A Study of the Comets with Large Perihelion Distances C/2019 L3 (ATLAS) and C/2019 O3 (Palomar)

This work analyzes the photometric data of the Oort spike comets C/2019 L3 (ATLAS) and C/2019 O3 (Palomar) obtained between 2016 and 2023 by the ATLAS network and the Belgian Olmen Observatory. The comets Palomar and ATLAS have a typical and unusually high activity level, respectively, based on the Afρ parameter corrected to phase angle zero at perihelion. The absolute magnitude of comets ATLAS and Palomar in the o-band is 4.71 ± 0.05 and 4.16 ± 0.02 respectively. The cometary activity of comets ATLAS and Palomar probably began at r > 13 au before perihelion and will end at r >14 au after perihelion, which means that they could remain active until the second half of 2026. The nucleus of comet ATLAS has a minimum radius of 7.9 km, and the nucleus of comet Palomar could be a little larger. The c − o colors of the comets ATLAS and Palomar are redder and bluer, respectively, at perihelion than the solar twin YBP 1194. These comets showed a bluish trend in the coma color with decreasing heliocentric distance. Comet Palomar probably had two outbursts after its perihelion, each releasing about 108 kg of dust. The slopes of the photometric profile of the comae of these comets were between 1 and 1.5, indicating a steady state during the observation campaign.