ESO SL9 NEWS BULLETIN
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Issue : 9
Date : Monday, July 18, 1994, 08:00 UT (10:00 CEST; 04:00 Chilean time)
Items : 9-A: Observations continue at La Silla
9-B: Plumes rising over all impact sites
9-C: Reflections from the moons
9-D: Spectroscopy
9-E: The G-impact
9-F: Press Conference in Santiago
9-A. OBSERVATIONS CONTINUE AT LA SILLA
Last night, all telescopes were in action at La Silla. Nine were
observing Jupiter and the cometary impacts; the SEST will start today.
Much of tonight's effort was directed towards the F-impact, predicted
at 00:29 UT. At about 1:27 UT, the plume of impact F was observed at
the south-east limb of Jupiter. The plume remained at the limb for
more than 20 minutes, indicating that the plume was observed prior to
the time it actually crossed the limb. It is inferred 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 was detected in infrared filters from 5 microns to 12
microns.
It later became clear that the spot seen at shorter wavelengths was not F,
but that of the E impact that took place about 9.5 hours before and
which had in the meantime performed one full rotation. The F spot is
unusual in that observations at 10 micron were still possible more than
1 hour after the first sighting (Benoit Mosser) in contrast to the
behaviour of the earlier impacts.
Klaus Jockers (2.2-metre) reported the following intensity ratios,
measured at 01:34 UT:
Wavelength I(E)/I(D) total I(E)/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 found that
the F-spot was well visible at 8937 A (CH4), but not at 7271 A (CH4),
nor 8920 A (continuum). The spot was elongated in latitude (about 2.5
arcsec). The visibility at 8937 A was confirmed by U. Carsenty at the
60 cm Bochum telescope.
Two new infrared images of Jupiter are available in the ESO WWW Portal
and also as photographic prints at today's Press Conference
at the ESO Headquarters.
9-B: PLUMES RISING OVER ALL IMPACT SITES
Following the observations of plumes over the A, B and C impact sites,
such features were also observed over those of fragments D, E and F.
Although the plumes were of very different size and brightness, the
fact that all of the impacts have produced this phenomenon does hint
at a certain similarity of these events.
The possible, double impact associated with fragment C (item 8-C) soon
turned out to be the sighting of the C imapct plume, together with the
A-plume that had made one full rotation. While the features seemed to
persist rather long when observed in near-infrared light, the
far-infrared brightness peaked steeply and then disappeared within one
hour or less. This wavelength-dependency is not yet fully understood,
but points to a high-altitude phenomenon, in the stratosphere.
In addition to the observatories mentioned in yesterday's issue of
this Bulletin, the fireball from the impact of fragment A was also
observed in the K-band (2.2 micron) with the PtSi camera mounted on
the SAAO 0.75 m telescope at Sutherland. It appeared at the predicted
location on the SE limb of Jupiter. The images were taken at 30 second
vintervals. The earliest faint signs of the fireball appeared at about
20:17-20:18 UT, and at peak brightness it was comparable in brightness
to Io. After 10 minutes, the fireball image seemed to change shape,
becoming elongated along the limb, presumably as the heated plume
settled back. The last traces along the limb were visible at least as
late as 20:38 UT. The rise in brightness was much faster than the
decline.
In the first report from Okayama Astrophysical Observatory (Japan),
J. Watanabe, T. Yamashita, H. Hasegawa, S. Takeuchi, M. Abe,
Y. Hirota, E. Nishihara, A. Mori and S. Okumura report observing the
plumes of C and D with Near-IR camera attached to 188cm telescope at
Okayama Astrophysical Observatory, National Astronomical Observatory
of Japan. The plume of C appeared 07:17 UT on July 17 on 2.36 micron
images and it was brightest around 07:21. The decay phase was followed
over one hour. The thermal plume of D appeared 12:01 UT on July 17,
and was fainter than that of C.
The SPIREX (South Pole) fragment D data were significantly compromised
due to the sudden onset of low blowing snow. The telescope was
heroically cleared of accumulated snow by Joe Spang of the AMANDA
project, and John Briggs of the ATP project, in strong winds at
temperatures of -60 degrees Celsius.
