Analysis of past comet apparitions

P/2006 T1 (Levy)

2006


On Oct. 2, 2006 the well known American comet discoverer David Levy discovered a 10 mag comet in the constellation Leo - a mere 45' north of the planet Saturn! On CCD-images comet P/2006 T1 (Levy) showed a 3' coma with a central condensation and a 14' tail in p.a. 295°. The comet passed perihelion only a few days later. It follows a 5.3 year elliptical orbit around the Sun (IAUC 8757, MPEC 2006-V23). The comet approaches the Earth to within 0.006 AU if the perihelion occurs on Dec. 31! Applying the discovery brightness it could then get as bright as -2.0 mag, displaying a 12° coma (according to my empiric formula).

However, this scenario seems quite unlikely. Orbital calculations do not hint to any close approach to a major planet during the last centuries, meaning that the comet orbits the sun on its present orbit since a long time, thereby making closer approaches to Earth quite regularly. That it was not discovered until now indicates that it may have experienced a major outburst at its current perihelion passage, explaining also the discovery very close to Saturn.

In the meantime this assumption is confirmed by 25 international observations. These show that the comet already started to fade steadily a few days after the discovery, according to the formula (see also the diagram)

m = 8.5m + 5×log D + 0.075×|t-T|

Such a brightness evolution is typical of a comet shortly after an outburst. Thus the discovery magnitude of 9.5 was also the maximum brightness the comet reached.

Total Brightness and Coma diameter

In the same way the coma shrinked rapidly from 3' (200.000 km) at discovery to less than 1.5' (90.000 km) at the start of November - also typical for an outburst. Contrary the degree of condensation was rather constant at about 4 during the whole visual apparition.

In mid-November the MPC informed, that the astrometric observations achieved since the end of October, could not be linked in a satisfying manner, indicating that different brightness centers were measured - again an indication for an outburst (MPEC 2006-W07).

Andreas Kammerer


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