THE COMET’S TALE
Newsletter of the Comet Section of the British Astronomical Association
Volume 7, No 1 (Issue 13), 2000 April
A Brief History of Comets II (1950-1993)
The following text is adapted considered to be heavenly omens surprising that, continuing the from a major review on Comets, and were not yet clearly earlier investigations by Swings prepared by Michel C. Festou established as celestial and McKellar, most spectroscopic (Observatoire Midi-Pyrenees, (astronomical), rather than studies between 1950 and 1970 Toulouse, France), Hans Rickman meteorological phenomena in the were devoted to a never-ending (Astronomiska Observatoriet, terrestrial atmosphere. Then attempt at discovering and Uppsala, Sweden) and Richard followed two centuries of mostly identifying new emission lines M. West (European Southern positional measurements with and bands, as well as at Observatory, Garching, Germany) emphasis on the motions and the unraveling the structure of the and published in the review orbits, lasting until the early 19th rotational and vibrational bands journal Astronomy & century, when the era of cometary of the comet radicals and ions. A Astrophysics Reviews (A&AR) physics was inaugurated, in special reference must here be (Part I, Vol. 4 pp. 363-447, 1993) particular by the passage of made to the numerous and P/Halley in 1835. The next major important contributions from the This is the second part of a brief step forward occurred in 1950 Liege school, reviews of which historical review, covering the with the sudden emergence of the are given by Swings (1956) and period from 1950 to 1993, i.e. modern picture of comets as Arpigny (1965). During this until just before the crucial years being essentially very old solar epoch rather complete models 1994-1997 that saw the impact of system objects made of primordial were made of the fluorescence of Comet Shoemaker-Levy 9 on ice and dust, generally in unstable the CN, CH, OH, and C2 Jupiter (1994), the apparition of orbits and intensively interacting radicals. The advent of high Comet Hyakutake that passed with the solar electromagnetic resolution spectroscopy in the late only 15 million km from the and corpuscular radiation. 1950's allowed the identification Earth (1996), as well as the Finally, the space missions to of many unknown lines, most of bright Comet Hale-Bopp that was P/Giacobini-Zinner in 1985 and which were due to C2 and NH2. discovered in 1995 and put on a especially to P/Halley in 1986 It is worth mentioning here that marvellous display when it passed provided the first in situ this effort has never been carried perihelion in early 1997. It observations of comets and through to completion and many includes some references to major dramatically widened our observed cometary spectral lines papers in this period (by author of scientific horizon, but also posed have still not been assigned an year of publication), but the many new questions which are emitter; the most likely are CO+, original version of this review in yet to be answered. CO2+ and C3 in the near-UV, C2 Astronomy & Astrophysics and NH2 in the optical and NH2 Reviews must be consulted for the 1952 - 1984: The modern era and H2O+ in the IR. full details about these. Following the break-throughs in 1950-51, the entire concept about The following Sections, divided comets had to be revised. This according to the main areas of process was a gradual one, as new investigative thrust during this observational facts were collected, period, illustrate how cometary and also because these research over the most recent observations were becoming decades has vindicated the ideas increasingly quantitative, put forward in 1950-51. allowing a progressively more detailed verification of the new Continued on page 4 ideas. Although number density estimates for cometary comae had Contents Hale-Bopp 1997 March 28 Robert Bullen been derived since the time of Comet Section contacts 2 Wurm's investigations in the Section news 2 Introduction The history of 1930's, the figures obtained were Tales from the Past 3 cometary astronomy is naturally rather uncertain and their Professional Tales 8 divided into five major periods, reliability was limited by the lack Comet History (cont) 4 the transitions being marked by of quantitative studies about the Review of observations 10 important new insights. Before excitation mechanisms of the Comet hunting notes 18 1600, comets were essentially light. Thus it is not too BAA COMET SECTION NEWSLETTER 2 THE COMET’S TALE
The Delta Effect 18 Observations of 109P/ 20
BAA COMET SECTION NEWSLETTER 2000 April 3
Comet Section contacts
Director: Jonathan Shanklin, 11 City Road, CAMBRIDGE. CB1 1DP, England. Phone: (+44) (0)1223 571250 (H) or (+44) (0)1223 221400 (W) Fax: (+44) (0)1223 362616 (W) E-Mail: [email protected] or [email protected] WWW page : http://www.ast.cam.ac.uk/~jds/
Assistant Director (Observations): Guy Hurst, 16 Westminster Close, Kempshott Rise, BASINGSTOKE, Hampshire. (and also Editor of RG22 4PP, England. The Astronomer magazine) Phone & Fax: (+44) (0)1256 471074 E-Mail: [email protected] or [email protected]
CCD Advisor: Nick James, 11 Tavistock Road, CHELMSFORD, Essex. CM1 5JL, England. Phone: (+44) (0)1245 354366 E-mail: [email protected] or [email protected]
Photographic Advisor: Michael Hendrie, Overbury, 33 Lexden Road, West Bergholt, COLCHESTER, Essex, CO6 3BX, England Phone: (+44) (0)1206 240021
Subscription to the Section newsletter costs £5 for two years, extended to three years for members who contribute to the work of the Section in any way. Renewals should be sent to the Director and cheques made payable to the BAA. Those due to renew should receive a reminder with this mailing.
Section news from the Director
Dear Section member, more before my departure for the data allows me to quickly enter Antarctic. The first of these was more recent observations. I write this introduction on my a faint non Kreutz group object, way home from Antarctica at the whilst the second was a I hope to have the Section guide end of March. My visit this year moderately bright Kretuz group on comet observing reprinted was a relatively short one, and my member. This discovery during the autumn. If anyone has work went very smoothly. With it prompted Michael Oates to have a suggestions for additions or other approaching autumn in go and he soon spotted one, improvements do let me know. Antarctica the nights became though it turned out to have The Tycho catalogue is the best darker and longer throughout my already been discovered. Nothing source of magnitude information stay. Although a generally cloudy daunted he has continued and this has recently been summer, we did have a few clear searching and has found several upgraded and now has fainter nights in which to experience the more, including a couple in stars than in the first edition. I grandeur of the southern skies. archived SOHO observations. On have added a section on reporting Surprisingly light pollution is a my return from Antarctica I found discoveries, as it is important to problem about the station, as another whilst in the process of follow the correct steps if you there are a number of badly compiling material for this issue think you have made one. I plan designed floodlights which create of The Comet's Tale. to drop the CCD and considerable glare. However once photographic reporting forms you are over a bluff overlooking Comet LINEAR 1999 S4 offers because no-one has ever used the station the skies are truly the hope of a naked eye comet them. dark, the milky way is bright over the summer. Do make every enough to cast shadows and on effort to observe it, but when you I would like to develop a standard most moonless nights the faint send the observations up please for submitting CCD images in glow of the diffuse aurora is try to submit them by email in order to make it easier to archive visible to the south. either the ICQ format to me or the images from many observers. Unfortunately there were no TA format to Guy. Try to get it The standard needs to allow for comets to observe, but I was able exactly right as we both have the name of the comet, the name to spend time on the voyage north more than enough to do without of the observer, the date and time typing in the some more archival having to edit observations. of the image, the telescope and observations from TA for 1980 to There is a template for both camera details, the scale of the 1989. This was over 2200 formats on the section web page, image and different image types observations, bringing the total so copy this if you are uncertain. (gif, jpeg etc). It is good practice number up to over 28,000. Don’t worry if you don’t have to include much of this email – paper copy is still information on the image, but if My success in discovering one acceptable, but send your this is not possible an auxiliary SOHO comet was followed by two observations to me as the program file may be needed. that I use to enter the archival BAA COMET SECTION NEWSLETTER 4 THE COMET’S TALE
A possible suggestion would be to Panther, Jonathan Shanklin, (Spacewatch), 1999 E1 (Li), 1999 name image files as David Storey, David Strange, H1 (Lee), 1999 H3 (LINEAR), comet_yyyymmddl_obs.img and Cliff Turk and Alex Vincent auxiliary files as 1999 J2 (Skiff), 1999 J3 comet_yyyymmddl_obs.txt, where and also from: Jose Aguiar, (LINEAR), 1999 K8 (LINEAR), comet is the comet identifier, Alexandr Baransky, Nicolas 1999 L3 (LINEAR), 1999 N2 yyyymmdd is the date, l the image Biver, John Bortle, Jean-Gabriel (Lynn), 1999 S3 (LINEAR), 1999 number taken by the observer on Bosch, Reinder Bouma, Nicholas S4 (LINEAR), 1999 T2 that date, obs the first three letters Brown, Paul Camilleri, Jose (LINEAR), 1999 T3 (LINEAR), of the observers surname, and Carvajal, R Ferrando, Stephen img the image format. As an Getliffe, Bjorn Granslo, Andreas 1999 U1 (Ferris), 1999 U3 example Kammerer, Heinz Kerner, Atilla (P/LINEAR), 1999 U4 (Catalina- 1999s4_19991128a_mob.jpg Kosa-Kiss, Martin Lehky, Skiff), 1999 XS87 (P/LINEAR), would be the first jpeg image that Rolando Ligustri, Maik Meyer, 1999 Y1 (LINEAR). Martin Mobberley took of 1999 Antonio Milani, Andrew Pearce, S4 on that date and if he felt that Stuart Rae, San, Seg, Oddleiv Many of the fainter comets were further information was needed Skilbrei and the Ageo Survey observed by the AGEO team of there would be a supporting file Team (KenIchi Kadota and KenIchi Kadota and Seiichi 1999s4_19991128a_mob.txt. The Seiichi Yoshida) (apologies for Yoshida who are using a CCD second gif image of any errors or omissions). Without camera on an 18 cm reflector to 141P/Machholz 2 by David these contributions it would be very good effect. I hope to begin Strange on the same date would impossible to produce the using the Cambridge be 141p_19991128b_str.gif. The comprehensive light curves that Observatories 3-mirror telescope advantage of the sequence appear in each issue of The designed by Roderick Wilstrop for comet_date_observer is that it Comet’s Tale. some astrometric and photometric allows sequential sorting. I have observations over the coming canvassed opinion from regular Comets under observation were: months and so may be able to imagers, but other comments are 4P/Faye, 10P/Tempel 2, contribute some observations. welcome. 37P/Forbes, 50P/Arend, Perhaps the Supernova searchers would like to add the odd comet Since the last newsletter 59P/Kearns-Kwee, 74P/Smirnova-Chernykh, to their list - they might discover observations or contributions have one in outburst! been received from the following 63P/Wild 1, 84P/Giclas, BAA members: Len Entwisle, 106P/Schuster, 114P/Wiseman- Jonathan Shanklin Werner Hasubick, Guy Hurst, Skiff, 141P/Machhol 2, 1995 O1 Nick James, Martin Mobberley, Michael Oates, Gabriel Oksa, Roy (Hale-Bopp), 1997 BA6 Tales from the Past
This section gives a few excerpts 1264 and 1556 which was would be useful in determining from past RAS Monthly Notices, thought due to return. He had the mass of the giant planet and BAA Journals Sky. computed search ephemerides, Jupiter. No 5 has a list of comets but on hearing from Mr Hind that seen since 1889 compiled by A C 150 Years Ago: A large number recent calculations suggested a D Crommelin. Interestingly only of astrometric observations of delay in the return of several the periodic comets were Gambart's (Biela's) comet from years, the Editor did not publish "named". He did not include the the Cape of Good Hope were them. In April Norman Pogson comet seen at the total eclipse of published in November. [Biela gave a note about the comet 1893 April 16 as it was not seen actually discovered it ten days observed by Pons in Marseilles in again. before Gambart] T Maclear 1818. He noted that the elements comments in his notes "This computed from three positions 50 Years Ago: The December comet is perhaps the most were almost identical to those of a Journal includes a review of interesting on record, on account comet seen in 1772, which was "Comets in Old Cape Records" by of the appendage, which was supposed to have been that of Donald McIntyre. At the January probably a portion of the original Biela. [The comet of 1772 was meeting Dr Merton spoke about mass." [The comet had split just Biela's, but that of 1818 was comets. 1949 had been a quiet before its 1845 return, and its Crommelin's]. year, particularly the second half next return was its final one, when only two observations were though remains were seen in the 100 Years Ago: The November received. The March Journal has form of meteors for another 50 Journal has a note: Biela's Comet a paper on "The Statistics of years or more.] In January a - The discovery of this comet was Comet Orbits" by Harley W paper by J R Hind on the past reported from Santiago, Chile at Wood. He concluded: 1) 77% of history of Halley's comet was the end of October, but no comets have parabolic orbits. 2) published. Here he traced past confirmation has been obtained of No comets have certainly apparitions of the comet and the report, and no credence hyperbolic orbits on approach to made new links for several should be attached to it. In the Sun. 3) None have hit the apparitions, including that of December John Tebbutt wrote to Sun. [No longer true, I 1066. In March Mr Hind say that he had made astrometric discovered another one that did informed the Society about measurements of 10P/Tempel 2 shortly before I compiled these computations on the comet of on 43 nights, which he hoped notes!] 4) The elements, BAA COMET SECTION NEWSLETTER 2000 April 5 particularly a and e are affected by planetary perturbations. 5) Comets are subject to wastage. 6) Their origin and history must account for the presence of volatiles.
