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Hale- Bopp ESO Press Releases

Richard M. West, ESO

______ESO Press Releases

Comet Hale-Bopp Update (August 2, 1996)

This is a summary of recent developments around this ; the previouswas published on the ESO Web on January 9, 1996. It is based on information received directly by email and also from IAU Circulars and on other Hale-Bopp WWW pages.

C/1995 O1 (Hale-Bopp) has been observed at AU). This distance then increases and reaches a many professional and amaterur observatories maximum of 455 million km (3.053 AU) in late during the past months. Various reports have October 1996 after which it will begin to appeared which all indicate that this decrease until it reaches its smallest value on extraordinary comet continues to develop in a March 22-23, 1997, at 197 million km (1.315 way that permits us to hope that it will indeed AU). become a beautiful and unusual sight early next Comet Hale-Bopp will thus remain quite far year. The following information does not pretend away from the Earth, over 13 times more distant to be complete, but rather to concentrate on some than bright that came within of the critical issues in this connection. 15 million km only, when it passed the Earth in late March 1996. Orbit and ephemeris Comet Hale-Bopp is now located in the Improved orbital elements and the southern constellation of Serpens Cauda (The corresponding ephemerides have recently been Serpent's Tail), well inside the bright band of the computed by Syuichi Nakano (Japan) and Don Milky Way. It moves steadily northwards and Yeomans (USA), based onmore than 1000 will pass the celestial equator on December 6. It accurate positions available up to July 1996. The will reach its northernmost position (+45 deg derived orbital elements agree very well and declination) a few days before the perihelion already now allow to predict the comet's passage. positions early next year to an accuracy of the During the period when it is brightest, it will order of 10 arcsec. There is little doubt that be best observable from the northern hemisphere. further observations will reduce this uncertainty In February and most of March 1997 the best to about just a few arcsec in due time. The orbital time will be in the morning twilight and later in calculations now definitively confirm that the the evening twilight. image found on a photographic plate obtained in April 1993, does indeed belong to this comet. Current appearance and activity The deduced (at perihelion) is Recent reports, many of which are published around 2500 years. However, this period changes on the List of Recent Comet Brightness with time because of the gravitational attraction Estimates by the International Comet Quarterly, of the large planets and it was apparently longer indicate that Comet Hale-Bopp reached naked- in the past. At this moment, it is not yet possible eye brightness (visual magnitude 6) in late June to calculate with reasonable accuracy the time of 1996. This, however, is only true for perfectly the previous apparation, but further positional dark sites; in most places, a small binocular observations will gradually improve this. It is not telescope will still be needed to see the comet. likely, though, that it will be possible to identify The size of the is now visually historical observations of this comet from the estimated at about 20 arcminutes and some earlier return. observers have reported a short dust tail of up to The perihelion passage takes place at about 0.5 - 1 deg, possibly even 1.5 deg. This tail will 3:22 UT in the morning of Tuesday, April 1, undoubtedly develop further during the coming 1997. The perihel distance will be about 136.8 months. From the geometry, it is almost certain million km (0.914 AU) and the comet will be that there will be interesting tail displays in early placed on the opposite side of the , as seen 1997. A set of predictions by Klaus Beisser from the Earth, cf. the view of the orbit. (Nuremberg) will be placed at this Website In 1996, the comet will make the closest shortly. approach to the Earth on August 3, at which time Interesting CCD pictures have been published the distance will be about 409 million km (2.733 recently on the Web, showing the gradual

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 2 ______ESO Press Releases development of the comet, e.g. at the Crni Vrh It would be important to know the size of the Observatory in Slovenia. Exposures with higher nucleus of Comet Hale-Bopp to support these spatial resolution have also been obtained in the estimates. Unfortunately, no further second half of July, for instance at the Calar Alto measurements, direct or indirect, have been Observatory (Spain) and with the Mons telescope reported, since an upper limit of about 40 km of the IAC on the Canary Islands, which show up was found from exposures with the Hubble to six jets in the inner coma. Space Telescope. Most astronomers believe that Thus there is little doubt that the dramatic it will turn out to be somewhat larger than that of outflow of dust from Comet Hale-Bopp's nucleus Comet Halley (largest dimension 15 km), but we continues. Moreover, an analysis of images cannot be sure yet. In the same connection, it has obtained with the ESO Schmidt telescope in not yet been possible to measure the rotation August 1995 ESO Press Photos 24a-c/95 show period of the nucleus. During the second half of that some of the dust must have emanated from 1995, outburst were seen to occur at a mean time the nucleus more than three years earlier. interval of about 19.5 days, but it is not certain Together with the April 1993 image which was that this really represents the rotation period. obtained when Comet Hale-Bopp was still nearly The further development of Comet Hale-Bopp 2,000 million km (13 AU) from the Sun, this will be followed with great interest. We shall proves beyond doubt that the comet was active probably have to wait until early 1997, before we already at a very large heliocentric distance. will know how bright this comet will become at The emission of gaseous species has also perihelion. been vigorous. CO molecules were detected already at a heliocentric distance of 7 AU and the Molecules in Comet Hale-Bopp current production rate at 4 AU is about 10e29 Due to its unsual brightness at large mol/s. From measurements of the OH emission, heliocentric distance, it has already been possible the water production has been found to be of the to observe Comet Hale-Bopp with some of the same order. This is very high when compared to best sub-millimetre telescopes in the world and other at the same distance. several molecules have been found during the past months. As was the case for Comet How bright will Comet Hale-Bopp become Hyakutake, some of these molecules are 'parents', in 1997? i.e. molecules which are emitted from the This is the most urgent question, now asked nucleus and which later break down into by all astronomers who prepareobservations for 'daughter' molecules in the coma. next year. As is usual in such cases, no one can Until the advent of infrared and sub- give an answer that is completely trustworthy. millimetre techniques, it was not possible to Nevertheless, the currently observed activity and observe the 'parent' molecules directly. Now, its continued and steady increase, combined with however, their numbers and distribution, as well the fact that this comet must have been near the as the motions, can be measured and already Sun several times before, makes it rather unlikely yield interesting clues about the composition of that it will deceive its many fans. the cometary nucleus. A current, conservative brightness prediction Information about these observations have is that Comet Hale-Bopp will reach a total visual recently been published on several IAU magnitude of at least -1 at perihelion. In fact, by Circulars. Another place to look for the latest combining about 300 amateur observations up to news on this front is the Comet Hale-Bopp (1995 the end of July 1996, Alan Fitzsimmons finds a O1) Observers' Bulletin Board and Archives at perihelion magnitude of -2.6. This calculation the University of Maryland (USA). In addition to also indicates that the , i.e. the above mentioned molecules, CO and H2O, the brightness the comet would have, it it were which were detected earlier at larger heliocentric seen at exactly 1 AU geocentric and 1 AU distances, the following have now been found: heliocentric distance, is extremely bright, H2S (IAUC 6408; May 27) and CS, H2CO, HCN actually the second brightest cometary absolute and CH3OH (IAUC 6421; June 19). A dramatic magnitude since the year 1450, after Comet increase was observed in the H2S production Sarabat of 1729. Nevertheless, Charles Morris between May and June. (So now we know that finds a less steep brightening, although itstill Comet Hale-Bopp does not smell good!) predicts a negative magnitude at perihelion.

