1997 Hale-Bopp

ESO Observations Show Persistent Dust Jets at Comet Hale-Bopp Text & Images

After having passed behind the Sun (as seen from the Earth), Comet Hale-Bopp is now again well visible to observers in the southern sky. Although this famous object is now three times farther away than when it passed its closest point to the Sun (the perihelion) on April 1, 1997, it is still quite bright, especially when compared to other comets that have been observed at the same distance. Its magnitude is now around 5, i.e. when seen in a dark sky it is just visible with the unaided eye. However, it is seen better through moderate-size binoculars and is of course still more interesting when observed with a large, professional telescope. The dust tail is now about 2 degrees long when seen under good viewing conditions (no moon). It will probably be possible to follow the comet with the unaided eye for another 1, perhaps even 2 months. New observations at ESO now show persistent dust jets at Comet Hale-Bopp. Thus, the comet is still very active.

Hal Weaver, Johns Hopkins University, Hubble Space Telescope HB-STIS Principal Investigator

The above image is a composite of two STIS CCD exposures taken at 04:05 UT (2 sec integration) and 04:06 UT (20 sec integration) on 27 Aug 1997. The heliocentric and geocentric distances of the comet were 2.476 AU and 2.989 AU, respectively. A "long-pass" filter was used that transmits all light longward of approximately 5500 angstroms (10 angstroms = 1 nanometer) and rejects light shortward of that wavelength. The image has been divided by a circularly symmetric image that gives the best match to the azimuthally-averaged surface brightness profile of the comet. The azimuthally-averaged image has been subtracted from the data. This "ratio" image thus shows the deviations of Hale-Bopp's dust production from spherically symmetric, steady-state outflow. We see from the above image that Hale-Bopp is still clearly showing the strong jet activity that started becoming prominent towards late summer in 1996.

Olivier Lardiere, Haute-Provence Observatory (France)

On May 8, 1997, a huge concentration of dust is ejected from the nucleus toward the anti-solar direction. (Hale-Bopp on May 8, 1997 at 19h44 UTC. Sum of 5 exposures of 2s each, with I filter, unsharp masking. Field of view: 3.6'x3.6'. North is on left, East is up.) Full Text & Images

• more images

Ian Griffin, Astronaut Memorial Planetarium & Observatory, Cocoa, Florida

1. 16 x 20 second exposures of Hale Bopp, taken through a Lumicon Swann Band filter have been processed using a rotational gradient filter, with rotation 10 degrees and amplification 10. Images obtained using 12 inch Maksutov, with SBIG ST8 CCD working in HIGH RESOLUTION MODE (9 micron Pixels) Images obtained between 01:00 and 01:30 UT.

The "tails" of Hale-Bopp. During the night of the first of May we observed the differents features of the comet tails with a sodium filter to see the Na neutral emission, but also with a H2O+ filter, a B filter to see C0+ emissions and a continuum filter. The goal of the observations was to compare the morphology of the "differents tails". On May 2nd we have made a 26 minutes exposure through our 2.8 nm wide interference filter centered on the 579.3 nm sodium D line. The sodium feature is about 9 degrees long (90 000 000 km), and incredibly narrow. Text & Images

The mysterious shells around the nucleus are still active, even if the comet brightness is fading, . More, the simple concentric system is now becoming more complex : on this image taken on May 2nd evening, at least three different shell systems are visible. This image was obtained with the 105 centimeter telescope with a Gunn 6 filter.

Neutral sodium from comet Hale-Bopp: a third type of tailAbstract & Paper (Oct 2 1997)

Isaac Newton Group on La Palma, 2.5m Isaac Newton Telescope. Observations carried out in the past few days to study the distribution of sodium atoms in Comet Hale-Bopp have led to the discovery of a new type of comet tail. Sodium atoms have previously been seen near the centers of other comets, but these observations reveal for the first time in Hale-Bopp a straight tail of sodium atoms 6 degrees long. At the instigation of Gabriele Cremonese of the Padova Astronomical Observatory Italy, Don Pollacco of the Isaac Newton Group made several exposures of the comet through a narrow filter that isolates emission from sodium atoms. To their great surprise the astronomers found that these atoms are distributed over an enormous region in and around the comet. Contrary to earlier observations of bright comets near the sun, the sodium was present not only in the region next to the cometary nucleus, there were also large amounts in the region of the cometary tails. From spectra obtained on Apr. 19 and measured velocity distribution and surface brightness along the tail, it would appear that the data are consistent with a model in which neutral sodium atoms are released from still-unidentified sources within the coma and then accelerated in the antisolar direction by simple fluorescence. Full Text & Image

Detection of the neutral sodium tail confirmed by POLAR satellite scientists TextImage

Zdenek Sekanina (IAU Circular 6636, April 25) reports: Available information on the sodium tail shows that sodium atoms could not be released directly from the nucleus or from dust grains of any size (visible or invisible). The first option is eliminated because of the short destruction lifetime, the second - in addition - because the accelerations on all particulates in comets are more than one order of magnitude lower than required. Thus, a sodium tail of this kind would in the best case trace the leading boundary of the dust tail. The most probable parents consistent with observation are sodium-bearing molecular species with relatively long dissociation lifetimes, which could have been initially released from the comet in dust particles but separated soon after their ejection..... .

