Lect7 Radiometry (10-13-09)

Lect7 Radiometry (10-13-09) - Radiometry of Asteroids and...

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Radiometry of Asteroids and Comets October 13, 2009
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OUTLINE I. Introduction: Thermal Emission and Reflected Light II. Standard Thermal Model (STM) III. Deviations from the STM: Fast-rotating (ILM) Thermophysical Model NEATM Non-sphericity I. A Few Examples: 1 Ceres NEAs Comets Centaur 2060 Chiron I. Future Observations
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In addition to being diagnostic of the mineralogy of asteroids, infrared observations can also be used to derive their sizes and albedos. The observed thermal flux from any atmosphereless solar system object, in combination with a measurement of the reflected sunlight, can be used to derive the size and albedo of the object. The first application of thermal radiometry to derive the radii of asteroids was done in 1970. Several asteroids, including 4 Vesta, were found to be larger and darker than expected. I. INTRODUCTION
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II. Standard Thermal Model Basic Principles The principle is simple, the visible brightness of an asteroid is a function of the geometric albedo (p) and its cross section: Bv = π R 2 pSd -2 The total thermal emission is proportional to the total insolation, times (1-A), where A is the Bond albedo*, and the cross section B th ~ π R 2 (1-A)S d -2 “R” is the asteroid’s radius, “d” is the heliocentric distance of the asteroid in astronomical units, and S is the solar constant**. *This is close but not the same as the geometric albedo, more on this later ** If you do not know what the S is the solar constant, look it up and come see me .
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II. Standard Thermal Model Basic Principles (cont) - For a surface in equilibrium with the radiation field, the reflected and emitted radiation must add to the total solar radiation intercepted. Hence, simultaneous measurements of the reflected and emitted components are sufficient to determine both the size and albedo of the asteroid. -
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This note was uploaded on 11/09/2009 for the course AST 4142 taught by Professor Campins during the Fall '09 term at University of Central Florida.

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Lect7 Radiometry (10-13-09) - Radiometry of Asteroids and...

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