Updated 2004 January 5
The equations for the light curves of comets that are currently visible use only the raw observations and should give a reasonable prediction for the current brightness. If the comet has not yet been observed or has gone from view a correction for aperture is included, so that telescopic observers should expect the comet to be fainter than given by the equation. The correction is about 0.033 per centimetre. Values for the r parameter given in square brackets [ ] are assumed. The form of the light curve is either the standard m = H0 + 5 log d + K0 log r or the linear brightening m = H0 + 5 log d + L0 abs(t - T + D0) where T is the date of perihelion, t the present and D0 an offset, if L0 is +ve the comet brightens towards perihelion and if D0 is +ve the comet is brightest prior to perihelion.
Observations of individual comets are given below in ICQ format.
Traditionally the light curve is regarded as highly asymmetric with a late turn on. There is a rapid rise in brightness as perihelion approaches, which continues more slowly for a couple more weeks after perihelion, followed by a slow decline until activity switches off. An alternative view is that the light curve is linear with a peak about a month after perihelion, which at this return occurs in early September.
With a 5.5 year period alternate returns are favourable and this is one of them. It is closest to the Earth in July (0.65 AU) when it could be 9th magnitude and UK observers should be able to follow it until August, but it then moves too far south. More southerly observers may be able to observe it until the end of the year as it fades.
The comet is now around 9th mag, having brightened rapidly in the past few days. David Strange obtained an image of the comet on July 10. Jose Carvajal estimated it at 10.6 in 32cm L on August 5.9, but I was unable to see it with 20cm R on the same night. On Aug 10.9 Andrew Pearce and I observed it with 14x100B from just outside Penzance, Cornwall, my estimate was 8.7 (HS) and Andrew made it a little fainter. Back in Cambridge it was a very difficult object in the 0.20-m refractor, though it was observed during the IWCA. Andrew Pearce now back in Australia reports that the comet has faded to near 10th mag at the end of August. It is fading very slowly and it was still 12th mag in December.
111 observations received give an uncorrected preliminary light curve of m = 6.1 + 5 log d + 29.3 log r
Observations in ICQ format , last observation 1999 November 8, updated 1999 December 15.
The comet was first discovered by Michael Giacobini at Nice observatory in December 1900 and was thought to have a period of 6.8 years. The next two returns were expected to be difficult to observe, but in October 1913, Ernst Zinner, of Bamberg, Germany, discovered a comet whilst observing variable stars in Scutum. This turned out to be the same comet, but the period had been incorrectly determined. The comet was missed at three unfavourable returns, so this was the thirteenth apparition of the comet.
The comet is no longer visible. Martin Mobberley imaged the comet on October 14 and October 25 .
223 observations received give an uncorrected preliminary light curve of 8.9 + 5 log d + 13.6 log r
Observations in ICQ format , last observation 1999 April 29, updated 1999 July 7.
This annual comet has frequent outbursts and over the past couple of years seems to be more often active than not, though it rarely gets brighter than 12m. It is possible that its pattern of behaviour is changing. In the first half of 1998 it was in outburst on several occasions. The randomly spaced outbursts may be due to a thermal heat wave propagating into the nucleus and triggering sublimation of CO inside the comet. This comet is an ideal target for those equipped with CCDs and it should be observed at every opportunity. The comet is just past opposition on the borders of Hydra and Libra. It is in solar conjunction in November, passing into Scorpius. Unfortunately opportunities for UK observers may be limited as its altitude does not exceed 15 degrees from this country.
Observations in ICQ format , last observation 1999 July 1, updated 1999 August 12.
49 observations received give an uncorrected preliminary light curve of 10.6 + 5 log d + 11.8 log r
Observations in ICQ format , last observation 1999 October 10, updated 1999 October 31.
The comet reached perihelion and opposition in late January. This is the seventh observed return of the comet since its discovery in 1954 and it has never became brighter than 17th magnitude at previous returns. Normally it would not be expected to get brighter than 15th magnitude at this return, however it was found in outburst at 12th magnitude in July 1998 and was 7 magnitudes brighter than expected. It is well placed for UK observation, but is difficult to see with a magnitude between 11 and 13. I have glimpsed it a few times in mid March with the Northumberland, making it around 13th mag. Observing on April 9/10 with the Northumberland I could not see the comet, estimating it fainter than 13.8. NGC 2455 which lay nearby was clearly visible and estimated at 13.1 compared with the catalogued magnitude of 13.2.
Observations received so far (34) give an uncorrected preliminary light curve following the second outburst of m = 10.2 + 5 log d + 0.0416abs(t-T+23.1).
Observations in ICQ format, last observation 1999 April 29, updated 1999 August 12.
Observations in ICQ format, last observation 1999 March 22, updated 1999 May 24.
It was a difficult object of around 14th mag on January 5.
7 observations give an uncorrected preliminary light curve of 5.9 + 5 log d +  log r
Observations in ICQ format, last observation 1999 November 8, updated 1999 December 15.
Observations in ICQ format, last observation 1999 November 8, updated 1999 December 15.
With a low inclination orbit, the comet sticks to the zodiacal constellations. The comet was discovered in 1981 by Ellen Howell with the 0.46-m Palomar Schmidt. It passed 0.6 AU from Jupiter in 1978, which reduced the perihelion distance, but the biggest change to its orbit occurred in 1585 when an encounter reduced q from 4.7 to 2.4 AU.
Observations received (24) give an uncorrected preliminary light curve of 8.9 + 5 log d + 0.0330abs(t-T-18.7)
Observations in ICQ format, last observation 1999 February 6, updated 1999 April 05.
Observations in ICQ format, last observation 1999 April 19, updated 1999 August 12.
