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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.

Until the end of April 2017 360 observations from 41 observers of this comet had come to my knowledge. Die brightness estimates indicate a brightness evolution well below average, according to the formula

m = 6.8 mag + 5×log D + 6.7×log r

implying a peak brightness of only 7.8 mag during the first week of June 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' in mid-February 2017 to 5' in mid-March, 9' in mid-April and 11' at the end of April. The absolute coma diameter measured 250.000 km in mid-February, 325.000 km in mid-March, 500.000 km mid-April and 520.000 km at the end of April. While observers working with CCD cameras reported DC values of DC 67, visual observers reported a constant value of DC 4 to DC 4-5, indicating a significantly condensed coma. 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 from December 2016 onwards. At the end of April 2017 it measured a length of 0.3° (1.5 Mio. km). Its direction only changed from NW to WNW. However, it was clearly bend in spring 2017, which was obvious even for visual observers.

For mid-European observers the comet will remain observable in the evening sky until early July 2017. Until then it will move from Bootes to near the borders of the constellations Virgo/Hydra/Libra. Its brightness should decrease during that time interval from 7.8 mag to 8.5 mag.

Andreas Kammerer

FGK observations


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