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 3 ______ESO Press Releases

By means of optical spectra, the CN molecule, presumable a 'daughter' of HCN, was detected already in March 1996 (IAU 6361; March 28) and C2 and C3 emission was seen in April 1996 (IAUC 6400; May 17).

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 4 ______ESO Press Releases

Comet Hale-Bopp Update (April 01, 1997)

This is a summary of recent developments around this comet; the previous was published on the ESO Web on comet-hale-bopp-summary-mar25-97. It is based on information received directly by email and also from IAU Circulars and on other Hale-Bopp WWW pages.

basically with Alpha Aur, Beta Ori, and Sirius; Hale-Bopp passes perihelion the comet rivals , but it wasn't used because Comet Hale-Bopp passed its perihelion - the of the difference in color; to the naked eye, orbital point closest to the Sun - early this strongly-clockwise-curved dust fan spanning p.a. morning at about 03:19 UT. At that time the 340-350 deg; 10-deg gas tail near p.a. 5 deg (dust distance to the Sun was about 137 million km tail muchbrighter than gas tail) [Alfredo Pereira, and the orbital speed 44 km/sec. The distance to Cabo da Roca, Portugal]. the Earth was about 202 million km while the Mar. 28.07: to the naked eye, the comet looks comet was moving away from us at a speed of 13 like `Rigel with a tail', although the star is about km/sec. 7 deg higher up, and it is dramatically inferior to It is now located about 43 deg from the Sun in Sirius in brightness; there is a 10-deg ion tail in the sky and is moving at a rate of about 1.7 p.a. 3 deg and a broad 16-deg dust tail that is deg/day. he next perihelion passage will take initially directed toward p.a. 348 deg [J. Bortle, place some 2380 years from now, in the late 44th Stormville, NY]. century. The ion and dust tails, now seen on a competely dark sky background, have lengths of Where to observe the comet. up to about 20 deg and 15 deg, respectively. During the past week, the comet's magnitude The full span of the tails in the sky is only has been stable around -0.7. Hale-Bopp is now a visible at completely dark sites and after full wonderful evening object, high above the night adaptation of your eyes - this may take northwestern horizon. Don't miss this great from 15 - 30 minutes. It should therefore be no opportunity to see a really bright comet! surprise if you do not see a 20 deg tail the On March 25-26, Hale-Bopp passed a few moment you step out of your house! degrees north of the Great Andromeda Nebula, a Experienced observers, whose reports indicate galaxy similar to the Milky Way galaxy in which tail lengths of this order always prepare we live, and consisting of hundreds of billions of themselves carefully and know where to find the stars like our Sun. It is about 2 million light-years `darkest' sites before they estimate the tail distant, i.e. its light takes about 2 million years to lengths. reach us, travelling at a speed of 300,000 kilometres per second. The 'fuzzy spot' seen The intrinsic brightness south of the comet on those days by many As mentioned in the "comet-hale-bopp- observers with binoculars was therefore most summary-mar17-97-rw.html", Comet Hale-Bopp certainly this galaxy. is definitely one the intrinsically brightest comets ever observed. Observing conditions Jacques Sauval (Belgium) has commented on The present, optimal observing period will this point: Comet 1729 (Sarabat) with perihelion last until new moon on April 7, after which distance 4.05 AU and apparent magnitude m1 = moonlight will begin to interfere in the evening. 5 is also one of the most luminous comets The very best time will probably be during the (absolute agnitude H around -3; a probable first days in April when the comet is expected to diameter of about 100 km (?) as found in the be at its maximum brightness and the tails are the literature), but it remained barely visible to the longest and most impressive. naked eye, in addition to the famous and very As examples, here are two excerpts from bright comet of 1577. recent, typical reports by experienced observers, reflecting the importance of the observing About the tails conditions:Mar. 26.85: excellent conditions, The following email has been received from Zodiacal light is glaringly obvious; comparison Andrew Fastow in response to an earlier

