On July 29, 2002, an apparently asteroidal object of magnitude 20 was reported by LINEAR near the borders of Bootes/Ursa Major/Canes Venatici, which was subsequently found to be cometary. Comet C/2002 O7 (LINEAR) was slightly diffuse with a coma of diameter 8" and a total brightness of 17.5mon Aug. 2 (IAUC 7949). It was at a solar distance of 5.4 AU, but will get as close as 0.9 AU to the sun in September 2003 (expected magnitude 7). However, at this time it will be situated on the far side of the sun and far to the south of the ecliptic, which means that only observers in the southern hemisphere have a chance to observe it around that date. Observers in mid-Europe could follow it until the start of June 2003 (expected magnitude 10-11) in the morning sky and beginning in mid-December in the evening sky (expected magnitude 9).
Three members of the German comet section reported nine estimates of this comet. By adding 70 international observations the brightness evolution can be derived as m0=10.1m / n=1.4. Problematic, however, is the large scatter (up to 1.5m) inherent to the brightness estimates. If the comet should have followed this trend, it should not have become brighter than 10th magnitude.
Total Brightness and Coma diameter
Whereas the apparent coma doubled in diameter since the beginning of the apparition (0.8' to 1.7') the absolute diameter increased only from 100.000 km to 150.000 km. Prior to its conjunction with the sun the coma was rather diffuse: the degree of condensation increased from DC 1-2 to DC 3 during April and May 2003, thereafter starting to decrease.
This comet should have become visible again in September 2003. However, a CCD-image by the australian amateur M. Mattiazzo on Sep. 27 revealed only a diffuse sunward-pointing 'antitail' of debris. Observations by H. Boehnhardt et.al. with the 3.6m-ESO-telescope on Dec. 3 did not show any object brighter than R=20.5m within an area 30'x30' centered on the predicted position (IAUC 8250). Thus this comet disintegrated at the time of its perihelion passage.
Andreas Kammerer
