THERMAL MODELS AND FAR INFRARED EMISSION OF ASTEROIDS

Abstract

ASTRO-F /FIS will carry out all sky survey in the wavelength from 50 to 200 <TEX>${\mu}m$</TEX>. At far infrared, stars and galaxies may not be good calibration sources because the IR fluxes could be sensitive to the dust shell of stars and star formation activities of galaxies. On the other hand, asteroids could be good calibration sources at far infrared because of rather simple spectral energy distribution. Recent progresses in thermal models for asteroids enable us to calculate the far infrared flux fairly accurately. We have derived the Bond albedos and diameters for 559 asteroids based on the IRAS and ground based optical data. Using these thermal parameters and standard thermal model, we have calculated the spectral energy distributions of asteroids from 10 to 200 <TEX>${\mu}m$</TEX>. We have found that more than <TEX>$70\%$</TEX> of our sample asteroids have flux errors less than <TEX>$10\%$</TEX> within the context of the best fitting thermal models. In order to assess flux uncertainties due to model parameters, we have computed SEDs by varing external parameters such as emissivity, beaming parameter and phase integral. We have found that about 100 asteroids can be modeled to be better than <TEX>$5.8\%$</TEX> of flux uncertainties. The systematic effects due to uncertainties in phase integral are not so important.