Ionisation of inner T Tauri star discs: effects of in-situ energetic particles produced by strong magnetic reconnection events
Date Issued
2023
Author(s)
Abstract
Magnetic reconnection is one of the major particle acceleration processes in
space and astrophysical plasmas. Low-energy supra-thermal particles emitted by
magnetic reconnection are a source of ionisation for circumstellar discs,
influencing their chemical, thermal and dynamical evolution. The aim of this
work is to propose a first investigation to evaluate how energetic particles
can propagate in the circumstellar disc of a T Tauri star and how they affect
the ionisation rate of the disc plasma. To that end, we have collected
experimental and theoretical cross sections for the production of H$^+$,
H$_2^+$ and He$^+$ by electrons and protons. Starting from theoretical
injection spectra of protons and electrons emitted during magnetic reconnection
events, we have calculated the propagated spectra in the circumstellar disc
considering the relevant energy loss processes. We have considered fluxes of
energetic particles with different spectral indices and different disc magnetic
configurations, generated at different positions from the star considering the
physical properties of the flares as deduced from the observations obtained by
the Chandra Orion Ultra Deep point source catalogue. We have then computed the
ionisation rates for a disc whose structure has been calculated with the
radiation thermo-chemical code {\tt ProDiMo}. We find that energetic particles
are potentially a very strong source of local ionisation with ionisation rates
exceeding by several orders of magnitude the contribution due to X-rays,
stellar energetic particles and radioactivity in the inner disc.
Volume
519
Issue
4
Start page
5673
Issn Identifier
0035-8711
Rights
open.access
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