High-mass star-forming sources known as 'hot cores' are characterized by rich MM/sub-MM molecular emission spectra, with excitation temperatures typically ranging from ~100-300 k. Many of the most…

This $422,941.36 federal grant was awarded by the Shared Services Center, a civilian agency, to the Rector & Visitors of the University of Virginia (UVA) to conduct research on the physical and chemical characteristics of high-mass star-forming regions known as "hot cores". The research aims to develop more sophisticated models of hot core formation and evolution, including the influence of temperature, density, and radiation on the chemistry that occurs during the infall and warm-up of material from the envelope onto the central protostar. The work will combine hydrodynamic models, chemical kinetics, and spectroscopic simulations to better understand the complex organic chemistry in hot cores and how it relates to observations. No set-aside was used for this award, which has a performance period ending on February 26, 2024. As a leading research institution, UVA has extensive experience managing complex federally-funded projects across a range of scientific disciplines.

High-mass star-forming sources known as 'hot cores' are characterized by rich MM/sub-MM molecular emission spectra, with excitation temperatures typically ranging from ~100-300 k. Many of the most complex organic molecules yet detected in the ISM are found in hot cores, including acids, amines, alcohols and aldehydes. Production of these molecules is understood to begin in the formation of simple dust-grain ices, which are further processed and desorbed as a result of the physical changes associated with the star-formation process. While the central hot-core region is often unresolved, the brightness of these sources and the high molecular column densities found within them allow a greater range of molecules to be detected than toward any other type of source. Hot cores therefore provide a unique window into the complex organic chemistry of the interstellar medium, and offer the most stringent testing ground for theories of interstellar organic molecule production. However, while models of hot-core chemistry have advanced over the past few years to match the increasingly large family of detected interstellar molecules, physical treatments of the hot-core stage remain simplistic, using only basic approximations to the in fall and warm-up of material from the envelope onto the central source. This has two main consequences: (i) the influence of temperature, density and radiation field on the ICE and gas-phase chemistry during in fall is poorly represented; (II) simulations of the spectral emission from hot cores cannot take accurate account of source structure. The fact that the central hot-core region is usually unresolved means that the structure of the main emission region cannot be observationally determined. Furthermore, the use of observational physical profiles of the extended envelopes of hot-cores, to determine the physical conditions for parcels of gas at earlier stages of in fall, provides only a snapshot of present conditions, which may not be indicative of the physical histories of current hot-core material. They will combine state-of-the-art hydrodynamics, chemical kinetics, and spectroscopic models to investigate the conditions of high-mass star formation that lead to hot cores. The HD models will have a particular emphasis on the physical development and in fall of the envelope material that eventually develops into the compact hot core, with a detailed consideration of the propagation of radiation from the central source (which can retard the collapse and heat up the dust grains upon which important chemistry occurs). Tracer particles will be used to extract trajectories for mass-conserved gas parcels during the entire in fall process, producing a final simulated hot core that is well-sampled both spatially and in the physical history of those sample-points. Astrochemical models will then be applied to each trajectory, allowing both the physical and chemical history of the hot core to be traced over space and time. Finally, dedicated spectral-simulation tools will be used to predict accurately the emission from molecules in the hot core. This generic approach will be applied under varied initial conditions, to explore the effects of protostellar parameters such as mass and magnetic field on the chemistry and spectral emission of hot cores. A 3D model of binary star formation will also be produced. Results will be compared quantitatively and directly with observed sources, using spectral simulations. Our coupled treatment of gas and dust chemistry will allow molecular observations from instruments like alma to be analyzed in tandem with ICE data from the upcoming james webb space telescope and the past spitzer mission. Our team incorporates leading experts in the hydrodynamics of star formation, radiative feedback, astrochemical modeling and spectroscopy. Through a comprehensive approach, this project will bring much-needed rigor to our understanding of the most chemically-complex interstellar sources.