Comet Hale-Bopp (August 1, 1997)

This is a summary of recent developments around this comet; the previous was published on the ESO Web on June 13, 1997. It is based on information received directly by email and also from IAU Circulars and on other Hale-Bopp WWW pages. A complete list of these Updates is also available.

Richard M. West (ESO) 
Munich, August 1, 1997 

1. Current state

Comet Hale-Bopp is now moving deeper into the southern celestial hemisphere; at the beginning of this month (August 1, 0 UT), it is located in the constellation of Canis Major (The Greater Dog) at declination -13 o , and less than 10 o from Sirius , the brightest star in the sky.

The distance from the Sun is 2.15 AU (322 Million km) and from the Earth, 2.87 AU (429 million km). It is moving outwards from the Sun at about 22 km/sec and is now approaching the asteroid belt beyond the orbit of Mars. It will `cross' the orbit of Jupiter at about 5.2 AU during the first days of May 1998.

The latest reported visual observations, most from Australia, indicate a magnitude of about 4, close to that predicted and about 100 times fainter than at maximum. However, since the comet is still quite near the Sun in the sky - the elongation (the Sun-Earth-comet angle) is now 37 o - it is not very easy to observe.

The tails have shrunk in size and only the dust tail is visible now. We now see it almost head-on and the tail therefore appears as a small extension in the south-west direction to the diffuse head.

Various overviews about the overall performance of Hale-Bopp have been published, some of which are also available on the WWW, e.g. Comet Hale-Bopp's Memorable Performance by Edwin L. Aguirre (Sky & Telescope).

Just a few days ago, Andreas Kammerer has called attention to the very comprehensive English/German-language Comet Webpage of the Comet Section of the German Society of Amateur Astronomers (in German: VdS-Fachgruppe Kometen; VdS = Verein der Sternfreunde - literally: `Society of Friends of the Stars'). This site contains many interesting references and includes, within the section on `Analysis of Currently Observed Comets', comprehensive information about Comet Hale-Bopp. Note also the rather complete light curve, displaying the observed heliocentric magnitude before perihelion.

2. New ephemeris

A new ephemeris is available for observers. While is has been computed specifically for the ESO La Silla observatory, the comet is now so far from the Earth that the indicated positions may be equally well used by observers from all other ground-based sites. They are based on elements published in April 1997 (the `newest' ones available at this moment).

3. New images

As long as Comet Hale-Bopp was very close to the Sun in the sky, it has not been possible to obtain conventional images with optical detectors. However,Hans-Ulrich Kaeufl (ESO) and Yan Fernandez (Univ. of Maryland, USA) recently succeeded in taking the first mid-infrared images after the perihelion passage from the ESO La Silla Observatory, by means of the TIMMI (Thermal Infrared MultiMode Instrument) at the ESO 3.6-m telescope.

An impressive CO + -image was obtained by Mike A'Hearn and Yan Fernandez (Univ. of Maryland) with the Lowell 8-inch Takahashi Astrographic Telescope (mounted on the 42-inch Hall Telescope) at Anderson Mesa, Arizona, on 1 May 1997 at 0330 UT. The exposure time was 300 seconds, and the detector was a 1-K Spectral Instruments SI500-32 CCD Camera with a narrowband `CO+' filter.

You will undoubtedly also enjoy the excellent images of Hale-Bopp obtained with the 60-cm telescope at the observatory of the Naturwissenschaftlicher Verein Osnabrueck on Oldendorfer Berg near Melle in northern Germany. This website includes a very interesting animation sequence (in AVI format) of changes in the coma between September 1996 and May 1997.

A beautiful photographic spectrum of Comet Hale-Bopp was obtained on April 2, 1997, by Austrian observer Johann Reifberger (Salzburg), by means of a Swarowsky-prisma in front of an objective (300/f5.5). It is here [GIF, 20k] and shows the individual colours in the comet's light. The blue part is mostly emitted by the gas in the coma, while the more diffuse, extended red part includes the sunlight reflected in the particles in the dust tail.

4. Meetings

Professional astronomers have been meeting this week in Cambridge (Mass., USA) at the 29th Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society. The programme includes several sessions (nos. 32, 34 and 37) on comets Hale-Bopp and Hyakutake.

Information about the Special Hale-Bopp session at the Kyoto General Assembly of the International Astronomical Union on Saturday, August 23, 1997, is now available on the Web. Abstracts of many of the oral and poster papers are included.

The Second Announcement of the Hale-Bopp Conference at Tenerife in February 1998 has been published, together with a provisional programme. Please note the deadlines for registration, etc.

5. More sodium observations

IAUC 6686 (June 24, 1997) contains more information about observations of sodium in Hale-Bopp.

M. Sakamoto and colleagues in Japan communicate: Neutral- sodium emission images of comet C/1995 O1 were obtained since Feb. 20, using a narrow-band filter set that was designed for neutral- sodium emission at 589 nm at the Misato 1.05-m reflector (+ liquid- N 2 -cooled CCD camera). The size of the images correspond to 500 000 km x 500 000 km. The most remarkable phenomenon is the 'sodium jet' structure released in the solar direction from the nucleus. The sodium distribution of the near-nucleus region resembles the dust profile, though the sodium jet slips off of the dust jet in the anti-solar direction. In a similar way, the Na distribution is more sensitive than is the dust tail to radiation pressure. More detailed information can be found on the web.

