# # Program information file # PROGRAM_ID 2024B086 PROGRAM_TITLE iSHELL Observations of the CO Fundamental Toward Face-on Protostars PROGRAM_INV1 Sam Federman PROGRAM_INV2 Tom Megeath PROGRAM_INV3 Adam Rubinstein PROGRAM_INV4 Neal Evans PROGRAM_INV5 Dan Watson PROGRAM_SCICAT galactic/interstellar medium PROGRAM_ABSTRACT_BEG JWST 2.9-28 micron IFU mapping of highly inclined protostars shows the CO fundamental in both bright emission and absorption, yet the origin of the CO emission is difficult to establish. Due to their inclination and the coarse spectral resolution of NIRSpec, CO emission from the inner disks seen in scattered light is juxtaposed on emission from winds and jets and is difficult to disentangle. We propose to observe four deeply embedded protostars with iSHELL. These objects are inclined such that the protostar is visible at < 5 microns through cavities carved in their envelopes by outflows, and they appear to be face-on analogs of the inclined protostars observed with JWST. With 5.6 km/s velocity resolution, we will resolve the complex CO line profiles in both emission and absorption, while with the broad wavelength coverage we will construct excitation diagrams of the rotational levels using 13CO to correct for extinction. We will observe all four protostars using the M1 and M2 filters with the 0.75' slit. Assuming 0.8' seeing, with 15 second exposures, 2 coadds and 60 cycles, we will achieve over 75 S/N for all four protostars. This results in 1.03 hours clock time per source, for 4.13 hours each in M1 and M2. Assuming an extra 25 minutes per source for calibration and setup, we request a total of 12 hours. With these data, we will trace CO emission/absorption down to the central disks. We will use the line profiles, excitation diagrams, and spatial extents to distinguish emission/absorption from disks, winds and jets, and from the heated walls of the cavity. These data will provide a unique perspective needed to understand the origin of the CO emission/absorption detected by JWST. PROGRAM_ABSTRACT_END