BAA COMET SECTION NEWSLETTER 6 THE COMET’S TALE
A Brief History of Comets II (1950-1993)
Continued from Page 1 molecules is the main production also measured the scalelength of mechanism and that not only OH (in comet Bennett) and found The ultraviolet, infrared and radio oxygen but also hydrogen atoms a value in complete agreement windows were explored in the must exist in large amounts in with that found for comet early 1970's, the emissions of H I, comets, with resulting production Kohoutek. The definitive clue that O I and OH were observed and rates of e.g. log Q (mol s-1) ~ 30 H2O was the main source of both the dissociation products of the for a bright comet, or much larger the H-atoms and the OH radicals main volatile constituent of the than those of the parents of CO+, came when the velocity of the H- nucleus were finally detected CN or C2. In some sense, the atoms was measured directly from observationally. The first radar discovery in 1970 by the Orbiting COPERNICUS observations detection of a comet in 1980 Astronomical Observatory (OAO- (Drake et al. 1976) and, (P/Encke, Kamoun et al. 1982), 2) and the Orbiting Geophysical indirectly, from the analysis of H and the first recording of an Observatory (OGO-5) of huge I Lyman-alpha observations (cf. image of a comet nucleus in 1986 Lyman-alpha haloes of neutral the review by Keller 1976), and convinced the last sceptics that hydrogen ( 1.5 x 107 km) around was found to be compatible with Whipple was correct. From comets Tago-Sato-Kosaka (1969 the water photolysis scheme. This refined studies of the orbital IX) and Bennett (1970 II) did not was confirmed by the direct motion of comets it was come as a complete surprise. observation of water in P/Halley demonstrated that Oort's distant However, the origin of these in 1986. reservoir was fully justified, even hydrogen atoms was not yet though some shortcomings of the known with certainty. After the discovery of the 18 cm theory are only now being maser emission of OH (Biraud et overcome and have led to new While the OH emission band at al. 1974; Turner 1974), OH radio and exciting developments. 3090 AA was first identified in observations became routine and Above all, however, a wealth of comet Cunningham (1941 I) by the evidence for the ubiquitous quantitative data became Swings, the first quantitative OH presence of water in comets was available, making truly abundance measurements only overwhelming. The emission of comparative studies of comets date from the early 1970's (Code an unknown ion was observed in possible. In a not too distant et al. 1972; Blamont and Festou comet Kohoutek (1973 XII) by future this should enable us to 1974; Keller and Lillie 1974). Herbig (1973) and Benvenuti and learn whether the differences we The analysis of the Lyman-alpha Wurm (1974). Herzberg and Lew observe between individual isophotes of comet Bennett (1970 (1974) had just obtained the first comets are the results of II) revealed that the velocity of laboratory spectra of the H2O+ evolutionary processes or rather the H-atoms was about 8 km s-1 ion and tentatively identified this reflect intrinsic diversity. (Bertaux et al. 1973). Following ion as the source of the new an investigation of the photolysis cometary emission. The same Water as the main constituent of water molecules by sunlight, emission was later found in of comets In 1958, high this led these authors to speculate cometary spectra recorded as resolution spectroscopy allowed about the possibility that the early as 1942 (Swings et al. the separation of the terrestrial majority of the observed H-atoms 1943). Although the water ion oxygen lines from the cometary were coming from the might be an abundant species in ones and also led to the definitive dissociation of OH radicals. To comet tails, its presence there is confirmation of the presence of prove this assertion, Blamont and not conspicuous: this is a clear the isotopic lines of 13C, long Festou (1974) measured both the indication that the ion is lost suspected to be present in comets. then unknown scalelength of OH rapidly, unlike the other tail ions. The detection of the [O I] red and the production rate of that Aikin (1974) showed that the lines in comet Mrkos (1957 V) radical in comet Kohoutek (1973 main loss mechanism is a charge (Swings and Greenstein 1958) XII). They proposed for the first exchange reaction with water created a completely new time, on a quantitative basis, that molecules leading to the problem: it was soon shown by water was the parent of most of formation of the H3O+ ion, and Wurm (1963) that if fluorescence the hydrogen atoms and the OH this latter is likely to be destroyed is at the origin of the emission, radicals. Horst Uwe Keller and in electron recombination then very large amounts of co-workers reached similar reactions. H3O+ was indeed oxygen are implied, much larger conclusions in a series of found to be one of the main ions than those of for instance C2. It independent papers: Keller (1971) in the comae of P/Giacobini- seemed preferable to assume discussed the possibility that the Zinner and P/Halley. another emission mechanism and observed H-atoms in comet Wurm proposed corpuscular Bennett might arise from the Quantitative studies and excitation. The idea that some direct dissociation of water and comparative cometology Many coma species may be produced later (Keller 1973a, 1973b) parameters for the OH radical directly into an excited state can developed these ideas further. His were derived from radio be traced back to McKellar investigation though, as well as observations at 18 cm. The (1943), but this suggestion was that of Bertaux et al. (1973), was detailed mechanism by which not explored in detail until 1964 limited by the fact that the comets emit photons at that (Biermann and Trefftz 1964). parameters governing the water wavelength was investigated by Their work led to the prediction photolysis were not well known at Despois et al. (1981). The that photodissociation of parent that time. Keller and Lillie (1974) methodology for determining OH BAA COMET SECTION NEWSLETTER 2000 April 7 velocity profiles was worked out abundances in comae of different comets as well as the preparation by Bockeee-Morvan and Gerard comets. As direct sources of of ephemerides for upcoming (1984). An overview of the detailed information and for apparitions, even for long-lost production rate and velocity additional references on this comets. determinations is given by subject as well as the radio OH Bockelee-Morvan et al. (1990). measurements quoted above, we Whereas Oort had been working Beginning with comet Bradfield refer the reader in particular to on a small sample of comets to (1979 X), a long series of high the papers by A'Hearn and Millis build his theory, Marsden et al. quality observations of the UV (1980), Cochran (1987), Newburn (1978) improved the earlier spectrum of comets was obtained and Spinrad (1989) and Osip et statistics by using 200 well- by the International Ultraviolet al. (1992). A list of all individual determined long-period orbits. Explorer (IUE), from which a observations made with the IUE They found a concentration of self-consistent set of water until late 1989 and a discussion of inverse semimajor axes production rates was derived (e.g. the resulting comparative corresponding to an average Festou and Feldman 1987). The cometology have been published aphelion distance of about 45,000 radio and UV determinations of by Festou (1990). The most AU, only about half as remote as these rates do not agree perfectly, striking observational fact is that, Oort's original distance. A major because the models used in the at first sight, all comets look alike problem remained the apparent interpretation of the data differ (Cochran 1989). There are just a overabundance of Jupiter family markedly. Schloerb (1988) and few well-known objects for which comets. Edgar Everhart (1972) Gerard (1990) have discussed this the chemical composition of the found a possible route of direct problem. coma departs notably from that of transfer from the Oort cloud via an average comet, e.g. a few CO+ Jovian perturbations at repeated The 1970's saw the development rich comets or those that seem to encounters with the planet, of quantitative observations of contain only one or a few of the beginning with a special type of comet emissions, mainly by actual compounds of comet initial orbits with perihelia near means of narrow-band comae. For instance, P/Giacobini- Jupiter's orbit and low photoelectric filter photometry Zinner is C2 and C3 depleted inclinations. However, some through diaphragms (Cochran 1989), while comet authors questioned the efficiency encompassing a more or less large Yanaka (1988 XXIV) seems to be of this transfer or the fit of the part of the coma. A review of the made almost exclusively of NH2 orbital distribution of the captured early observations and the and water (Fink 1992). As comets. An alternative scenario observing techniques is given by suggested by the direct inspection came from orbital integrations of A'Hearn (1983). One of the of optical (Swings 1948) and UV the observed comets by Elena I. shortcomings of standard spectra (Festou 1990b), the main Kazimirchak-Polonskaya (1972): photoelectric photometry is the difference between individual the comets might not be captured contamination by an underlying comets is the continuum to gas by Jupiter alone, but rather by a continuum and by gaseous emission ratio. Observations of stepwise process involving all the emissions in the wings of the P/Halley in 1986 added an giant planets. spectral transmission curve interesting piece to the puzzle: defined by the filter. It was CO and some other observed The ideas about the long-term therefore not surprising that gases require an extended source dynamics of the Oort cloud spectrophotometry developed in the coma. A key issue is now to evolved considerably. While rapidly in the early 1980's when determine the relationship passages of individual stars were linear detectors and image between this source and the dust mostly considered in earlier intensifier tubes became particles. The general picture investigations, the tidal effects of available; see the review by beginning to emerge is that all the Galaxy as a whole, A'Hearn (1982). This method comets basically have similar preliminarily modelled by provided both a good separation molecular abundances and that Chebotarev (1965), have become of the band or line emissions and the observed differences might recognized in recent years as the also spatially well-resolved only reflect a variable dust to gas prime mechanism to provide new information about the distribution production ratio. It remains to be comets from the outer cloud. The of coma species. In parallel, determined whether this ratio is dramatic effects that might follow numerous theoretical studies, an intrinsic property or the result upon close encounters with aimed at calculating the of an evolutionary (i.e. ageing) massive perturbers, such as giant fluorescence efficiencies of the process. molecular clouds (Biermann and coma radicals and ions, resulted Luest 1978), also received a great in the establishment of reliable Dynamical evolution From the deal of attention. In particular, conversions of observed surface point of view of cometary the question of the stability of the brightness into column densities dynamics, the modern era is first outer, classical regions of the Oort of the different species. The last of all distinguished by the advent cloud over the age of the solar step in the data analysis process is and development of efficient and system has been debated. then the derivation of gas powerful computers. This production rates. allowed, for the first time, A major step forward taken extensive numerical simulations during this period dealt with the The data accumulated during the of the orbital evolution resulting modelling of nongravitational last 20 years or so by many from repeated close encounters effects in cometary motions. dedicated observers, using both with Jupiter and other planets. It Based on Whipple's concepts, ground- and space-based also revolutionized the work on Brian Marsden (1969) introduced instruments, have made possible orbit determination and linkage of a nongravitational force into the the comparison of the relative past apparitions for observed Newtonian equations of motion BAA COMET SECTION NEWSLETTER 8 THE COMET’S TALE with simple expressions for the the spin axes. They treated the jet interstellar clouds. Cometary radial and transverse components force in a physically more origin thus would not be coupled in the orbital plane. These realistic way than the g(r) to the origin of the solar