Gemini and Apache Point Multi-band Optical Imaging Characterization of Fragmenting Long-period Comet C/2025 K1 (ATLAS)

Carl Ingebretsen; Bryce T. Bolin; Meredith A. MacGregor; Carey M. Lisse; Matthew Belyakov; Gracyn Jewett; Mukremin Kilic; Marco Micheli; Davide Farnocchia; Brian Lemaux; Hyewon Suh

arXiv · 2608.29698

Gemini and Apache Point Multi-band Optical Imaging Characterization of Fragmenting Long-period Comet C/2025 K1 (ATLAS)

Carl Ingebretsen·Bryce T. Bolin·Meredith A. MacGregor·Carey M. Lisse·Matthew Belyakov·Gracyn Jewett·Mukremin Kilic·Marco Micheli·Davide Farnocchia·Brian Lemaux·Hyewon Suh

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Abstract

We present results from multi-band g, r, and i, observations of C/2025 K1 (ATLAS) taken with the Gemini North 8.1-m/GMOS imager on 2025 December 6 and December 24, and u, g, r, i, and z observations with the Astrophysical Research Consortium (ARC) 3.5-m/ARCTIC imager on 2025 December 8. We identify at least four distinct fragments in the Gemini and ARC images, designated as A, C, D, and E in these data taken between 2025 December 6 and 24. Color indices are determined from the December 8 ARC observations of fragments A and C, and from the Gemini observations on December 24 for A, C, and D. K1 has an unusually blue g-r color of $\sim$0.40. The color difference between the comet and its fragments at the two epochs may be explained by particle size and light-scattering effects. We used the Gemini observations to calculate dust mass-loss rates for fragments A, C, and D. We conclude that C/2025 K1 has moderate dust mass-loss rates for millimeter-sized dust of $\sim$50 kg/s for the A and C fragments.

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Carl Ingebretsen, Bryce T. Bolin, Meredith A. MacGregor, Carey M. Lisse, Matthew Belyakov, Gracyn Jewett, Mukremin Kilic, Marco Micheli, Davide Farnocchia, Brian Lemaux, Hyewon Suh. 2026-08-30. Gemini and Apache Point Multi-band Optical Imaging Characterization of Fragmenting Long-period Comet C/2025 K1 (ATLAS). https://arxiv.org/abs/2608.29698

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