CN imaging of recent bright comets 12P/Pons-Brooks, 13P/Olbers, C/2021 S3 PanSTARRS, and C/2023 A3 Tsuchinshan-ATLAS

We report on recent and upcoming CN imaging of four comets obtained from Lowell Observatory, SOAR, and the U.S. Naval Academy (USNA). Halley-type comet 12P/Pons-Brooks was observed on eight epochs between 2024 Jan 31 and 2024 Feb 16 using the Lowell 42in (1.1-m) telescope and USNA's Hopper Hall (0.5-m) telescope. CN imaging revealed two apparently face-on spiral features ~180 deg apart. We used their motion to conclude that the apparent rotation period is 57 ± 1 hr (Knight et al., ATEL 16508, 2024). Post-perihelion observation with SOAR (4.1-m) on 2024 Jul 9 again revealed two jets. A single epoch of CN imaging of returning Oort cloud comet C/2021 S3 PanSTARRS was acquired at SOAR on 2024 Mar 14, revealing a face-on spiral feature. We obtained CN imaging of Halley-type comet 13P/Olbers on four epochs from January through April using the Lowell 42in and SOAR. It exhibited a broad sunward enhancement at each epoch. 13P passed perihelion on 2024 Jun 30 and remains at solar elongations below 40 deg until 2025 making post-perihelion observations challenging. Despite this, we will attempt to obtain additional CN imaging and will present any new observations. Dynamically new comet C/2023 A3 Tsuchinshan-ATLAS reaches perihelion at 0.39 au on 2024 Sep 27, followed by an interval where it may attain naked-eye brightness. We obtained CN imaging on three epochs from 2024 Apr 3 to 2024 Jun 11 using the Lowell 42in. The CN morphology looked similar to broadband-r morphology at all epochs, implying that the morphology was dominated by dust at these epochs. Its solar elongation also remains low until well after perihelion, but we will report on any successful additional observations.

These observations are part of a larger study utilizing imaging obtained over the past two decades, primarily from Lowell Observatory. Our dataset contains dust and CN data on ~80 comets, which we are using to explore how coma morphology varies with dynamical classification.

Based in part on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia e Inovações (MCTI/LNA) do Brasil, the U.S. National Science Foundation NOIRLab, the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).