# # Program information file # PROGRAM_ID 2023B084 PROGRAM_TITLE Using iSHELL to Investigate Chemical Evolution and Variability in Young Stellar Objects PROGRAM_INV1 Rachel Smith PROGRAM_INV2 Adwin Boogert PROGRAM_INV3 PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Observations of young stellar objects [YSOs] trace protoplanetary chemistry, and high-resolution spectroscopy enables meaningful connections between these solar nebula analogues and isotopic measurements in the oldest meteorites. With the very high spectral resolution of iSHELL, one can investigate the significance of variations in CO reservoirs as a function of time, as well as chemical inheritance within YSOs in the same parent cloud. By obtaining precise isotope ratios of C and O via CO rovibrational spectroscopy, this project will adress the following: [1] How do the isotopic ratios of CO vary over time in YSOs? [2] Is there a dependency on the YSO environment, e.g., strengths of the radiation fields, low-mass vs. high-mass YSOs, single vs. binary YSOs? [3] How much do the isotope ratios vary among YSOs within the same and between molecular clouds, and what can this tell us about inheritance from the cloud to the disk? We will also explore short-term chemical variability in YSOs. We plan to use IRTF-iSHELL at R~88,000 [M band] and R~78,000 [K band] to add statistical significance to the variable trends seen in previous work. We aim to build datasets to include at least four observations per target, as well as investigate variations between gravitationally bound binaries. For each run we request 120 minutes of on-source time for the 6 targets in M1 mode and 110 minutes on-source time in K3 mode for each run, for a total [including overhead and the 3 runs] request of 11.5 hours. We will use Spextool's Xtellcor_model in the reduction. We are requesting three ~half-night runs, with two of the runs spaced one- to two-days apart, and one run separated by at least one month. This will enable us to explore systematic and observational uncertainties. The run separated from the two paired runs would assess short-term variability in these targets. PROGRAM_ABSTRACT_END