system involved a function of the formula. However, the results but to capture events throughout heliocentric distance r expressing were still dependent on model its lifetime. This scenario never a standard `force law', multiplied assumptions and thus received as much support as the by a coefficient whose value was questionable (cf. Sekanina 1988). one due to Kuiper, since it faced determined along with the obvious difficulties, e.g. in osculating orbital elements by Cometary origin The explaining the cometary 1/aorig minimizing the residuals of the fit introduction of the basic concepts distribution and nongravitational to positional observations. The of the Oort cloud and the icy effects. As both Oort's and radial coefficient was called A1 conglomerate nucleus have Whipple's concepts have been and the transverse A2. It was naturally influenced modern ideas consolidated in recent years, the realized that the model might not about the origin of comets. Oort basis for Lyttleton's picture has be physically realistic and that (1950) already paid attention to now virtually disappeared. more meaningful parameters the problem of formation of the might be derived from a cloud and hypothesized that it However, the idea of interstellar generalized formalism, but could have originated as a result comets embraces many different attempts in this direction were not of Jovian perturbations after the scenarios that are subject to successful (Marsden 1970). The explosion of a planet-sized body continued investigations. Aspects final update of the model was in the asteroid belt. Thereby the that have attracted particular made in 1973 (Marsden et al. asteroids and comets would have attention are the distribution of 1973), stimulated by calculations a common origin, the former aphelion directions of long-period of the H2O sublimation rate as a being devolatilized variants of the comets and the possible signature function of r (Delsemme and latter. However, this revival of of the solar apex, the mechanisms Miller 1971). This was taken as Olbers' old idea did not gain wide for formation of cometary nuclei the model force law, expressed as acceptance, partly due to the under interstellar cloud an algebraic function g(r) whose growing evidence that meteorites, conditions, the role of comets in parameters were chosen to fit obviously part of the same galactic chemical evolution, and Delsemme and Miller's results. complex of minor bodies, have the significance of the fact that no Eventually more realistic models nearly solar elemental abundances hyperbolic comets have as yet were constructed for the jet force and can not originate from a been observed. as resulting from asymmetric planet-sized parent body. H2O outgassing, including the The standard concept of the solar heat flow in the surface layers of Around 1950, the Kant-Laplace nebula was criticized by Alfven the nucleus (Rickman and nebular hypothesis for the origin and Arrhenius (1970, 1976), who Froeschle 1983). As a result it of the solar system was also argued for the importance of was found that the true force law reconsidered in the light of the electromagnetic forces in the might be very different from the chemical compositions of the collapsing cloud, leading to a g(r) formula, and hence there planets and their variation with different picture of the radial should be room for an improved heliocentric distance. Edgeworth arrangement of orbiting material model. (1949) and Gerald P. Kuiper and a different scenario for the (1949, 1951) argued that it is accretion of larger bodies. In The long-term variations of the unlikely for the solar nebula to particular, the formation of nongravitational forces were have ended abruptly at the comets was considered to occur by found to involve a wide range of position of Neptune's orbit, and longitudinal focussing produced behaviour. Thus the well- thus a large population of planet by self-gravitation and inelastic determined A2-values found over precursors with a generally icy collisions in narrow streams of different periods of time for the composition would have existed particles, so-called jet streams. same comet usually vary in a outside the giant planets. Kuiper This idea has not gained general more or less regular fashion, often (1951) claimed that such bodies acceptance, however. An eruptive including changes of sign. This could be identified with Whipple's origin of comets continued to was generally interpreted in terms cometary nuclei and suggested attract attention as well. Van of spin axis precession, which in that Pluto's gravitational action Flandern (1977, 1978) proposed, turn may be caused by the torque (its mass was then thought to be based on the distribution of orbits associated with the jet force of in the 0.1 - 1 Earth-mass range) of long-period comets, that outgassing. An early suggestion might have scattered the objects comets and asteroids originate of such a scenario was made for into Neptune's zone of influence, from the break-up of a 90 Earth- P/Kopff (Yeomans 1974). whereupon ejection into the Oort mass planet in the asteroid belt Quantitative models were first cloud would ensue. In particular, only 5.5 x 106 years ago. This derived by Whipple and Zdenek outside Pluto's orbit, the suggestion did not gain support, Sekanina (1979) to fit the secular population might still remain mainly on physical grounds (see decrease of the nongravitational intact. the discussion following Van perihelion shift of P/Encke. These Flandern 1977). It was in stark models, and similar ones During the following decades, disagreement with the picture developed later on for a number Lyttleton (1952, 1974) challenged building up during the 1970's and of other comets (Sekanina 1984- both basic concepts (the solid 80's, according to which minor 85; Sekanina and Yeomans nucleus and the Oort cloud), bodies in general, and comets in 1985), led to predictions of some arguing instead for cometary particular, represent physical parameters of the nuclei formation by aggregation of dust undifferentiated, pristine solar - in particular, the orientations of during the Sun's passages through system material (Delsemme BAA COMET SECTION NEWSLETTER 2000 April 9
1977). Sergej K. Vsekhsvyatskij 1990); the IHW Archive with from 1 to 100 amu. were detected (1972, 1977) continued to favour more than 25 Gbytes of data was by mass spectroscopy, and the a variant of the Lagrange ejection released in December 1992 (IHW likely presence of large organic hypothesis, involving the 1992) and the associated polymeric molecules was satellites of the giant planets, but Summary Volume (Sekanina and indicated. The maximum he remained quite isolated in a Fry 1991) contains detailed measured production rates were community dominated by the information about the data larger than 104 and about 3 x 104 view of comets as primordial obtained within the various IHW kg/sec for dust and gas, bodies probing the solar nebula. Networks. The observations were respectively, i.e. a dust/gas ratio The idea is fraught with many carried out in all wavebands from larger than 0.3. The integrated problems of different nature - let the UV at 120 nm to the mass loss experienced by the us mention here only that of radioband at 18 cm, by nucleus at this passage, of the explaining the abundance of long- professionals and amateurs. It order of about 4 x 1011 kg (but period comets. has proven particularly fruitful to very uncertain) was about 0.5 combine space- and Earth-based percent of the total mass of the 1985 - 1986: Encounters with observations for calibration and nucleus, estimated at 1 - 3 x 1014 P/Giacobini-Zinner and long-term monitoring purposes. kg. The brightness of the central P/Halley Following the In general, the earlier developed condensation appears to be enormous increase of interest for cometary models were confirmed varying with pseudo-periods of comets in the late 1970's, another and could now be quantified by in about 2 and 7 days, but it was not giant leap in our understanding of situ measurements, leading to possible to determine comet phenomena occurred in many new insights. unambiguously the rotational March 1986 when six spacecraft state of the nucleus. The various (henceforth `S/C') observed predicted plasma effects were P/Halley in situ, and future confirmed, including the cometary scientists will existence of a bow shock and the undoubtedly speak about the pre- adjacent interplanetary medium and post-Halley eras, much as was found to be kinematically and historians describe the transition magnetically extremely turbulent. from the dark ages to the Several disconnection events in renaissance period. However, the the ion tail were observed, also at first cometary encounter took the time of the encounters, and place already six months earlier the suspected connection with on September 11, 1985, when the magnetic field reversals was ISEE-3 spacecraft, released from partly confirmed. its earlier task of monitoring the Earth's radiation belts and, Comet Halley's Nucleus. Credit: Halley 1986 - 1993: P/Halley follow-up renamed as the International Much of the period after the Cometary Explorer (ICE), passed Multicolour Camera Team, Giotto, ESA ©: Halley encounters has been spent through the tail of P/Giacobini- MPAE reducing the enormous amount of Zinner, about 8000 km from the The nucleus was observed at close data on this comet. Ground-based nucleus. The main results were distance for the first time; it was observations of a number of other the confirmation of the plasma found to be larger (equivalent bright comets, including Wilson tail model, indications about the radius about 5.5 km) and darker (1987 VII), Austin (1990 V), ion composition and the detection (albedo about 4 percent) than P/Brorsen-Metcalf (1989 X) and of a neutral current sheet at the expected. Surface features Levy (1990 XX), have served for center of the tail. ICE flew on to (craters, ridges, mountains etc.) comparison and have also register the effects of P/Halley on and the emitting vents were resulted in several important the interplanetary medium from a observed. The coma was found to discoveries, for instance of some distance of 28 x 106 km sunward. be highly structured on all scales new parent molecules, e.g. H2CO, (jets, shells, ion streamers, etc.) H2S and CH3OH. Thanks to The detailed results from the and the gaseous component improved instrumentation and extraordinary P/Halley campaign (parent molecules, radicals, ions reduction techniques, it has during the 1985-86 apparition fill and atomic species) was analyzed become possible to observe fainter many volumes - it will here in situ; H2O was confirmed to be and more distant comets than ever suffice to give a very condensed by far (about 85 percent by before. To some surprise it has overview of the main results. weight) the most abundant been found that several comets constituent in the gas phase. A continue to be active many years Five spacecraft encountered cavity devoid of magnetic field after perihelion passage, in some P/Halley in early 1986: Vega 1 was detected within about 5,000 cases at heliocentric distances (closest approach on March 6 at km of the nucleus. The dust was well beyond 10 AU; this has 8890 km distance), Suisei (March analyzed by size and composition; implications for the models of the 8; 150,000 km); Vega 2 (March there was an unexpectedly high nuclei. 9; 8030 km), Sakigake (March fraction of very small grains, 6 down to the sensitivity limit 11; 7 x 10 km) and Giotto -19 Another space encounter with a (March 14; 600 km). At the same (about 10 kg). In addition to comet took place on July 10, time, an unequalled long-term those of possibly chondritic 1992, when the Giotto spacecraft Earth-based observational effort composition, carbonaceous flew through P/Grigg-Skjellerup was coordinated by the `CHON' particles were seen for during the Giotto Extended International Halley Watch the first time; they may be a new Mission (GEM), cf. Schwehm and (IHW) (Newburn and Rahe source of gas. Atomic masses Grensemann (1992). A BAA COMET SECTION NEWSLETTER 10 THE COMET’S TALE preliminary overview of some of the early results was published by Boehnhardt et al. (1992). The foremost virtue of GEM has been to provide direct comparison between a very active and a supposedly less active comet and to search for the underlying causes. However, P/Grigg- Skjellerup was found to be at least as active as expected, and the first presence of cometary ions was detected at a distance of about 6 x 105 km, while a magnetic disturbance resembling a bow shock or wave was passed at about 1.5 x 104 km distance. A few dust impacts occurred just after the closest approach which took place at about 200 km from the nucleus.
