Infrared observations and thermal emission models of asteroids
A review of the classification of asteroids according to their orbital and physical properties is presented and the technique of numerical taxonomy is applied to catalogued optical data. The size distribution of minor bodies is of fundamental importance for theories of the origin and formation of the Solar System. Methods of diameter determination are reviewed with particular reference to the radiometric method. Thermal emission models of asteroids are essential for the reduction of infrared observations to obtain radiometric diameters and albedos. Various thermal models are described, with an emphasis on the assumptions made, and their limitations. The models are applied to observations in the 8-13?m region to examine possible variations of emissivity with wavelength, to remove the thermal component from reflection spectra in the 3-4?m region, and to determine the nature of the surface of the unusual asteroid (3200) 1983TB. The Infrared Astronomical Satellite (IRAS) was launched in 1983 to provide an all-sky survey in four infrared wavebands. In order to prevent detections of the thermal emission from moving objects from being lost, software was written to search the rejected survey data in near real-time. As well as detecting several hundred numbered asteroids and five known comets, two main belt asteroids, two Apollo asteroids, six comets and an infrared tail on comet Tempel-2 were discovered. A description of the moving object software and its implementation is presented, together with estimates of the selection effects and completeness of the search, and analysis of the data. The ground-based observations of the Apollo asteroid (3200) 1983TB do not support the cometary nucleus hypothesis inferred from its orbital characteristics. A preliminary analysis of some IRAS additional observations of asteroids is also presented.