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

该项目的主要目标是获取信息，从而导致或有助于查明构成热的外黄道尘盘和太阳F-日冕的材料。外索虫经常被观察到，并且被认为是由亚微米颗粒组成的，可能热达2000 K，因为它们的位置非常接近星星。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。鉴于热exozodiacal颗粒的存在是揭示了他们的热发射在近红外和中红外波长，我们的目标是获得的信息包括在高温下的红外波长范围内的相关材料的光学常数。这些数据将使我们能够计算不同颗粒几何形状和尺寸的热发射光谱，我们将与现有或正在获取的天文观测数据进行比较，以确定或限制热exozodis和F-日冕的组成。项目材料的选择考虑到热的外生黄道尘埃颗粒所表现出的或预期的性质，如化学成分和升华温度。因此，我们选择了碳的同素异形体，Fe，Fe 2 O3，Fe 3 O 4，Fe 3C和SiC，我们保持开放的列表。它们的光学常数将从傅里叶变换红外（FTIR）热发射光谱与FTIR反射光谱的补充分析。将材料从室温逐步加热到1800 K用于发射光谱，到1000 K用于反射光谱，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该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1800 K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。热发射光谱将使用相关形式的纳米粉末和散装样品进行测量。模拟的发射效率的基础上的散装数据与直接测量的纳米粉末发射率的比较，将使我们能够评估晶粒的几何形状对热发射的影响，并评估预测晶粒特性的模型的有用性。这些结果应用于解释天文观测，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系外地球。此外，通过一个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.