Analysis of past comet apparitions

9P/Tempel

2005


In preparation of the "Deep Impact" space probe arrival comet 9P/Tempel was observed visually since the beginning of March 2005. Until beginning of September 24 observations by 8 members of the German Comet Section have been received. Together with 265 international estimates the brightness evolution can be well simulated with the formula

m = 6.2m + 5×log D + 25×log r

Thus, maximum brightness of 10.3 mag - about 1 mag fainter than expected - occurred during June.

Besides the brightness the coma diameter increased significantly during the first four months. Whereas the comet brightened from 13.5m to 10.5m during this period, the coma swallowed from 0.7' to 5' at the beginning of June where it hovers since. However, due to the coma becoming progressively more diffuse with the altitudes decreasing, the scatter in the estimates increase significantly after May. The absolute coma diameter increased from 35.000 km in March to 125.000 km in mid-May and finally 175.000 km during June/July. The degree of condensation was 3-4 at the start of the apparition, increasing to a maximum of DC 5 by the end of April. Thereafter the coma grew more and more diffuse with the DC reaching 2-3 at the end of July. During the first weeks of the apparition the coma was fan-shaped toward west, with the prominent false nucleus displaced toward east. In the course of May, however, the coma grew more symmetrical, with the false nucleus becoming less prominent.

Total Brightness and Coma Diameter

The impact of the Deep Space Probe projectile on July 4 was awaited with much anticipation. The experiment was successful and very interesting results were recorded. However, observers on Earth were widely disappointed, because the impact did not result in any significant brightening of the overall brightness of the coma. Many observers did not even see the comet at all at the time of impact, because at that time it had grown very diffuse at low altitude. Those who were lucky to observe the comet at impact time reported an increase of the degree of condensation and the appearance of a short-lived inner coma. Very few observers with large amateur instruments noticed and documented a brightness increase of the very center by about 1-2 mag within the first hours after impact.

Andreas Kammerer

FGK observations


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