1997 Hale-Bopp

David McDavid, Limber Observatory, Pipe Creek, Texas

This image is a composite of eighteen 2 s exposures of the inner 5 arcmin of the coma of Comet Hale-Bopp, taken in red light (Cousins R filter with polarizers) betweeen 01:39 and 02:04 UT on March 29 with a Photometrics CCD camera (Thomson 512 chip) on the 0.4 m telescope at Limber Observatory. It has been processed with unsharp masking to bring out the "arcs" in the inner region of the coma. The mask was made by smoothing the original image with a Gaussian with a sigma of 7 pixels (about 6 arcsec), truncated at 3 sigma. Then 85% of the mask intensity was subtracted from the original image. Logarithmic compression and a false color table were chosen to show the surrounding coma as well as the nuclear region.

The gemstone connection: ISO links comets to stars and Earth's origin

ISO sees the same materials in Comet Hale-Bopp as in dust clouds around other stars," Crovisier comments. "A key ingredient of both stardust and comet dust is olivine in crystalline form. This is also one of the main constituents of the Earth's interior. Now we can say with real confidence that we stand on a congealed pile of mineral dust, like that contained in the comets swarming around the Sun 4500 million years ago." - European Space Agency Information Note N° 10-97 - Paris, 28 March 1997.

Comet Hale-Bopp yields secrets in the infrared, Cornell-NASA investigators say

Using a combination infrared spectrometer and camera designed and built by Cornell University researchers and attached to the 200-inch telescope at Palomar Observatory, Cornell and NASA scientists have made ground-based measurements in an effort to learn what kind of stuff the comet is sloughing off as it approaches perihelion, that is, its closest approach to the sun. Full Text

Richard M. West (European Southern Observatory's)

Did the nucleus split? I received on March 20 an email from David Bridges: "I believe that this image obtained on March 6.45 UT is showing a fragment being sublimated as it falls behind the comet. It appears it did not take very long to sublimate below the visibility of my camera.... The film I used was Fuji SG+ 400. The grain size is small. I got the opinon of a PhD at the university I attend, that it is not a film defect." While I cannot rule out that this photo documents a real splitting event, I am quite sceptical, for several reasons. First, in view of the large number of images being obtained at any time, it would be strange if it had not been recorded by somebody else. Second, a fragment of the indicated size and brightness would not normally disappear within a few minutes, nor hours. Third, from my own experience, this very much looks like a `double' exposure, during which the image of the comet `jumped', possibly due to a guiding problem. On Mr. Bridges' website, trailed stellar images are visible on the photo, but they are probably too faint to have resulted in double images, if this is the correct explanation.

March 27. Mark McCaughrean (Max-Planck-Institut fuer Radioastronomie, Bonn, Germany): There are enough bright star trails in the wide-field image to see that they all have small `companions' at exactly the same distance and position angle as the apparent fragment does from the body of Hale-Bopp. Thierry Pauwels (Royal Observatory of Belgium, Brussels): There is now no doubt that the effect is due to a `guiding error' (a `jump') during the exposure, or possibly a `double' exposure. Same considerations could apply to the image taken by Natale Suardi on March 16.

Gianluca Masi, Ceccano, Italy

Image taken on 21 march 03:18 UT, processed using Larson-Sekanina algorithm to underline jets and dust waves. Vixen SP R150S 15 cm f/5 reflector, CCD SBIG ST-7. Image processing: QMiPS32. Location: Ceccano (FR) Italy, 213 meters above sea level.

David McDavid, Limber Observatory, Pipe Creek, Texas

Here's a panel of 3 polarization images of Hale-Bopp from Limber Observatory. In these images of the inner coma of Comet Hale-Bopp, the brightness is proportional to the linear polarization. North is up, east is left, and the field is about 2.5 arcmin on a side. Each image was made by combining 3 separate frames taken with a Photometrics CCD camera (Thomson 512 chip) on the 0.4 m telescope at Limber Observatory, using polaroid filters with their transmission axes at position angles of 45, 90, and 135 degrees. The reduction was done with the IRAF task "linpol." Most of the polarization is due to the scattering of sunlight by the dust and gas of the comet, so it is useful for mapping features where the dust and gas are especially dense.