BAA COMET SECTION NEWSLETTER 2000 April 11
Professional Tales
Many of the scientific magazines was that it enabled scientists to the discovery of the 200th member have articles about comets in use the same instruments to of the Transneptunian Belt. Also them and this regular feature is compare the fairly inactive Grigg- known as the Kuiper Belt or the intended to help you find the ones Skjellerup with Comet Halley, its Edgeworth-Kuiper Belt, the you've missed. If you find others much larger, more active cousin. Transneptunian Belt is a let me know and I'll put them in A number of experiments on collection of bodies orbiting the the next issue so that everyone board Giotto were functioning sun generally at distances can look them up. during both encounters. somewhat larger than that of Neptune. The following abstracts (some One of these was EPONA, which shortened further for publication) has the capability to record As with the PHA discoveries, the are taken from the Cambridge charged particles -- protons and rate of TNO discoveries has Conference Network (CCNet), heavier ions -- with energies increased very dramatically which is a scholarly electronic ranging from several tens of keV recently. Fully half of the TNOs network devoted to catastrophism, to several tens of MeV. have been found during just the but which includes much Characteristic fluctuations in the last 12 months, with the first information on comets. To energetic particle records allowed discovery having been in 1992 or subscribe, contact the moderator EPONA to detect the same 1930, according as to whether one Benny J Peiser at cometary boundaries at Halley does not or does choose to
The information in this report is a full report of the comets seen 10P/Tempel 2 continued to fade, synopsis of material gleaned from during the year will be published and was generally too far south IAU circulars 7281 – 7399 and in the Journal in due course. for observation from the UK. It The Astronomer (1999 October – was last seen in early January at 2000 March). Note that the 4P/Faye was observed by the 14th magnitude. Overall the figures quoted here are rounded AGEO team of Seiichi Yoshida comet was well observed, off from their original published and KenIchi Kadota by CCD in however there is considerable accuracy. Lightcurves for the November when it was 16th scatter in the observations. brighter comets are from magnitude. observations submitted to The Astronomer and the Director. A BAA COMET SECTION NEWSLETTER 14 THE COMET’S TALE
earlier given the minor planet Comet 10P/Tempel 2 designation 1967 EU. For a few Comet 106P/Schuster 8 years around 2025 it will be 10 9 11 10 captured by Jupiter and then a 11 further encounter with the planet 12 12 at the end of the century will 13 13 move the perihelion distance 14 14
15 outside that of Jupiter. Due to the 15
Observed magnitude 16 low eccentricity of its orbit the Observed magnitude 17 comet is visible even at aphelion 16 18 17 19 but it is faint at about magnitude 20 16. At this return it doesn't reach 18 FebMar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Nov Dec Jan Feb Mar 1999 - 2000 perihelion until January 2001, 1999 - 2000 however the AGEO team are th The preliminary uncorrected light imaging it and it has reached 15 114P/Wiseman-Skiff had a curve m = 5.4 + 5 log d + 32.3 magnitude. favourable apparition and also log r is only a fair fit to the 200 reached 14th magnitude in observations. 76P/West-Kohoutek-Ikemura December and was still this bright makes a close approach to Mars in January. The 55 observations A couple of further observations on June 5, passing only 0.043 AU give an uncorrected preliminary of 50P/Arend were received, but from the red planet. The light curve of m = 8.9 + 5 log d + the comet was never brighter than apparition is not a good one for 28.9 log r. 14th magnitude. At its best ever earth based observers, but if we return the comet reached a similar were on Mars the comet would be Comet 114P/Wiseman-Skiff magnitude and this apparition around mag 7.5 in a dark sky, 12 was not a good one. although very close to Jupiter and 13 Saturn. From Earth it is nine 59P/Kearns-Kwee had a rather magnitudes fainter and not 14 unfavourable return and was surprisingly is close to Mars, another comet which didn’t which is at an elongation of only 15 th become brighter than 14 7° from the Sun. Observed magnitude 16 magnitude. It was around this brightness during the autumn. 84P/Giclas made its fourth 17
observed return since its discovery 18 in 1978 by Henry Giclas of the Oct Nov Dec Jan Feb Mar 63P/Wild 1 Nakano reported 1999 - 2000 observations made by T. Kojima, Lowell Observatory. The Chiyoda, on October 24.83 of this perihelion distance is fairly 141P/Machholz 2 (1999 P1) put 13-year-period comet, missed at constant at present and Jupiter on a disappointing performance its 1986 return. These encounters only make significant and never reached the brightness observations confirm a single- changes to the angular elements. achieved at the last return. This night detection at mag 22.4 by However around 2300, a low was not entirely unexpected as the Hergenrother (1.5-m Catalina velocity close encounter with comet had fragmented last time reflector) on February 14. The Jupiter will transfer the comet to round and this undoubtedly prediction on MPC 27082 an orbit outside that of the planet. boosted its performance. It was It was yet another faint comet, requires correction by Delta T = - th never well placed from the UK 0.35 day. Further details were which perhaps reached 14 and was difficult to observe. Two given on MPEC 1999-V18. magnitude in the autumn. components were recovered. Kojima (0.25-m f/6.3 reflector) Component A peaked at 9th reported the comet at m1 = 16.5 106P/Schuster was discovered in magnitude in early January and and as diffuse without a tail on 1977 October at La Silla, though component D was at least two October 24, at m1 = 15.9 and a month earlier it had been magnitudes fainter. diffuse with condensation and a recorded as an asteroid. It was coma diameter of 30" on not seen at its second return, November 4. [IAUC 7302, 1999 which was unfavourable. The November 6]. The comet orbit is relatively stable. This was th its third observed return and it brightened and reached 12 th th magnitude in January. Moving remained at 13 - 14 magnitude south, it was lost to view from the from late October into January. UK, but Southern Hemisphere The light curve is indeterminate observations continued. The 25 from the observations received so observations received so far give a far. preliminary light curve of m = 10.6 + 5 log d + 7.5 log r, The 79 observations received so however the fit to the observations far give a preliminary, is not good. uncorrected light curve of m = 13.6 + 5 log d + 11.8 log r. Close encounters with Jupiter in 1955 and 1963 changed the orbit of 74P/Smirnova-Chernykh drastically and it was discovered in 1975, though it had been BAA COMET SECTION NEWSLETTER 2000 April 15
Comet 141P/Machholz 2 (A) Comet Spacewatch (1997 BA6) Comet LINEAR (1999 H3)
8 12 11
9 12 10 13
11 13
12 14
14 13 Observed magnitude Observed magnitude Observed magnitude
14 15 15 15
16 16 16 Nov Dec Jan Feb DecJanFebMarAprMayJunJulAugSepOctNovDecJanFebMarAprMayJunJul Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1999 - 2000 1998 - 2000 1999 - 2000
Hale-Bopp (1995 O1) is still Only a few further observations of 1999 J2 Skiff is slowly fading being observed from the Southern LINEAR (1998 M5) were and has now reached 16th Hemisphere, but it will soon be received as the comet faded past magnitude. too faint for further visual 15th magnitude. The observations observation. The observed arc give an uncorrected preliminary 1999 J3 LINEAR peaked in now covers 1712 days with light curve of 6.0 + 5 log d + 10.2 brightness at around 7m in mid observations made on 796 days. log r October. Thereafter it faded and The equation -0.64 + 5 log d + was last seen in late November by 7.53 log r fits the aperture The AGEO team made a couple Andrew Pearce at 10th magnitude corrected daily means very well, of further observations of 1999 E1 in 20x80B. but there are long period (Li) as it faded. variations about this mean light 197 observations give an curve of around a magnitude, 1999 H1 Lee reached peak uncorrected preliminary light which are shown plotted with an brightness in early October, but curve of 9.0 + 5 log d + 11.8 log r offset of -2. It is currently close became markedly harder to to the value indicated by the observe later in the month. The Comet LINEAR (1999 J3) equation. comet continued to fade and was 6 last seen in early January by 7 Comet Hale-Bopp (1995 O1) Andrew Pearce. 8 -4 9 -3 -2 10 -1 546 observations give an 0 11 1 uncorrected preliminary light 2 12
3 Observed magnitude curve of 6.7 + 5 log d + 11.5 log r 13 4 5 14 6 Comet Lee (1999 H1) 7 15 8 5 9 16
Observed magnitude (daily mean) 10 6 Jun Jul Aug Sep Oct Nov Dec Jan Feb 11 1999 - 2000 12 7 13 14 8 SepDecMarJunSepDecMarJunSepDecMarJunSepDecMarJunSepDecMarJun 1999 J6 was a SOHO comet 1995 - 2000 9
The residuals on the fitted curve are shown above. 10 (SOHO-109), though not a
11 member of the Kreutz group and Observed magnitude Spacewatch (1997 BA6) reached 12 was discovered by Michael Oates perihelion at 3.4 AU in late 13 on 2000 March 20 using archival November and as expected was 14 images on the SOHO website. th around 12 magnitude. First 15 Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb observed visually in 1998 1999 - 2000 Scattered observations of 1999 December it will be around for K8 LINEAR have continued, most of this year, but only for 1999 H3 LINEAR is in a distant with observers estimating it at Southern observers. The comet is parabolic orbit and hasn’t become around 14th magnitude. Reaching currently a little brighter than much brighter than 13m. It was perihelion in April, it will expected from the uncorrected in conjunction with the sun continue to be observable for preliminary light curve, which during November and December, some time. was a good fit to m = 4.5 + 5 log albeit at an elongation of 40° and d + 10.0 log r from 68 therefore fairly difficult to 49 observations give an observations. observe. It faded rapidly during uncorrected preliminary light the early spring as its distance curve of -1.4 + 5 log d + 18.7 log from Earth increased. r but this is a poor fit.
