The weather was perfect, with good seeing, good transparency, and not a single cloud or even thin cirrus ! It was a very good night for astronomical observations and the bright moon in the sky was a beautiful sight.
As feared (and expected), it turned out to be impossible to obtain any images of SL9 last night with the NTT or the Danish 1.5 metre telescope. Even if it would have been possible to keep Jupiter, now just a few arcminutes away, out of the camera field its very strong light would still have entered by multiple reflections in the telescope optics. It would most probably have damaged the detectors and the observers decided that it was too risky to try.
Exactly for this reason, the spider which carries the f/35 IR secondary mirror at the top of the 3.6-metre telescope was wrapped with black velvet to minimize the diffraction of the light and the spikes on the image. The TV camera of that telescope was also changed to a more suitable one, since the standard one is optimized for very faint objects.
The special infrared instrument TIMMI was mounted and is working fine and last night it was already observing Jupiter in all the filters which will be used during the next days. A fine occultation of the bright star Spica (Alpha Virginis) by the Moon was also monitored in thermal IR by TIMMI, as well as by a group of enthusiastic astronomers from the cat-walk! When the Moon moves in front of such a bright star, you can really see how fast is our satellite is moving in the sky.
The observations at the Dutch 90-cm have now really started. It will work in two modes: 1) taking images of the planet and 2) trailing the satellites on the CCD to record possible brightness variations. Both modes have now been tested, and give satisfactory results.
The Munich special high-speed photometer is also in good shape.
Among the SL9/Jupiter observers, Klaus Jockers and Keith Horne arrived on July 14th; Rita Schulz, Joachim A. Stuewe, Therese Encrenaz, Laurent Jorda yesterday, the 15th; the teams are now almost complete. Nick Thomas, Pierre Colom, Dominique Bockelee-Morvan, Didier Despois and Anne-Marie Lagrange will arrive today, since they start later.
Two Chilean teams have been to La Silla. The Canal 13 team was there
on the 14th and expects to present daily updates on the collision;
they filmed a lot of things and should have enough material. Last night,
the TV news of Canal 7 showed what they filmed on the 13th at La Silla. A
Chilean friend of one of the ESO astronomers, quite satisfied with the
fine presentation of the work at La Silla, but also having seen the
impressive beards of some of the observers in very close-up, called
the mountain and remarked on "the wild astronomers of ESO" !
The discovery and subsequent investigations of comet Shoemaker-Levy 9 have been documented in the Circulars of the International Astronomical Union (IAUC). Below is a condensed overview from this source of the major steps forward in our knowledge and understanding of this very peculiar object:
Date IAUC Information
On IAUC 6019 (July 14, 1994), T. Rettig, J. Hahn, S. Tegler and
G. Sobczak, University of Notre Dame; and M. Mumma and M. DiSanti,
NASA Goddard Space Flight Center, communicate that preliminary
analysis of images of the cometary fragments (excluding fragments T =
4 and P1 = 8a) obtained with the Hubble Space Telescope wide-field
camera between January and July 1994 shows that the inner 0.3 arcsec
regions have remained relatively constant or have slowly decreased in
brightness over the seven-month period. Similar results are noted
with larger diaphragms. The fragments show minimal brightness
activity through the May observations. However, for six fragments
observed during June and July, there is a rather dramatic brightness
decrease from the May observations. In a 1.1 arcsec diaphragm, five
fragments (W, V, S, R and H) show a brightness decrease by about 50
percent, and fragment U by about 30 percent. Also in the June and
July images, the brightness profiles of fragment P2 show a very much
more distributed source of dust within the inner 1 arsec. These
profiles indicate that the central source may have been disrupted and
may suggest initial tidal dispersal of the swarm material. We note
that between May and June most of the fragment images have become
elongated in the direction of Jupiter."
Zdenek Sekanina (JPL, Pasadena) writes in IAUC 6020 (July 15) that preliminary results of his analysis of CCD photometry obtained with the HST Planetary Camera in late January, late March, and early July 1994 suggest the presence of a major point source in the center of most of the condensations and offer consistent values for the dimensions of the largest fragments. Under a reasonable assumption about the reflectivity of the surface of the nuclei (4 percent of the infalling light in the red spectral region), Sekanina finds the following that the largest effective diameters (km) in Jan., Mar., and July, are: F: 2.3, -, -; G: 4.2, 3.6, -; H: 3.2, -, -; P1: 1.3, <1, -; P2: 2.4, -, -; Q1: 3.9, 3.0, 3.7; Q2: 3.2, 1.6, 2.4; R: 2.6, 2.7, 2.2; S: 3.6, -, -; T: 4, 1.4, -; U: 1.3, -, -.
The peak of the dust cloud is found to be displaced with respect to the primary fragment in the general direction away from the Sun.
Sekanina remarks that although the evidence points to an apparently continuing disintegration of the large fragments in numerous discrete events, objects a few km across still seem to have been present in early July, and the temporal variations in the effective diameters are likely to be primarily a rotational effect of strongly irregular shape.
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: http://http.hq.eso.org/eso-homepage.html) and by fax to the media (on request only). News items contained therein may be copied and published freely, provided ESO is mentioned as the source.
Sequence of images showing evidence for a plume near the terminator of Jupiter at the time of the A impact. A bright feature appears 1000-1500 km above the limb of Jupiter at 20:18:17 in the 953 nm filter. (An image at 20:15:17 did not show a detached feature). A possible interpretation is that the feature is visible by reflected sunlight, and the apparent detachment is due to the shadow of Jupiter on the plume. During the temporal sequence from top to bottom, spreading of the feature is clearly resolved. The feature is visible at wavelengths ranging from the ultraviolet through the near infrared.
Credit: HST Jupiter Imaging Science Team