Observations in ICQ format, last observation 1999 June 12, updated 1999 July 7.
25 observations give an uncorrected preliminary light curve of 12.7 + 5 log d +  log r
Observations in ICQ format, last observation 1999 November 28, updated 1999 December 15.
25 observations give an uncorrected preliminary light curve of 9.8 + 5 log d +  log r
Observations in ICQ format , last observation 1999 May 1, updated 1999 August 12.
Donald Machholz discovered P/Machholz 2 (1994 P1) with his 0.25-m reflector at 10m in August 1994. It proved to have multiple components, first reported by Michael Jager (Vienna, Austria). The four secondary components could all be described by the same orbit, but with perihelion delayed by up to half a day from the primary. At times there seemed to be a faint trail of material linking the components. The comet has a short period of 5.2 years with a perihelion distance of 0.75 AU and aphelion just inside the orbit of Jupiter. The orbit has been slowly evolving, with progressive changes occurring about every 50 years, thanks to approaches to Jupiter. The most recent close approach was in 1982. With a relatively stable perihelion distance, which is slowly increasing, it is perhaps surprising that the comet was not discovered earlier. There was a favourable return in autumn 1978 when it might have reached 8th magnitude and very favourable returns in the autumns of 1920, 1937 and 1957 when it might have reached 6th magnitude. The fact that it was not discovered at any of these returns suggests either that the orbital evolution is slightly inaccurate, or that the absolute magnitude at the 1994 return was not typical. At present the earth passes about 0.25 AU outside the descending node and the orbital evolution will slowly decrease this distance, raising the possibility of meteor shower from the comet in a few hundred years time.
This return is moderately favourable with the comet moving rapidly eastwards through Serpens (October), Scutum and Aquila (November), Aquarius and Capricornus (December) as it brightens from 14th to 7th magnitude. UK observers should be able to observe it from November at 10th magnitude, though more southerly observers may find it a month earlier.
Robert H. McNaught recovered the comet on CCD images obtained with the 1.0-m f/8 reflector at Siding Spring on August 3.55. The object was of stellar appearance. The indicated correction to the prediction by B. G. Marsden on MPC 27082 (for component A) is Delta T = +0.8 day. Seeing was good on Aug. 4, and there was no sign of any other components within Delta T = +/- 1.5 days.
Further orbital computations by Brian Marsden confirm that if the observations are of the same object that was observed at Siding Spring on 1995 Mar. 29 and 30 (MPC 25097), this is indeed component A. However, attempts to link all the observations (back to 1994 Aug. 15), even using the nongravitational parameters A1 and A2, have not been satisfactory. But a gravitational solution gives an acceptable fit to 67 observations back to 1994 Oct. 2 (mean residual 0".9; earlier residuals increasing to 20") [IAUC 7231, 1999 August 04] Z. Sekanina (1999, A & Ap 342, 285; Table 7) tabulates the expected offsets of components B and D from component A. In terms of Delta T, these amount to +0.21 and +0.82 day, respectively. [IAUC 7232, 1999 August 04]
On Oct. 17 R. H. McNaught, Research School of Astronomy and Astrophysics, Siding Spring Observatory, reported his single-night detection of another component of this comet, with m2 fainter by 0.5 mag but with brighter m1 and a larger coma (diameter 8", as opposed to 5") that night than the object reported on IAUC 7231 (presumed to be the 1994 component A, which he measured to be 260" to the east and 346" to the north). It seemed likely that the new object was component D. On Oct. 23 S. Nakano reported an independent detection of the new component by A. Sugie, Dynic Observatory, on Oct. 21 (m1 = 16.2, coma 10") and 23 (m1 = 17.3), and calculations by him and by the undersigned confirmed this to be component D, linkable to the complete 1994 arc without allowance for nongravitational effects. October astrometry and linked orbital elements are given on MPC 36175 and 36213, the Delta T difference from component A (for which Nakano gave on MPC 35815 a complete 1994-1999 linkage using three nongravitational components) being +0.69 day. McNaught searched for but failed to find component D on images obtained on Oct. 6 and 7, when it must have been at least 1 mag fainter than component A. On Oct. 31 H. Luthen, Hamburg, reported the photographic detection by M. Jager, Vienna, on Oct. 27 and by Jager and G. Rhemann on Oct. 29 and 31 of an object with a 1'.5-2'.0 coma and m1 = 12.8-13.0. Astrometry by E. Meyer, E. Obermair and H. Raab, Linz, on Nov. 1 confirms this also to have been component D, with coma 0'.5 and m1 = 15.4. [IAUC 7299, 1999 November 1]
The comet is located on the border of Sagitarius and Aquila, relatively low in the evening sky from the UK. The two components are currently some 55' apart. The A component brightened significantly in the last week of 1999 and is now around 10th mag, though beginning to fade and get more diffuse. The D component is perhaps two magnitudes fainter. The comet is still several magnitudes fainter than expected.
45 observations received give an uncorrected preliminary light curve of 11.7 + 5 log d + 0.0440 abs(t-T-21.0)
Observations in ICQ format , Last observation 1999 December 1, updated 1999 December 1.
Observations in ICQ format , last observation 1999 February 17, updated 1999 April 05.
Information about the latest discoveries is available from the LASCO comet observations web site. SOHO experienced a malfunction on 1998 June 25 and contact with it was lost. It was located by radar on July 29, communication was established in early August and it resumed pointing at the Sun in mid September. The LASCO cameras were reactivated in October but further problems were encountered and the spacecraft did not return to action until February 1999. Further control problems were encountered in late November 1999.