Alan Fitzsimmons, Gabriele Cremonese (IAU Circular 6638, April 28) reports: The 4.2-m William Herschel Telescope at Observatorio del Roque de los Muchachos was used on Apr. 23.9 and 24.9 UT to obtain spectra with a 4.5 x 1.1 arcsec slit at various positions on the dust tail up to 2 deg from the nucleus. Broad sodium emission lines were seen at all locations, with a blue edge corresponding to the geocentric velocity of the comet and a width of typically about 50 km/s. These observations imply that dust grains are a major source of sodium in this comet.

The sodium tail confirmed by the Pic-du-Midi team (April 29) Text & Image

Comet Hale-Bopp ion tail may be disrupted: NASA/ESA scientists on "watch" status

NASA/ESA scientists say that between 28 April and 15 May, comet Hale-Bopp and especially its blue "ion" tail will be most susceptible to influences from the Sun's solar wind and magnetic field. Its ion tail is expected to begin showing fluctuations, kinks, and perhaps moving structures. Also, it is possible that a disconnection event might occur, when the ion tail breaks off from the comet's head and reforms a few hours later. Full Text

HUBBLE AND IUE HALE-BOPP OBSERVATIONS SURPRISE ASTRONOMERS

D. Savage, NASA HQ; T. Jones, NASA GSFC; R. Villard, STSI; E. Venere, Johns Hopkins

Completing an unprecedented year-long study of Comet Hale- Bopp using two NASA observatories, the Hubble Space Telescope and the International Ultraviolet Explorer, astronomers report that they are surprised to find that the different ices in the nucleus seem to be isolated from each other. They also report seeing unexpectedly brief and intense bursts of activity from the nucleus during the monitoring period. Full Text

M. J. Mumma and V. A. Krasnopolsky (NASA-GSFC, IAU Circular 6625-April 14) report the detection of soft X-rays, He I (58.4 nm), and O II (53.8 nm) during 1996 Sept. 14-19 UT (r = 3.07 AU) with the EUVE orbiting observatory.... The central brightness was displaced from the nucleus by 140 000 +/- 60 000 km in the sky plane. A region of extended x-ray emission is also seen, and this is anticorrelated with the dust jets imaged simultaneously in the visible. He I 58.4-nm and O II 53.8-nm lines were detected with S/N = 4. The absence of Ne lines shows a depletion of Ne in the comet by more than 25 times relative to the solar abundance.

Infrared radiation from comet Hale-Bopp

By Chandra Wickramasinghe and Sir Fred Hoyle, naturalSCIENCE

Laurent Jorda, Max-Planck-Institut fuer Aeronomie, Lindau, Germany (IAU Circular 6620, April 9) The apparent rotation of the nucleus was clockwise on images obtained before Feb. 1997 and became distinctly anticlockwise during March, showing that the north pole is now directed toward the earth. The spiral jets appeared straight on visible and infrared images taken at Pic du Midi Observatory on Mar. 1 +/- 2 days, showing that the line of sight crossed the equatorial plane of the nucleus at that date. This implies that the source of the bright jet observed since January is located in the northern hemisphere. This jet, observed in the hemisphere directed toward the sun, now has the appearance of concentric arcs with increasing curvature....

Physicist Finds Similarities Between Comet Hale-Bopp and Comets Outside Earth's Solar System. University of Cincinnati astronomer Michael Sitko and his collaborators have found similarities between the composition of Comet Hale-Bopp and what appear to be similar-sized comets in other solar systems. "They're almost identical," said Sitko, an associate professor in the physics department at UC. "We compared the spectrum of our star with the spectrum of Hale-Bopp. It looks as if the material we see in these stars is exactly equal to the material that's being seen in Comet Hale-Bopp." Full Text

Three images of Observatoire de Haute Provence illustrate the changes taking place in the plasma tail of Comet Hale-Bopp after perihelion passage. They were taken by Eric W. Elst on 2, 4 et 6 April 1997. Note that Louis S. Binder, Houston Astronomical Society Clear Skies, Texas reported the appearance of a `second ion tail' on April 5.

Joao Porto, Azores Islands

April 7th was the best night since last couple months. I`ve just got this HB images obtained with the Sirius CCD camera,the CWIP-S model and the ETX 90mm f/13.8 with exposure times between 2500 and 5000ms. Some images after been treated with the PaintShopPro software revealed a secondary nuclei and 3 main fountains. I don't know if anybody else got some results with this kind of HB images.

Jean Lecacheux, Francois Colas, Pic du Midi Observatory, France

Image 2 hours after perihelion showing a double shell system. This image was taken on April 1st, at 5h03 UT just after comet perihelion (April 1st, 3H18 UT). This image is representative of our extensive comet survey using Gunn 6 filter and the 105 cm telescope. The comet is now difficult to observe in the morning sky, we can point the telescope only 1 hour before sunrise, the comet is at only 10 degrees of elevation. The image was processed with a radial gradient to enhance the shell structure. The dust shells visible since the end of january are now showing a double structure. Each "wave system" have the same interval but not the same curvature. This double structure have to be study in relation with the two jets now clearly visible, close to the nucleus.

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1997 Unusual Observations Synthesis

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