Exclusion of Cosmic Rays in Protoplanetary Disks. II. Chemical Gradients and Observational Signatures

Abstract

The chemical properties of protoplanetary disks are especially sensitive to their ionization environment. Sources of molecular gas ionization include cosmic rays, stellar X-rays and short-lived radionuclides, each of which varies with location in the disk. This behavior leads to a significant amount of chemical structure, especially in molecular ion abundances, which is imprinted in their submillimeter rotational line emission. Using an observationally motivated disk model, we make predictions for the dependence of chemical abundances on the assumed properties of the ionizing field. We calculate the emergent line intensity for abundant molecular ions and simulate sensitive observations with the Atacama Large Millimeter/Sub-millimeter Array (ALMA) for a disk at D=100 pc. The models readily distinguish between high ionization rates ($\zeta \gtrsim 10^{-17}$ s${}^{-1}$ per H${}_2$) and below, but it becomes difficult to distinguish between low ionization models when $\zeta \lesssim 10^{-19}$ s${}^{-1}$. We find that \htdp\ emission is not detectable for sub-interstellar CR rates with ALMA (6h integration), and that \ntdp\ emission may be a more sensitive tracer of midplane ionization. HCO${}^{+}$ traces X-rays and high CR rates (${\zeta }_{\mathrm{CR}}\gtrsim 10^{-17}$ s${}^{-1}$), and provides a handle on the warm molecular ionization properties where CO is present in the gas. Furthermore, species like HCO${}^{+}$, which emits from a wide radial region and samples a large gradient in temperature, can exhibit ring-like emission as a consequence of low-lying rotational level de-excitation near the star. This finding highlights a scenario where rings are not necessarily structural or chemical in nature, but simply a result of the underlying line excitation properties.

arXiv comment25 pages, 14 figures; accepted to ApJ

References in corpus (64)

• The chemical composition of the Sun
• An atomic and molecular database for analysis of submillimetre line observations
• Protoplanetary Disks and Their Evolution
• Resolved Images of Large Cavities in Protoplanetary Transition Disks
• The Birth Environment of the Solar System
• Secondary antiprotons and propagation of cosmic rays in the Galaxy and heliosphere
• The effect of dust settling on the appearance of protoplanetary disks
• Magnetic Fields in the Formation of Sun-Like Stars
• N2H+ and C18O Depletion in a Cold Dark Cloud
• An Old Disk That Can Still Form a Planetary System
• Investigating the Cosmic-Ray Ionization Rate in the Galactic Diffuse Interstellar Medium through Observations of H3+
• Benchmark problems for continuum radiative transfer. High optical depths, anisotropic scattering, and polarisation
• On the Formation of CO2 and Other Interstellar Ices
• Molecular Inventories and Chemical Evolution of Low-mass Protostellar Envelopes
• The ionization fraction in alpha-models of protoplanetary disks
• LIME - a flexible, non-LTE line excitation and radiation transfer method for millimeter and far-infrared wavelengths
• Complete Depletion in prestellar cores
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• Warm Molecular Layers in Protoplanetary Disks
• Organic molecules in protoplanetary disks around TTauri and HerbigAe stars
• The FUV spectrum of TW Hya. I. Observations of H${}_2$ Fluorescence
• Exclusion of Cosmic Rays in Protoplanetary Disks: Stellar and Magnetic Effects
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• Chemical evolution of turbulent protoplanetary disks and the Solar nebula
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• The importance of the ortho:para H2 ratio for the deuteration of molecules during pre-protostellar collapse
• Gas and Dust Emission at the Outer Edge of Protoplanetary Disks
• Disk Imaging Survey of Chemistry with SMA: II. Southern Sky Protoplanetary Disk Data and Full Sample Statistics
• Disk Imaging Survey of Chemistry with SMA (DISCS): I. Taurus Protoplanetary Disk Data
• Empirical Constraints on Turbulence in Protoplanetary Accretion Disks
• Chemistry of a protoplanetary disk with grain settling and Lyman alpha radiation
• Reprocessing of Ices in Turbulent Protoplanetary Disks: Carbon and Nitrogen Chemistry
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• Three-dimensional dust radiative-transfer models: The Pinwheel Nebula of WR104
• The propagation of Lyman-alpha in evolving protoplanetary disks
• Chemo-dynamical deuterium fractionation in the early solar nebula: The origin of water on Earth and in asteroids and comets
• The Origin of Jovian Planets in Protostellar Disks: The Role of Dead Zones
• High-resolution Ultraviolet Radiation Fields of Classical T Tauri Stars
• Effects of magnetic fields on the cosmic-ray ionization of molecular cloud cores
• Chemistry and line emission from evolving Herbig Ae disks
• Detection of DCO+ in a circumstellar disk
• 26Al in the Early Solar System: Not so Unusual After All
• High Resolution X-ray Spectroscopy of T Tauri Stars in the Taurus-Auriga Complex
• The Ionization Fraction of Barnard 68: Implications for Star and Planet Formation
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• Sulfur chemistry: 1D modeling in massive dense cores
• The Cosmic Ray Intensity Near the Archean Earth
• Radionuclide Ionization in Protoplanetary Disks: Calculations of Decay Product Radiative Transfer
• Photoelectric cross-sections of gas and dust in protoplanetary disks
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• A deep search for H2D+ in protoplanetary disks
• Effects of Turbulence on Cosmic Ray Propagation in Protostars and Young Star/Disk Systems

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