Analysis of Comet Apparitions

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C/2015 V2 (Johnson)

On CATALINA images taken on Nov. 3, 2015 in the constellation Lynx (near the borders of the constellations Ursa Major and Camelopardalis) J.A. Johnson discovered a comet, which showed a highly condensed 10-15" coma and a hint of a tail. Follow-up observations of comet C/2015 V2 (Johnson) showed a strongly condensed 8" coma of total magnitude 16.5 with a central condensation and a 15" tail in p.a. 235°. The comet will reach perihelion in mid-June 2017 and will approach Earth to within 0.80 AU. At this time it should peak at magnitude 6.0, expected to show a coma diameter of about 12' (CBET 4161 / MPEC 2015-W09). It should be brighter than 13 mag between October 2016 and its disappearance above the mid-European horizon during the first days of July. Except of the last three weeks of this apparition it will be visible in the morning sky. Until April 2017 it will move rather slowly through the constellations Ursa Major, Bootes and Hercules. Between May and July it will accelerate, moving through Bootes, Virgo and Hydra, thereafter plunging deep into the Southern Sky.

The comet became a nice binoculars object in spring 2017. According to 692 observations from 57 observers this comet showed different brightness developments pre- and post-perihelion. Surprisingly, the comet faded faster post-perihelion than it had brightened pre-perihelion. The whole brightness development can be well described by the following formulae

pre-perihelion: m = 6.8 mag + 5×log D + 6.8×log r
post-perihelion: m = 6.1 mag + 5×log D + 10.4×log r

resulting in a peak brightness of 7.8 mag around June 7, 2017.

Total Brightness and Coma Diameter

CCD observations show a continuous increase of the coma from 0.2' (60.000 km) in February 2016 to 1.0' (125.000 km) in September 2016. In early December 2016 the coma diameter was estimated to be 1.5' (175.000 km). During the following weeks the apparent coma diameter increased due to the rapidly decreasing distance to Earth, from 2.5' (250.000 km) in mid-February 2017 to 5' (325.000 km) in mid-March and 11' (520.000 km) at the end of April. The maximum diameter of 17' (620.000 km) was reached at the end of May. Thereafter it decreased, measuring 7' (410.000 km) at the opening of August and 1.5' (190.000 km) at the end of October. The comet showed a moderately condensed coma, with a constant degree of condensation of DC 4-5 during most of the apparition. Starting in July the degree of condensation decreased, reaching DC 3 at the end of this month and DC 1-2 at the end of October. It showed a well-defined central condensation in which a false nucleus of magnitude 13.0-13.5 could be discerned in March/April 2017.

Visual tail sightings were reported between December 2016 and June 2017, with the tail pointing constantly towards WNW. Its maximum length of 20' (1.8 Mio. km) was reached at the end of May. During March/April it was clearly bend, which was obvious even for visual observers.

Andreas Kammerer

FGK observations