POWRE: Construction of an Infrared Spectroscopic Database for Direct Comparison with Astronomical Observations of Stardust

POWRE：构建红外光谱数据库，用于与星尘天文观测直接比较

• 批准号: 9805924
• 负责人: Anne Hofmeister
• 金额: $ 7.41万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-09-01 至 2002-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9805924&HistoricalAwards=false
• 关键词: POWRE; Construction; Infrared; Spectroscopic; Database

HofmeisterAST-9805924Information on circumstellar dust particles pertains to basic questions of origin and process in the galaxy. A first order problem is identification of "stardust" through comparison of astronomical infrared (IR) spectra to laboratory data on solids. Although the concept is straightforward, implementation is problematic. For example, dust features in the IR spectra of cold, carbon stars have been interpreted as hexagonal-rhombohedral SiC. This result disagrees with identification of presolar SiC grains in meteorites as exclusively the cubic polymorph. The discrepancy is fundamental because such stars are major dust producers. The comparison of data from thin film, or raw dispersion spectra, for O.1 micron grains to the data of carbon star spectra shows that circumstellar SiC is cubic, just as it is in meteorites. Correct identification is crucial as presolar silicates have not yet been found in meteorites. A matrix-free IR database will be constructed that can be directly compared with astronomical dust features, not only from distant stars, but also from near-by objects such as comets. The thin film method provides randomly orientated particles, and hence "average" extinction coefficients, yet is quantitative. Absorption data will be collected from the far-IR to the visible wavelengths, with emphasis on spectral regions frequently used in astronomy, remote sensing, and on materials expected to be fairly abundant in stardust. Determination of film thickness through interference fringes will yield the mass dependence of peak heights and indicate crystal sizes appropriate for bulk properties. Over 100 complete thin film spectra will be collected from various planetary materials (e.g., silicates, refractory substances, and phases found in meteorites and interplanetary dust particles). Materials will be selected by consulting other scientists in the field. The data will then be compared to astronomical spectra of stardust.Of equal importance to the database is the understanding the physical processes producing absorption vs. scattering features in IR spectra. Mie scattering theory will be modified to account for the presence of bulk absorption processes, and to test the model through comparison with reflection, thin film, and dispersion data from selected phases (e.g., SiC, SiO2, olivine and gamet). The size of grains in the dispersions will be limited to sizes appropriate for surface effects, 0.05 micron. The revised theory should allow calculation of spectra with variable amounts of scattering and absorption components from laboratory absorption data. The results of the project will be useful in the fields of astronomy, planetary science, and remote sensing. It will also be important to mineralogy, in that physical properties such as ordering or concentrations of hydrous species are currently extracted from dispersion spectra without accounting for the component of scattering inevitably present and without considering that particles with sizes more than three times larger than the skin depth can falsify peak profiles.This research effort is a new, interdisciplinary direction involving an international collaboration. Strong links with active research areas in the department will help to rebuild a graduate program.The Office of Multidisciplinary Activities in the Directorate of Mathematical and Physical Sciences and the Division of International Programs are providing the funds for this award.***

HofmeisterAST-9805924关于星周尘埃粒子的信息涉及星系起源和过程的基本问题。 一个首要问题是通过比较天文红外光谱和固体实验室数据来识别“星尘”。 虽然概念简单明了，但实施起来却有问题。 例如，冷碳星的红外光谱中的尘埃特征被解释为六方菱形SiC。 这一结果不同意陨石中的前太阳SiC颗粒完全是立方多晶型的鉴定。 这种差异是根本性的，因为这些恒星是主要的尘埃制造者。 将0.1微米颗粒的薄膜或原始色散谱的数据与碳星星光谱的数据进行比较，表明星周SiC是立方的，就像陨石中的SiC一样。 正确的鉴定是至关重要的，因为在陨石中还没有发现前太阳硅酸盐。 将建立一个无矩阵的红外数据库，不仅可以与遥远恒星的天文尘埃特征进行直接比较，还可以与彗星等近距离物体的特征进行比较。 薄膜方法提供随机取向的颗粒，因此提供“平均”消光系数，但是是定量的。 吸收数据将收集从远红外到可见光波长的吸收数据，重点是天文学、遥感中经常使用的光谱区域以及预计星尘中相当丰富的材料。通过干涉条纹确定膜厚度将产生峰高的质量依赖性，并指示适合于本体性质的晶体尺寸。 将从各种行星材料（例如，硅酸盐、难熔物质以及陨石和行星际尘埃颗粒中发现的相）。 材料将通过咨询该领域的其他科学家来选择。 对数据库同样重要的是了解产生红外光谱吸收和散射特征的物理过程。 米氏散射理论将被修改，以解释体吸收过程的存在，并通过与来自选定相（例如，SiC、SiO2、橄榄石和石榴石）。 分散体中颗粒的尺寸将限于适于表面效应的尺寸，0.05微米。 修订后的理论应允许计算光谱与变量的散射和吸收成分的实验室吸收数据。 该项目的成果将在天文学、行星科学和遥感领域发挥作用。 这对矿物学也很重要，因为目前从色散光谱中提取的物理性质，如含水物质的有序性或浓度，没有考虑到不可避免地存在的散射成分，也没有考虑到尺寸大于趋肤深度三倍的颗粒可能会伪造峰形。这项研究工作是一个新的跨学科方向，涉及国际合作。 与该系活跃研究领域的紧密联系将有助于重建研究生课程。数学和物理科学局多学科活动办公室和国际项目司为该奖项提供资金。*