Periodic changes in positional observations of comet 3I/ATLAS (C/2025 N1)

ATel #17437; Yuri Medvedev (IAA RAS), Sergei Pavlov (IAA RAS)
on 8 Oct 2025; 10:35 UT
Credential Certification: Yuri Medvedev (medvedev@iaaras.ru)

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We report the results of the analysis of the O-C distribution of positional observations (Δα, Δδ) for the interstellar comet 3I/ATLAS (C/2025 N1) taken from MPC. A Lomb-Scargle periodogram was constructed based on the O-C values obtained for the moments when the comet's heliocentric distance became less than 4 AU. It was found that the (Δα·cosδ)²+Δδ² values undergo variations with a statistically significant period of 4 hours. We also constructed a periodogram for 19 photometric observations obtained between July 4 and 6 (60860.9796 - 60862.1202 mjd) from the paper John L. Tonry et al. (2025).Values with the maximum aperture (m14) were used. The identified period coincided with the O-C period and is equal to 4 hours.