Wed Jul 20 07:33:33 1994
We are continuing to use the InfraRed Imaging Spectrometer (IRIS) on the 3.9 m Anglo-Australian Telescope (AAT) at Siding Spring Observatory (near Coonabarabran, Australia) to monitor the impacts of the fragments of Comet Shoemaker-Levy 9 with Jupiter. On 20 July, observations were initiated at 06:30 UT. The sky was clear, and the seeing was initially 1 to 2 arcsec. The impact sites of fragments H, F, E, C, K, L, and G were clearly visible as bright clouds at K-band wavelengths within strong methane bands. These features were also visible as dark features on our guiding TV, which was using a 0.55 micron filter. Unlike previous nights, when K-grism drift scanning was used to monitor the impact event, this evening, we used rapid-sampling imaging photometry with a 2.34 micron filter. The readout time was 0.45 seconds.
The impact sites of fragments D and G were very close to the morning limb at the predicted impact time, frustrating efforts to detect the impact flash of fragment N. The seeing worsened somewhat just before the predicted impact time, with occasional periods of 3 arcsec.
The impact flash from fragment N was first detected on the morning limb at 10:35 UT. The intensity of this flash increased slowly until about 10:37 UT, but never exceeded 70% of the mean surface brightness of the south polar hood at 2.34 microns. At about 10:38, we had an instrument problem, which took us off the air until about 10:42. When we resumed our observations, there was no evidence of the impact site of fragment N.
At 10:49, we reconfigured IRIS for drift scanning with the K-grism, and continued to monitor the impact longitude of the site as it rotated onto the Jovian disk. There was still no evidence of the N impact site at 11:00 UT.
AAT 3.9 m Observing Team - David Crisp (JPL)
Vikki Meadows (JPL)
Stuart Lumsden (AAO)
Jonathan Pogson (AAO)