There are three LASCO (Large Angle Spectroscopic Coronographs) on the SOHO spacecraft, which orbits the sun at the earth's L1 Lagrangian point, 1.5 million km ahead of the earth. C1 has a field from 1.1 to 3 solar radii, C2 from 1.5 to 6 and C3 from 3.5 to 30. Brighter objects are often discovered in the real time data, but the fainter ones have to wait for the archival data to be searched which runs three or four months behind. SOHO has now discovered 94 comets (93 with LASCO), of which the majority are all members of the Kreutz group. of sungrazing comets. [Updated 1999 October 29]. So far, only 7 are not Kreutz group sungrazers. Further background information on the SOHO comets can be found from the LASCO comet observations web site. If you look at the archive of LASCO real-time movies, you will see two bright sungrazers in the C2 field at the same time at Christmas 1996. The LASCO images are downloaded every half an hour and you can view the Latest images or use the real-time JAVA movie player.
Observations in ICQ format , last observation 1999 March 22, updated 1999 April 05.
Observations in ICQ format , last observation 1999 April 19, updated 1999 August 12.
Observations in ICQ format , negative observation 1999 May 7, updated 1999 July 19.
Observations in ICQ format , last observation 1999 June 30, updated 1999 July 27.
Observations in ICQ format , last observation 1999 April 13, updated 1999 May 18.
I picked it up in 14x100B on July 27.09 at mag 6.1, though it was a difficult object in a bright twilight sky. It was again just visible on July 30.09 at aroung mag 6.5. It was any easy object on August 6.1 at mag 7.5. I observed it low down on August 11.1 and made it 6.9 (HS) in 14x100B. Andrew Pearce also observed it in mid August, making it a little fainter. Denis Bucynski imaged the comet on Aug 29.9. On August 30.9 it was around 7.5. It was an easy object from the centre of Cambridge on September 4.1 in 14x100B. It shows a prominent anti-tail in this image by Rolando Ligustri on September 8th. From a dark sky site on September 12.1 it was easy in 20x80B at mag 7.9. The coma was quite large and well condensed. It was still a little brighter than 8th mag on September 18.14. The comet is becoming less condensed and has faded to around 9th magnitude at the beginning of October. On October 18.08 it was large and diffuse in my 14x100B at 9.3. It rapidly became very diffuse in the last week of October and may now be very difficult to spot.
274 observations give an uncorrected preliminary light curve of 6.6 + 5 log d + 11.3 log r
Observations in ICQ format , last observation 2000 January 6, updated 2000 August 16.
102 observations give an uncorrected preliminary light curve of 4.1 + 5 log d + 12.5 log r
Observations in ICQ format , last observation 2000 June 1, updated 2000 November 22.
T. Fukushima, T. Nakajima, and J. Watanabe, National Astronomical Observatory of Japan (NAOJ), report that I-band CCD images of comet 1999 J2 taken with the NAOJ 0.50-m telescope show a dust antitail at the large heliocentric distance of 7 AU (the comet having passed perihelion on April 5): April 26.687, 2'.60 in p.a. 12 deg; May 2.576, 3'.31 in p.a. 18 deg. Coma diameters were about 0'.4 on both dates, and m_1 = 15.6 in V and 14.9 in I on April 29. The earth will cross the comet's orbital plane on May 10.4. [IAUC 7415, 2000 May 5]
93 observations received so far give an uncorrected preliminary light curve of -1.2 + 5 log d + 13.4 log r
Observations in ICQ format , last observation 2001 June 25, updated 2002 April 2.
117 observations received so far give an uncorrected preliminary light curve of 9.1 + 5 log d + 10.4 log r
Observations in ICQ format , last observation 1999 November 21, updated 2000 February 25.
Observations in ICQ format , last observation 1999 May 31, updated 1999 June 14.
Observations in ICQ format , last observation 1999 August 13, updated 1999 August 17.
26 observations received so far give an uncorrected preliminary light curve of 6.8 + 5 log d + 8.1 log r
Observations in ICQ format , last observation 2000 October 19, updated 2000 November 22.
Observations in ICQ format , last observation 1999 July 31, updated 1999 August 30.
69 observations give an uncorrected preliminary light curve of -2.3 + 5 log d + 20.0 log r
Observations in ICQ format , last observation 2000 December 23, updated 2001 May 8.
Observations in ICQ format , last observation 1999 June 30, updated 1999 July 27.
The comet was visible to UK observers, and at its brightest in late January. I observed it with my 0.20-m SCT on January 10.17 from a dark sky site and made it 12.3, DC2 and diameter 2.0'. A brief observation on January 31.0 with the Northumberland refractor revealed a well condensed object of between 11th and 12th magnitude. On February 8.8 it was around 11.5, but slightly less condensed than the day before. It is no longer visible.
18 observations received give an uncorrected preliminary light curve of 4.3 + 5 log d +  log r
Observations in ICQ format , last observation 2000 April 7, updated 2000 August 16.
R. P. Binzel, Massachusetts Institute of Technology, reported that 0.5-1.0-micron spectra of 1999 LD_31, obtained on 2000 March 1.3 using the Kitt Peak 4-m reflector, display a constant reflectance spectral slope of 0.12 +/- 0.02 per 100 nm (consistent with that of a typical D-type minor planet). [IAUC 7376, 2000 March 7]
In a communication to the Minor Planet Center on Mar. 3, R. Kracht suggested that, on the basis of the apparent motion, there was some loose association between C/1999 M3 and C/2000 O3 (cf. MPEC 2000-Q09), despite the evident difference in the usual orbital elements. Nevertheless, it can be noted that the perihelion directions are L = 103.9, B = +11.4 (degrees, J2000.0) for C/1999 M3 and L = 100.6, B = +10.8 for C/2000 O3. On Mar. 4, Kracht wrote that, again despite differences in the usual orbital elements, the perihelion direction for C/2000 O3 is close to the average value, L = 102.6, B = +9.7, for the four clear members of the Marsden group (cf. IAUC 4832). A more extended relationship among these comets is therefore suggested. [MPEC 2002-E18, 2002 March 7]
73 observations (including CCD) give an uncorrected preliminary light
curve of 8.6 + 5 log d + 7.7 log r
66 observations (excluding CCD) give an uncorrected preliminary light curve of 8.5 + 5 log d + 6.7 log r
Observations in ICQ format , last observation 2000 January 9, updated 2002 June 23.