Richard M. West (European Southern Observatory's)

Hale-Bopp brighter than expected. Comet Hale-Bopp continues to surprise and during the last days, its brightness has risen steeper than the predictions. Mark Kidger provides the following comments, among others: If this linear brightening were to continue to perihelion, Hale-Bopp would easily go past magnitude -2, although this rate of increase surely cannot continue for much longer. Even if the light curve starts to flatten-out, as it should do, we can expect a maximum around magnitude -1.5 and certainly the comet will be no fainter than -1, although no comet should ever be relied-upon to behave itself beyond the last datum point.

The Tails. The ion tail as seen in the sky now spans an angle of the order of 15^o - 20^o, i.e. the real length is approaching 100 million kilometres! The tail appearance is characterised by the excellent separation between the blueish ion tail and the more reddish dust tail; this is due to the particular spatial geometry (current position of the Sun, the comet's orbit and the Earth).

Rotation of the nucleus. Further observations from Pic-du-Midi by L. Jorda and collaborators confirm a main rotation period between 11.20 +/- 0.10 hr and 11.65 +/- 0.10 hr. The motion is quite complex and there appears to be a superperiod (precession ?) of 22 +/- 2 days, i.e. not too far from the earlier period of variation of about 19 days, first observed in 1995.

Structures in the coma. Ring and spiral-like structures have been detected in the coma by K. Birkle and H. Boehnhardt on exposures from Calar Alto (Spain). Confirming observations were obtained by the European Comet Hale-Bopp Team with the 1m Jacobus Kapteyn Telescope of the Observatorio del Roque de los Muchachos. The astronomers also write that the observations were taken through a CN and a blue continuum filter and.... reveal both spiral-jet and arc structures.... A bright shell is also seen in both filters 20 arcsec to the southwest of the nucleus, which corresponds to a recently separated jet.... Assuming, as in IAUC 6583, that the two arcs are ejected by the same active spot and that the nucleus rotates with an 11.47 hour period we obtain an expansion velocity for CN of 1.3 km/s for a 60 degree rotation between arc emissions.

Russell Sipe

Has HB Nucleus Split Into Six Fragments? For several weeks now I have read reports of visual observations of Comet Hale-Bopp appearing to have a split nucleus. I have also read explantions suggesting there is no photographic evidence of the split and speculation that the visual observations of a supposed split or pseudo-nucleus was actually part of the jet plume activity. However www.halebopp.com has received a series of photos that would seem to support not only a split nucleus but a six-way split.

David McDavid, Limber Observatory, Pipe Creek, Texas

Comet C/1995 O1 (Hale-Bopp) at 11:27 UT, March 13, 1997. North is up, east is left, and the field of view is about 7 arcmin square. The main image is the average of three 1.2 s exposures with a Photometrics CCD camera (Thomson 512 chip) at the f/12 Cassegrain focus of the 0.4 m telescope at Limber Observatory. The inset is a polarization image of the inner coma, to the same scale as the main image, but with brightness representing linear polarization. It was constructed by combining sums and differences of images taken through four polaroids with their transmission axes oriented at 0, 45, 90, and 135 degrees. The "jet" and "ripple" structures in the inner coma are strongly polarized, from over 25% in the innermost jet to about 15% in the outer ripple. This is evidence that both structures are dense concentrations of dust that produce polarization by scattering sunlight.

Pavel Kubicek, Observatory and Planetarium, Teplice, Czech Republic. Images taken with 150mm (6") Maksutov - Cassegrain f/15 + Barlow lens 1.3x and Cookbook 245 CCD camera.

First Image shows envelopes and faint radial structures in inner coma of comet Hale-Bopp. Image is a mosaic of ten original, processed images taken at 2:24 UT (midtime of exposures) on 03/08/97, 20 seconds each. Second Image is a composite of sixteen original, processed images taken at 3:10 UT (midtime of exposures) on 03/10/97, 15 seconds each. Third Image is a sum of ten original, processed images taken at 18:40 UT (midtime of exposures) on 03/12/97, 12 seconds each. It shows dramatic changes in appearance of envelopes!

