GROUND-BASED THERMAL IR IMAGES OF COMET TEMPEL-2

We present ground-based thermal infrared images of Comet Tempel 2 obtained on UT September 21.29, 21.15, 23.12, and 24.13 1988. At that time the heliocentric and geocentric distances were approximately 1.4 and 1.0 AU, respectively. A well defined structure in the extended dust emission was observed on all 4 days and can be interpreted in three ways: as a large (centimeter sized) grain tail; as a result of an outburst that occured between 3 and 2.5 AU preperihelion; or as a sunward fan. The brightness of the nuclear condensation showed a temporal variability slightly larger than our observational uncertainty. We estimate that during our observations the dust coma contributed approximately 50% of the brightness in the nuclear pixel. © 1990.