Observations in ICQ format , last observation 2000 August 27, updated 2000 November 22.
73 observations give an uncorrected preliminary light curve of 4.9 + 5 log d +  log r
Observations in ICQ format , last observation 2000 February 11, updated 2000 August 16.
D. Schleicher, Lowell Observatory; and C. Eberhardy, University of Washington, used the Hall 1.1-m telescope at Lowell Observatory to obtain narrowband photometry of comet C/1999 S4, with the following averaged results: June 10-12, log Q(OH) = 28.41, log Q(CN) = 25.54, log Af(rho) = 2.83 (cf. IAUC 7342); July 13 (seven sets), log Q(OH) = 28.24, log Q(CN) = 25.45; log Af(rho) = 2.55. The equivalent log Q(water; vectorial) is 28.42 for July 13, and no significant temporal or aperture variations were observed. Significant variability was observed during the June observations, with the gas-production rates on June 11 being 30--50 percent larger than on June 10, and then on June 12 dropping to 10 percent less than on June 10. [IAUC 7455, 2000 July 16]
Brian Marsden has issued several orbital updates, the latest on MPEC 2000-O07. Although the previous orbital elements (MPEC 2000-O02) predicted the comet's position to at worst 0'.1, many users were unable to reproduce the ephemeris correctly for themselves because of the need to incorporate the nongravitational parameters. These parameters are quite large for this comet, and their effect on the ephemeris computed back from the standard 2000 Aug. 4 epoch was augmented by the rather small value of Delta. Since the effect vanishes at the epoch, the new elements above are provided also the epochs 2000 July 15 and 25. Some users have also commented on the fact that the eccentricity in the nongravitational solution is significantly smaller than that in a gravitational solution, such as that on MPEC 2000-N15. This is a normal phenomenon and does not alter the likelihood that this is a "new" comet in the Oort sense. [MPEC 2000-O07, 2000 July 19]
H. Weaver, Johns Hopkins University, on behalf of the Hubble Space Telescope (HST) ToO comet team, reports the following results: "HST images of the comet show a dramatic increase in activity on July 5, with the flux in a 0".15 square aperture increasing by a factor of about 1.5 in just under 4 hr (from July 5.776 to 5.940 UT). During HST observations one day later (July 6.717-6.889), the activity levels were decreasing and were about 3 times lower for the final observation, compared to the peak value from the previous day. The flux in the last HST image (on July 7.961) was about 7 times lower than the peak value measured on July 5. On July 7, at least one 'fragment' is seen 0".85 (460 km, projected) from the nucleus in the tailward direction, and a sharp tailward spike of emission is observed, reminiscent of the morphology observed during the outburst in C/1996 B2 (Hyakutake) in late-March 1996. HST spectroscopic data taken on July 5 with STIS show evidence for emissions from CO, C, H, O, and possibly S. S_2, CS, and OH were detected during STIS observations on July 6, and OH, CS, NH, and possibly S_2 were detected on July 7. Preliminary production rates are 5 x 10**26 (July 5), 1.4 x 10**24 (July 6), and 1.2 x 10**29 (July 6) for CO, S_2, and H_2O, respectively, but the CO and S_2 values could change by a factor of about 2 or so, pending final analysis. Nevertheless, one firm conclusion is that CO is strongly depleted in C/1999 S4, relative to the observed abundances in C/1996 B2 and C/1995 O1." [IAUC 7461, 2100 July 20 (sic)]
C. Lisse and D. Christian, Space Telescope Science Institute; K. Dennerl, Max-Planck-Institut fur Extraterrestrische Physik; F. Marshall, R. Mushotzky, R. Petre, and S. Snowden, NASA/Goddard Space Flight Center; H. Weaver, Johns Hopkins University; B. Stroozas, University of California; and S. Wolk, Harvard- Smithsonian Center for Astrophysics, report the first detection of x-ray line emission due to charge exchange between cometary neutrals and solar-wind minor ions using Chandra and EUVE: "Using a 960-s ACIS-S observation of comet C/1999 S4 on July 14.20 UT, the comet was detected with a rate in the S3 chip of 0.3 count/s, with a total integral flux of 8 x 10**-13 erg s**-1 cm**-2 over 0.2-0.7 keV and a total x-ray luminosity of 6 x 10**14 erg/s. The ACIS-S spectrum showed a strong line at 570 eV detected at greater than 10 sigma, due to charge exchange to O VII. Other lines due to charge exchange are also present (e.g., N VI, N VII at 300-500 eV, O VIII at 650 eV) at lower S/N. The best fit to the preliminary spectrum is the MEKAL multiple-line emission model (Mewe et al. 1986, A.Ap. Suppl. 65, 511) using solar elemental abundances with enhanced oxygen and nitrogen abundances, and a plasma temperature of 0.17 keV. The EUVE Lexan B count rate at July 14.21 was 0.06 count/s in 5400 s, for an equivalent luminosity of 1 x 10**15 erg/s at 0.16 keV. The observed emission was found to be highly time variable on the order of hours, enhanced by a strong solar flare propagating radially from the sun." [IAUC 7464, 2000 July 25]