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 5 ______ESO Press Releases comment, posted under `Latest News': After 6607 (March 29) that In observations at the reading your web site [March 30], I was walking NRAO 12-meter on March 23 UT we detected H along looking at the comet from 8,000 ft up in 2CS for the first time in Hale-Bopp....Assuming Utah [USA]. I recalled that your web site said the a rotational temperature of 80 K we derive a comet is 125 million miles away and its tail is 60 production rate of 5.4 x 10 26. OCS J(12-11) million miles long. It suddenly struck me that the [was] measured on March 22 UT ... [and] using tail should look much longer than it actually does the same temperature the production rate of OCS with the naked eye. If for example I was looking is 6.1 x 10/sup mol/sec. We also observed H2S at a 60 ft wide building from 125 ft away it and mapped CS during this period. would obscure much more of my field of vision N. Dello Russo (NASA) and colleagues than the tail of comet did. I would estimate that report (IAU Circular 6604, March 26) the the visible tail of the comet appears to be about 2 detection of water in Comet Hale-Bopp on Jan. million miles assuming it's 125 millionn miles 21.5, Feb. 23.9-24.1, and Mar. 1.7-1.9 UT, using away. Is this becaus the visible part of the tail to the NASA Infrared Telescope Facility (+ the human eye only a small fraction of the total CSHELL cryogenic infrared spectrometer) on length of the tail, or is the comet and thus its tail Mauna Kea....The water-production rate (x 10 moving at an angle such that the tail appears to x30 molecules/sec) was 2.7 on Jan. 21.5, 4.3 on be a lot smaller than it actually is? Probably a Feb. 23.9, and 4.0 on Mar. 1.8, assuming a combination of the two? Please could you rotational temperature of 70 K and an ortho-para- enlighten me on this issue; how much of the tail ratio of 2.45. After detailed data reduction, we is visible to the naked eye and what angle is the report that spectral lines of HDO (100 vibrational comet moving relative to a mountain top in band) were not detected, contrary to the report on Utah? Thank you. IAUC 6573. The preliminary reductions were The answer is indeed a combination of the adversely affected by high and variable telluric two effects - see also the remark above about the HDO. (`Telluric' means in the Earth's need to dark-adapt your eyes. Once you have atmosphere). estimated the angle spanned by the tail in the An account by astronomers from Ohio State sky, you may calculate the `true' length of the University and Lowell Observatory (USA) was tail. published in the journal. At some moment, it was thought that cyanogen gas is released only after a Grains in the coma comet has entered the H 2 O sublimation zone An infrared image of Hale-Bopp obtained (approximately when the temperature increases with the 200-inch telescopeat Mt. Palomar on to about the freezing point), i.e. at about 3.0 AU February 19 is now available at a (450 million km) from the Sun. However, these "http://www.news.cornell.edu/science/March97/c observations were made when Hale-Bopp was omet.lb.html"CornellUniversity sitte. It shows (at 6.5 AU from the Sun. Sublimation or evaporation wavelength 10.3 microns) thecomet and at this distance may be driven by things other submicron-size dust grains being ejected from than water - carbon dioxide or carbon monoxide, the surface as the comet is warmed by the Sun. for example. In this connection, the detection of Some of the grains are crystalline, in contrast to cyanogen gas in the (2060) Chiron the more amorphous structure of the rest, which was made some years ago at an even indicating that the grains were subjected to greater distance, is also of significance. strong heating sometime in their history, before On IAU Circular 6607 (March 29), M. K. they were incorporated into the frozen comet Bird (University of Bonn, Germany) and nucleus about 4.5 billion years ago. This photo collaborators at the Max-Planck-Institut fuer was taken using a combination spectrograph- Radioastronomie (MPIfR, Bonn), report the camera designed and built at Cornell for the 200- detection of ammonia (NH 3) in comet Hale- inch telescope at Mt. Palomar. The photo is part Bopp using the 100-m MPIfR radio telescope at of a Press Release referring to a corresponding Effelsberg near Bonn. They measured the three article in Science. individual K-band lines of this molecule, i.e. (3,3) at 23.870 GHz, (2,2) at 23.723 GHz, and More molecules observed (1,1) at 23.695 GHz and found that the lines Laura Woodney (University of Maryland) and are centered symmetrically on the velocity of the collaborators have announced on IAU Circular cometary nucleus. The full width at half-

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 6 ______ESO Press Releases

The Light Curve of Comet Hale-Bopp (April 04, 1997)

Mark Kidger (IAC, Tenerife,Spain) maximum of the (3,3) line is 1.6 km/s. No +0.5 last year (which lasted only very briefly), noticeable changes in the strengths of the lines hence Hale-Bopp appears to have been about 1.5 could be detected between the two observation magnitudes (a factor of 4) brighter. dates on Mar. 13.4 and 25.5. The observation of this molecule in a comet is a rare event.

The light curve of the comet through What about the comparison with Comet perihelion reveals various conflicting tendencies West? in estimates. This comet has what must be the reached about magnitude -3.5 best light curve coverage ever for a comet around very briefly around perihelion. However, it was perihelion and, with the vast archive of data not visible to the naked eye at this time (rather since discovery, is going to provide enormous like which also reached about quantities of information for future research. magnitude -3, but was only observable to the Here is a quick summary of the situation as of naked-eye for the Skylab astronauts in Earth yesterday: orbit). Comet West was only a negative magnitude object for a few days, while Hale- How bright did Hale-Bopp get? Bopp will remain negative magnitude for as The dispersion in magnitudes at perihelion much as 5 or 6 weeks in total. In this sense, was very large. The comet was large and Comet Hale-Bopp is a much brighter comet. The extremely condensed, making estimation very tail however was much more spectacular and tough. My own peak estimate was only -0.4, but better developed in Comet West. that was in very poor conditions in England (limiting magnitude around 4.5). Good observers How did the light curve develop in the end? in very good sites estimated much brighter It seems that the linear brightening stopped magnitudes on the whole. The estimate will about 3 weeks before perihelion. However, depend a lot on how the comparison was made many of the observations very close to perihelion by individual observers (I ended up using Mars are consistent with an almost unchanged rate of and Capella as my own comparison stars). This brightening right through. The point where the has a complication in that the comet, which is light curve most obviously flattens out conicides strongly blue, was a very different colour to the with the Full Moon in late March, so those best comparison stars and this can exagerate the estimates are not necessarily the full brightness peak magnitude which was estimated (red stars of the comet anyway. Even the faintest estimates appear rather fainter to the eye, so comparing (generally the ones by observers who estimated with red stars makes the comet seem brighter the magnitude in poorer skies), show the comet than it really is). still increasing in brightness steadily THROUGH The brightest individual estimate that I have perihelion. This is a major surprise because, in seen was -1.6, but this is an isolated point. From theory, the comet should have peaked in late good sites the peak magnitude seems to have March and then started to decline noticeably by been about magnitude -1.0+/-0.1 with the perihelion. At the moment it is a little hard to tell average peak magnitude being around - what happened to the light curve at perihelion 0.7. and after because some of the observations are consistent with both a small outburst at How much brighter than Comet perihelion, followed by a fade and others with a Hyakutake was Comet Hale-Bopp? slow increase in brightness even after perihelion. Another good question for the reasons given above. Hale-Bopp was definitely much brighter How does Hale-Bopp compare intrinsically and will remain brighter for some days than with other comets of the past? Hyakutake was at maximum. Most observers Very favourably indeed. If Comet Hale-Bopp estimated a peak magnitude of Hyakutake around had passed as close as Comet Hyakutake did last

