The observers at the 3.6-metre and 2.2 metre telescopes (Tim Livengood, Ulli Kaeufl, Klaus Jockers) report sighting the F-plume at the limb at about 01:20 UT. More to follow.
On behalf of the observers,
Richard West
The impact F site is now as big as the Great Red Spot and shows two components, one many degrees of latitude south of the other, at 2.3 microns. Considerably brighter than the south polar cap now (at 02:10 UT). South component is fainter.
How do the impact sites get so big so fast?
The MacDonald team may be right that the very bright and complex spot we are now observing is the old E site, not the new F site. Perhaps the complex morphology is due to the overlap of the two impact sites, though?
We now are observing the A impact site coming into view at the start of its 4th rotation.
Spencer, DePoy, OSIRIS, CTIO 4-meter
Since the mentioned spot is also visible at 10 micron (3.6-metre, TIMMI) and the earlier spots have been very short-lived at this wavelength, it must be presumed that it is really the F plume which is now visible (see remark in Report from McDonald observatory). The E-site is probably very nearby. The F-spot is however unusual in that observations at 10 micron are still possible after more than 1 hour after the first sighting (Benoit Mosser).
Klaus Jockers (2.2-metre) reports the following intensity ratios, measured at 01:34 UT:
Wavelength I(F)/I(D) total I(F)/I(D)max.surf.brightness 2.09 micron 2.4 1.4 2.36 micron 18.6 4.5
Laurent Jorda and Nick Thomas (DK 1.54 metre), at 02:00 UT find that the F-spot is well visible at 8937 A (CH4), but not at 7271 A (CH4), nor 8920 A (continuum). The spot is elongated in latitude (about 2.5 arcsec). The visibility at 8937 A is confirmed by U. Carsenty at the 60 cm Bochum telescope.
On behalf of the observers,
Richard West
European Southern Observatory
3.6 m - TIMMI
At about 1:27 UT (~45 min post impact), the plume of impact F was observed at the south-east limb of Jupiter. The plume remained at the limb for > 20 minutes, indicating that the plume was observed prior to the time it actually crossed the limb. We infer that the plume extended to a substantial altitude above the cloud tops; determination of the precise altitude will depend on detailed analysis of the impact-spot's longitude.
The F impact residual was detected in infrared filters from 5 microns to 12 microns.
Benoit Mosser, IAP Paris
Tim Livengood, NASA/GSFC
Hans Ulrich K"aufl, ESO
Observations at 2.2 microns from Observatorio Astronomico Nacional at San Pedro Martir (Baja, MX) at Jul 18 ~3 hours UT with the Camila NICMOS III camera showed 3 distinct spots. The brightest was in the center of the latitude band and brighter (in this wavelength) than the Great Red Spot. This is tentatively identified as the E or F impact site. The 2nd spot was 1/4 of the way across the disk and was probably the A impact site. The apparently faintest spot was on the eastern edge and clouds prevented many followup observations.
Jim Klavetter (CSUS)
Steve Levine (UNAM)
Irene Cruz-Gonzalez (UNAM)
Luis Carrasco (UNAM)
Luis Salas (UNAM)
Elfego Ruiz (UNAM)
A more detailed analysis of the data obtained this morning of the F-impact has brought to light some errors in the earlier email that described the observations at ESO. While the F-impact was actually detected at wavelengths from 5 - 12 microns, it was not detected at shorter wavelengths; instead, the E-impact was seen. Therefore:
Wavelength I(F)/I(D) total I(F)/I(D)max.surf.brightness 2.09 micron 2.4 1.4 2.36 micron 18.6 4.5 -------> These are E/D ratios, as F is not visible at 2.mum
-----> This feature was later resolved into E + Z5 spots by Jorda and Thomas. F is invisible at both telescopes.
Sorry for any inconvenience that this may have caused.
Richard West
Report from McDonald Observatory for 18 July UT.
Observations with ROKCAM on the 2.7m telescope show significant structure in several of the impact sites. The D impact spot was clearly visible at 2.3 microns. The E/F area showed a bright peak about 1.5 arcsec to the east and north of a fainter and possibly more diffuse region at 2.3 microns. The A impact site was elongated to the northeast when viewed both at 2.12 and 2.3 microns. This elongation appeared to be double peaked, with a separation of about 1.2 arcsec. Site C became visible on the east limb just as ROKCAM observations were terminated. While these features are visible in the 1.50 micron (NH3) band, they are not nearly as prominent as at 2.12 or 2.3 microns. In a sum of several images at 2.3 microns, we are able to see a faint and thin connection along the limb of the planet between the polar hoods.
