Infrared spectrophotometry of Comet IRAS-Araki-Alcock (1983d) - A bare nucleus revealed?

Spectra of the central core and surrounding coma of Comet IRAS-Araki-Alcock (1983d) were obtained at 8-13 microns on May 11 and 2-4 microns on May 12, 1983. Spatially resolved measurements at 10 microns with a 4-arcsec beam showed that the central core was more than 100 times brighter than the inner coma only 8 arcsec away; for radially outflowing dust, the brightness ratio would be a factor of 8. The observations of the central core are consistent with direct detection of a nucleus having a radius of approximately 5 km. The temperature of the sunlit hemisphere was greater than 300 K. Spectra of the core are featureless, while spectra of the coma suggest weak silicate emission. The spectra show no evidence for icy grains. The dust production rate on May 11.4 was about 100,000 g/sec, assuming that the gas flux from the dust-producing areas on the nucleus was about 0.00001 g/sq cm per sec.