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 7 ______ESO Press Releases year it would have been around magnitude -7 and perhaps the second or third brightest comet since the 17th century! Assuming a maximum magnitude of -1.0, the absolute magnitude of Comet Hale-Bopp was 1.3. These are the ten very brightest recorded values:

1729 Comet Sarabat -3.0 1577 Comet Tycho -1.8 1997 Comet Hale-Bopp -1.3 1747 Comet De Cheseaux -0.5 1811 Comet Flaugergues 0.0 1744 Comet De Cheseaux +0.5 1882 Comet Cruls +0.8 1914 Comet Delavan +1.1 1433 +1.2 1962 Comet Humason +1.35

For comparison, Comet Halley has an absolute magnitude of +4.0 and an "average" new comet is around +6.5. Comet Hale-Bopp is thus about 130 times brighter than Comet Halley at the same distance and 1300 times brighter than an "average" comet would have been.

How long is the tail? The longest estimates at perihelion, from dark sites were 20 degrees. This works out at exactly 1.0 AU, or 150 million km. This is a much longer tail length than for Comet Hyakutake and about 3 times the true length of Comet Halley's tail. We can expect the tail to grow even longer over the next couple of weeks.

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 8 ______ESO Press Releases

Comet Hale-Bopp Update (April 07, 1997)

This is a summary of recent developments around this comet; the previous was published on the ESO Web on "comet-hale-bopp-summary-apr01-97-rw.html". It is based on information received directly by email and also from IAU Circulars and on other Hale-Bopp WWW pages.

center of tail; telescopically, central axis of A brief introduction to this Update comet measured to be at p.a. 24 deg. Some of the news items presented below have already been displayed during one of the Where and when to observe the comet preceding days as Latest News at the "http://www.eso.org/comet-hale-bopp/comet- Here is a link to the "http://www.skypub.com/ hale-bopp.html" Comet Hale-Bopp Homepage. comets/charts/aprpm1.jpg" map of Hale-Bopp's They are here re-edited andcombined with other trajectory in April Telescope. items of the same general category with the aim Several visitors to the ESO website who are of providing a better overview of the current located in the southern hemisphere have been situation. asking when the comet will become well visible from the south. Hale-Bopp remains an impressive sight According to the "http://www.skypub.com/ It is apparent that in some media, the comets/hbguide.shtml" Observing Guidelines perihelion passage on April 1, 1997 was (where you will find the full details, including a presented as the absolute culmination of the section entitled `The View from the Southern current Comet Hale-Bopp show (expression Hemisphere'), by about the end of April, viewers quoted from various newspaper articles). While in South America, South Africa, Australia, and it is true that the comet's brightness probably New Zealand should be able to catch sight of the reached its peak at about that time, it would be comet very low in the northwest in early evening entirely wrong to believe that Hale-Bopp is no hours. In any case, the comet will cross the longer of interest! On the contrary, it now celestial equator on June 26, but it will then be appears that the exceptional, total brightness very close to the Sun in the sky persists and also that the tails are developing (22o) and not easily observable. further, see below. Later in the year, however, southern observers It is therefore strongly recommended to have with small telescopes will be able to enjoy it another look at this Great Comet, before the when it moves outwards. moonlight again begins to interfere, a few days from now. The comet's lightcurve John Bortle (Stormville, NY, USA) provides The mean of 11 estimates of the brightness on this recent, detailed observational account on the April 4-5 is -0.7 +- 0.2. This shows that the "//cfa-www.harvard.edu/cfa/ps/icq/ magnitude has remained virtually unchanged CometDesc.html"International Comet Quarterly since perihelion, one week ago. Descriptive page. The most recent lightcurve, currently Apr. 5.03: to the unaided eye, as viewed in- available on the Web, is that from focus, the comet's head matches the star Rigel (at "http://www.iac.es/ comet/obser.html #000" a similar altitude) in brightness; ion tail 13 deg in (Canary Islands, Spain), maintained by Mark p.a. 19 deg, dust tail 19 deg in p.a. 12 deg; w/ Kidger and, whenever possible, updated every 7x50 B, coma dia. 15', DC = 9, very broad dust day. A "phot-apr07-mk.gif" preview-, at this tail has several components or layers of moment updated with observations until April 5, brightness; w/ 41-cm L (70x), coma's sunward is available here. It shows a large spread in the radius is 5'.5; brilliant non-stellar nucleus estimates around perihelion, reflecting the surroundded by three bright envelopes inner- inherent difficulty of such estimates as well as most joined with nucleus at p.a. 246 deg; most the different methods of the observers. of coma, plus nucleus, distinctly yellow or orangish-yellow in color; great dust streamer in Is the ion tail `awakening'? tail very weak tonight; weak void or darkness in

