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黄道带尘埃盘和太阳f -日冕的物质的信息。系外行星经常被观测到，并且被认为是由亚微米颗粒组成的，温度可能高达2000k，因为它们的位置非常靠近恒星。这些颗粒的组成和来源目前还不确定。同样的问题也涉及到f冕的尘埃颗粒。考虑到热外黄道带颗粒的存在是通过近红外和中红外波段的热发射来揭示的，我们的目标是获得相关材料在红外波段高温下的光学常数。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，我们将与现有或正在获得的天文观测数据进行比较，以确定或限制热系外行星和f -日冕的组成。项目材料的选择考虑了热外黄道带尘埃颗粒所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，我们保持开放的列表。它们的光学常数将通过分析傅里叶变换红外（FTIR）热发射光谱和FTIR反射光谱得到。将材料从室温加热到1800 K（发射光谱），到1000 K（反射光谱），将使我们能够表征光学常数的温度依赖性。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光谱仪将配备一个扩展，用于在高达1800k的温度下进行热发射测量。它将在项目的第一阶段进行设计、建造、安装和测试。热发射光谱将用相关形式的纳米粉末和块状样品进行测量。将基于块状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，将使我们能够评估晶粒几何形状对热发射的影响，并评估预测晶粒性质的模型的有效性。这些结果应用于天文观测的解释，将提高我们对碎片盘的物理和化学的理解，并将帮助天文学家寻找系外地球。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.