Presentation #412.01 in the session Dusty and Icy Cometary Comae (iPosters).
Long-period Comet C/2014 UN271 (Bernardinelli-Bernstein) (hereafter UN271) provides an unusual opportunity for us to probe cometary history and behavior. It is very large (>100 km nucleus diameter [1,2]); it will be visiting the Saturnian area of our planetary region for possibly the first time [3,4]; it has a perihelion (11 au) that means it will never enter the water-sublimation zone; and it was discovered early enough that we may eventually establish a multi-decade record of its behavior. We report here visible-wavelength imaging and visible + near-IR spectroscopy of UN271 over several epochs from December 2021 to August 2022, while the comet was approaching the Sun from 19.6 to 18.7 au. Ground-based observations were obtained from Gemini-S with GMOS-S and Flamingos 2, and space-based observations were obtained from HST with WFC3. The analysis goals were to characterize the comet’s inner dust coma with the high spatial resolution afforded by those facilities. As there is some indication that CO2 or NH3, instead of the more-volatile CO, could be driving the activity at large heliocentric distances , we aim to use these and future observations to investigate UN271’s activity driver and behavior as it approaches the Sun. We will present dust color maps and Afρ measurements, describe the changes in those from epoch to epoch (e.g. as a secular light curve), and compare those to other published reports of the comet’s activity at larger heliocentric distances (e.g. [4,5,6]). We will also present our preliminary assessments of the nucleus’s cross section and of the water-ice signatures in the spectroscopy of the dust grains. Acknowledgement: Research based on observations made with the NASA/ESA HST, obtained at STScI, and the international Gemini Observatory, a program of NSF’s NOIRLab. STScI and NOIRLab are managed by AURA, respectively, under NASA contract NAS5-26555 and a cooperative agreement with NSF on behalf of the Gemini Observatory partnership. References:  Lellouch et al. 2022, A&A 659, L1.  Hui et al. 2022, ApJL 929, L12.  CBET 4983.  Bernardinelli et al. 2021, ApJL 921, L37.  Farnham et al. 2021, PSJ 2, 236.  Kelley et al. 2022, ApJL 933, L44.