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 9 ______ESO Press Releases

The dust tail continues to appear No further observations of new molecules comparatively diffuse, although there are have been published during the past days. interesting structures that are well visible on However, a most interesting "http://iram.fr/hale- high-resolution images. The total length, as seen bopp/comet.html" Hale-Bopp website with on a dark sky background, is estimated at about related information has been set up at the 15 deg. "http://iram.fr/" Institut de Radio Astronomie After a period of relative tranquility, there are Millimetrique (IRAM) in Grenoble (France) now signs of increased `activity' in the plasma whose powerful antennas in France and Spain (ion) tail, most probably as a result of the comet have been repeatedly used to observe this and entering more `turbulent' regions where the rapid other comets. particles in the solar wind interact with those The site includes a comprehensive graphical from the comet. Look for instance at the "phot- presentation (here reproduced in reduced format apr07-hm-small.jpg" image from Crni Vrh (half- for "phot-apr04-iram-small.gif" displaying the size preview version; JPEG - 29k) , obtained on evolution of the molecular production rates of April 2 by Herman Mikuz and his colleagues Hale-Bopp with heliocentric distance. Filled there. Access their "http://www.fiz.uni- symbols with error bars correspond to detections, lj.si/~herman/hbopp.html" site to get the full-size open triangles are upper limits. OH: black version, in which many fine details are visible. squares; CO: green circles; CHOH: blue squares; HS: red triangles; HCO: green squares ; HCN: The comet's motion black triangles; CS: red circles); CHCN: dark Today (April 7, at 12 UT), the distance from blue triangles; HNC: blue triangles. The vertical the Earth to the comet is 1.412 AU = 211.2 bars at r = 1 AU correspond to the ranges of million km. The corresponding light travel time molecular abundances measured in previous is 704 seconds or 11 minutes 44 seconds. The comets near perihelion. This clearly distance between the comet and the Earth is demonstrates the exceptional activity of Comet increasing at a rate of about 20 km/sec. Hale-Bopp. At that moment, the comet is 0.921 AU = 137.8 million km from the Sun; this distance Observing conditions increases by about 4 km/sec. The comet's orbital Some of the best observing conditions are speed is about 43 km/sec. those you find on the glaciers in the high Alps in Europe. A group of amateur astronomers from More about size the of the nucleus Tyrolia (Austria) has become quite known in the On IAU Circular 6609 (April 2), H. Matthews Central European area for their photographic (JAC, Hilo, Hawaii and National Research expeditions into such territory. Many of their Council of Canada) and colleagues report about impressive images may be accessed at their the first images of Comet Hale-Bopp obtained German-language http://sunkisti.uibk.ac.at/nori" with the SCUBA bolometer array at the James Hale Bopp page (a "phot-apr07-nori-small.gif“ Clerk Maxwell Telescope on Mauna Kea: here a small-size preview - 54k. Don't worry Images taken at 850 microns on Mar. 30.92 about the spelling mistake in the cxomet's name - UT show an approximately spherical coma that is the images are splendid! This website also has extended relative to the 14 arcsec diffraction- fine views some of the very harsh places from limited resolution..... The surface-brightness where the photos very made "phot-apr07-nori- profile appears slightly steeper than expected on site-small.gif" (small size preview from the the basis of steady-state ejection. The inferred Nockspitze (Nock Peak) - GIF; 30k). central excess (210 mJy) places a strong upper limit of 49 km to the radius of the nucleus. This Hale-Bopp on the Web limit is about twice that inferred from Following a very hectic time around observations in 1996 with the Hubble Space perihelion, it would appear that the Hale-Bopp Telescope and recently related traffic on the Web is now slowly abating. "http://oposite.stsci.edu/pubinfo/PR/97/08/PR.ht This is most likely a combined result of ml". exceptional media interest at that time and a certain `saturation' - by now, many people have Spectroscopic observations seen the comet and realised that it does not look very different from evening to evening. In fact,

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 10 ______ESO Press Releases many members of the public may have gotten the perihelion on March 14, 1997. It is now being impression that it is quite normal that a bright observed with professional telescopes, but it is a comet like Hale-Bopp should be visible for such relatively faint object, especially when compared a long period! If so, they do not fully understand to Hale-Bopp. how privileged we all are at this moment. Also NASA in the USA is planning a Nevertheless, the overall interest in Hale- cometary mission with the Bopp is still very high and the number of hits per "http://pdc.jpl.nasa.gov/stardust/home.html"Stard day at the ESO site runs into tens of thousands. ust spacecraft. A 1999 launch is planned that will How many Hale-Bopp sites are there on the capture samples of from the comet WWW? Nobody knows for sure, but when Wild 2 in 2004 for return to Earth in 2006. Also running the search Engine at the this comet is observable in 1997. For more "http://altavista.digital.com/"AltaVista site with information, see this "http://galileo.ivv.nasa.gov/ the search string `Hale' NEAR `Bopp' (i.e., the comet/news67.html"report. word Hale is within 10 words of the word Bopp, The Stardust spacecraft is protected from ensuring thatthe document really refers to the oncoming cometary particles with a front comet) results in about 6000 documents Whipple Bumper, a shield named for renowned matching the query! It is obvious that not all of astronomer Fred Whipple (who first described these are bona-fide Hale-Bopp sites, but the the `dirty snowball' nucleus of a comet and who number is still impressive and clearly shows the recently celebrated his 90th birthday), with a great interest in this event. By the way, adding composite structure that includes metals and the word ESO to the search gave about 300 several curtains of the same material as bullet- matching documents; adding gave about 700. proof vests. However, the bumper does not offer "http://www.jpl.nasa.gov/comet/"JPL Hale- unlimited protection against a barrage of Bopp site now comprises nearly 2600 images, numerous, large particles. mostly obtained by well-equipped amateurs. It would be interesting to learn whether use of this The return of a famous comet enormous material for scientific purposes is While the entire world is now following planned anywhere? Although this collection is Comet Hale-Bopp with great interest, it has gone clearly very inhomogeneous in terms of almost unnoticed outside professional circles that resolution and overall quality for such purposes, another famous comet for which recorded these images do provide a continuous record of observations date back to the year 1366, is now the development of the comet, in particular the being observed with some of the largest tails and the major structures in the coma. telescopes in the world. Although such a project would demand a large This comet is known as Tempel-Tuttle and it effort, it would indeed be a pity, if this unique is the parent body of the Leonid meteors, which opportunity would remain unused! are visible in early November each year. This means that the dust grains that cause the Space-based observations of comets numerous `shooting stars' when they enter the Cometary scientists all over the world are Earth's atmosphere at this time, originally come following the preparation of space missions to from this comet. You may learn more about all of comets with great interest. More information this if you read the detailed about two of these has just become available. "http://www.eso.org/astronomyonline/market/col The "http://www.esrin.esa.it/htdocs/tidc/info/ laboration/meteor/"information about a 1997/9711.html" Rosetta mission by the collaborative project on the Leonid meteors that "http://www.esrin.esa.it European Space Agency took place within the "http://www.eso.org/ (ESA) aims at the soft landing on the nucleus of astronomyonline/"Astronomy On-Line Program Comet Wirtanen in 2013, at a time when the me. comet is at aphelion, the point in its orbit farthest On March 10, 1997, a message was published from the Sun. This will ensure that there are in IAU Circular 6579 that Comet 55P/1997 E1 relatively few dust particles around the nucleus (Tempel-Tuttle) had been recovered on CCD which may hurt the spacecraft and endanger this frames obtained on March 4 with the 10-metre mission during the final approach. Keck Telescope at Mauna Kea (Hawaii) by Comet Wirtanen moves in an elliptical orbit Karen Meech and her collaborators. One of with a period of about 5.5 years. It passed its these, Olivier Hainaut, reported the

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 11 ______ESO Press Releases corresponding astrometric measurements on the better than 1999. (From a UK RAS Press Release Keck frames and also on a frame from the ESO of April 7, 1997) 3.5-metre New Technology Telescope (NTT), taken 3 days later by a group of astronomers at La Silla.