I. de Pater, University of California, Berkeley, with M. R. Hogerheijde, M. C. H. Wright, R. Forster, W. Hoffman, L. E. Snyder, A. Remijan, L. M. Woodney, M. F. A'Hearn, P. Palmer, Y.-J. Kuan, H.-C. Huang, G. A. Blake, C. Qi, J. Kessler, and S.-Y. Liu, report the detection of HCN from comet C/1999 S4 at the Berkeley-Illinois- Maryland-Association (BIMA) Array in autocorrelation mode: "The peak antenna temperature in a 130" beam, averaged over July 21-24 (about 10 hr total on source), was 3.5 +/- 1 mK (a signal suggesting an outgassing rate a few percent that of C/1995 O1). No signal was detected in cross-correlation mode with the combined Owens Valley Radio Observatory and BIMA data (the virtual Combined Array for Research in Millimeter-wave Astronomy). This suggests a source size slightly larger than expected for a Haser model." M. Kidger, Instituto de Astrofisica de Canarias, writes that nightly observations made since July 23 in U, B, V, R, and Z broadband filters with the 1-m Jacobus Kapteyn Telescope show what appears to be the complete disruption of the comet's nucleus: "The central condensation was highly condensed and showed the typical 'teardrop' form on July 23.9 and 24.9 UT, although its brightness decreased by a factor of about 3 between the two nights. On July 25.9 the central condensation was seen to be strongly elongated (length about 15") in p.a. 80 deg, with a very flat brightness distribution. The condensation's brightness faded further and its length increased to about 30" and 45"-50" (p.a. 80 deg) on July 26.9 and 27.9, respectively. On July 27.9, there was no evidence of any local brightness peak that would indicate the presence of subnuclei. The expansion velocity of the condensation is about 40 m/s, indicating that it is particulate material and not gas. The gas tail, which virtually disappeared between July 23.9 and 24.9, has reformed as an extension of the major axis of the central condensation." [IAUC 7467, 2000 July 27]
J. Licandro, G. Tessicini, and I. Perez, Centro Galileo Galilei; and S. Hidalgo, Instituto de Astrofisica de Canarias, report that the inner coma of C/1999 S4 appears extremely elongated in the tailward direction on J, H, and K_s images obtained with the 3.6-m Telescopio Nazionale Galileo (+ ARNICA camera) at La Palma on July 26.9 and 27.9 UT. There is no clear central condensation, but the photometric peak appears to move from the anti-tailward border of the coma toward p.a. 81 deg on July 26.9 and 84 deg on July 27.9, with a velocity of 7".4/day (26 m/s). The brightness of the central coma decreased from J = 8.83 +/- 0.04 on July 26.9 to 9.46 +/- 0.07 on July 27.9, as measured in a 30"-diameter aperture around the peak. Color maps do not show any major structure, the mean colors being J-K = +0.61 +/- 0.05, and H-K = +0.12 +/- 0.06 on July 26.9. These data suggest that a major event has occurred in the nucleus of the comet. A. V. Filippenko and R. Chornock, University of California at Berkeley, report that inspection of a CCD spectrum (range 320-1000 nm) of this comet obtained on July 28 UT with the Shane 3-m reflector at Lick Observatory reveals no clear emission lines superposed on the solar reflection spectrum, unlike the case in spectra they obtained with the same instrument on July 6 and June 27. There is no evidence for the normally strong CN emission near 380 nm. The comet's morphology is peculiar, lacking an obvious head that is brighter than the adjacent tail, although the leading edge of the head/tail combination is very sharply defined. S. Nakano, Sumoto, Japan, writes that A. Asami (Bisei Spaceguard Center) was unable to find a peak in the comet's central-condensation brightness to determine an astrometric position from a CCD image taken in fair conditions on July 28.490 UT with a 0.25-m f/5 reflector. [IAUC 7468, 2000 July 28]
Further to their item on IAUC 7468, Filippenko and Chornock report that full reduction of their CCD spectrum obtained on July 28 shows that CN emission near 380 nm is actually present; the CN was not initially noticed in the two-dimensional spectrum because it spans the entire slit, making it resemble a night-sky emission line. In contrast, the continuum (reflected sunlight) is visible only on part of the slit, ending abruptly (as mentioned on IAUC 7468). [IAUC 7470, 2000 July 30]
Z. Sekanina, Jet Propulsion Laboratory, reports: "The unusually large nongravitational forces found by B. G. Marsden (MPEC 2000-O07) suggest that comet C/1999 S4 was a trailing fragment of a more massive comet that has been moving in the same orbit, arrived at perihelion long (centuries?) ago but (not surprisingly) was missed. Trailing fragments of known comet pairs have a tendency to sudden disintegration (e.g., Sekanina 1997, A.Ap. 318, L5). If much of the comet's mass did indeed dissipate into a cloud of dust in the recent event, as suggested by M. R. Kidger (IAUC 7467) and others, the total mass involved could be estimated by further monitoring the tail. Experience with the past initially bright comets that later became headless and disappeared shows that a narrow, bandlike tail--a developing synchronic formation--should survive the head by several weeks or even longer (Sekanina 1984, Icarus 58, 81). A very preliminary analysis suggests that the event may have begun as early as July 23.6 UT and involved submillimeter-sized and larger dust (repulsive accelerations up to 0.024 of the solar attraction). The position angle and approximate length of this tail feature are then predicted to reach: July 30.0 UT, 90 deg, 2'; Aug. 4.0, 98 deg, 4'; 9.0, 102 deg, 7'; 14.0, 104 deg, 10'; 19.0, 105 deg, 12'; 24.0, 106 deg, 15'; 29.0, 106 deg, 17'. Especially toward the end of this period, the predicted length probably is a crude upper bound. If no such tail persists, the comet's upper mass limit should be tightly constrained, or the amount of dust lost in the event did not represent a substantial fraction of the total mass." [IAUC 7471, 2000 July 30]
