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# Program information file
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PROGRAM_ID           2024B084
PROGRAM_TITLE        Comet C/2023 A3 [Tsuchinshan-ATLAS]: Serial measurements of volatiles and isotopes in an unusually bright dynamically new comet
PROGRAM_INV1         Michael DiSanti
PROGRAM_INV2         Neil Dello Russo
PROGRAM_INV3         Erika Gibb
PROGRAM_INV4         Ronald Vervack
PROGRAM_INV5         Boncho Bonev
PROGRAM_SCICAT       comets
PROGRAM_ABSTRACT_BEG
C/2023 A3 is a dynamically new comet from the Oort cloud that is predicted to reach magnitude ~1 near perihelion [0.391 AU on UT 27 September]. Its 2024B apparition offers an unprecedented opportunity to conduct detailed serial measurements over a range of heliocentric distances [Rh], spanning ~1.1 AU pre-perihelion to 1.1 AU post-perihelion. Owing to limited solar elongation constraints, the proposed program is largely daytime [and predominantly post-perihelion]. Therefore, IRTF/iSHELL is uniquely capable of conducting this study.

The proposed study is motivated by two distinct yet related Tasks: [1] Measure the composition of a dynamically new comet as a function of Rh. Production rates and relative abundances for the suite of parent molecules [those housed as ices in the nucleus] normally measured in comets [H2O, HCN, C2H2, NH3, CH4, C2H6, CH3OH, H2CO, CO, and OCS], combined with the high expected levels of activity, provide excellent sensitivity, even for species having traditionally lower abundances and/or weaker emissions [e.g., C2H2, NH3, and OCS] near or beyond Rh = 1 AU. [2] Measure rarely detected species in a dynamically new comet. The exceptionally high brightness near perihelion allows sensitive measures of species with low abundances. This study emphasizes C2H4, a chemical intermediary between C2H2 and C2H6, and the isotopes HDO and 13CO that test fractionation of hydrogen and carbon, respectively, during solar system formation. H2O and HDO spectra will be obtained and processed in a consistent manner, constraining HDO/H2O ratios near or below the terrestrial value. We also test additional trace molecules [HNC, H3CN, C4H2], to better inform chemistry in the natal environment.
PROGRAM_ABSTRACT_END