Olivier Hainaut has also prepared a composite photo; it is available here in two versions ("phot- apr05-oh.gif"[GIF; 432k] and "phot-apr05-oh- small.gif"[GIF; 120k]) and shows the point-like image of the comet's nucleus among the trailed images of stars (because the telescopes were set to follow the comet's motion). At the time of these observations, it was about 3.6 AU (540 million km) from the Earth and 4.4 AU (660 million km) from the Sun. The magnitude was about 22.5, i.e. about 60,000 times fainter than Comet Hale-Bopp was at the time of discovery at nearly twice the distance. This again shows the exceptional activity of the latter! Comet Tempel-Tuttle has a period of 33.2 years and the earliest recorded observations which can be associated with it, were made in October 1366 by Chinese, Japanese and Korean astronomers. Among the periodical comets, Comet Halley is the only one for which earlier observations are available. It was next seen in October 1699 by Gottfried Kirch in Germany. At the return in 1866 (when it was first seen by the two observers whose names it now carries), some astronomers noted the similarity between the orbits of the Leonid stream whose bodies give rise to the Leonid meteors and this comet. This was the first time that the close connection between comets and meteors was demonstrated. Comet Tempel-Tuttle will come within 0.356 AU (53.3 million km) of the Earth on January 17, 1998, just before it passes it perihelion on February 28 at a distance of 0.977 AU (146.1 million km) from the Sun. It is not expected to reach naked-eye brightness at this apparition, but should become well visible in small telescopes at magnitude 8-9. The Leonid is expected to produce a particularly spectacular display in November 1998 according to Iwan Williams (Queen Mary and Westfield College, University of London, UK). He will present his findings at the UK's National Astronomy Meeting at Southampton University on April 11, 1997. The Leonids produce grand displays about every 33 years, just after the return of the parent comet. The last time was in 1966, but 1998 could be

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 12 ______ESO Press Releases

Comet Hale-Bopp Update (April 13, 1997)

This is a summary of recent developments around this comet; the previous was published on the ESO Web on April 7, 1997. It is based on information received directly by email and also from IAU Circulars and on other Hale-Bopp WWW pages.

against a darkish sky till May 24. However, I A brief introduction to this Update think the viewing will be better in early May Some of the news items presented below have when the comet will be brighter. Note also the already been displayed during one of the very useful information contained in the News preceding days as Latest News at the ESO Comet Bulletin from Sky and Telescope that is updated Hale-Bopp Homepage. They are here re-edited every Friday. and combined with other items of the same Additional information about Comet Hale- general category with the aim of providing a Bopp, including the coverage of the associated better overview of the current situation. media event, is available at the CNN interactive - a stargazer's guide site. 1. Less optimal viewing conditions The viewing conditions are now rapidly 3. The brightness deteriorating, as the Moon moves higher in the The mean of 13 visual estimates of the evening sky, increasingly illuminating th brightness of Hale-Bopp obtained on April 6 - 8 background around the comet. This condition was magnitude -0.6 +- 0.2. On April 10 - 12, the will last until a few days after the next full moon mean was slightly fainter at -0.5. This is still on April 22. Then it will again become possible somewhat brighter than that predicted from a to enjoy the comet in a dark sky, but for a shorter simple extrapolation of the pre-perihelion time than before, as it will be seen progressively observations. This is a typical effect, observed in closer to the Sun in the sky. many comets, including Comet Halley in 1986. The reason why many comets are relatively 2. Comet Hale-Bopp soon visible from the brighter after perihelion is connected to the south effects of cumulative heating - at the same As the comet continues its motion towards the distance from the Sun, the overall temperature of south, now at a rate of about half a degree per the surface of the nucleus is higher after day, observers on southern continents may perihelion than before. Thus the gas and dust finally begin to get a glimpse of the beautiful production is higher after perihelion, resulting in sight that has fascinated their northern colleagues an asymmetrical lightcurve. during the past months. Preparations are now On April 9, the experienced amateur underway in Australia, South Africa and South astronomer John Bortle (Stormville, NY, USA) America to `receive' Comet Hale-Bopp in th noted that: comet clearly not as brilliant as three appropriate way. nights ago; ion tail traced 6 deg ... with naked For instance, Anthony C. Beresford eye, 10 deg with 7x50 Binocular; dust tail (Astronomical Society of South Australia - immense, very broad near its terminus, stretching ASSA, Adelaide) draws attention to the ASSA 21 deg with the naked eye ... the nucleus looks Website which contains a viewing guide with an like a star ... three envelopes, all weaker and animated diagram of the horizon path for Hale- more diffuse than previously ... only just a trace Bopp for 35 South latitude. The time shown of the great dust streamer in the comet's tail (18:15 Adelaide time) corresponds to 18:02 tonight, and the tail void has essentially filled in Local Mean time. It fits the observing conditions completely... for Sydney, Adelaide, Auckland and Capetown (South Africa), as well as in Chile at 4. Changes in the ion tail the latitude of Santiago (beware that the The length of the ion tail is currently mountains there may obstruct the view!). He estimated as 10o - 15o. No reports have yet been adds that if one applies the standard astronomical received here about observations of the expected criteria, also espoused by ASSA member Bill effects on this tail, caused by the recent, major Bradfield, here in Adelaide, we won't see it outburst on the Sun. This event which was

