K温度下进行热发射测量的延伸件，它将在项目的第一阶段进行设计、建造、安装和测试。热发射光谱将使用相关形式的纳米粉末和块状样品来测量。将基于大量数据的模拟发射效率与直接测量的纳米粉末发射率进行比较，将使我们能够评估颗粒几何形状对热发射的影响，并评估预测颗粒性质的模型的有效性。将这些结果应用于天文观测的解释，将提高我们对碎片盘中的物理和化学的理解，并将有助于天文学家寻找地外地球。此外，通过可公开访问的数据库提供的热发射光谱将有助于研究原行星盘内部区域的热尘埃。

The main objective of the project is to obtain information that will lead to or contribute to the identification of the materials that compose hot exozodiacal dust disks (exozodis) and the Solar F-corona. Exozodis are frequently observed and are thought to consist of submicronic grains possibly as hot as 2000 K because of their location very close to the star. The composition and therefore the origin of these grains are currently undetermined. The same issues concern the dust grains of the F-corona. Given that the presence of hot exozodiacal grains is revealed by their thermal emission at near- and mid-infrared wavelengths, the information we aim to obtain consists of the optical constants of relevant materials at high temperatures in the infrared wavelength range. These data will allow us to compute thermal emission spectra for different grain geometries and sizes, which we will compare to astronomical observation data, available or being acquired, in order to identify or constrain the composition of hot exozodis and that of the F-corona. The project materials are selected considering properties exhibited by or expected from hot exozodiacal dust grains such as chemical composition and sublimation temperature. Hence, we have chosen carbon allotropes, Fe, Fe2O3, Fe3O4, Fe3C, and SiC, a list that we keep open. Their optical constants will be derived from the analysis of Fourier-transform infrared (FTIR) thermal emission spectra complemented with FTIR reflection spectra. Heating the materials in steps from room temperature to 1800 K for emission spectroscopy, to 1000 K for reflection spectroscopy, will allow us to characterize the temperature dependence of the optical constants. In order to perform FTIR thermal emission measurements, an objective of the project is to bring this technique into our laboratory. The existing FTIR spectrometer will be equipped with an extension for thermal emission measurements at temperatures up to 1800 K. It will be designed, built, installed, and tested during the first stage of the project. The thermal emission spectra will be measured using samples in the relevant form of nanopowder and also in that of bulk. The comparison of simulated emission efficiencies based on the bulk data with directly measured nanopowder emissivities will allow us to evaluate the effect of grain geometry on thermal emission and to assess the usefulness of models for predicting grain properties. These results, applied to the interpretation of astronomical observations, will improve our understanding of the physics and chemistry in debris disks and will assist astronomers in their search for exo-Earths. Moreover, the thermal emission spectra, made available through a publicly accessible database, will be useful to the study of hot dust in the inner region of protoplanetary disks.