M. Kidger, Instituto de Astrofisica de Canarias, reports analysis of continued observations of C/1999 S4 at La Palma: "A 100-s exposure in R, taken by R. Corradi and N. O'Mahoney (Isaac Newton Group of Telescopes) on Aug. 1.9 UT with the Wide Field Camera on the 2.5-m Isaac Newton Telescope, shows no evidence of a nuclear condensation or subnuclei within the coma. The seeing (measured from a short exposure at the same airmass) was 1".5. It is thus highly improbable that any fragments of the nucleus of significant size exist within the coma. The coma shows a similar structure to that reported previously, with a well-defined sunward boundary to the coma similar to the point of a lance, although the brightest part of the coma is now displaced > 1' tailwards. The tail can be traced at least 20'." [IAUC 7472, 2000 August 3]
Further to IAUC 7472, M. Kidger reports that the limiting magnitude for a 5-sigma point source detection in the Isaac Newton Telescope images taken on Aug. 1.9 UT is R = 22.0. He adds that the continued presence of a well-defined leading edge or point to the coma suggests that an unresolved fragment of the nucleus in this position continues to release dust. However, this structure has faded considerably since the disruption occurred. Measurements of the coma brightness distribution indicate that the maximum of light is about 75" from the leading border of the coma. [IAUC 7474, 2000 August 5]
D. Schleicher and L. Woodney, Lowell Observatory, write: "We used the Hall 1.1-m telescope (+ 95"-diameter aperture) at Lowell Observatory to obtain narrowband photometry of comet C/1999 S4 (centered at the nominal ephemeris position; cf. MPEC 2000-O02), yielding the following production rates: log Q(OH) = 27.4; log Q(CN) = 24.4; log Af(rho) = 1.5 (cf. IAUC 7342). The equivalent log Q (water; vectorial) is 27.6. The values are 8-10 times less than those measured on July 13 (cf. IAUC 7455)." [IAUC 7475, 2000 August 7]
H. Weaver, Johns Hopkins University, and R. West, European Southern Observatory, on behalf of a large group of collaborators, report the following results: "Hubble Space Telescope (HST) images taken during Aug. 5.167-5.396 UT and Very Large Telescope (VLT) images (image quality about 0".6) taken during Aug. 6.978-6.999 revealed about a dozen active fragments, most of them located within about 20" of the western tip of the dust tail (cf. IAUC 7474). The correspondence between fragments in the HST and VLT images is generally very good, but the brightest fragment in the HST image is not seen in the VLT image, indicating rapid variability in the activity levels. The dynamic nature of the fragments was further highlighted by a dramatic change in the appearance of the fragments in VLT images taken during Aug. 9.976-9.996, when they were barely detectable. Although the latter images were taken under mediocre observational conditions (image quality about 1"-1".3, thin cirrus, and nearly full moon), that alone seems unlikely to account for the observed changes. A very preliminary estimate for the R magnitude, within a circular aperture of radius 0".23, of one well-isolated fragment is about 24. A completely inactive fragment with a diameter of 100 meters observed under these conditions (r = 0.79 AU, Delta = 0.69 AU, Phase = 86o) would have R about 25.9 (assuming a 4-percent albedo and 0.04 mag/deg phase law). We urge ground-based observers to continue monitoring the comet and to report any unusual changes near the 'tip', both in brightness and morphology." [IAUC 7476, 2000 August 10]
The comet is making its first visit into the inner solar system and such comets often brighten less quickly than expected. Professional observations show highly variable emissions. The orbit requires large non gravitional parameters and this combined with the faint absolute magnitude suggests that it is a small variably active object. As described above recent observations suggest that it may have fragmented, though there is some 'hype' on the topic, for example from Space Science. All reports of the comet's decease should be taken with a modicum of caution. Note the amateur observations suggest that a burst of activity between July 20 and 21, caused a brief brightening of the comet, followed by a more rapid fade, although the professionals persist in giving a later date. Hubble images taken on August 5 show the the comet fragmented into a number of cometisimals, confirming the concept that comets are a loose aggregation of smaller bodies, cemented together by ice and dust. Further images taken the next day by the ESO VLT show significant changes to the distribution of the cometisimals.
Martin Mobberley imaged the comet on October 13.9. David Strange imaged the comet on January 23.8.
Seiichi Yoshida reported a negative CCD observation on April 28, implying that the comet was fainter than at least 11th magnitude. KenIchi Kadota succeeded in recovering the comet on May 4, when he estimated it at 13.0, though at very low altitude. Several observers recovered it at the beginning of June with C Segarra reporting it at 10.5 visually. Rolando Ligustri imaged it with CCD on June 1 when it was 9.9 and on June 4, June 23, July 1, July 2, July 6, July 18 July 20, July 21, July 26, July 30. Pepe Manteca imaged the comet on June 9, June 22, June 28, July 2, July 12, July 14, July 22. Martin Mobberley imaged the comet on June 22 when it was about 9th mag and on July 17. Denis Buczynski has imaged it on June 26, June 27, July 03, July 04, July 11, July 15/16, July 16/17 July 19, July 23 David Strange has imaged it on June 26, July 21 and on July 25 as it fragmented. Nick James imaged it on July 2, July 18 July 19 July 20. R Ferrando imaged it on July 9, July 28. John Fletcher imaged it on July 20 Maurice Gavin imaged the comet on July 16 and also obtained a spectrum. Christian Buil imaged the comet and obtained spectra on July 17. Gabriel Oksa imaged the comet on July 25 .
