Stellar cosmic rays as an important source of ionisation in protoplanetary disks: a disk mass dependent process

Abstract

We assess the ionising effect of low energy protostellar cosmic rays in protoplanetary disks around a young solar mass star for a wide range of disk parameters. We assume a source of low energy cosmic rays located close to the young star which travel diffusively through the protoplanetary disk. We use observationally inferred values from nearby star-forming regions for the total disk mass and the radial density profile. We investigate the influence of varying the disk mass within the observed scatter for a solar mass star. We find that for a large range of disk masses and density profiles that protoplanetary disks are "optically thin" to low energy ($\sim$3 GeV) cosmic rays. At $R\sim 10$au, for all of the disks that we consider ($M_{\mathrm{disk}}=6.0\times 10^{-4}-2.4\times 10^{-2}{M}_{\odot }$), the ionisation rate due to low energy stellar cosmic rays is larger than that expected from unmodulated galactic cosmic rays. This is in contrast to our previous results which assumed a much denser disk which may be appropriate for a more embedded source. At $R\sim 70$au, the ionisation rate due to stellar cosmic rays dominates in $\sim$50% of the disks. These are the less massive disks with less steep density profiles. At this radius there is at least an order of magnitude difference in the ionisation rate between the least and most massive disk that we consider. Our results indicate, for a wide range of disk masses, that low energy stellar cosmic rays provide an important source of ionisation at the disk midplane at large radii ($\sim$70au).

arXiv comment11 pages, 6 figures, accepted for publication in MNRAS

References in corpus (20)

• Global simulations of protoplanetary disks with ohmic resistivity and ambipolar diffusion
• Time dependence of the proton flux measured by PAMELA during the July 2006 - December 2009 solar minimum
• Thanatology in Protoplanetary Discs: the combined influence of Ohmic, Hall, and ambipolar diffusion on dead zones
• The ionization fraction in alpha-models of protoplanetary disks
• Magnetic fields in protoplanetary disks
• Constraining the X-ray and Cosmic Ray Ionization Chemistry of the TW Hya Protoplanetary Disk: Evidence for a Sub-interstellar Cosmic Ray Rate
• Exclusion of Cosmic Rays in Protoplanetary Disks: Stellar and Magnetic Effects
• Heat and Dust in Active Layers of Protostellar Disks
• Hall-effect Controlled Gas Dynamics in Protoplanetary Disks: I. Wind Solutions at the Inner Disk
• Inside-Out Evacuation of Transitional Protoplanetary Disks by the Magneto-Rotational Instability
• Direct magnetic field detection in the innermost regions of an accretion disc
• Unlocking CO Depletion in Protoplanetary Disks I. The Warm Molecular Layer
• Energetic Protons, Radionuclides and Magnetic Activity in Protostellar Disks
• Stellar energetic particle ionization in protoplanetary disks around T Tauri stars
• Exploration of Cosmic Ray Acceleration in Protostellar Accretion Shocks and A Model for Ionization Rates in Embedded Protoclusters
• The ionising effect of low energy cosmic rays from a class II object on its protoplanetary disk
• X-ray ionization rates in protoplanetary discs
• Mottled protoplanetary disk ionization by magnetically-channeled T Tauri star energetic particles
• Multifluid simulations of the Magnetorotational Instability in protostellar disks
• Global multifluid simulations of the magnetorotational instability in radially stratified protoplanetary disks

Cited by in corpus (7)

• Chemical Diversity in Protoplanetary Disks and Its Impact on the Formation History of Giant Planets
• The Galactic cosmic ray intensity at the evolving Earth and young exoplanets
• Stellar versus Galactic: The intensity of cosmic rays at the evolving Earth and young exoplanets around Sun-like stars
• Towards First-principle Characterization of Cosmic-ray Transport Coefficients from Multi-scale Kinetic Simulations
• Cosmic-ray ionization rate in protoplanetary disks with sheared magnetic fields
• Charting nearby stellar systems: The intensity of Galactic cosmic rays for a sample of solar-type stars
• Modeling Hadronic Gamma-ray Emissions from Solar Flares and Prospects for Detecting Non-thermal Signatures from Protostars