100 observations give a somewhat indeterminate uncorrected preliminary light curve of -1.1 + 5 log d + 21.9 log r
BAA COMET SECTION NEWSLETTER 16 THE COMET’S TALE
1999 S3 LINEAR reached School of Astronomy and around 12th magnitude in Astrophysics, Siding Spring November and early December Observatory, reported his and was quite well followed. The discovery of a 15th magnitude preliminary light curve from 106 comet on a plate taken by observations is m = 0.7 + 5 log d Malcolm Hartley with the 1.2-m + 39.8 log r U.K. Schmidt Telescope on October 7.64. The strongly Comet 1999 S3 (LINEAR) condensed comet showed a 8" 10 coma and a very faint 1' tail in 11 p.a. 320°. Additional astrometry was published on MPEC 1999- 1999 L3 LINEAR brightened to 12 within visual range at the end of T42. I. P. Griffin, Auckland November. It peaked at around 13 Observatory, reported a th 11 magnitude in early February, 14 condensed coma of diameter 7"
Observed magnitude on CCD exposures taken on with several observers following 15 it. October 11.4 UT (0.5-m 16 telescope). A. Becker and C. Comet 1999 L3 (LINEAR) 17 Stubbs, University of Oct Nov Dec Jan Feb 10 1999 - 2000 Washington; and J. Perez, Cerro Tololo Interamerican Observatory 11 1999 S4 LINEAR has brightened (CTIO) noted a tail in p.a. 328° 12 quite slowly, which seems to be a on a CCD exposure taken with feature of ‘new’ comets. the CTIO 0.9-m telescope on Oct. 13 Astrometric observations show 11.19. [IAUC 7273, 1999 October
Observed magnitude 14 that it is making its first visit to 11]. the inner solar system and may 15 well behave in a similar fashion This comet may reach binocular brightness, though there are 16 to comet Kohoutek. Dec Jan Feb Mar Apr insufficient observations to make 1999 - 2000 an accurate prediction. Initially
1999 N2 Lynn became difficult to at far southern declinations it will observe after late Autumn, but come within range of large became better placed as its apertures in July and binoculars elongation increased in the new in October. It moves far enough year. Observations by Jonathan north for observation by UK Shanklin suggested a magnitude observers in December when it around 13 in early January, but no reaches perihelion and moves other observers reported seeing it. It is currently in conjunction, but through Hydra, Virgo and Libra. after conjunction it should Comet Lynn (1999 N2) brighten rapidly and will become 1999 T2 LINEAR F. Shelly 5 visible in the northern sky. The reported the discovery by th 6 best fit light curve prior to LINEAR of an 18 magnitude 7 conjunction, using observations comet on October 14.16. 8 corrected for aperture is m = 8.5 Additional observations were 9 + 5 log d + 5.9 log r. This reported following posting on the 10 suggests that it could reach at NEO Confirmation Page [IAUC m 11 least 5 , and the first observations 7280, 1999 October 14]. The 7 Observed magnitude 12 after conjunction will be observations suggest that the 13 important in making the final absolute magnitude is around 5.5, 14 predictions. The light curve but don't place any constraint on 15 Jul Aug Sep Oct Nov Dec Jan Feb shows the observations and the the slope parameter. The comet 1999 - 2000 range of possible extrapolation. will reach perihelion in November 2000 and may reach 150 observations give an At its best the comet could have a tail a few degrees long. 13th magnitude or a little uncorrected preliminary light brighter, in the late summer. curve of 8.6 + 5 log d + 7.7 log r Comet 1999 S4 (LINEAR) 3 4 5 1999 T3 LINEAR Linkage at the 6 Minor Planet Center of 7 8 observations by LINEAR on 9 several nights during October 10 th 11 3.34 - 21 revealed an 18 12 magnitude object with a nearly- 13 Aperture corrected magnitude 14 parabolic retrograde orbit. This 15 orbit also represented a single- 16 17 night detection of an object by E. Oct NovDec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov W. Elst and S. Ipatov at Uccle on 1999 - 2000 October 18. Following placement 1999 T1 McNaught-Hartley of an ephemeris on The NEO Robert H. McNaught, Research Confirmation Page further BAA COMET SECTION NEWSLETTER 2000 April 17 observations were made on perihelion and will fade from 16th has a perihelion distance of 3.2 October 24 and 25. In response magnitude. AU and a period of ten years. to enquiries, Elst remarked that [IAUC 7368, 2000 February 18] the object was diffuse and had a 1999 U4 Catalina-Skiff On possible tail to the north; J. Ticha October 31 T. B. Spahr, Lunar P/1999 X1 Hug-Bell Amateurs and M. Tichy, Klet, reported the and Planetary Laboratory, Gary Hug and Graham E. Bell, object as slightly more diffuse reported the discovery by the Eskridge, KS, reported their than stars of comparable Catalina Sky Survey on October discovery of a 19th magnitude brightness and deduced a coma 31.25 of a slow-moving 17th comet on December 10.33, size of 9"; and D. Durig, magnitude object that was showing a faint tail in p.a. 285° Sewanee, TN, in poor conditions independently discovered on on CCD images taken with a 0.3- (strong wind, full moon), also November 1.28 by B. A. Skiff m Schmidt-Cassegrain reflector noted the object's diffuse (measurer B. W. Koehn) of the during the course of their minor appearance. [IAUC 7289, 1999 LONEOS survey. In response to planet search and follow up October 25]. The comet is a Skiff's alert, R. L. Millis and L. program. Following posting on distant one and will not get any H. Wasserman, on a 5-min R- the NEO Confirmation Page, L. brighter. band exposure with the Perkins Sarounova (Ondrejov, 0.65-m 1.8-m reflector, detected a coma reflector) obtained observations A/1999 TD10 Details of a distant extending 8" southeastward from on December 11.2 UT showing a asteroid discovered by the nucleus. After a posting in tail 20" long in p.a. about 300°. Spacewatch on October 3.19 were The NEO Confirmation Page, M. C. Hergenrother, Lunar and announced on MPEC 1999-T46 Tichy and Z. Moravec, Klet, also Planetary Laboratory, reports that [1999 October 11], with further reported that the object had an 8" a co-added 1200-s R-band image observations and a new orbit coma [IAUC 7298, 1999 obtained with the 1.54-m Kuiper given on MPEC 1999-V07 [1999 November 1]. The object is very telescope on December 11 shows November 2]. The 19th distant, but could brighten to 14th a 15" coma and a slightly curved magnitude asteroid is in an magnitude when at perihelion in tail 1' long in p.a. 280°. All of unusual high eccentricity orbit, 2001. the available astrometry which has perihelion at 11.6 AU, 4 observations received so far give (including prediscovery and a nominal semi-major axis of an uncorrected preliminary light observations on October 10 and 155 AU giving a period of 1900 curve of 4.6 + 5 log d + [10] log r December 7 by LINEAR) gives years. elliptical orbital elements, with A/1999 UG5 Details of another perihelion in 1999 June and a 1999 U1 Ferris LONEOS (0.59- unusual asteroid, discovered by perihelion distance of 1.9 AU. m Schmidt + CCD) reported the the Catalina sky survey on [IAUC 7331, 1999 December 11]. discovery of a 17th magnitude October 29.25, were given on The comet will fade. comet on October 18.38. MPEC 1999-V09 [1999 Additional observations were November 3]. This 18th A/1999 XS35 Details of another reported following posting on the magnitude object has a perihelion unusual asteroid, discovered by NEO Confirmation Page [IAUC distance of 6.6 AU and a period the LONEOS program on 7283, 1999 October 18]. The of 65 years. December 2.42, were given on comet was at perihelion last year MPEC 1999-X19 [1999 and will fade. 1999 V1 Catalina C. W. December 9]. This 17th Hergenrother, Lunar and magnitude object has a perihelion 1999 U2 SOHO Doug A. Planetary Laboratory, reported the distance of 0.95 AU and a period Biesecker, SM&A Corporation discovery of another comet of 18th of 79 years. The orbit approaches and Goddard Space Flight Center, magnitude by the Catalina Sky very close to the Earth at the reported observations of a comet Survey on November 5.44. [IAUC ascending node, so the object is (not a Kreutz sungrazer) 7302, 1999 November 7] The classed as a PHA. The orbital discovered independently by S. comet is close to perihelion and in miss distance is only 0.008 AU Gregory (Stanford University) a distant orbit. It will remain at a from the Earth and the asteroid and by J. D. Shanklin (Comet similar brightness until early next passed this point only 2.9 days Section, British Astronomical year, then fade. ahead of the Earth. If it produced Association) in SOHO/LASCO a meteor shower, slow meteors C3 data. The comet is very faint, 1999 WJ7 P/Korlevic An would have been seen by and not visible in very many apparently asteroidal 18th Southern Hemisphere observers frames. It was first visible on magnitude object discovered on on or around November 11.1, October 25.21 and remained November 28.94 by Korado with a radiant point of RA 17h visible until October 25.74. Korlevic at Visnjan with a 0.41-m 55m, Dec -70. Next year the [IAUC 7292 and MPEC 1999- f/4.3 reflector + CCD was shower would be expected around U29, 1999 October 28] I made the indicated on some of his November 10.3. co-discovery on October 26.35. December images to be possibly "fuzzy", and the cometary nature 1999 XB69 P/LINEAR An 1999 U3 P/LINEAR R. Huber has been confirmed by C. apparently asteroidal, 18th reported the discovery by Hergenrother and S. Larson, magnitude object discovered by LINEAR of an 18th magnitude Lunar and Planetary Laboratory, LINEAR on December 7.29, with comet on October 30.32. who found a 13" coma elongated a cometlike orbit has been Additional observations were in p.a. 80 deg on a 600-s co- observed by C. Hergenrother, reported following posting on the added R-band exposure taken on Lunar and Planetary Laboratory, NEO Confirmation Page [IAUC 2000 Feb. 7.25 UT with the 1.54- on February 27 with the Catalina 7295, 1999 October 31]. It is past m Catalina reflector. The comet 1.54-m reflector to show a 5" BAA COMET SECTION NEWSLETTER 18 THE COMET’S TALE
