Analysis of Comet Apparitions

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C/2018 V1 (Machholz-Fujikawa-Iwamoto)

The well-known comet observer Donald Machholz succeeded on Nov. 7, 2018 in discovering another comet, this time with a 47cm-reflector. The comet showed a 3' coma and was situated in Virgo. Independent discoveries were reported by Shigehisa Fujikawa und Masayuki Iwamoto, leading to the designation C/2018 V1 (Machholz-Fujikawa-Iwamoto). Additional observations revealed a strongly condensed, 4 coma of total brightness 10.0 mag. The comet will pass its perihelion at the solar distance of only 0.39 AU on Dec. 3, 2018, but should not get brighter than 6.0 mag (CBET 45569/72). It should be brighter than 10 mag until Christmas, being situated in the northern part of Sagittarius at that time. The comet will only show moderate to small elongations, remaining low above the morning eastern horizon until the end of November for mid-European observers. In the first half of December it could be glimpsed low above the WSW evening horizon.

For the analysis I could use 71 observations from 32 observers. These clearly indicate a major outburst during the days prior to discovery. This resulted in a rapid brightening until Nov. 10, 2018 (23 days prior to perihelion), when it was of magnitude 8.5. Thereafter the brightness developed steadily according to the formula

t > -23d: m = 9.5 mag + 5×log D + 0.045×(t-T)

Since the comet was still approaching Earth, its brightness peaked at 8.3 mag on Nov. 24, 2018. In the days around Dec. 10 the comet, still of magnitude 9.5, disappeared in the twilight.

Total Brightness and Coma Diameter

Due to the low altitudes for all locations worldwide the estimates of the coma diameter show a great scatter. It measured about 4' (175.000 km), showing no clear development due to the scatter and the short observing apparition. The degree of condensation, however, showed the typical decrease following an outburst. At DC 6-7 on Nov. 10 it decreased to DC 3-4 on Dec. 10. During the first 10 days of the apparition a tail of maximum length 0.3° (800.000 km) was reported, pointing towards NE.

Andreas Kammerer

FGK observations