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# Program information file
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PROGRAM_ID           2023A074
PROGRAM_TITLE        Surveying the Structure of Massive Protostellar Disks
PROGRAM_INV1         Adwin Boogert
PROGRAM_INV2         Andrew Barr
PROGRAM_INV3         Curtis deWitt
PROGRAM_INV4         Jialu Li
PROGRAM_INV5         Xander Tielens
PROGRAM_SCICAT       galactic/interstellar medium
PROGRAM_ABSTRACT_BEG
Circumstellar disks are expected to play a key role in the star formation process. However, disks around massive protostars have only been studied in a handful of objects through near-IR studies of CO bandhead profiles and sub-mm rotational lines. Because of their high infrared luminosity, disks around massive protostars are ideal background sources for mid-IR absorption line studies. Each vibrational mode contains many rotational transitions of simple molecules. These originate in the photospheres of highly optically thick accretion disks. Unexpectedly, the lines of these molecules in the iSHELL L-band spectrum of AFGL 2591 are observed in emission at relatively cool temperatures [~200 K]. The lack of absorption is attributed to an absence of these molecules in the inner region of the disk where the 3 micron continuum originates. The emission lines, on the other hand, are thought to reflect scattering in the upper layers of a flaring disk. Here, we propose a survey of the L-band spectra of 12 massive protostars. The proposed iSHELL observations will determine the line profiles, temperatures and column densities of HCN, C2H2, CH4, and H2CO in this sample, and will also enable a deep search for the key organic species CH3OH. The spectral resolving power of R=80,000 will resolve the lines. The observations can be carried out with the iSHELL L2 and Lp2 settings covering ~2.91-3.66 micron. We aim to observe each source in the survey sample at a minimum S/N of 200. The goal of this survey is to determine how widespread the presence of molecular emission and absorption lines is in these types of objects and how this relates to the characteristics of the star, the characteristics of the disk, and the evolutionary stage of the object.
PROGRAM_ABSTRACT_END