coma and a 10" tail in p.a. 80°. faint tail in p.a. 60° on December 1999 O2 SOHO (IAUC 7376, 2000 March 07) The comet is intrinsically faint, 27 (0.60-m reflector). The initial 1999 O3 SOHO (IAUC 7376, 2000 March 07) with a perihelion distance of 1.6 orbit is parabolic with perihelion 1999 P3 SOHO (IAUC 7367, 2000 February 15) AU and a period of 9.4 years. in March 2001. [IAUC 7338, 1999 P4 SOHO (IAUC 7376, 2000 March 07) [IAUC 7370, 2000 February 29] 1999 December 27] The comet 1999 P5 SOHO (IAUC 7376, 2000 March 07) could reach 13th mag at the end 1999 Q1 SOHO (IAUC 7376, 2000 March 07) 1999 XS87 P/LINEAR An object of the year. 1999 Q2 SOHO (IAUC 7376, 2000 March 07) that was assumed to be asteroidal 1999 Q3 SOHO (IAUC 7376, 2000 March 07) was found by LINEAR on 1999 1999 Y2 SOHO Kazimieras 1999 R3 SOHO (IAUC 7376, 2000 March 07) December 7.38 and 8, and it was Cernis, Vilnius, Lithuania, 1999 R4 SOHO (IAUC 7383, 2000 March 17) later linked to observations by discovered an apparent comet at 1999 S5 SOHO (IAUC 7383, 2000 March 17) LINEAR on 2000 January 6 and 7 magnitude about 5 on SOHO 1999 S6 SOHO (IAUC 7383, 2000 March 17) by G. V. Williams, Minor Planet images taken on 1999 December 1999 S7 SOHO (IAUC 7383, 2000 March 17) Center. Following a request from 28.28 that were posted on the 1999 U5 SOHO (IAUC 7386, 2000 March 24) the Minor Planet Center after SOHO website. D. A. Biesecker, 1999 W1 SOHO (IAUC 7386, 2000 March 24) seeing that the orbit appeared SM&A Corporation and Goddard 1999 Y3 SOHO (IAUC 7386, 2000 March 24) comet-like, M. Tichy and Z. Space Flight Center, reported that 2000 B1 SOHO (IAUC 7349, 2000 January 24) Moravec obtained observations at the comet was visible on both 2000 B5 SOHO (IAUC 7386, 2000 March 24) Klet on January 11 and 12 that LASCO C2 and C3 images and 2000 B6 SOHO (IAUC 7386, 2000 March 24) showed this object to be diffuse that no tail was detected. 2000 B7 SOHO (IAUC 7386, 2000 March 24) with a coma diameter of 15". Astrometric measurments by 2000 C6 SOHO (IAUC 7364, 2000 February 12) [IAUC 7344, 2000 January 12] Biesecker and D. Hammer 2000 D1 SOHO (IAUC 7370, 2000 February 29) The comet is in a long period (University of Maryland), reduced 2000 D3 SOHO (IAUC 7386, 2000 March 24) orbit (73 years) and was at by Marsden, appeared on MPEC 2000 E1 SOHO (IAUC 7376, 2000 March 07) perihelion in 1999 August at 2.8 2000-A36, together with 2000 F1 SOHO (IAUC 7393, 2000 April 04) AU. parabolic orbital elements (q = 0.048 AU, i = 111.4 deg), were discovered with the SOHO 1999 XN120 P/Catalina An showing that the comet is not a LASCO coronographs and have apparently asteroidal, 17th Kreutz sungrazer. Magnitude not been observed elsewhere. magnitude object discovered on reductions by Biesecker and They were sungrazing comets of December 5.19 by the Catalina Hammer show that the comet the kreutz familly and were not Sky Survey, with a cometlike faded from magnitude 6.1 to 6.8 expected to survive perihelion. orbit was also observed by during December 28.58-28.79, Some of these comets show no tail Hergenrother on February 27 with and thence from view while still at all and it is possible that some the 1.54-m reflector to show a 12" in the C3 field. [IAUC 7343, supposed observations of Vulcan coma but no tail. The comet has 2000 January 10]. The comet were actually tiny Kreutz group a perihelion distance of 3.29 AU should have still been brightening comets. and a period of 8.5 years. [IAUC at this point, implying that its 7370, 2000 February 29] volatiles had probably been SOHO 74 (1999 O1) and exhausted. SOHO-76 (1999 P3). D. A. 1999 Y1 LINEAR A 17th Biesecker, SM&A Corporation magnitude object with unusual Kazimieras provided the and Goddard Space Flight Center, motion and reported as asteroidal following information about the repored measurements of two by LINEAR on December 20.22 discovery: I discovered this comet apparent Kreutz sungrazing was found to be cometary in due to your two discoveries and comets (both tailless) discovered appearance following posting on information which helped me for with the LASCO C3 coronagraph the NEO Confirmation Page. Z. looking at CCD images. The aboard SOHO on 1999 July 31.51 Moravec, Klet, reported that the object at C2 was difficult for and August 3.24 [IAUC 7367, object appeared slightly diffuse detecting at 1024x1024 too. I say 2000 February 15]. 1999 O1 was with a possible coma of diameter that because I detected found by T. Lovejoy in movies about 10" on images taken in poor independently SOHO-94 with a posted at the SOHO website. seeing on December 21 and 22. bright tail after A. Vourlidas 1999 P3 was found by D. Lewis. G. Billings, Calgary, AB, without problem on December 21. reported an apparent nebulosity of C/1999 Y2 was without tail and I discovered SOHO-97 (2000 B1) diameter about 12" on December its brightness was similar to on January 24. I had to leave 23 CCD images taken with a Sgr24 in orange filter (about 5 work early on January 24 in order 0.36-m reflector, and he noted a mag). Then I discovered SOHO- to pick up my car which had been faint tail about 20" long in p.a. 95 at C3 images (from December in for servicing (an expensive 70° on December 27. S. Nakano, 27 23 hours) and sent more than business as several repairs were Sumoto, Japan, reported that H. 20 positions to B. Marsden. D. needed) and went straight home Abe (Yatsuka, 0.26-m reflector) Biesecker did not reply me for 6 afterwards as it was clear and I found the comet to be evidently days. It was a holidays. If the wanted to grab a bite to eat before diffuse, T. Kojima (Chiyoda, comet has absolute magnitude it got dark. I then cycled out to 0.25-m reflector) found a 10" about 18, it could be detectable the Cambridge Observatories and coma and a short tail toward the with CCD in the evening sky as got out the great Northumberland northeast, and T. Oribe (Saji 15.5 mag with elongation about refractor at around 17:50. I Observatory, 1.03-m reflector) 40 deg these days before bright observed 141P/Machholz 2 (a bit found a 20" coma and a 30" tail moonlight coming. iffy at 13m), 114P/Wiseman-Skiff in p.a. 60°, all on December 27. (glimpsed with averted vision at m A. Nakamura, Kuma, Japan, 1999 E2 SOHO (IAUC 7377, 2000 March 09) 14 ) and 1999 S4 (LINEAR) (not found coma diameter 0'.35 and a 1999 O1 SOHO (IAUC 7367, 2000 February 15) seen and [13.8). I could see BAA COMET SECTION NEWSLETTER 2000 April 19 clearly several galaxies SOHO-99 (2000 B7) was also Q1 were first noted by T. Lovejoy catalogued at 13m. I also discovered by Maik Meyer, and via the SOHO Web page. observed a few binocular almost simulataneously by Terry variables and then thought about Lovejoy. SOHO-108 (1999 E2) D. A. going bell-ringing (one of my Biesecker, SM&A Corporation other hobbies) at 19:30, though as Three more comets, including and Goddard Space Flight Center, the practice started at 19:00 I SOHO-100 were discovered reported that M. Oates, would be late. However, I between February 3 and 5, Manchester, England, found decided to have a quick look at moving in similar trajectories another Kreutz sungrazing comet the SOHO images first on the diagonally across the upper left in archival SOHO LASCO C3 IOA Starlink system. As soon as quadrant. There seems to be a Web data from 1999 March 2.51. the java loop had downloaded it swarm of these objects, with a [IAUC 7377, 2000 March 9] was obvious that a Kreutz fourth discovered by Michael fragment was heading in towards Oates and visible on the C2 On IAUC 7383 [2000 March 17], the sun. I immediately emailed images from 18:54 - 20:44 on D. A. Biesecker reported Doug and Brian Marsden, though February 7. observations (measures by D. this one was so obvious that I was Hammer and himself, reductions sure there would have been prior SOHO-104 (2000 C6) was a by B. G. Marsden) of four more claims. It turned out that there Kreutz fragment discovered by tailless, Kreutz sungrazing weren't and Doug posted the Terry Lovejoy on February 9. comets seen in SOHO C3 data, discovery on his web page and SOHO-105 (2000 D3) was during 1999 September, which quickly got the positions for Brian another Kreutz fragment. were discovered by K. Schenk, to compute the orbit, which except for C/1999 R4, which was appeared on IAUC 7349 at 23:10. SOHO-106 (2000 D1) D. A. first noted by T. Lovejoy via the The comet peaked in brightness at Biesecker, SM&A Corporation SOHO Web page. around 5th magnitude on the and Goddard Space Flight Center, morning of January 25, and began reports observations of an evident On IAUC 7386 [2000 March 24] to grow a tail, but also to fade. It Kreutz sungrazing comet with a D. A. Biesecker reported disappeared from the C3 frames tail discovered by D. Lewis in observations (measures by D. but a ghostly image was visible SOHO/LASCO C3 data on Hammer and himself, reductions for a couple of hours on the C2 February 28.57. Biesecker by B. G. Marsden) of four more frames between 16:06 and 18:30. provides apparent magnitudes comets seen in 1999 SOHO data, brightening from V = 7.4 +/- 0.2 all but C/1999 J6 being presumed on Feb. 28.971 to 5.8 +/- 0.1 on Kreutz sungrazers. Comets Feb. 29.404 UT. [IAUC 7370, C/1999 J6 (visible in both C2 and 2000 February 29] C3 data) and C/1999 U5 (visible in only the C3 telescope) show no SOHO-107 (2000 E1) D. A. tail. However, C/1999 W1 and Biesecker, SM&A Corporation C/1999 Y3, which were both and Goddard Space Flight Center, visible with only the C2 telescope, reports that several people did show tails. Selected V browsing the SOHO Web site magnitudes from Biesecker for (including M. Meyer, M. Boschat, C/1999 J6: May 10.750 UT, 8.1; T. Harincar, and M. Oates) noted 10.833, 7.3; 10.935, 6.5; 11.088, another Kreutz sungrazing comet 5.9; 11.269, 5.5, 11.338, 4.9; in SOHO LASCO data on March 11.462, 5.1. Comet C/1999 J6 Faint Kreutz fragment SOHO-98 4.40. Observed in both the C2 (SOHO-109) was first noted by (2000 B6) was discovered by and C3 telescope data, this object M. Oates in archival data via the Maik Meyer on January 29, showed a tail of length about 10'. SOHO Web page on ? 2000 however an independent [IAUC 7376, 2000 March 7] March 20; C/1999 U5 and C/1999 discovery was made by Michael On the same IAUC Biesecker also W1 were discovered by Biesecker, Oates of the SPA on January 30. reported observations (measures and C/1999 Y3 was discovered by He had heard a talk that I gave on by D. Hammer and himself, A. Vourlidas of the SOHO team. January 29 about my discovery of reductions by B. G. Marsden) of SOHO-97 and decided to try it some older Kreutz sungrazing On the same IAUC Doug himself. He wasn't aware of the comets seen in SOHO C3 data; Biesecker also reported real time movie loops and so full astrometry and parabolic observations of four additional downloaded individual high orbital elements appear on the Kreutz sungrazing comets resolution frames and made a MPECs indicated below. Comet detected by SOHO in the first few movie himself. Looking at the C/1999 O2 developed a short tail, months of 2000. Comet C/2000 sequence he spotted the moving C/1999 O3 had a short tail B5 was discovered by Biesecker; image of the Kreutz fragment, evident, C/1999 Q3 showed a tail, the other three comets were found however he was beaten to it by and C/1999 R3 showed evidence by several people browsing the Maik Meyer. Terry Lovejoy also for a tail; the other four comets SOHO web site, as follows: spotted the object. I was quite showed no evident tail. Comets C/2000 B6, M. Meyer, T. surprised therefore to get some C/1999 O2 and C/1999 P4 were Lovejoy, J. Shanklin, and M. credit on IAUC 7386 as I thought discovered by D. Lewis, C/1999 Oates; C/2000 B7, Meyer and that I had only confirmed the P5 by A. Vourlidas, C/1999 Q2 Lovejoy; C/2000 D3, Meyer and discovery. and C/1999 R3 by K. Schenk, and K. Cernis. C/2000 D3 was visible C/1999 Q3 by Biesecker, while with both the C2 and C3 comets C/1999 O3 and C/1999 telescopes and showed a short BAA COMET SECTION NEWSLETTER 20 THE COMET’S TALE tail; the other three comets from 3.5 to 30. Brighter objects the NEO Confirmation Page. showed no apparent tail and were are often discovered in the real CCD observations by P. Kusnirak visible only in the C3 data. time data, but the fainter ones (Ondrejov, 0.65-m f/3.6 reflector) have to wait for the archival data and by M. Tichy and Z. Moravec I discovered SOHO-110 (1999 to be searched which runs three or (Klet, 0.57-m f/5.2 reflector) F1) on April 1 at 09:09 UT whilst four months behind. SOHO has indicate that the object appears compiling material for this issue now discovered 110 comets (109 slightly diffuse. [IAUC 7354, of Comet's Tale at the Institute of with LASCO), of which the 2000 February 1] The comet is a Astronomy. I'd looked at the C3 majority are all members of the distant one, past perihelion and frames and seen nothing and Kreutz group of sungrazing will fade. whilst waiting for the C2 frames comets. So far, only 13 are not to download I was updating the Kreutz group sungrazers. Further 2000 B3 P/LINEAR A 19th web pages and collating notes background information on the magnitude object with unusual from the Journals. I thought that SOHO comets can be found on motion that was reported as I glimpsed a moving object on the Doug Biesecker's web pages. The asteroidal by LINEAR on January