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 13 ______ESO Press Releases extensively covered by the press, resulted in a periods remai virtually unchanged at 4206 and temporary increase in the number of particles 2380 years, respectively. There are three ejected, i.e. in a higher intensity of the solar additional sets of 3-hour ephemerides at this site wind. This will normally lead to rapid changes in geocentric' as well as for observers from the La the ion tail and it is therefore likely that a study Silla (Chile) and La Palma (Spain) observatories. of wide-field images obtained during the past On April 13, at 12 UT, Comet Hale-Bopp will days will show the related effects. be 1.489 AU (222.8 million km) from the Earth, Sergio A. Ilovaisky (Observatoire de Haute corresponding to a light travelling time of 743 Provence, France) calls attention to the recent seconds (12 minutes 23 seconds). It will be 0.941 images on their OHP Hale-Bopp Web page, in AU (140.8 million km) distant from the Sun and particular three impressive ones taken by Eric W. the orbital speed is about 43 km/sec. Elst with the Schmidt telescope on April 2-6 and In the evening of April 12, I received this showing the dramatic changes in the ion tail at email from Al Rubin ([email protected]): that time in great detail (texts in French and Hi. I'm an amateur skywatcher who follows the English). progress of comets by plotting the positions of comets on a sky chart. I've done this with four of 5. The dust tail them so far. I've noticed an interesting A truly amazing dust tail length of 42o was coincidence that I believe others would reported by C. Miranda and C. S. Morris on appreciate but I don't quite know how to reach April 9.2 UT, from observations at Whitaker them. I'm e-mailing you to solicit any suggestions Peak (California, USA). They write that the that you may have for disseminating the comet brightness [is] less than last night's obs., information, which is that the position of Hale- but the dust tail is definitely longer; spent a lot of Bopp, on April 9, 1997, was in almost exactly obs. time examining and tracing the dust-tail the same position that Hyakutake was on April 9, length; the dust tail `edge' skimmed the top of 1996! I just thought it was interesting. Thanks! Epsilon Cas and passed under Gamma Cep and Al is (almost) right - what a strange traced to Iota Cep (CM) .... for whatever reason, coincidence! Here are the positions (J2000; last night the longer tail was very obvious; geocentric; 0 UT) of the two comets during a Carmelita Miranda's description, given above, small interval around these dates: details what we both independently saw; a couple of comments are appropriate -- the width 1996 Hyakutake of the dust tail at its end was at least 10 deg; as I 1997 Hale-Bopp know the skeptic will jump on this (they always do), I performed a test; I blocked out both the April 08 03h 04h 16.7s +42o 21' 56" comet and the Milky Way, and the end of the tail April 08 02h 45h 37.9s +41o 08' 26" was still obvious (I don't think my eyes were being fooled!)... (CSM). April 09 03h 03h 22.2s +41o 24' 50" A study of the striae in Comet Hale-Bopp's April 09 02h 52h 54.4s +40o 32' 26" dust tail, based on a set of wide-angle images obtained at regular time intervals with a number April 10 03h 02h 27.5s +40o 33' 03" of different telescopes, has been initiated by April 10 02h 59h 55.5s +39o 55' 18" Zdenek Sekanina (JPL) and his collaborators. It is expected that it will throw more light on the April 1103h 01h 31.6s +39o 45' 28" still not fully understood processes that are April 11 03h 06h 41.3s +39o 17' 13" responsible for this peculiar phenomenon, which was first seen in the tail of the bright comet in April 12 03h 00h 34.0s +39o 01' 11" 1976. April 12 03h 13h 12.4s +38o 38' 20"

6. New orbital elements and a coincidence If these positions are plotted in a graph, it will New orbital elements by Don Yeomans (JPL, be seen that the time of the `closest passage', i.e. Pasadena) and corresponding ephemerides have the moment when the two comets, with a time become available. The new orbital elements are interval of 1 calendar year, were closest to each based on 2158 observations up to March 29, other in the sky, was at approx. April 10.5 UT. 1997. The pre- and post-perihelion orbital The corresponding angular distance in the sky is

