X-ray ionization rates in protoplanetary discs
  Low-mass young stellar objects are powerful emitters of X-rays that can
ionize and heat the disks and the young planets they harbour. The X-rays
produce molecular ions that affect the chemistry of the disk atmospheres and
their spectroscopic signatures. Deeper down, X-rays are the main ionization
source and influence the operation of the magnetorotational instability,
believed to be the main driver for the angular momentum redistribution crucial
for the accretion and formation of these pre main-sequence stars. X-ray
ionization also affects the character of the dead zones around the disk
midplane where terrestrial planets are likely to form. To obtain the physical
and chemical effects of the stellar X-rays, their propagation through the disk
has to be calculated taking into account both absorption and scattering. To
date the only calculation of this type was done almost 15 years ago, and here
we present new three-dimensional radiative transfer calculations of X-ray
ionization rates in protoplanetary discs. Our study confirms the results from
previous work for the same physical parameters. It also updates them by
including a more detailed treatment of the radiative transfer and by using
ionizing spectra and elemental abundance more appropriate for what is currently
known about protoplanetary disks and their host stars. The new calculations for
a typical ionizing spectrum yield respectively lower and higher ionisation
rates at high and low column densities at a given radius in a disc. The
differences can be up to an order of magnitude near 1 AU, depending on the
abundances used
