Physical characteristics of near-Earth asteroids from thermal infrared spectrophotometry

Thermal infrared spectrophotometric observations of the near-Earth asteroid s 433 Eros, 1980 Tezcatlipoca, and 3671 Dionysus are presented and their im plications for the physical characteristics of the objects discussed. Sizes and albedos are derived on the basis of published thermal models and compa rison of the infrared data with optical observations. The results for 433 E ros are in very good agreement with radar and other earlier findings and de monstrate the accuracy achievable with one of the thermal models used. The new data, together with earlier results from the literature, suggest the su rface thermal inertia of 433 Eros is no larger than three times that of the Moon. The derived effective diameter and optical albedo of 1980 Tezcatlipo ca (around lightcurve maximum) are D = 6.7 +/- 1.0 km and p(V) = 0.15 +/- 0 .05, and for 3671 Dionysus D = 1.0 +/- 0.2 km and p(V) = 0.40 +/- 0.15. The se diameters are significantly different from previous estimates. The therm al continua of Tezcatlipoca and Dionysus are indicative of high surface the rmal inertias. A near-infrared spectrum of Dionysus, coupled with the high albedo, suggests an hi or E classification. Such taxonomic types are relati vely rare amongst near-Earth asteroids. (C) 1999 Academic Press.