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Analysis of Comet Apparitions


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252P/LINEAR

2016


Comet 252P/LINEAR (P=5.33a), discovered in 2000, approaches the Earth to within 0.036 AU on Mar. 21, 2016. The predicted maximum brightness is 10 mag. However, it was only observed during two perihelion passages with only a small number of estimates. On Mar. 20 the comet will be positioned near the Southern Sky Pole, but will appear above the southern morning horizon already on Mar. 26. It will then be expected to be of magnitude 11, positioned near the stinger of Scorpius. During the next days it will rapidly gain altitude. However, it should rapidly fade, reaching magnitude 16 already at the start of May. It is expected that the comet will only show a faint coma around a stellar false nucleus.

Actually this comet became the surprise of spring 2016. Instead of peaking at 10 mag it reached 4.8 mag on Mar. 23 (closest approach to Earth was on Mar. 21 at 0.036 AU)! At that date the apparent coma was bigger than the Moon, but very diffuse (about DC 2-3) – thus its full extent could only be seen under perfectly dark skies. Despite these suboptimal conditions the analysis can nevertheless be based on 30 observations from 7 members of the German Comet Section and 260 international observations. These show four different phases of the brightness evolution, which can be best described with time-dependent formulae. Pre-perihelion the comet showed an extremely steep brightness increase with the comet brightening from 14 mag on Feb. 27 to 6.3 mag on March 15. After the perihelion passage the activity continued to increase for 28 more days (until Apr. 12). During that interval the comet was closest to Earth, peaking at 4.8 mag. Although the activity reached its maximum during this interval the comet started to fade - primarily a result of the increasing distance to Earth - reaching 6.0 mag on Apr. 12. During the next three weeks (until May 4) the comet showed a constant activity. Thereafter the activity decreased - slower than the increase during the previous phases but still rapidly when compared with other comets. In early June the comet was of magnitude 10.5. The appropriate formulae are as follows:

t < 0d: m = 12.2 mag + 5×log D – 0.372×(t-T)
0d < t < +28d: m = 12.6 mag + 5×log D – 0.080×(t-T)
+28d < t < +50d: m = 10.4 mag + 5×log D
t > +50d: m = 7.9 mag + 5×log D + 0.052×(t-T)

The apparent coma diameter increased rapidly between the last days of February (1') to mid-March (45'). Until early April the coma remained quite constant in diameter, reaching a maximum value of 47' during the days of perigee. The decrease of the apparent coma diameter grew slower. On Apr. 6 35' were reported, on Apr. 14 25', on May 1 18' and on May 31 still 6'. In absolute dimensions, the coma diameter increased from 5.000 km at the start of the apparition to the maximum value of 200.000 km on May 5. Thereafter it decreased, still measuring 110.000 km at the start of June.

Total Brightness and Coma Diameter

The degree of condensation of the coma was estimated at DC 2 until Apr. 1, rapidly increasing to DC 3 until Apr. 5. From Apr. 15 onward the coma slowly got more diffuse, with the degree of condensation estimated at only DC 1 in mid-May. Visually no tail was reported.

Andreas Kammerer

FGK observations


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