CONSTRAINING THE X-RAY AND COSMIC-RAY IONIZATION CHEMISTRY OF THE TW Hya PROTOPLANETARY DISK: EVIDENCE FOR A SUB-INTERSTELLAR COSMIC-RAY RATE

2014/12/03 by L. Ilsedore Cleeves, Edwin A. Bergin, Chunhua Qi +3 · 10 citations
Chemistry · Physics and Astronomy · #Astro and Planetary Science #Astrochemistry #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Cosmic ray #Galaxy #Interstellar medium #Ion #Ionization #Molecular Spectroscopy and Structure #Physics #Planet #Protoplanetary disk #Spectral line #Star formation #Stars #Submillimeter Array #T Tauri star #astro-ph.SR

paper · pdf · doi:10.1088/0004-637x/799/2/204

20 pages, 14 figures, Accepted in ApJ

arxiv created 2014/12/03 · openalex publication_date 2015/01/30 · arxiv updated 2015/06/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

We present an observational and theoretical study of the primary ionizing agents (cosmic rays (CRs) and X-rays) in the TW Hya protoplanetary disk. We use a set of resolved and unresolved observations of molecular ions and other molecular species, encompassing 11 lines total, in concert with a grid of disk chemistry models. The molecular ion constraints comprise new data from the Submillimeter Array on HCO + , acquired at unprecedented spatial resolution, and data from the literature, including ALMA observations of N 2 H + . We vary the model incident CR flux and stellar X-ray spectra and find that TW Hya's HCO + and N 2 H + emission are best-fit by a moderately hard X-ray spectra, as would be expected during the "flaring" state of the star, and a low CR ionization rate, ζ CR ≲ 10 −19 s −1 . This low CR rate is the first indication of the presence of CR exclusion by winds and/or magnetic fields in an actively accreting T Tauri disk system. With this new constraint, our best-fit ionization structure predicts a low turbulence "dead-zone" extending from the inner edge of the disk out to 50–65 AU. This region coincides with an observed concentration of millimeter grains, and we propose that the inner region of TW Hya is a dust (and possibly planet) growth factory as predicted by previous theoretical work.

Citations

• The size distribution of interstellar grains
• Evidence for a Developing Gap in a 10 Myr Old Protoplanetary Disk
• The Far‐Ultraviolet Spectra of TW Hydrae. II. Models of H2Fluorescence in a Disk
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• A DEEPCHANDRAX-RAY SPECTRUM OF THE ACCRETING YOUNG STAR TW HYDRAE
• Chemistry in Protoplanetary Disks
• Synthetic infrared images and spectral energy distributions of a young low-mass stellar cluster
• Near-Infrared Coronagraphic Imaging of the Circumstellar Disk around TW Hydrae
• The Submillimeter Array
• Complex Chemistry in Star‐forming Regions: An Expanded Gas‐Grain Warm‐up Chemical Model
• THE TW Hya DISK AT 870 μm: COMPARISON OF CO AND DUST RADIAL STRUCTURES
• A powerful local shear instability in weakly magnetized disks. I - Linear analysis. II - Nonlinear evolution
• Disks around the Young Stars TW Hydrae and HD 100546 Imaged at 3.4 Millimeters with the Australia Telescope Compact Array
• The Balbus-Hawley instability in weakly ionized discs
• Validation of the new Hipparcos reduction
• The State of Protoplanetary Material 10 Million years after Stellar Formation: Circumstellar Disks in the TW Hydrae Association
• Three-dimensional dust radiative-transfer models: the Pinwheel Nebula of WR 104
• Reduction of chemical networks

Cited by

• Ortho–Para Chemistry of H 2 CO in the Protoplanetary Disk TW Hya
• Sulfur Chemistry in Protoplanetary Disks: CS and H2CS
• Molecules with ALMA at Planet-forming Scales (MAPS). XVI. Characterizing the Impact of the Molecular Wind on the Evolution of the HD 163296 System
• How do T Tauri stars accrete?
• Unlocking CO Depletion in Protoplanetary Disks. I. The Warm Molecular Layer
• The Role of C/O in Nitrile Astrochemistry in PDRs and Planet-forming Disks
• The TW Hya Rosetta Stone Project IV: A Hydrocarbon-rich Disk Atmosphere
• Cosmic-Ray Propagation in Turbulent Spiral Magnetic Fields Associated with Young Stellar Objects
• Nitrogen isotope fractionation in protoplanetary disks
• Detection of HC18O+ in a protoplanetary disk: exploring oxygen isotope fractionation of CO