C/2007 W1 (Boattini)

In the course of the Mt.Lemmon Survey A. Boattini discovered a comet of magnitude 18 near the border of the constellations Virgo/Leo on Nov. 20, 2007. Comet C/2007 W1 (Boattini) presented a condensed 6x7" coma and a very faint 9" tail in p.a. 293°. It will pass perihelion in June 2008 and could reach magnitude 6. In mid-June it will pass earth at a distance of only 0.20 AU (IAUC 8899 / MPEC 2008-B22). However, at both dates the comet will not be visible for mid-European observers. For them it will disappear below the evening horizon in mid-May (expected to be of magnitude 8), after moving through the constellations Corvus, Crater and Hydra. In mid-July it will reappear above the morning horizon (at magnitude 7) in Cetus, thereafter moving through Aries and Pisces.

Finally, only 19 observations by 7 members of the German Comet Section were received. For the analysis additional 365 international observations have been taken into account. These show a very smooth and average brightness evolutions and a maximum brightness of 4.6 mag around June 15. The formula is:

The apparent coma diameter was in the order of 1' at the beginning of the apparition, increasing only slowly to 2.5' at the end of March. It followed a phase of rapid increase to the maximum of 24' in mid-May. The following decrease of the apparent coma diameter was much slower. At the end of June it still measured 17' and in mid-August 10'. Until the end of September it decreased to 3.5', measuring 1' at the beginning of November. The evolution of the absolute coma diameter was quite different. At the beginning of the apparition it measured only 60.000 km, increasing until the end of March to only 110.000 km. This was followed by a phase of rapid increase to the maximum coma diameter of 400.000 km at the beginning of May. Around perihelion the coma shrunk considerably to 200.000 km, probably, by a good part, due to the difficult observing conditions. Until the beginning of August a second phase of increase followed with a secondary maximum of about 260.000 km. After that the absolute coma diameter decreased to 150.000 km at the end of September and to 60.000 km at the beginning of November. The coma was only medium condensed (DC 3 at first, end of May: DC 2). Near perihelion the coma was considerably condensed (DC 5). After that the degree of condensation decreased quite steadily to DC 3-4 at the end of July, DC 2 at the end of August and DC 0 in the last days of September. Visual tail observations were only reported at the beginning of July and at the end of August with maximum values of 10' (appx. 250.000 km).

Total Brightness and Coma Diameter

Andreas Kammerer

FGK observations