# # Program information file # PROGRAM_ID 2021A095 PROGRAM_TITLE Surveying the Structure of Massive YSO Disks PROGRAM_INV1 Adwin Boogert PROGRAM_INV2 Andrew Barr PROGRAM_INV3 Xander Tielens PROGRAM_INV4 Jialu Li PROGRAM_INV5 Curtis DeWitt 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 around the protostars. However, ro-vibrational transitions of these molecules in the iSHELL L-band spectrum of AFGL 2591 are observed in emission at relatively cool temperatures [~200 K]. This is attributed to an absence of these molecules in the inner region of the disk where the 3 micron continuum originates, reflecting chemical processing in hot gas. In contrast, these emission lines are thought to reflect scattering in the upper layers of a flaring disk. Here, we propose a survey of the L-band spectra of 7 massive protostars. The proposed iSHELL observations of the L-band will determine the line profiles, temperatures and column densities/abundances of HCN and C2H2 in the sample of massive protostars. With a slit width of 0.375'', a spectral resolving power of R=80,000 will allow for transitions to be fully resolved. The observations can be carried out with the iSHELL L2 setting covering 2.91-3.22 micron. We aim to observe each source in the survey sample at a minimum S/N of 200-300. The goal of this survey is to determine how widespread the presence of molecular emission 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