I picked up the comet in my 20cm LX200 x75 on June 7.05, it was mag 9.9, DC3, coma diameter 1.1'. I did not seen again for 34 days due to a lengthy spell of cloudy weather over eastern England. I saw it again on July 11.94 it was 7.4 in 20x80B, coma diameter 3.1', DC5. Unusually it cleared as it became dark on July 14 and I made another observation on July 14.9, the comet was 7.1 in 20x80B, DC5, coma diameter 3', tail 20' in pa 310. On July 16.9 the comet had brightened to 6.8 in 20x80B despite the nearly full moon. It was a similar magnitude on July 18.9 and 19.9. It was markedly brighter on July 21.9 than it was on July 20.9 with a prominent stellar condensation. Observations with 8x30B on July 21.9 gave a mag of 6.0 suggesting it could be seen with the naked eye from a really dark site.
282 observations give an corrected
preliminary light curve of 8.6 + 5 log d + 4.4 log r
The extrapolation to the end of the year is shown in the light curve. The comet is currently at least two magnitudes fainter than the mean.
Observations in ICQ format , last observation 2000 August 6, updated 2001 May 2.
D. Schleicher, Lowell Observatory, reports that he obtained eight sets of narrowband photometry of comet C/1999 T1 on 2000 Dec. 28 and 2001 Jan. 2 with the Hall 1.1-m telescope at Lowell Observatory, yielding the following averaged results: log Q(OH) = 28.67; log Q(CN) = 26.10; log Af(rho) = 3.06 (cf. IAUC 7342). The equivalent log Q(water; vectorial) is 28.76. No significant temporal or aperture variations were observed. [IAUC 7558, 2001 January 9]
N. Biver, D. Bockelee-Morvan, and J. Crovisier, Observatoire de Paris-Meudon; D. C. Lis, California Institute of Technology; and H. Weaver, Johns Hopkins University, report: "The CO J(3-2) line at 345.8 GHz has been detected on Jan. 5.7 UT at the Caltech Submillimeter Observatory (CSO) with a line area of 0.17 +/- 0.03 K km/s in main-beam brightness temperature. During Jan. 5-7 at CSO, we also detected the HCN J(3-2) line (0.19 +/-0.01 K km/s) and CH_3OH lines at 307.2 (0.23 +/- 0.02), 304.2 (0.16 +/- 0.02), and 241.79 GHz (0.17 +/- 0.03 K km/s). The average production rates relative to water, using the water-production rate from Schleicher et al. (cf. IAUC 7558), are: CO, 40 percent; CH_3OH, 5 percent; HCN, 0.11 percent. This is until now the highest mixing ratio of CO observed in a comet that is relatively close to the sun." [IAUC 7559, 2001 January 11]
M. J. Mumma, N. Dello Russo, and M. A. DiSanti, Goddard Space Flight Center, NASA; K. Magee-Sauer, Rowan University; R. Novak, Iona College; and A. Conrad and F. Chaffee, W. M. Keck Observatory, report: "Water and CO were detected simultaneously near 4.67 microns on Jan. 13.7 UT in observations made at the NASA Infrared Telescope Facility (+ CSHELL). Three lines in the 1-0 band of CO (R0, R1, and P2) and two lines in the nu_3-nu_2 band of H_2O yielded production rates (x 10**27 molecules s**-1) of 14 for CO and 82 for H_2O. On Jan. 14.7, C_2H_6 (nu_7, nine Q-branches), CH_3OH (nu_3 Q-branch and other lines), and OH 'prompt' emission were detected using NIRSPEC at the W. M. Keck Observatory. The water-production rate derived from OH 'prompt' emission (P12.5 1- and 1+, near 3042 cm**-1) was 160 (calculated using g-factors from comet C/1999 H1), and other production rates were 2.7 for CH_3OH and 1.1 for C_2H_6. A residual 2-sigma signal was seen at the expected position of CH_4 R0 (nu_3 band), and this is formally consistent with a 3-sigma upper limit of 2.5 for CH_4. The mixing ratios are then H_2O:CO = 100:17 on Jan. 13.7, and H_2O:CH_3OH: C_2H_6:CH_4 = 100:1.7:0.65:(<1.6) on Jan. 14.7. A rotational temperature of 70 K was adopted for all species on both dates. Multiple lines of HCN and C_2H_2 were detected on Jan. 14, and quantitative analysis is in progress. The CO mixing ratio in this comet is similar to that found for native CO in comets C/1996 B2 and C/1995 O1, but it is much higher than those found for comets C/1999 H1 and C/1999 S4. Abundances of C_2H_6 and CH_3OH are similar to those in comets C/1996 B2, C/1995 O1, and C/1999 H1." [IAUC 7578, 2001 February 2]
D. K. Lynch, R. W. Russell, and D. Kim, The Aerospace Corporation; and M. L. Sitko and S. Brafford, University of Cincinnati, report 3- to 14-micron spectroscopy of this comet on Jan. 31.62 and Feb. 1.7 UT using BASS at the Infrared Telescope Facility: "The spectrum on the first night showed a silicate emission feature extending about 12 percent above the continuum defined by a blackbody fitted to the 8- and 13-micron points. Two prominent emission features at 10.3 and 11.2 microns appeared above the silicate band, the latter seemingly indicative of crystalline olivine. The 8- to 13-micron color temperature was 260 +/- 10 K, about 10 percent above the blackbody radiative equilibrium temperature of 235 K. The magnitude at 10.5 microns was [N] = 3.0 +/- 0.1. On the second night, the two prominent emission features were absent, although the silicate emission feature maintained its trapezoidal shape with breaks at 9.5 and 11.1 microns." [IAUC 7582, 2001 February 13]
