A photometric study of centaurs 29P/Schwassmann–Wachmann and (2060) Chiron

Abstract

ABSTRACTThis study presents the analysis of forced photometry data in the o and c filters of centaurs 29P/Schwassmann–Wachmann and (2060) Chiron obtained by the ATLAS network between 2015 and 2022. Centaur 29P had 24 outbursts with a median peak brightness of −3.0 and a range of −3.7 mag, regardless of spectral band. Some of these outbursts exhibited an asymmetric light curve with respect to peak brightness, with brightness decreases ranging from −0.22 to −7.6 mag h−1 and durations from 2.8 min to 1.4 d. The slope m of the photometric profile of the coma after/before and during an outburst was ≤1 and >1, respectively, reflecting an increase in brightness at the optocenter of the object. Without the outbursts, 29P has an absolute magnitudes H0 of 9.3 ± 0.2 and 9.10 ± 0.01 in the c and o filters, respectively, and activity indices of n = 11.56 ± 0.08 and 2.1 ± 0.1. Using the Lomb–Scargle periodogram, a periodicity of 0.97 d was found in the c magnitudes after perihelion, probably related to nuclear rotation. The absolute magnitude of Chiron in the HG1G2 system in the o filter is nearly constant between 2017 and 2020, with a weighted mean of 5.35 ± 0.03. In 2021, the brightness increases to H = 4.54 ± 0.03 and decreases to 5.04 ± 0.04 in 2022. This increase in 2021 is not due to outbursts that did not occur during the entire observing campaign, but is related to the increase in opposition effect.