IRTF Data Archive Program Information

# # Program information file # PROGRAM_ID 2024A993 PROGRAM_TITLE MIRSI Observations of the Approaching Oort Cloud Comet C/2023 A3 (Tsuchinshan-ATLAS) PROGRAM_INV1 Quanzhi Ye PROGRAM_INV2 PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT comets PROGRAM_ABSTRACT_BEG The approaching Oort cloud comet C/2023 A3 (Tsuchinshan-ATLAS) is following a trajectory that will permit observations from Earth at phase angles from 3 degrees to 173 degrees in 2024, providing a rare opportunity to constrain the scattering phase function of dust from a comet over such an exceptionally wide range of phase angles. We request, one such block of 3 hours near local midnight within a few days of April 17 (or as close as possible) to observe the comet near its opposition at 3 degrees phase angle using MIRSI/MOC. We request another set of three 1 hour blocks at the beginning of three nights in late June and/or early July to observe the comet at a higher ~30 degrees phase angle while brighter at r~2 au, bridging the gap between the low phase angle opposition observations and the high phase angle observations that will become possible a few months later in semester 2024B. PROGRAM_ABSTRACT_END