Junichi Watanabe, Public Information Office,National Astronomical Observatory, Japan

Synchronic Bands in Dust Tail of Comet Hale-Bopp. Several filaments in dust tail were recognized at least on March 6. The most prominent filament was located at 2 degrees apart from the nucleus, and extended over 24 arcmin. The P.A. of this straight, narrow filament is about 340 degree, which is almost coincident with the P.A. of the Sun-Comet line. We can recognize at least 5 similar filaments in the dust tail. The color of these filamentary structure is clearly that of the dust, which is shown in our RGB color composite picture taken on March 7.83 UT. Full Text

Richard M. West (European Southern Observatory's)

Will the nucleus split? The possibility of a splitting of the nucleus of Comet Hale-Bopp has been discussed on various occasions. This refers to more or less dramatic events, i.e. from the `breaking-off' of smaller pieces from this nucleus (the dirty snowball at the centre) to a complete `break-up'. In both cases, fresh surfaces would be subjected to the heating effect of the sunlight, resulting in an overall increase of the evaporation of gas and emission of dust particles and therefore an increase in brightness. The only feature of Hale-Bopp that may possibly increase the chances for a splitting is its incredible level of activity. There is no doubt that the continuing, extremely intensive outflow of dust and gas must create rapid changes near the vents on the surface and around the reservoirs within the nucleus from where this matter comes. That may conceivably lead to internal stresses, perhaps even cracks that may further widen so that smaller or larger pieces eventually `fall off'.

Spectroscopy. On March 4, J. M. Veal and collaborators in the USA and Taiwan report the detection of HCO+ using seven antennae of the Berkeley-Illinois-Maryland-Association Array (IAU Circular 6575)... We believe this to be the first detection of HCO+ in a comet. On the same IAU Circular, T. Kawabata and his colleagues in Japan report observations of sodium lines at the BAO 1-m telescope. It appears that the Na emission has an asymmetric spatial profile and is more extended toward the south (dust-tail side) than the north. On March 3, D. C. Lis and collaborators reported the radio detection of sulfur monoxide (SO), carbonyl sulfide (OCS), ionized carbon monoxide (CO+), and the cyanogen radical (CN) at the Caltech Submillimeter Observatory (CSO) on Feb. 20-23 (IAUC 6573). M. J. Mumma and colleagues have continued their observations at the NASA Infrared Telescope Facility in early March. The water production rate is running about 1e31 molecules/sec, and the spectral lines are bright. However, the continuum longward of 3 mum has brightened enormously since Jan. 21.5, so the line/continuum brightness ratio is small - typically 0.1 for bright lines.... We believe we are seeing the signature of organic grain emission in the continuum intensity vs. wavelength.

More about the jets. I have received a detailed message from F. Manzini and his colleagues (Istituto di Fisica dello Spazio Interplanetario del CNR di Frascati, Italy) concerning some Hale-Bopp images which they took on September 11 - 13, 1996, with a 33.5 reflector of SAS Observatory (Novara, Milano, Italy). More images were obtained on Feb. 9 - 22, 1997. They remark that 1) Both bursts (or bright `blobs') we observed (on Sept. 11 and Feb. 9), evolved from a single jet. This seems to us to speak against the Sekanina hypothesis about the origin of multiple Hale-Bopp jets (as reported in IAU Circular 6542 and in your Jan. 8 UPDATE, every double, symmetrical jet should arise from an emission cone of dust and gas produced by near-polar active areas continuously in sunlight). Really, if Sekanina is right, a burst inside a jet must produce a counterpart of it also inside a second, symmetrical jet. But both bursts we observed on both Sep 11, 1996 and Feb. 9, 1997, are located only in a single position! 2) The multiple shell systems are astonishing and difficult to explain, above all because they show different geometrical centers.

Alain Klotz, Pic du Midi Observatory, France

This image is the result of the substraction between one image taken on March 5.24 and one other taken on March 4.25. Bright areas are seen at the outer edges of the Z features. It is the demonstration that the dust flow expands from the nucleus. The nucleus can be seen by the two perpendicular small bars. The scale of 1 arc min is the vertical bar on the left. North is down. Image taken with the infrared camera (MOICAM) on the Telescope Bernard Lyot .

Pavel Kubicek, Observatory and Planetarium, Teplice, Czech Republic

Mosaic of seven original images taken at 4:10 UT (midtime of exposures) on 03/05/97, 11 seconds each with 150mm (6") Maksutov - Cassegrain f/15 + Barlow lens 1.3x and Cookbook 245 CCD camera. Image is a result of processing of the same images and reveals inner coma structures - envelopes present there (they are not an artefact of image processing), caused probably by rotating jets.

Nick James, Chelmsford, United Kingdom

Taken from Chelmsford, UK (05:46 UT ) using a 0.30m, f/5.25 Newt. + SX CCD. Both the main image and the inset have been processed using unsharp masks. The images shows structure in both the inner and outer coma with around seven jets and at least five "waves".

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