THE COLOR TEMPERATURE OF (2060)CHIRON - A WARM AND SMALL NUCLEUS

We present three sets of thermal-infrared observations of (2060) Chiron, obtained in 1991, 1993, and 1994. These observations allow the first estimates of the color temperature of Chiron as well as refined estimates of the radius and albedo of its nucleus. 10/20 μm color temperatures of 126-6+11 and 137-9+14 K are obtained from the 1993 and 1994 observations, respectively. These temperatures are consistent with the Standard Thermal Model [STM; Lebofsky & Spencer, 1989, Asteroids II, p. 128 (University of Arizona, Tucson)] but significantly higher than those predicted by the Isothermal Latitude Model. Our estimates of Chiron's radius based on the STM are in agreement with each other, with the observations of Lebofsky et al. [Icarus, 60, 532 (1984)], and with recent occultation results [Buie et al, IAU Cire. 5898 (1993)]. We obtained values for the radius of 74±11 km in 1991, 88±10 and 104±10 km in 1993, and, 94±6 and 91±13 km in 1994.