The impact of fragment D was detected just before 11:55 UT (July 17)
with the CASPIR infrared camera on the Australian National University
2.3 -metre telescope and the IRIS instrument on the Anglo-Australin
Telescope at Siding Spring. Both the CASPIR 2.34 micron images and the
IRIS K-grism cubes revealed a faint flash that faded within seconds;
it was four times brighter than the fragment C impact site (Peter
McGregor, Mark Allen, David Crisp, Vikki Meadows, Stuart Lumsden and
Jonathan Pogson).
Calar Alto reported the detection of the fireball from fragment E with
the 3.5-metre telescope in the 2.3 micron band. The event was first
noted at 15:17:30 and rapidly increased to more than 30 times the
brightness of Europa. By 15:23, the fireball has dimmed to less than
Europa's brightness. At 18:26 UT, three spots were visible, a bright
one just past the central meridian, a fainter one approaching the
central meridian, and the faintest one just coming over the East
limb. The positions of the spots corresponded to the predicted
locations of fireballs E, A, and C, respectively. At 2.3 micron, the
brightest spot was 15-20 times fainter than Io, and the fainter spots
were down by further factors of about 1.5 and 2.2.
SPIREX detected the fragment E impact site shortly after expected
impact at 15:18 UT on July 17, at a comparable brightness to fragment
A, at a wavelength of 2.36 microns. This data only became available
12 hours later as the South Pole communications satellites are only
intermittently visible from this distant site (Mark Hereld, Hien
Nguyen, Bernard J. Rauscher, Scott A. Severson Astronomy &
Astrophysics Center, University of Chicago, USA).
Impact E was seen at 10 microns with the CAMIRAS camera mounted on the
Nordic Optical telescope at about 15:17 UT. It was fainter than impact
A seen on July 16 (French-Swedish-Spanish team)
9-C. REFLECTIONS FROM THE MOONS
Heinz Barwig and Otto Bearnbantner observed the light of the Jovian
moons during the F-impact, but due to non-photometric conditions, it
will be difficult to decide whether a reflection of the initial flash
has been observed. The astronomers will continue these difficult
observations and hope for better sky conditions tomorrow.
Mike A'Hearn has performed CCD imaging at the Perth observatory
(Western Australia) of Io, Europa, and the limb of Jupiter did not
reveal any obvious flashes associated with the impact of fragments D
and E.
D. Rabinowitz and H. Butner at the Las Campanas observatory (just
north of the La Silla observatory) may have obtained an interesting
result. The believe that Io may have changed colour during the time
that fragment B impacted Jupiter. The spectrum became increasingly red
starting around 02:50 UT (July 17) compared to its colour 20 minutes
later and 3 minutes earlier. The reddening continued to increase until
2:53 UT. Then the color started to drop back to the color we
consistently observed from 2:57 until 3:07 UT. These observations
were obtained with a coronograph/spectrograph built by Steve Larson of
the University of Arizona. If Io's colour change is the effect of
reflected light from the impact, then the observations imply a
duration of 7 minutes for the impact flash from fragment B. This would
be an indication that fragment B was a diffuse cloud of large meteors
by the time it hit Jupiter.
9-D. SPECTROSCOPY
Spectroscopic observations of the plumes will be extremely interesting
in order to determine their composition. Will they for instance contain
unknown molecules which come from the inner part of the cometary
fragments or from deep down in the Jovian atmosphere.
Near IR spectra were recorded with the IRSPEC spectrometer at the
3.5-metre NTT Telescope with a 4.4 arcsec slit aligned along the
parallel of the impact sites. On July 17 around 01:00 UT, the 2.12
micron H2 quadrupole line was detected with a resolving power of 2000
at the position of the A impact site as it moved along the jovian
disk. On July 17, 22:30 UT, H3+ has been detected in 4 transitions
around the strong 3.534 micron line, with a resolving power of 1700.
The region of the emission appears significantly extended in longitude
with respect to the site of impact C (T. Encrenaz, R. Schulz,
J. A. Stuewe, G. Wiedemann),
A team of Milagros Ruiz, Chad Engelbracht, George and Marcia Rieke,
and Patrick Frawley observed the fragment A impact site with a near
infrared spectrometer on the Steward Observatory 90-inch telescope.
The spectrum of the plume, with the spectrum of the belt next to the
plume subtracted off, is flat and featureless between 2.1 and 2.4
microns. If the plume were frozen gas particles, most candidate
materials would have features in this range. The data were obtained
between 00:00 and 02:00 on July 17.
