IRTF Data Archive Program Information

# # Program information file # 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