bit of the movie that I could see LASCO images are downloaded 27.24 was found to be cometary in and on checking it was an obvious every half an hour and you can appearance following posting on Kreutz fragment, visible from view them individually or as the NEO Confirmation Page. 04:30 to 07:31. I immediately movies on the web. CCD observations by P. Kusnirak emailed the search team and (Ondrejov, 0.65-m f/3.6 reflector) almost instantly got a message 2000 A1 Montani J. Montani, on Feb. 1 show a coma diameter from Maik Meyer saying that he Lunar and Planetary Laboratory, of 6" and a faint tail in p.a. 120 had also found it. reported his discovery of a faint deg, and F. Zoltowski (Edgewood, 19th magnitude comet on CCD NM, 0.3-m f/3.3 reflector) reports images taken with the 0.90-m a small faint tail about 30" long Spacewatch telescope at Kitt Peak in p.a. 100 deg and a dense coma on January 12.33. The comet about 10" across. The comet is shows a coma with diameter 5"- near perihelion. [IAUC 7356, 6", slightly elongated in p.a. 245- 2000 February 2] 250°. An R CCD image taken by S. Kern with the 2.3-m Steward 2000 B4 D/LINEAR Another telescope on January 13 shows the apparently asteroidal object, of comet to be clearly extended 19th magnitude, was reported by toward the southwest, and she LINEAR on January 29.25 and derived mag 18.1. W. Shook posted on the NEO Confirmation found the object to be nonstellar Page. This object has the orbit of with a 2".6 tail toward the a centaur and was noted as Information about the latest southwest on an image taken with appearing perhaps slightly diffuse discoveries is available from the 3.5-m WIYN telescope on (P. Kusnirak, Ondrejov, 0.65-m Doug Biesecker who is a member January 13. [IAUC 7346, 2000 reflector, February 10) and 'soft' of the SOHO team. To mark January 14] The comet is very and slightly larger than star SOHO-100 ESA issued a Press distant (9.8 AU) and close to images (D. Balam, Victoria, 1.82- release and more information and perihelion. The perihelion m reflector, Feb. 11). The images are on NASA hotshots. distance is the largest on record perihelion distance is 6.8 AU and for a confirmed comet, though the period 77 years [IAUC 7368, SOHO was launched on 1995 Trans-Neptunian-Objects (for 2000 February 18] December 2. It experienced a example 1999 DP8) have greater malfunction on 1998 June 25 and perihelion distances. A/2000 BD19 MPEC 2000-C09 contact with it was lost. It was reports the discovery by LINEAR located by radar on July 29, A/2000 AB229 Details of an of a sun-approaching asteroid on communication was established in unusual asteroid with a 400 year January 26.26. The 18th early August and it resumed period, a high inclination orbit magnitude object has a period of pointing at the Sun in mid and a perihelion distance of 2.3 0.8 years, and a perihelion September. The LASCO cameras AU were given on MPEC 2000- distance of 0.09 AU. If entirely were reactivated in October but B20. The 18th magnitude object asteroidal it would be 12th further problems were was discovered by LINEAR on magnitude at perihelion, but if it encountered and the spacecraft January 5.38 and was just past shows cometary activity it could did not return to action until perihelion. The next MPEC gave reach 6m and be visible on SOHO February 1999. Further control details of another unusual object LASCO images. It was last at problems were encountered from 2000 AC229, which has a period perihelion on 1999 Oct 17.3 and time to time during the winter of of 8.8 years, an inclination of 53 will next be at perihelion in 2000 1999/2000. degrees and a perihelion distance August. of 1.8 AU. This was discovered There are three LASCO (Large by LINEAR on January 8.24. 2000 C1 P/Hergenrother Carl Angle Spectroscopic Hergenrother, Lunar and Coronographs) on the SOHO 2000 B2 LINEAR A 19th Planetary Laboratory, reported a spacecraft, which orbits the sun at magnitude object with unusual 17th magnitude object on 2000 the earth's L1 Lagrangian point, motion and reported as asteroidal February 4.46 that showed an 11" 1.5 million km ahead of the earth. by LINEAR on January 29.24 was tail in p.a. 300 deg on one of four C1 has a field from 1.1 to 3 solar found to be cometary in CCD images taken with the 0.41- radii, C2 from 1.5 to 6 and C3 appearance following posting on m Schmidt telescope at Catalina. BAA COMET SECTION NEWSLETTER 2000 April 21
Following posting on The NEO February 5.67. C/2000 C5, found of the orbit, and the object was Confirmation Page, numerous by Michael Oates on February placed in The NEO Confirmation CCD observers reported cometary 7.79, was at V = 7.5-8.0 on Page. Isolated observations from appearance: February 5.3 UT, February 7. Comets C/2000 C2 LINEAR on February 7, from the coma diameter about 12", brighter and C/2000 C5 may also be Catalina Sky Survey on March 1 60" tail in p.a. 290 deg, extending related to each other. [IAUC (when observer T. B. Spahr had more faintly to 180" (J. E. 7364, 2000 February 12] in fact drawn attention to the McGaha, Tucson, AZ, 0.62-m object's "slowish" motion) and reflector); February 5.5, tail about 2000 CT54 LINEAR Yet another from LONEOS on April 2 were 12" long toward the northwest (G. apparently asteroidal LINEAR then also linked. Neither these Billings, Calgary, AB, 0.36-m object, of 19th magnitude, observers nor those responding to reflector); February 5.7, slightly discovered on February 2.44, that the Confirmation Page made a diffuse with very faint tail about was posted on the NEO definite remark about the object's 10" long to the northwest (G. J. Confirmation Page was noted to cometary appearance, even in Garradd, Loomberah, N.S.W., have a 15"-16" tail toward the response to specific enquiries 0.45-m reflector); February 6.1, north-northwest on February 12 from the Central Bureau coma diameter 0'.1, tail 0'.3 long by J. G. Ries, McDonald (although strong moonlight has in p.a. 290 deg (P. Pravec and P. Observatory (0.76-m reflector). recently been a factor). Following Kusnirak, Ondrejov, 0.65-m The comet reaches perihelion at a suspicion by Brian Marsden and reflector); February 6.4, faint tail 3.1 AU in 2001 June [IAUC an independent suggestion by C. < 10" long in p.a. about 290 deg 7368, 2000 February 18] W. Hergenrother, 2000 ET90 has (D. T. Durig, Sewanne, TN). been definitively identified with Prediscovery observations by 2000 D2 LINEAR An apparently comet D/1984 H1 = 1984 JD LINEAR on January 4 and 8 have asteroidal object of 18th (Kowal-Mrkos) = 1984n (IAUC also been identified. [IAUC 7357, magnitude, discovered by 3988, 4001) = 1984 X, for which 2000 February 6] The comet is LINEAR on February 25.20 and current predictions (ICQ Comet intrinsically quite faint and has posted on the NEO Confirmation Handbook for 2000, p. H87; OAA perihelion at 2 AU. It will Page was observed to be cometary Comet Handbook for 2000, p. 37) brighten a little. by F. B. Zoltowski (Edgewood, require correction by Delta T NM; very diffuse image on about -125 days. The comet 2000 C2 SOHO 2000 C3 SOHO February 28.1 UT; 12" tail in p.a. passed only 0.16 AU from Jupiter 2000 C4 SOHO 2000 C5 SOHO 270 deg on March 1.1) and by C. in March 1989. There was an 2000 C6 SOHO D. A. Biesecker, Hergenrother (Catalina 1.54-m unobserved return with T = 1991 SM&A Corporation and Goddard reflector; 8" coma and very faint Aug. 2. [IAUC 7403, 2000 April Space Flight Center, reported 15" tail in p.a. 105 deg on March 15] The original orbit was based measurements of five comets 1.3). The comet was near on only eight observations, so it is observed with the coronagraphs perihelion at 2.3 AU. [IAUC perhaps not surprising that the aboard SOHO. Only C/2000 C6 7372, 2000 March 1] prediction was somewhat in error. appears to be a Kreutz sungrazer; it was first noticed by Terry A/2000 DG8 The third asteroid 2000 G1 LINEAR F. Shelly, for Lovejoy on SOHO web images on with retrograde motion was the Lincoln Near-Earth Asteroid February 9.22, and Biesecker announced on MPEC 2000-E07. Research project, reported, in notes that its brightness ranged It has a perihelion distance of connection with the discovery on from V = 8.7 on February 9.43 to 2.19 AU and a period of 32.5 April 7.45 of a fast-moving 18th 7.7 on February 9.68 UT, and the years. mag object, that Lisa Brown- comet showed a tail at 13 solar Manguso noticed that the object radii on C3 images. The other A/2000 DQ110 and A/2000 showed clear cometary activity. It comets showed no tail. C/2000 C2 EB107 are another two asteroids is very likely that the comet is (SOHO's 100th comet) first noted with orbits similar to those of short period (with current by Kazimieras Cernis on February short period comets. Details of geocentric distance 0.24 AU), 3.70, remained relatively stable in the orbits of these and other though the initial elements are brightness (V = 6.5-6.9) during unusual asteroids are on the iau parabolic, with q 1.01 AU and T February 3.70-3.84. C/2000 C3, web page at http://cfa- 2000 March 9.02. [IAUC 7396, found by Biesecker on February www.harvard.edu/iau/lists/Others. 2000 April 8] The parabolic orbit 4.56, brightened from V = 6.7 on html suggests that the comet would February 4.59 to 5.9 on February have passed 0.15 AU from the 4.79, before fading to V = 7.0 on 2000 ET90 P/Kowal-Mrkos Earth in early March, reaching February 5.09. C/2000 C4, found MPS 11479 contained 15th magnitude, but was at high by Maik Meyer on February 5.16, observations on March 9.30 and southern declination. was on a trajectory closely 13 by LINEAR of an apparently following that of C/2000 C3, and asteroidal, 19th magnitude object For the latest information on it was assumed that the orbits are presumed to have a moderately discoveries and the brightness of identical with a difference eccentric orbit in the inner part of comets see the Section www page: Delta(T) = 0.60 day. C/2000 C4 the main belt. Linkage by G. V. http://www.ast.cam.ac.uk/~jds brightened from V = 5.9 on Williams to LINEAR or the CBAT headlines page at February 5.17 to 4.9 on February observations on April 4 and 8 http://cfa-www.harvard.edu/ 5.30, before fading to V = 6.7 on demonstrated the cometary nature cfa/ps/Headlines.html
BAA COMET SECTION NEWSLETTER 22 THE COMET’S TALE
Comet Hunting Notes Don Machholz
NOVEMBER 1999 : Until three search was shut down. In the begin soon. Robert McNaught years ago, the search for Near- meantime the Northern will manage it and all the Earth Objects (NEO's) was Hemisphere increased its search equipment is being updated. carried out in both the Northern capabilities, especially with the and Southern Hemispheres. addition of LINEAR, in New These notes are taken from Comet Then, in 1996 the Australian Mexico, about a year ago. Now Comments by Don Machholz, which is published on the government stopped the funding the Southern Hemisphere search Internet. so the Southern Hemisphere has been re-funded and should ICWA II : METHOD-RELATED BRIGHTNESS ESTIMATE DIFFERENCES, AND THE DELTA EFFECT Joseph N. Marcus
