Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Exclusion of Cosmic Rays in Protoplanetary Disks: Stellar and Magnetic
  Effects   (Abridged) Cosmic rays (CRs) are thought to provide an important source of
ionization in the outermost and densest regions of protoplanetary disks;
however, it is unknown to what degree they are physically present. As is
observed in the Solar System, stellar winds can inhibit the propagation of
cosmic rays within the circumstellar environment and subsequently into the
disk. In this work, we explore the hitherto neglected effects of cosmic ray
modulation by both stellar winds and magnetic field structures and study how
these processes act to reduce disk ionization rates. We construct a
two-dimensional protoplanetary disk model of a T-Tauri star system, focusing on
ionization from stellar and interstellar FUV, stellar X-ray photons, and cosmic
rays. We show that stellar winds can power a Heliosphere-like analogue, i.e., a
"T-Tauriosphere," diminishing cosmic ray ionization rates by several orders of
magnitude at low to moderate CR energies (E_CR<1 GeV). We explore models of
both the observed solar wind cosmic ray modulation and a highly simplified
estimate for "elevated" cosmic ray modulation as would be expected from a young
T-Tauri star. In the former (solar analogue) case, we estimate the ionization
rate from galactic cosmic rays to be zeta_CR~(0.23-1.4) x 1e-18 s^-1. This
range of values, which we consider to be the maximum CR ionization rate for the
disk, is more than an order of magnitude lower than what is generally assumed
in current models for disk chemistry and physics. In the latter case, i.e., for
a "T-Tauriosphere," the ionization rate by cosmic rays is zeta_CR<1e-20 s^-1,
which is 1000 times smaller than the interstellar value. Indeed, if winds are
as efficient at cosmic ray modulation as predicted here, short-lived
radionuclides (now extinct) would have provided the major source of ionization
(zeta_RN~7.3e-19 s^-1) in the planet-forming zone of the young Solar Nebula.

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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ex
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
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The categories of this paper are: stat
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The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
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The categories of this paper are: hep-lat
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The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
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The categories of this paper are: nlin
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The categories of this paper are: funct-an
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The categories of this paper are: bayes-an
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The categories of this paper are: patt-sol
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The categories of this paper are: comp-gas
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The categories of this paper are: adap-org