Sang Kim, Christophe Dumas, Jay Elias and Richard Elston have
unambiguously confirmed CH4 nu3 line emissions, which appeared in
their IRS/CTIO(1.5-m) spectra taken on the first impact area (A)
around UT 0:30 (July 17). They made a sophisticated model containing
Jupiter and Earth atmospheres and including Doppler shift between
Jupiter and Earth. The agreement between the model and the observed
emission structure is almost perfect. The covered spectral range is
between 3.47 and 3.6 microns. They did not see any notable increase
in H3+ emission around 3.53 microns, where a H3+ complex occurs.
Monitoring the H3+ ionospheric lines at 3.5 microns with CGS4 echelle
spectrometer on UKIRT, Mauna Kea, Hawaii, Steve Miller, Mary-Frances
Jagod, Tom Geballe and Tim Brooke saw a fivefold brightening of the
emission around the time of impact of fragment B (around 02:50 UT on
July 17) on the east limb of Jupiter. The spectrometer slit was
approximately aligned on the nominal impact latitude. This faded over
90 minutes.
Matt Griffin, Andre Marten, David Naylor, Gary Davis and Greg Tompkins
observed the HCN 4-3 line at 354.505 GHz on the James Clark Maxwell
Telescope. They tracked on the position of fragment B for over 1 hour,
but did not detect anything to antenna noise. Observations of the
location of the fragment C impact point over a 30-minute period as it
rotated into view produced a detection of HCN. The line half-width is
about 10 km/s. Subsequent observations did not result in a
confirmation of the detection, but Jupiter was setting and the system
temperature rapidly increasing. It is therefore not possible to say
whether or not the effect was short-lived.
The CGS4 instrument on UKIRT detected dramatic changes in the spectrum
near 3.5 micorn at the location where the C fragment struck
Jupiter. In addition to a bright continuum (where there previously was
essentially none), the relative strengths of pre-existing emission
lines of H3+ changed and many new lines appeared, very few of which
are identified by us at present. In particular, at the wavelength of
a previously undetectable "hot band" transition of H3+, a bright line
appeared whose strength surpassed that of all other pre-existing H3+
lines. A second line, unidentified at present, succeeded in
saturating its central pixel in a ten second exposure. Some of the
lines seem considerably (Doppler) broadened, but, due to the high
density of spectral features, confirmation will have to wait until
after the observers get some sleep. The emission faded with a 1/e
time of roughly 15 minutes. (Tom Geballe, Mary-Frances Jagod, Steve
Miller and Tim Brooke).
Observations were also conducted with the Fourier Transform
Spectrometer on the 3.5-metre Canada-France Hawaii Telescope. Impact
C was observed at the limb at the expected position. A strong, broad
emission was observed (near 3.3 micron) which could correspond to
methane thermal emission. This emission was observed to decrease
strongly within a few minutes. The impact sites A and C were observed
farther from the limb within a CO 1-0 filter (between 4.6 - 4.8
micron). Some variability in the spectra is observed compared to a
region outside the impacts. Further analysis of the data will be
necessary to determine if continuum variations can explain the
observed variability, or if some molecular absorption of Jupiter
constituents are changed. No obvious variation is observed within the
CO lines. (J.-P. Maillard, P. Drossart, J. Caldwell).
9-E. THE G-IMPACT
The nominal time is 09:29 CEST this morning. It is expected that the
first reports will begin to come in soon after 10:00 CEST. We shall
give more information in tomorrow's issue.
9-F. PRESS CONFERENCE IN SANTIAGO
On Sunday, July 17, at 12:00, ESO organised a Press Conference at its
offices in Vitacura, to inform the Chilean media about the important
observations that were made the night before of the first impact. More
than 50 journalists were present, together with the various Chilean TV
channels and CNN.
ESO astronomer Patrice Bouchet presented the latest news and described
the dramatic events of the night before. Printed material and photos
were distributed, and the many questions bore witness to the great
interest and desire for knowledge about this unique event. There were
many reports in TV and the newspapers in Santiago will today
undoubtedly publish much of this information.
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This daily news bulletin is prepared for the media by the ESO
Information Service on the occasion of the July 1994 collision between
comet Shoemaker-Levy 9 and Jupiter. It is available in computer
readable form over the ESO WWW Portal (URL:
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