6. Spectroscopic observations

On IAU Circular 6681 (June 16, 1997), D. Reuter and colleagues report the measurement of infrared molecular-line fluorescence: Observations were made on Feb. 26.7, Mar. 27.6-27.9, and Mar. 28.6-28.9 UT [1997] using the Kitt Peak 2.1-m telescope (+ Phoenix cryogenic grating spectrometer; spectral resolving power about 50000). Lines..... were observed.... of OCS near 4.861 microns. We also observed.... the nu 7 band of C 2 H 6 near 3.344 microns. Preliminary analysis of the line intensities indicates a rotational temperature of less than 120 K for both species.....

Three days later, on June 19, 1997, N. Dello Russo and collaborators at NASA's Goddard Space Flight Center and elsewhere reported (IAUC 6682) the detection of infrared emission from OCS and CN in C/1995 O1, using the NASA Infrared Telescope Facility (+ CSHELL cryogenic infrared spectrometer) on Mauna Kea..... For a rotational temperature of 100 K, the production rate (x 10 27 molecules/s) of OCS was 3.4 on Apr. 16.2, and 3.2 on Apr. 30.1 and May 1.2. The water-production rate was 5 x 10 30... The mixing ratio is then Q(OCS)/Q(H 2 O) = 7 x 10 -4. The OCS lines were sharply peaked on the nucleus, while the CN lines were extended over the length of the slit (+/- 15 arcsec about the nucleus), as expected.

7. Molecular update

This is the latest version of the list of moleucles observed in Comet Hale-Bopp:

H 2 O, HDO, OH, H 2 O + , H 3 O + 
CO, CO 2 , CO + , HCO + 
H 2 S, SO, SO 2 , H 2 CS, OCS, CS 
CH 3 OH, H 2 CO, HCOOH, CH 3 OCHO 
HCN, DCN, CH 3 CN, HNC, HC 3 N, HNCO, CN, NH 3 , NH 2 , NH 2 CHO, NH 
CH 4 , C 2 H 2 , C 2 H 6 , C 3 , C 2 
Na, K 
O + 

and the following isotopes:

H 13 CN, HC 15 N 
C 34 S

8. Request for observations

On July 26, Alan Stern (astern@swri.edu) has sent the following request for ground based observations of Comet Hale-Bopp: In support of the STS-85 Shuttle/SWUIS imaging experiment for Hale-Bopp, scheduled to be performed between 11 Aug and 21 Aug 1997, the SWUIS experiment team requests broadband images of Hale-Bopp be obtained between 26 Jul 1997 and 05 Aug 1997. These images will be used to help prepare Shuttle mission specialists Dr. Steve Robinson and Dr. Dan Davis for the expected appearance of Hale-Bopp during their Shuttle mission, which is set to launch 07 Aug 1997. Drs. Robinson and Davis are not astronomers, but will have to visually acquire the comet in the SWUIS finder telescope in order to properly place the SWUIS CCD on the comet for the desired SWUIS UV/Vis observations.

As such, the SWUIS imaging science team (A. Stern, D. Slater, M. A'Hearn, P. Weissman, M. Hanner, J. Parker, and L. Paxton) ask to be informed (at astern@swri.edu) of electronically-available Hale-Bopp images obtained during the next 10 days.

More information on the SWUIS experiment can be obtained at URL: http://www.boulder.swri.edu/swuis/.

9. A very sad note

The worldwide community of cometary scientists is mourning three of its distinguished members whose untimely and tragic deaths occured during the past weeks.

Dr. Jurgen H. Rahe , Science Program Director for Exploration of the Solar System at NASA Headquarters, Washington, DC, died tragically June 18, 1997, in the Washington, DC, area. Dr. Rahe was killed during a severe storm when a large tree fell on his car as he was driving near his home in Potomac, MD.

Dr. Rahe originally came from Germany and worked for many years at the Bamberg Observatory. He later went to the USA and had a distinguished career in NASA and in the field of astronomy and space exploration. In his most recent position, he was responsible for overall general management, budget, and strategic planning for NASA's Solar System Exploration programs, including the Galileo mission to Jupiter and several upcoming missions to Mars, including the July 4, 1997, landing of Mars Pathfinder.

Planetary scientist Dr. Eugene (`Gene') Shoemaker was killed in a two-car accident near Alice Springs, Australia, on the afternoon of July 18. His wife Carolyn Shoemaker suffered broken bones, and was hospitalized in stable condition. A geologist by training, Shoemaker is perhaps best known for discovering, with his wife Carolyn and colleague David Levy, the comet (Shoemaker-Levy 9) that collided with Jupiter in July 1994.

Dr. Shoemaker took part in the Ranger lunar robotic missions, was principal investigator for the television experiment on the Surveyor lunar landers (1963-1968), and led the geology field investigations team for the first Apollo lunar landings (1965- 1970). In 1961, he organized the Branch of Astrogeology of the U.S. Geological Survey in Flagstaff, AZ, and acted as its director from 1961 to 1966. On his retirement from the U.S.G.S. in 1993, Shoemaker became a staff member at Lowell Observatory in Flagstaff.

Information has just been received that Prof. Vladimir Vanysek of the Astronomical Institute at the Charles University in Prague (Czech Republic) died earlier this week of cancer in a hospital in that city. A noted specialist on comets, meteors and interplanetary dust, he collaborated with Juergen Rahe, among others, and he later worked for a period at the Bamberg Observatory.

He was the chief editor of the international journal Earth, Moon, and Planets .

I had the privilege of counting all three among my friends. My colleagues and I dearly miss them.

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