C. E. Woodward, J. E. Lyke, and R. D. Gehrz, University of Minnesota (UM), report 7- to 23-micron photometry of this comet on Feb. 21.51 UT at the Mt. Lemmon Observing Facility 1.52-m telescope (+ UM bolometer + IRTF narrowband 'silicate' filters). No evidence for strong silicate emission (cf. IAUC 7582) was observed at 11 microns; a blackbody fit to the observed spectral energy distribution yields a color temperature of 270 +/- 20 K. Observed magnitudes: [7.9 microns] = 3.19 +/- 0.25, [8.8 microns] = 3.24 +/- 0.22, [9.8 microns] = 2.93 +/- 0.27, [10.3 microns] = 2.91 +/- 0.12, [11.7 microns] = 1.68 +/- 0.12, [12.5 microns] = 2.05 +/- 0.22, [18.3 microns] = 0.42 +/- 0.23, and [23.0 microns] = 0.62 +/- 0.30. [IAUC 7594, 2001 March 6]
E. A. Bergin, Harvard-Smithsonian Center for Astrophysics (CfA); D. A. Neufeld, Johns Hopkins University; and S. C. Kleiner, Z. Wang, and G. J. Melnick, CfA, write: "The 1(10)-1(01) transition of water vapor near 557 GHz was detected toward comet C/1999 T1 by the Submillimeter Wave Astronomy Satellite. During the periods Feb. 2.01-11.06 and 23.01-28.95 UT, the average integrated antenna temperatures were 0.58 +/- 0.02 and 0.39 +/- 0.03 K km s**-1, respectively, within a 3'.3 x 4'.5 (FWHM) elliptical beam. For a spherical outflow model with an assumed water lifetime of 7.3 x 10**4 s and an assumed water ortho-para ratio of 3, the inferred total water production rates (x 10**28 molecules/s) are 5.7 and 4.4, respectively." [IAUC 7596, 2001 March 13]
The observations show that it reached a peak brightness of around 7.5, as was suggested by the preliminary light curve.
Andrew Pearce and Stuart Rae picked up the comet at around 13th magnitude in early June. It was 12.7 when Stuart Rae observed it on July 7.7. Observations from Andrew and Michael Mattiazzo in September made it a little brighter than 10th mag. I was able to observe it from the Falkland Islands on November 19 and 20. A gusty wind and ever brightening sky made observation difficult, however I located the 8th magnitude comet in my short focus 90mm refractor, noting a distinct central condensation in 4' diameter coma. I viewed it again from the UK on January 23.20 when it was an easy binocular object at 7.9. On observation in bright moonlight on February 12.09 put it at 8.2 in 20x80B. By early March it had become much more diffuse and was around 9th magnitude. On April 24 I estimated it at around 12th mag in the Thorrowgood refractor.
419 observations give an uncorrected
preliminary light curve of 6.3 + 5 log d + 9.4 log r
Observations in ICQ format, last 2001 September 15, updated 2002 April 2.
K. Hornoch, Lelekovice, Czech Republic, reports observations (0.35-m reflector + CCD) of an antitail on several occasions during the past month: Apr. 24.89 UT, 4'.0 long in p.a. 51 deg; May 10.92, 3'.0, 46 deg; 20.95, 5'.0, 57 deg; 24.94, 7', 50 deg. The main tail ranged from 1'.1 in p.a. 150 deg on Apr. 24 to 1'.5 in p.a. 175 deg on May 20; on May 24 there was a second broad tail 1'.8 long in p.a. 104 deg, a very bright 0'.6 jet in p.a. 270 deg and a much fainter 0'.5 jet in p.a. 200 deg. CCD observations by J. Manteca, Barcelona, Spain (0.31-m Schmidt-Cassegrain), on May 23.00 put this comet at R = 15.0. [IAUC 7633, 2001 May 25]
151 observations give an uncorrected preliminary light curve of 6.5 + 5 log d + 8.2 log r
Observations in ICQ format, last observation 2001 July 12, updated 2002 April 20.
Observations in ICQ format, last observation 1999 November 5, updated 1999 November 29.
Observations in ICQ format, last observation 1999 November 8, updated 1999 November 29.
Observations in ICQ format, last observation 1999 November 5, updated 1999 November 29.
55 observations received so far give an uncorrected preliminary light curve of 6.9 + 5 log d + 4.6 log r
Observations in ICQ format, last observation 2002 May 17 24, updated 2002 October 1.
The orbit passes only 0.008 AU from the Earth and the asteroid passed this point only 2.9 days ahead of the Earth. If it produced a meteor shower, slow meteors would have been seen by Southern Hemisphere observers on or around November 11.1, with a radiant point of RA 17h 55m, Dec -70. Next year the shower would be expected around November 10.3.
Observations in ICQ format, last observation 2000 January 15, updated 2000 January 29.
119 observations give an uncorrected preliminary light curve of 8.1 + 5 log d + 4.3 log r
Observations in ICQ format, last observation 2002 January 25, updated 2002 October 1.
Kazimieras provided the following information about the discovery: I discovered this comet due to your two discoveries and information which helped me for looking at CCD images. The object at C2 was difficult for detecting at 1024x1024 too. I say that because I detected independently SOHO-94 with a bright tail after A. Vourlidas without problem on December 21. C/1999 Y2 was without tail and its brightness was similar to Sgr24 in orange filter (about 5 mag). Then I discovered SOHO-95 at C3 images (from December 27 23 hours) and sent more than 20 positions to B. Marsden. D. Biesecker did not reply me for 6 days. It was a holidays. If the comet has absolute magnitude about 18, it could be detectable with CCD in the our evening sky as 15.5 mag with elongation about 40 deg these days before bright moonlight coming.