The ionising effect of low energy cosmic rays from a class II object on its protoplanetary disk

Abstract

We investigate the ionising effect of low energy cosmic rays (CRs) from a young star on its protoplanetary disk (PPD). We consider specifically the effect of $\sim 3$GeV protons injected at the inner edge of the PPD. An increase in the ionisation fraction as a result of these CRs could allow the magnetorotational instability to operate in otherwise magnetically dead regions of the disk. For the typical values assumed we find an ionisation rate of ${\zeta }_{\mathrm{CR}}\sim 10^{-17}{\mathrm{s}}^{-1}$ at $1$au. The transport equation is solved by treating the propagation of the CRs as diffusive. We find for increasing diffusion coefficients the CRs penetrate further in the PPD, while varying the mass density profile of the disk is found to have little effect. We investigate the effect of an energy spectrum of CRs. The influence of a disk wind is examined by including an advective term. For advective wind speeds between $1-100\mathrm{km}{\mathrm{s}}^{-1}$ diffusion dominates at all radii considered here (out to 10au) for reasonable diffusion coefficients. Overall, we find that low energy CRs can significantly ionise the midplane of PPDs out to $\sim 1$au. By increasing the luminosity or energy of the CRs, within plausible limits, their radial influence could increase to $\sim 2$au at the midplane but it remains challenging to significantly ionise the midplane further out.

14 pages, 12 figures, accepted for publication in MNRAS

References in corpus (6)

• Global simulations of protoplanetary disks with ohmic resistivity and ambipolar diffusion
• Constraining the X-ray and Cosmic Ray Ionization Chemistry of the TW Hya Protoplanetary Disk: Evidence for a Sub-interstellar Cosmic Ray Rate
• Heat and Dust in Active Layers of Protostellar Disks
• On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds
• Origin of Cosmic Rays
• Tentative Evidence for Relativistic Electrons Generated by the Jet of the Young Sun-like Star DG Tau

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• Aluminum-26 Enrichment in the Surface of Protostellar Disks Due to Protostellar Cosmic Rays
• Chemical transformation of CO in evolving protoplanetary discs across stellar masses: a route to C-rich inner regions
• Charting nearby stellar systems: The intensity of Galactic cosmic rays for a sample of solar-type stars
• Stellar Energetic Particle Transport in the Turbulent and CME-disrupted Stellar Wind of AU~Microscopii
• Stellar cosmic rays as an important source of ionisation in protoplanetary disks: a disk mass dependent process
• Galactic cosmic ray propagation through M dwarf planetary systems
• Galactic breeze origin for the Fermi bubbles emission
• The role of magnetic fields in shaping $\gamma$-ray emission from the Fermi bubbles
• Stellar versus Galactic: The intensity of energetic particles at the evolving Earth and young exoplanets