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 14 ______ESO Press Releases only about half a degree! However, this is Observatory on Mar. 1 +/- 2 days, showing that because of the perspective; the orbits in space do the line of sight crossed the equatorial plane of not cross each other. While Hyakutake was only the nucleus at that date. This implies that the 81 million km from the Earth on this date in source of the bright jet observed since January is 1996, Hale-Bopp was at a distance of 217 million located in the northern hemisphere, contrary to km in 1997. what we announced in a preliminary analysis (IAUC 6560). This jet, observed in the 7. X-rays observed from Hale-Bopp hemisphere directed toward the sun, now has the As was the case for Comet Hyakutake last appearance of concentric arcs with increasing year, X-rays have also been observed from Hale- curvature. Bopp. On IAU Circular 6614 (April 7), Alan Owens (ESA Space Science Department, 9. Spectroscopic observations Nordwijk, The Netherlands) and collaborators Yet another molecule has been detected. On announce - on behalf of the BeppoSAX team - IAU Circular 6614 (April 7), D. Mehringer the detection of soft X-rays from the direction of (Caltech Submillimeter Observatory - CSO) and this comet by the LECS instrument onboard the colleagues announce the identification of BeppoSAX spacecraft: The observations took formamide (NH2CHO) in Hale-Bopp: On Apr. 5 place between 1996 Sept. 10.16 and 11.18 UT. UT, we detected the lines of NH2CHO at After correcting for the comet's motion, a 10- 254.877 and 227.606 GHz with the CSO and sigma enhancement was found within 3 arcmin IRAM 30-m telescopes, respectively..... A of the expected location of the nucleus at much preliminary estimate of the NH2CHO production greater than 99.99-percent confidence.... The rate is 3 to 5 x 1027 molecules/s..... extracted LECS spectrum is well fit by a thermal Moreover, deuterated water (HDO; also bremsstrahlung model of kT = 0.36 keV -- known as `heavy water') has now also been consistent with that observed in other comets securely detected and a first measure of the (e.g., Lisse et al. 1996, Science 274, 205). The important D/H-ratio in Hale-Bopp has finally total 0.10-2.0-keV luminosity is 6 x 1016 erg/s, become available. On IAU Circular 6615 (April comparable with the observed luminosities of 7), R. Meier (University of Hawaii) and comets C/1996 B2 [Hyakutake] and C/1990 N1 collaborators report observations with the James [Tsuchiya-Kiuchi]. There is no evidence for Clerk Maxwell Telescope at Mauna Kea on Apr. fluorescent carbon or oxygen emission with 95- 4.8 UT: The integrated line intensity of the 101- percent-confidence upper flux limits of 1 x 10-4 000 HDO line at 464.925 GHz was (0.64 +/- photons cm-2 s-1 and 3 x 10-4 photons cm-2 s-1 0.11) K km/s on the antenna temperature scale..... for narrow line emission at 282 and 523 eV, Assuming a rotational temperature of 80 K, we respectively. This implies that if lines are derive a preliminary HDO production rate of 4 x present, their total luminosity must be < 10 1026 molecules/s. This makes the HDO/H2O percent of the continuum luminosity. The last ratio about 2 x 10-4, assuming a water- remark is of special interest in connection with production rate Q(H2O) = 2 x 1030 molecules/s the discussion of the possible mechanism(s) that (IAUC 6589). The corresponding D/H-ratio of cause the X-ray emission from comets. about 10-4 is consistent with other values for hydrogen in condensed matter in the outer solar 8. The rotation of the nucleus system and in seawater on earth, and is well Information about the recent coma structure above the values reported for H2 in the and the rotation of the nucleus has become interstellar medium or in outer- planet available on IAU Circular 6620 (April 9) by atmospheres. Thus Hale-Bopp, appears to be a Laurent Jorda (Max-Planck-Institut fuer `normal' comet in this respect with an origin Aeronomie, Lindau, Germany) and colleagues: similar to that of other comets, notably Halley The apparent rotation of the nucleus was and Hyakutake. clockwise on images obtained before Feb. 1997 Rita Schulz of the Comet Hale-Bopp (Kidger et al. 1996, Ap.J. 461, L119) and became European Team reports the first successful distinctly anticlockwise during March, showing spectroscopic observations with the 2.5-m that the north pole is now directed toward the Nordic Optical Telescope (NOT) and the SOFIN earth. The spiral jets appeared straight on visible instrument on La Palma at very high spectral and infrared images taken at Pic du Midi resolution (R = 160,000) in the visual region.

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 15 ______ESO Press Releases

One of the goals is to study the carbon isotopic semi-professional renderings of the finest details ratio. in the coma and tail systems. There are several new images at the Hale- 10. Molecular update Bopp Photo Gallery at the IAC website. Here is an updated list of molecules the Bengt Ask (Svaloev, Sweden) has established detection of which - to the best of my knowledge a Hale-Bopp website with impressive pictures. - has so far been announced in IAU Circulars or There is also a fine animation of the Partial Solar in research papers: Eclipse on October 12, 1996, on another page at this site. And while speaking about Hale-Bopp H2O, HDO, OH, H2O+ CO, CO2, CO+, and eclipses, you may also wish to check out HCO+ H2S, SO, SO2, H2CS, OCS, CS CH3OH, Dave Bridge's homepage with comet images and H2CO, HCOOH HCN, CH3CN, HNC, HC3N, an animation of the March 23-24 partial Lunar HNCO, CN, NH3, NH2, NH2CHO, NH CH4, Eclipse. C2H2, C2H6, C3, C2 Na Do have a look at the latest wide-field image by Eckhard Slawik (April 7, 1997), now and the following isotopes: available here.

H13CN, HC15N C34S 13. Hale-Bopp on the Web Ray Long (ESA; ISO Webmaster) calls This list may not be complete. Would attention to the availability of more ISO images anybody who has additional information kindly at contact the author via the email address given at http://isowww.estec.esa.nl/science/galleries/sso/h the bottom of this page? Thank you in advance. alebopp.html. Note also the link to ISO-related information at the Other Sites' page. 11. Amateur spectroscopists Two amateur astronomers, Nick Glumac and 14. News about other comets Joseph Sivo have obtained a spectrum (preview Joe Montani (Lunar and Planetary version; GIF; 16k) of Hale-Bopp in the range 350 Laboratory, Tucson, Arizona, USA) has reported nm to 520 nm, under light polluted urban skies (IAU Circular 6622; April 10) the discovery of a near New York City, on April 4, 1997 between comet (provisional designation C/1997 G1). The 8:00 and 9:00 PM Eastern Time. They used a 10- comet is located in the northern constellation of inch Meade LX-200 telescope, an Ocean Optics Gemini and is quite faint (magnitude 19). When S200 Fiber Optic Spectrometer (a miniature further observations had become available (IAU spectrometer with a linear 2048 CCD pixel Circular 6624; April 12), the comet was named array), a novel designed eyepiece-holder/fiber after the discoverer (Comet Montani). A first, optic coupler, a 15 watt photomultiplier tube very uncertain orbital calculation by Brian (PMT), and a laptop 486 computer. With this Marsden (IAU Central Bureau for Astronomical system, less than 1 nm resolution was achieved. Telegrams) and based on only 13 positions, More details are available at the JPL Hale-Bopp indicates that this comet is quite far from the site that now stocks over 2800 images. Earth (about 4.45 AU, or 666 million km), with Bob Fosbury (ST-ECF) calls attention to his perihelion time in September 1997 and perhaps special webpage about photographing spectra of short period. A better orbit may become with a transmission grating mounted in the filter available within the next few years when more adapter of a camera. It contains much useful measurements have been made. information and includes a montage with spectra Measurements of another comet of current of the Sun, some stars and Comet Hale-Bopp interest, 46P/Wirtanen, the target for the Rosetta (April 7). mission, show it at magnitude 9.6 - 10.0, that is 12. More images about 10,000 times fainter than Hale-Bopp. Images of Comet Hale-Bopp keep coming by the hundreds. No other comet has ever been so intensively observed! The JPL site now stocks over 3000 images of all types, ranging from snapshots with amateur cameras to advanced,

Jurasternwarte 1998,  H. Jost Hale- Bopp 2 - 16