Analysis of past comet apparitions

141P/Machholz 2

1999/2000


Comet P/1999 P1 (Machholz 2) received the final designation 141P/Machholz 2. In October 1999 component D was rediscovered, which during a short period in 1994 was almost as bright as the main component. A first sighting was reported at Siding Spring Observatory by R.H. McNaught, who found it on Oct. 17 located 260" west and 346" south of the main component. McNaught reported the false nucleus of D to be 0.5m fainter than that of the main component, but estimated the total magnitude of D to be brighter than that of A, due to the larger coma diameter (D=8", A=5"). On photographs taken Oct. 6 and 7 he was not able to find component D (IAUC 7299).

Independently, and unaware of the observations described above, Michael Jäger on Oct. 27 and he and Gerald Rhemann on Oct. 29 and 31 photographed component D. On the photograph of Oct. 27 it presented itself as a 13.0m faint uncondensed object with a coma 1.5' in diameter, about 7' apart from the main component. On October 29 D showed a compact 1.5 - 2' coma. On a photograph of Oct. 31 the component D was 12.7 mag bright and the 1.5 - 2' coma showed some condensation. On all these photographs the main component is either not or only faintly discernible. On Nov. 11 Michael Jäger estimated its brightness to be 12.5m, the fragment presented a 1.0' inner and a 2.5' diffuse outer coma, fragment A was not recorded. Finally, on Nov. 12, fragment D showed only the inner coma on a TP-photograph. In contrast, a blue-sensitive photograph on the same evening showed a 2.5', well-condensed coma at 12.0m. But on this photograph even fragment A was noticeable as a 1-1.5' diameter, weakly condensed object, estimated to be 13.8m bright.

The recent weeks confirmed the assumption that this comet will remain fainter than during its apparition in 1994, when it showed a higher than average activity due to the nucleus breakup. A very dark sky was necessary to observe the coma of this diffuse comet at 9.7m (maximum at new year 1999/2000) at small altitudes in its whole extent.

A first analysis of the observations of the main component by 4 FG members and 55 international observers results in the following brightness formulae:

pre-perihelion: m = 14.8m + 5×log D + 22×log r

post-perihelion: m = 13.1m + 5×log D + 14×log r

Yielding smaller activity factors compared to the first analysis, but still indicating that this comet gets significantly active only a short time prior to perihelion. The apparent coma diameter was at 1' (40.000 km) at first, increasing to 5' (90.000 km) at the turn of the year, only to decrease again until the beginning of February to 2' (40.000 km). The DC-value decreased continually during that time from DC 4 to DC 2.

Total Brightness and Coma diameter - Component A

The only fragment re-discovered during this apparition, component D, showed an extremely steep brightness increase which was displaced relative to perihelion. As a formula the 40 observations can be represented as follows:

m = 18.5m + 5×log D + 50×log r

with the maximum brightness of about 11m reaching 40 days prior to the main component. The very rapid brightening indicates a small or fastly consumed reservoir, making it uncertain if this component will show considerable activity during its next perihelion passage. In addition, the evolution of the coma diameter points in the same direction. Being 0.5' (25.000 km) at the beginning the coma increased rapidly (in only 20 days) to 80.000 km, only to decrease again to 1' (30.000 km) at the end of visibility. The DC-value was relatively constant at DC 2-3.

Total Brightness and Coma diameter - Component D

Andreas Kammerer

FG Observations


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