Observing Carbon & Oxygen Carriers in Protoplanetary Disks at Mid-infrared Wavelengths

Abstract

Infrared observations probe the warm gas in the inner regions of planet-forming disks around young sun-like, T Tauri stars. In these systems, H${}_2$O, OH, CO, CO${}_2$, C${}_2$H${}_2$, and HCN have been widely observed. However, the potentially abundant carbon carrier CH${}_4$ remains largely unconstrained. The James Webb Space Telescope (JWST) will be able to characterize mid-infrared fluxes of CH${}_4$ along with several other carriers of carbon and oxygen. In anticipation of the JWST mission, we model the physical and chemical structure of a T Tauri disk to predict the abundances and mid-infrared fluxes of observable molecules. A range of compositional scenarios are explored involving the destruction of refractory carbon materials and alterations to the total elemental (volatile and refractory) C/O ratio. Photon-driven chemistry in the inner disk surface layers largely destroys the initial carbon and oxygen carriers. This causes models with the same physical structure and C/O ratio to have similar steady state surface compositions, regardless of the initial chemical abundances. Initial disk compositions are better preserved in the shielded inner disk midplane. The degree of similarity between the surface and midplane compositions in the inner disk will depend on the characteristics of vertical mixing at these radii. Our modeled fluxes of observable molecules respond sensitively to changes in the disk gas temperature, inner radius, and the total elemental C/O ratio. As a result, mid-infrared observations of disks will be useful probes of these fundamental disk parameters, including the C/O ratio, which can be compared to values determined for planetary atmospheres.

Accepted for publication in The Astrophysical Journal

References in corpus (19)

• The NumPy array: a structure for efficient numerical computation
• Constraining the X-ray and Cosmic Ray Ionization Chemistry of the TW Hya Protoplanetary Disk: Evidence for a Sub-interstellar Cosmic Ray Rate
• Meridional flows in the disk around a young star
• Lupus disks with faint CO isotopologues: low gas/dust or large carbon depletion?
• Mass measurements in protoplanetary disks from hydrogen deuteride
• Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?
• Mass inventory of the giant-planet formation zone in a solar nebula analog
• Reprocessing of Ices in Turbulent Protoplanetary Disks: Carbon and Nitrogen Chemistry
• Disks around CQ Tau and MWC 758: dense PDR or gas dispersal?
• Composition of Early Planetary Atmospheres I: Connecting Disk Astrochemistry to the Formation of Planetary Atmospheres
• Formation of simple organic molecules in inner T Tauri disks
• Hints for icy pebble migration feeding an oxygen-rich chemistry in the inner planet-forming region of disks
• Exclusion of Cosmic Rays in Protoplanetary Disks. II. Chemical Gradients and Observational Signatures
• Exploring the Origins of Carbon in Terrestrial Worlds
• Chemistry in Protoplanetary Disks: the gas-phase CO/H2 ratio and the Carbon reservoir
• Destruction of Refractory Carbon in Protoplanetary Disks
• The spatial distribution of carbon dust in the early solar nebula and the carbon content of planetesimals
• Ro-vibrational excitation of an organic molecule (HCN) in protoplanetary disks
• Chemistry Along Accretion Streams in a Viscously-Evolving Protoplanetary Disk

Cited by in corpus (20)

• MINDS. The detection of ${}^{13}$CO${}_2$ with JWST-MIRI indicates abundant CO${}_2$ in a protoplanetary disk
• MINDS. Abundant water and varying C/O across the disk of Sz 98 as seen by JWST/MIRI
• The diverse chemistry of protoplanetary disks as revealed by JWST
• The Chemical Inventory of the Inner Regions of Planet-forming Disks -- The JWST/MINDS Program
• The kinematics and excitation of infrared water vapor emission from planet-forming disks: results from spectrally-resolved surveys and guidelines for JWST spectra
• New Constraints on Protoplanetary Disk Gas Masses in Lupus
• Simulating Observations of Ices in Protoplanetary Disks
• Bayesian Analysis of Molecular Emission and Dust Continuum of Protoplanetary Disks
• CO2-rich protoplanetary discs as a probe of dust radial drift & trapping
• Hydrocarbon chemistry in inner regions of planet forming disks
• Water UV-shielding in the terrestrial planet-forming zone: Implications for carbon dioxide emission
• Water shielding in the terrestrial planet-forming zone: Implication for inner disk organics
• CO isotopolog line fluxes of viscously evolving disks: cold CO conversion insufficient to explain observed low fluxes
• Physical conditions for dust grain alignment in Class 0 protostellar cores I. Observations of dust polarization and molecular irradiation tracers
• MINDS. Strong oxygen depletion in the inner regions of a very low-mass star disk?
• Tracking the Chemical Evolution of Hydrocarbons Through Carbon Grain Supply in Protoplanetary Disks
• First Detection of HC5N in a Class II Disk around TW Hya
• Protoplanetary Disk Chemistry
• Molecular Similarity and Water Diversity in Coeval Binary Disks: JWST/MIRI Observations of Sz 65 and Sz 66
• Water UV-shielding in the terrestrial planet-forming zone: Implications from water emission