The Comet’s Tale editor is to be Bobrovnikoff estimates were and brightness. Named after the commended for his extraordinary considerably fainter,” by 0.9 Greek letter D, which is used to efforts which made the Second magnitude. For C/1982 M1 connote the earth-object distance, International Workshop on (Austin), which was condensed, it can be studied through the Cometary Astronomy such a the difference was considerably formula success. Not only was Jonathan smaller, about 0.2-0.25 Shanklin key in organizing and magnitude. The author, the 1) m1 = mo + 2.5 k log D + administrating the program and venerable comet observer Reinder 2.5 n log r its finances, but he turned out a Bouma, further wrote: “From great synopsis of the goings-on in these two examples it is clear that where m1 is the observed issue 12 of The Comet’s Tale (1) there is a real difference between magnitude of the comet, r is that arrived in the U.S. mail only Bobrovnikoff and Sidgwick comet-sun distance, D is the six weeks after the event! At such estimates. The size of the absolute magnitude (reduced to a pace it was perhaps inevitable difference appears to be a D = 1 AU = r), and k and n are that an error or two may have function of the coma’s brightness, the indices of variation of m1 crept into the summary. I should size, and degree of condensation.” with log D and log r, respectively. like to correct one that occurred He warned that absolute Normally k is taken to be 2, i.e., it in the discussion of Charles magnitude mo and slope n value is assumed that comet brightness Morris’ presentation (“Why you of a cometary light curve can be varies as D-2, the familiar inverse don’t get your papers published in systematically affected by the type square law of distance, but in a the ICQ and other rants”) and of method used in the analysis. delta effect, k < 2. Eq. (1) is in offer some clarifying remarks. Don Machholz, a participant in the general form the Cambridge IWCA, was Contrary to what was reported on actually the first to present hard 2) a0 + a1 x1 + a2 x2 = 0 p. 12, I did not comment “…that data on methods differences in the extensive work by the Dutch Comet News Service (3), only two where x1 (= 2.5 log D) and x2 (= Comet Section did demonstrate years after the Morris method was 2.5 log r) are independent the delta effect.” Instead I noted published in the Western variables and a0 (= mo), a1 (= k) that the Dutch Comet Section had literature (4,5). Machholz had and a2 (= n) are unknown studied differences in brightness found the same thing for 1980 coefficients that can be solved for estimates between the the apparitions of comets through multiple linear regression Sidgwick and Bobrovnikoff 38P/Stephan-Oterma, 8P/Tuttle, (6) on a data set of m1, r, and D methods. My remarks addressed and 2P/Encke – the Sidgwick values. the misimpression that arose method yields brighter estimates during the discussion period that than the Bobrovnikoff, with the In his talk at IWCA II, Morris these differences were not Morris method in-between (3). In implied that doing multiple linear documented – a point over which summary, Morris’ assertion about regression on comet light curves Morris took some ribbing, as methods-related brightness in the above manner is not Shanklin noted. estimate differences is supported legitimate because r and D are by published literature. There is always “statistically correlated.” In fact, the Dutch Comet Section no need to attribute the claim This implication is not correct. had long ago published in the solely as a “personal Certainly r and D are always English language literature an communication.” mathematically related by the analysis of methods-related cosine law brightness estimate differences in The “delta effect” is an artifact in their observations of two comets which the outer part of the coma, 3) r2 = D2 + R2 – 2RD cosq in 1981-2 (2). For 64P/Swift- magnified by near-earth distance, Gehrels, a faint, large, diffuse is lost to human vision as its where R is the sun-earth distance comet, the “…Morris and contrast gradient falls below and q is the elongation. Morris Sidgwick estimates were threshold, leading to an confuses the concept of essentially the same, but the underestimate in coma diameter BAA COMET SECTION NEWSLETTER 2000 April 23
“mathematical relationship” with the International Comet introduced by observing a comet that of “statistical correlation.” r Quarterly, of which he is at, say, twice the magnification in and D may or may not have a Associate Editor, or any an instrument twice the aperture significant statistical correlation professional astronomical journal. is physically equivalent to depending on the geometry of the Charles’ choice of the word observing the comet in the apparition and the distribution of “rant” in the title of his talk was original instrument if the comet- the m1 observations. If, say, the amusing and appreciated for its earth distance were to be halved. comet is a periodic reaching a self-deprecating good humor. This symmetry is so direct that it close perigee at the time of its However, he should realize that should be no leap at all to accept perihelion, then r and D have a one of the definitions entered for that “delta effect” exists if high degree of covariance, and it it in the Oxford English “aperture effect” exists. would be difficult or impossible to Dictionary (apologies, do useful regression. However, if Cambridge!) is “empty Joseph N. Marcus a comet reaches close perigee at a declamation.” I think that it can 15209 Isleview Dr. time when it is solely on the be fairly concluded that it is this Chesterfield, MO 63017 heliocentric inbound or outbound entry which most accurately U.S.A. legs of its orbit, then the characterizes his specific rant Email: [email protected] covariance may be minimal and against regression on log D and legitimate regression would be log r in comet light curves References possible. Such was the case for because they are “correlated.” near earth-approaching comets 1. Shanklin J (1999). The 1P/1909 R1 (Halley), C/1975 T2 This being said, Charles and I Second International (Suzuki-Saigusa-Mori) and would probably agree that the best Workshop on Cometary C/1979 Y1 (Bradfield), for which way to look for a delta effect in a Astronomy. The Comet’s Tale delta effect k values were found comet light curve is not, 6:1 by multiple regression to be 1.41 paradoxically, through the light 2. Bouma RJ (1983). ± 0.07, 1.61 ± 0.12, and 1.37 ± curve itself. After all, comets can Methods-related differences in 0.09, respectively (7-9). The and quite often do behave comet brightness estimates. covariance between r and D can irregularly in brightness, in such Comet News Service 83(2):2 be assessed in two related ways. a manner as to violate the 3. Comparison of One is to compute the correlation assumption of linear behavior of brightness estimation methods coefficient between them directly heliocentric magnitude with log r. (1981). Comet News Serv using the variance-covariance It is this criticism of any log r 81(1):8 matrix in the regression formula regression analysis which is most 4. Morris CS (1979). A (6). For the Bobrovnikoff data set cogent in my view. Ideal analyses new method for estimating (10) for P/Halley in 1910, the of delta effect in light curves cometary brightness. Comet correlation coefficient between should take into account such News Serv 79(1):2 log D and log r can be computed potential irregularities by 5. Morris CS (1980). A as -0.047 – almost no correlation comparing m1 observations with review of comet observing at all! A second way, less direct independent data sets, such as techniques – I. Intnl Comet but more utilitarian, also dust and gas production rate Qrtly 2:69 employing the variance- photometry, which may be less 6. Walpole RE, Myers RH covariance matrix, is to look at prone to a delta effect. Such (1978). Probability and the sizes of the standard analyses have never been done, to Statistics for Engineers and deviations on k. The greater the my knowledge. And analyses for Scientists, 2d ed., MacMillan, co-correlation between log D and delta effect (and of comet light New York, 1978, pp. 314-364 log r, the larger the standard curves in general) are further 7. Marcus JN (1981). The deviation, and the less complicated by the need to adjust ‘delta effect’ in Halley’s 1910 determinate the solution for k. for systematic errors arising from light curve. Comet News Serv For the m1 data sets analyzed for the type of magnitude estimation 81(3):2 these three comets, the SDs on k method employed – discussed 8. Marcus JN (1981). The are small enough so that when above – as well as for other error delta effect in comets 1975 X assessed by Student t-test, all 3 k sources, such as instrument and 1979 X. Comet News values are significantly different magnification – noted below. Serv 81(3):4 from k = 2, with the level of 9. Marcus JN (1986). probabilities that the differences In my view, the best evidence for Halley’s true brightness in can be due to chance being much delta effect is the well- 1909-11 and comparison to less than p = 0.05 in all three documented artifact of 1985-86. Proc 20th ESLAB cases. underestimated coma diameter Symposium on the Exploration and brightness with increasing of Halley’s Comet, ESA SP- It should therefore be accepted instrument magnification, also 250, III:307 that multiple linear regression to referred to as “aperture effect” 10. Bobrovnikoff NT (1941, obtain m0, n, and k values for (10, 11). Charles Morris helped 1942). Investigations of the comet light curves is possible and to define it (11), and the effect is brightness of comets, parts I, that it is a legitimate method beautifully seen in his II. Contrib Perkins Obs No. when judiciously applied. It observations of C/Bradfield 1979 15-16 would be unfortunate if Morris’ Y1 (12). In the paradigm that 11. Morris CS (1973). On “rant,” in his word, at the each is an artifact of human aperture corrections for comet Cambridge IWCA should deter vision, “aperture effect” and magnitude estimates. Publ analysts from employing it for “delta effect” are identical in that Astron Soc Pacif 85:470 fear of having a paper rejected by the underestimation artifact BAA COMET SECTION NEWSLETTER 24 THE COMET’S TALE
12. Morris CS (1980). The (1979l). Intnl Comet Qrtly apparition of comet Bradfield 2:23 Observations of Comet 109P/Swift-Tuttle Alex Vincent
Comet Swift-Tuttle was daylight. I'd sure like to see that discovered by Lewis Swift and rascal! Horace Tuttle in 1862 and came to perihelion in the same year. It I made a number of observations was calculated to have a period of of comet Swift-Tuttle, the first 120 years and was due to return was on 1992 October 16 through in 1982, but it never came. Some a 20cm Celestron telescope and it astronomers thought that it came appeared as a large fuzzy smudge and went unseen while others with a short tail. My next thought that it had a longer observation was on October 30 period. where its tail was longer and the Sketches of Comet Swift-Tuttle comet more elongated. I took made between 1992 October and Its period is between 130 and 135 several photographs of it on a December. years and it last reached camera platform. perihelion on 1992 December 12. My best observation of the comet T Kiuchi recovered it on 1992 I made observations of it on was on 1992 December 4, again September 27. Comet Swift- November 6 through a Celestron through the 20cm Celestron, and again it looked impressive with its Tuttle is the parent comet of the 20cm and it looked great with its th Perseid meteor shower, which is tail. My next observation of it on tail. The comet was of 5 seen in August each year. November 17 was down on the magnitude and I took several beach. The comet's tail was thin photographs with the camera The comet will return again in as viewed through a x2 piggybacked on the telescope. My 2126 and will make a very close teleconverter attached to a camera last look at it was on December 5 approach to the Earth to just over lens through which I took some down at the beach with the naked 1 million kilometres and its tails photographs. eye also taking a number of will stretch half way across the photographs with my camera on a sky. The comet may be seen in tripod.
BAA COMET SECTION NEWSLETTER 2000 April 25
BAA COMET SECTION NEWSLETTER