The HCN-Water Ratio in the Planet Formation Region of Disks

Abstract

We find a trend between the mid-infrared HCN/H2O flux ratio and submillimeter disk mass among T Tauri stars in Taurus. While it may seem puzzling that the molecular emission properties of the inner disk (< few AU) are related to the properties of the outer disk (beyond ~20 AU) probed by the submillimeter continuum, an interesting possible interpretation is that the trend is a result of planetesimal and protoplanet formation. Because objects this large are decoupled from the accretion flow, when they form, they can lock up water (and oxygen) beyond the snow line, thereby enhancing the C/O ratio in the inner disk and altering the molecular abundances there. We discuss the assumptions that underlie this interpretation, a possible alternative explanation, and related open questions that motivate future work. Whatever its origin, understanding the meaning of the relation between the HCN/H2O ratio and disk mass is of interest as trends like this among T Tauri disk properties are relatively rare.

20 pages, 4 figures. To be published in the Astrophysical Journal

References in corpus (3)

• H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks
• Constraints on the Radial Variation of Grain Growth in the AS 209 Circumstellar Disk
• Formation of simple organic molecules in inner T Tauri disks

Cited by in corpus (55)

• Astrochemistry and compositions of planetary systems
• The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime
• Astrochemistry of dust, ice and gas: introduction and overview
• The Atomic and Molecular Content of Disks Around Very Low-mass Stars and Brown Dwarfs
• Hints for icy pebble migration feeding an oxygen-rich chemistry in the inner planet-forming region of disks
• Water vapor distribution in protoplanetary disks
• C/O Ratios of Stars with Transiting Hot Jupiter Exoplanets
• Chemo-dynamical deuterium fractionation in the early solar nebula: The origin of water on Earth and in asteroids and comets
• Volatile depletion in the TW Hydrae disk atmosphere
• Survey of cold water lines in protoplanetary disks: indications of systematic volatile depletion
• Molecules with ALMA at Planet-forming Scales (MAPS) VI: Distribution of the small organics HCN, C2H, and H2CO
• Modelling mid-infrared molecular emission lines from T Tauri stars
• MINDS. Abundant water and varying C/O across the disk of Sz 98 as seen by JWST/MIRI
• Measurements of water surface snow lines in classical protoplanetary disks
• Ro-vibrational excitation of an organic molecule (HCN) in protoplanetary disks
• Disk Dispersal: Theoretical Understanding and Observational Constraints
• The diverse chemistry of protoplanetary disks as revealed by JWST
• The chemistry of disks around T Tauri and Herbig Ae/Be stars
• The composition of the protosolar disk and the formation conditions for comets
• Gas lines from the 5-Myr old optically thin disk around HD141569A. Herschel observations and modeling
• Numerical Simulations of Gaseous Disks Generated from Collisional Cascades at the Roche Limits of White Dwarf Stars
• The Chemical Inventory of the Inner Regions of Planet-forming Disks -- The JWST/MINDS Program
• Understanding the water emission in the mid- and far-IR from protoplanetary disks around T~Tauri stars
• The kinematics and excitation of infrared water vapor emission from planet-forming disks: results from spectrally-resolved surveys and guidelines for JWST spectra
• Observing Carbon & Oxygen Carriers in Protoplanetary Disks at Mid-infrared Wavelengths
• Candidate Water Vapor Lines to Locate the H${}_2$O Snowline through High-Dispersion Spectroscopic Observations I. The Case of a T Tauri Star
• Shielding by Water and OH in FUV and X-ray Irradiated Protoplanetary Disks
• JWST Observations of Young protoStars (JOYS): overview of program and early results
• A high resolution mid-infrared survey of water emission from protoplanetary disks
• Rocky Planet Formation: Quick and Neat
• If you like C/O variations, you should have put a ring on it
• OH mid-infrared emission as a diagnostic of H${}_2$O UV photodissociation. III. Application to planet-forming disks
• The nitrogen carrier in protoplanetary disks
• Burned to ashes: How the thermal decomposition of refractory organics in the inner protoplanetary disc impacts the gas-phase C/O ratio
• MINDS. JWST-MIRI reveals a peculiar CO${}_2$-rich chemistry in the drift-dominated disk CX Tau
• Resolved molecular line observations reveal an inherited molecular layer in the young disk around TMC1A
• Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): A Panchromatic View of DO Tau's Complex Kilo-au Environment
• Candidate Water Vapor Lines to Locate the ${\mathrm{H}}_2\mathrm{O}$ Snowline through High-dispersion Spectroscopic Observations. III. Submillimeter ${\mathrm{H}}_2$${}^{16}\mathrm{O}$ and ${\mathrm{H}}_2$${}^{18}\mathrm{O}$ Lines
• Spectrally Resolved Mid-Infrared Molecular Emission from Protoplanetary Disks and the Chemical Fingerprint of Planetesimal Formation
• Emission from Water Vapor and Absorption from Other Gases at 5-7.5 Microns in Spitzer-IRS Spectra of Protoplanetary Disks
• Water shielding in the terrestrial planet-forming zone: Implication for inner disk organics
• Probing UV-Sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
• Chemical transformation of CO in evolving protoplanetary discs across stellar masses: a route to C-rich inner regions
• Effect of Different Angular Momentum Transport mechanisms on the Distribution of Water in Protoplanetary Disks
• XUE. JWST spectroscopy of externally irradiated disks around young intermediate-mass stars
• Water-Cooled (sub)-Neptunes Get Better Gas Mileage
• Mid-infrared blends and continuum signatures of dust drift and accretion in protoplanetary disks
• On the diversification and dissipation of protoplanetary disks
• Gas kinematics of key prebiotic molecules in GV Tau N revealed with an ALMA, PdBI, and Herschel synergy
• Water vapor emission at the warm cavity wall of the HD 100546 disk as revealed by ALMA
• Molecules with ALMA at Planet-forming Scales (MAPS). XV. Tracing protoplanetary disk structure within 20 au
• How leaky? A large parameter study of leaky dust traps to quantify the transport of pebbles and ice in protoplanetary discs
• Linking Outer Disk Pebble Dynamics and Gaps to Inner Disk Water Enrichment
• Protoplanetary Disk Chemistry
• Molecular Similarity and Water Diversity in Coeval Binary Disks: JWST/MIRI Observations of Sz 65 and Sz 66