THERMAL INFRARED LIGHTCURVES OF THE IMPACT OF COMET SHOEMAKER-LEVY-9 FRAGMENT-R

The impact of fragment R was observed at thermal infrared wavelengths of 7.85, 10.3 and 12.2 mu m from the NASA/Infrared Telescope Facility on July 21 UT, using the MIRAC2 mid-infrared array camera. Thermal emi ssion at the three wavelengths was sampled sequentially using a 1.8% c ircular variable filter, with an average time interval of 17 seconds b etween observations at different wavelengths. Continuous imaging of Ju piter in this mode began at 5:08 UT and extended to 5:55 UT. We presen t calibrated lightcurves for the three wavelengths. Clear evidence for enhanced emission from the impact region first appears at 5:41 UT, wi th the peak in emission at all three wavelengths occurring similar to 3.5 minutes later. The information content of the data is presented in terms of plots of the product of emissivity times angular size versus source temperature for each wavelength. Assuming that the peak in the lightcurves is due to rotation of the hot impact site into view from Earth, we estimate a diameter of similar to 1900 km for the source emi tting area at 5:44:30 UT and estimate a lower limit on the source temp erature at this time of similar to 1350 K. This lower limit drops to 8 00 K if the diameter of the emitting region was actually a factor of t wo larger.