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The ATLAS team discovered an asteroidal object of magnitude 19 in the constellation Draco on images taken on Oct. 25, 2022. Follow-up observations showed cometary morphology. Comet C/2022 U2 (ATLAS) showed a very diffuse coma of diameter about 50" and total magnitude 17.5, displaying an obvious central condensation, but no tail. Images of Michael Jäger on Nov. 2 showed a diffuse 3' coma of total magnitude 16.1, but again without a tail. The comet will pass perihelion at the solar distance of 1.34 AU on Jan. 14, 2023, expected to reach magnitude 14.0 (CBET 5187). It will pass Earth at a distance of 0.58 AU on Jan. 29, preventing the comet of fading until then. It should be brighter than 16 mag until mid-March. During this period it will move through the constellations Draco, Cepheus, Cassiopeia (perihelion), Camelopardalis (perigee), Auriga, Taurus and Orion, being a comfortably postioned object in the evening sky.
The comet became nearly 4 mag brighter than predicted. Based on 96 observations from 36 observers the comet reached a maximum brightness of 10.2 mag on Jan. 25, 2023. In addition, it showed a significantly higher activity pre-perihelion than post-perihelion, which may indicate the activation of a gas/dust reservoir. In mid-April the comet had already faded to 14.5 mag. The brightness development can be simulated moderately well with the following formulae:
pre-perihelion: m = 8.5 mag + 5×log D + 30×log r post-perihelion: m = 9.5 mag + 5×log D + 15×log rTotal Brightness and Coma Diameter
The apparent coma diameter increased from 2.5' at the beginning of the apparition to 5' around Jan. 20, 2023, shrinking rapidly thereafter, measuring just 1' by mid-March. The absolute coma diameter increased only from 125,000 km at the start of the apparition to 135,000 km around Feb. 10, 2023. Thereafter the the coma shrunk rapidly, measuring only 50,000 km by mid-March. Throughout the apparition the coma was quite diffuse with a constant degree of condensation around DC 3. No tail reports have been published.
Andreas Kammerer