CCD imagery with the 0.8m telescope at 893nm showed a horseshoe shaped bright region at the E/F complex. The horseshoe opens towards the south pole. A, C and D were also visible, and the leading edges of E/F, A and C were to the south of the trailing edges. The E/F complex appears as a dark horseshoe and the A and C features appear as dark spots in the continuum and 619nm methane band.
Low resolution spectra from 550 to 1080nm taken with the 2.1m telescope showed an enhancement of 10-15% of the residual intensity in the 890nm methane band at the locations of the E/F and A impact sites. None of these enhancements were as bright as the Great Red Spot at this wavelength.
High resolution (R=60,000) visible spectra from 350 to 1100 nm were obtained of the E/F and A impact locations, as well as undisturbed areas. Spectra were taken with the 2.7m telescope 2dcoude cross-dispersed echelle spectrograph. These data will require extensive analysis.
We also obtained 1.5 hours of continuous video recording of Jupiter taken with the 0.8m MLRS (laser ranging) telescope. The E/F complex appeared as an elongated dark spot. Impact sites A and possibly C were also seen.
The McDonald Comet Impact Science Team
Lick Observatory 120" Telescope: visible-wavelength speckle imaging of Jupiter
July 18 1994, 04:25 - 05:23 UT
We performed speckle imaging of Jupiter at 550nm (40nm bandwidth) at the 120" telescope, with a bare CCD camera having 0.063" pixels.
Three very dark black spots were clearly visible at the positions of impacts C, A, E (or perhaps F). Surrounding the dark spots of impacts E and A were dark partial rings or crescents. The spots were about one arc sec in diameter.
THe spot at the position of impact E (or F?) was considerably darker than that at the position of impact A at the time we observed it.
We have also observed the face of Jupiter in a methane filter (8800 A with 300A bandwidth). We saw no clear spots on the face of the planet. When impact site A was coming around the dawn limb, it appeared as a brighter region at the limb and as it rotated into view.
We plan to post some of these processed speckle images under the home page of the Lawrence Livermore National Laboratory at the WWW address http://www.llnl.gov in the "What's New" section.
The dark spots which we saw at 5500A were also seen at Lick by visual observers on the 36 inch refractor, as well as with CCD camera on the 40 inch Nickel telescope (Mike Brown and colleagues).
Claire Max, Don Gavel, Erik Johansson, LLNL
Mike Liu, UC Berkeley
Bill Bradford, UC Santa Cruz
REPORT FROM THE LICK OBSERVATORY 36" REFLECTOR
After several frustrating nights, we have finally detected the impact sites using the 36" Crossley telescope and our high-speed CCD system. (Is this telescope the oldest being used in this campaign? (1895))
We detected 3 bright, diffuse regions corresponding to impact sites A, E, and possibly C in 8900A methane filter images. Images at 7500A and 9500A showed two dark regions corresponding to the bright spots seen at 8900A; only impact site A did not show a corresponding dark continuum region.
Frequent observations throughout the night failed to detect any impact signature from the putative fragment G2 (=15b), which was predicted to occur sometime between 0440 to 0510 UT. We observed down to 10.7 airmasses (!) but did not detect any obvious signature from fragment G itself as of 0733 UT.
Analysis will continue, and our data volume is now over 750 Mbytes...
Jim Bell, Ted Dunham, Dominique Toublanc, Bob Thompson
Lick Observatory Crossley 36"
Three dark features were observed visually using a 36 cm (f/11) Schmidt- Cassegrain Telescope. The first crossed the central meridian of Jupiter at 3:50 UT, July 18, 1994 and appeared almost like a Galilean moon shadow (roughly 6000 km in diameter). There was an irregular feature to the south-preceding edge of this dark spot. Perhaps the dark spot and irregular feature were the impact sites of F and/or E.
The second feature crossed the central meridian at 4:38 UT, July 18, 1994 and appeared gray (about 9000 km in diameter). This one may have been the impact site of fragment A. The third feature was similar to the second and was probably the impact site of fragment C. The transit time of this feature could not be measured accurately but was roughly 5:40 UT, July 18, 1994.
Dan Bruton
Richard Schumde
Texas A&M Observatory
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