We successfully observed the R impact from the 200-inch Hale
telescope at Palomar, with simultaneous observations at 3.6 microns,
5 microns, interleaved with 10-micron spectra at 10-minute intervals.
The first indications were seen at 5:35 UT at 3.6 and 5 microns.
We recorded rapid brightening of the site at 5:41, reaching a peak
at 5:46 UT when diffraction spikes were observed at 5 um. 5-um
flux dimmed by a factor of 40 by 5:50 UT. The image was observed
to be extended along the limb at 5:51 UT and approximately 2" long
at 5:54 UT. By 5:59 UT, the 5-um flux had dropped to the level in
the first images. After approximately 6:00 UT, the 10-um flux
appeared to be constant. By 6:12 UT, the 5-um feature had faded to
a brightness comparable with the planet. At 6:23 UT, the 5-um
feature was almost gone, at an airmass of 4.17. By 6:39, impact
site Q also appeared on the eastern limb. Observations ceased at
6:50 when the horizon limit was reached.
Colleen McGhee, Phil Nicholson, Gerry Neugebauer, Keith Matthews, Tom Hayward, Jeff Van Cleve, Alycia Weinberger, John Miles, Dave Shupe