Some time ago, several people wrote messages to the exploder comparing times for various SL9 impacts, in particular H and L, as observed by Galileo PPR and by ground-based telescopes. Some of the times quoted for various observations were taken from the original exploder results which, as Clark Chapman correctly points out, should be taken with a grain of salt. In particular, the times that we initially reported from the Calar Alto 3.5m telescope corresponded to times when we first saw "something" in our simple sky-subtracted infrared images. These times were obviously improved as more careful reductions were done -- flat-fielding, averaging sky frames, optimizing the "stretch" of displayed images, defining what "something" was, etc.
Here then, is the current status -- with accurate times -- of the ten impacts that were available to us at Calar Alto.
Calar Alto 3.5 meter SL9 Data
|-----------------------------------------------------------------------|
|Impact Date Impact Time Start of Start of Precursor- |
| (July) (Accepted) Precursor Plume Plume Delay|
|-----------------------------------------------------------------------|
|A 16 20:11 +/- 3 20:11 20:18 7 min |
|E 17 15:11 +/- 3 ? 15:17:30 - |
|H 18 19:31:59 +/- 1 19:33 19:38 5 min |
|L 19 22:16:48 +/- 1 22:16:30 22:17:30 1 min |
|Q2 20 19:44 +/- 6 19:44 19:52 8 min |
|Q1 20 20:12 +/- 4 20:13 20:20 7 min |
|S 21 15:15 +/- 5 ? detected - |
|U 21 21:55 +/- 7 ? detected - |
|P2 20 15:23 +/- 7 ? ? - |
|T 21 18:10 +/- 7 ? ? - |
|-----------------------------------------------------------------------|
Data were taken from the 3.5 meter telescope at 2.3 microns. Times are UT; those with seconds are accurate to +/- 15 seconds or so, those without seconds to +/- 1 min. The accepted impact times are from the orbital solutions of Yeomans and Chodas (errors are in minutes); H and L impact times are from Galileo PPR.
As a cautionary note, we see faint spots at the impact site BEFORE the precursor for both the H and L impacts. In the case of L, a faint spot was already present on the planet when our 2.3 micron observations began at 21:58. The spot was continuously observed until it was swamped by much brighter light from the L precursor. The longitude of the "bogey" does not correspond to a pre-existing spot; we suspect that it is due to the fresh impact of a very small, previously unknown SL9 fragment. For H, a faint spot first appeared at 19:29 but the B spot was scheduled to round the eastern limb at about this time.
We will have a poster on these and other Calar Alto results at the DPS meeting in Washington D.C.
Sincerely,
Doug Hamilton
Tom Herbst
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