Analysis of past comet apparitions

52P/Harrington-Abell

1998/99


The big surprise in the summer of 1998 was comet 52P/Harrington-Abell. On a CCD-exposure taken on July 21, 1998 A. Maury at the Observatoire de Cote d'Azur discovered this comet as a bright 12m object, rather than being 21m as expected (IAUC 6975)! Follow-up observations confirmed this extraordinary outburst (in 1973 comet 41P/Tuttle-Giacobini-Kresak experienced an even more violent outburst with an amplitude of at least 10m). However, as the graph shows, the maximum brightness of the outburst could have been even greater, implying an even greater amplitude!

During summer 1998 this comet was an interesting object, slowly declining in brightness, despite the decreasing distance to the sun. But since fall the brightness, contrary to the expectations, slowly increased again, indicating a maximum brightness of 10.4m at the end of January. This evolution may be explained by the assumption that a gas/dust-reservoir (near the pole?) was released last summer and fall. As expected the heliocentric magnitude decreased shortly after perihelion, but about 35 days thereafter it seems to have experienced another slow brigthening. This, however, is far from certain since during this period the part of observers estimating comets too bright on average is relatively high. At least there is no doubt that the normal decrease of the heliocentric brightness stopped during this period.

Analysing 81 observations by 9 members of the Fachgruppe Kometen and 160 international observations yields the following formulae:

        t < -100d: m = 13.5m + 5×log D + 0.022×|t-T|
-100d < t <    0d: m = 10.8m + 5×log D - 0.005×|t-T|
   0d < t <   35d: m = 10.8m + 5×log D + 0.01×|t-T|
        t >   35d: m = 11.2m + 5×log D

The apparent coma diameter increased from 1.5' to almost 3' (2.7') towards perihelion. At the end of this apparition the diameter was 1.7'. The absolute coma diameter decreased, due to the immense outburst, from 180.000 km to 80.000 km at the end of 1998. Since then it slowly increased again, reaching 150.000 km at the end. The coma itself was diffuse at first (DC 2), but condensed close to perihelion (DC 4). Until May the DC-value decreased again to DC 1-2. Visual tail estimates were reported in December and January. The maximum length was about 0.1° (1 million km).

Total Brightness and Coma diameter

Andreas Kammerer

Observations


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