Analysis of past comet apparitions

C/2003 T3 (Tabur)


The australian amateur Vello Tabur discovered an 11.5m comet near the border of the constellations Pavo/Telescopium on Oct. 14, 2003. On a CCD-exposure, taken with a 140mm, f/2.8 telephoto lens comet C/2003 T3 (Tabur) showed a coma of 0.5' diameter. Additional CCD-observations showed a 0.7' coma and a fan-shaped 1' tail towards p.a. 90° (IAUC 8223/25). This comet will pass perihelion in April 2004, but will then be situated on the far-side of the sun. Therefore it is not expected to get any brighter than 8m, although its absolute brightness is in the order of 5m. For mid-European observers its apparition will start at the end of April 2004 above the eastern morning horizon. Because it will then move through the constellations Pisces, Perseus, Camelopardalis and Lynx it will be observable both in the evening and morning sky for several weeks. However, it will not reach altitudes of more than 15-20°. Not until September will it be observable at comfortable altitudes, but by then it should have faded to about 11m.

Until it disappeared in twilight in mid-December 2003 the comet brightened much slower than expected. Then at about magnitude 12.0 it was already 1m fainter than predicted. Furthermore observers reported a very diffuse coma. Thus, it was unclear in which state it would be at the time of its reappearance above the morning horizon at the onset of May 2004 (originally expected to be of magnitude 8.5). It could not even be ruled out that the comet would suffer the same fate than its namesake in 1996.

On Apr. 17 and 18, 2004 the comet was again observed - at an elongation of only about 18°, ending all speculations.

Not a single observation by a member of the German Comet Section was received. In addition, it was also only marginally observed by international observers, so only 85 reports could be used for the followig analysis. The photographers found it in the morning of April 26 - unintentionally - on their frames, because at that date the comet was superimposed on the tail of comet Bradfield, faking a tail cloud at first.

Total Brightness and Coma diameter

The analysis demonstrates that the pre-perihelion brightness increase was slower than the post-perihelion brightness decrease, according to the formulae

pre: m = 6.6m + 5×log D + 6.6×log r

post: m = 6.4m + 5×log D + 9.0×log r

yielding a maximum brightness of 9.6 mag at the end of April 2004. While the apparent coma diameter was around 1.0' during the first months, it was estimated as larger than 2.0' (maximum: 2.5') after the re-appearance of the comet after solar conjunction. The absolute coma diameter during the first months measured about 125.000 km, post-perihelion it remained relatively constant at 250.000 km. The coma itself was moderately condensed. The degree of condensation was mainly DC 4, but seems to have decreased to DC 3 in August.

Andreas Kammerer


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