Stellar energetic particle ionization in protoplanetary disks around T Tauri stars
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Context. Anomalies in the abundance measurements of short lived radionuclides in meteorites indicate that the protosolar nebulae was irradiated by a large number of energetic particles (E ≳ 10 MeV). The particle flux of the contemporary Sun cannot explain these anomalies. However, similar to T Tauri stars the young Sun was more active and probably produced enough high energy particles to explain those anomalies. Aims. We aim to study the interaction of stellar energetic particles with the gas component of the disk (i.e. ionization of molecular hydrogen) and identify possible observational tracers of this interaction. Methods. We used a 2D radiation thermo-chemical protoplanetary disk code to model a disk representative for T Tauri stars. We used a particle energy distribution derived from solar flare observations and an enhanced stellar particle flux proposed for T Tauri stars. For this particle spectrum we calculated the stellar particle ionization rate throughout the disk with an accurate particle transport model. We studied the impact of stellar particles for models with varying X-ray and cosmic-ray ionization rates. Results. We find that stellar particle ionization has a significant impact on the abundances of the common disk ionization tracers HCO+ and N2H+, especially in models with low cosmic-ray ionization rates (e.g. 10-19 s-1 for molecular hydrogen). In contrast to cosmic rays and X-rays, stellar particles cannot reach the midplane of the disk. Therefore molecular ions residing in the disk surface layers are more affected by stellar particle ionization than molecular ions tracing the cold layers and midplane of the disk. Conclusions. Spatially resolved observations of molecular ions tracing different vertical layers of the disk allow to disentangle the contribution of stellar particle ionization from other competing ionization sources. Modelling such observations with a model like the one presented here allows to constrain the stellar particle flux in disks around T Tauri stars.
Rab , C , Güdel , M , Padovani , M , Kamp , I , Thi , W -F , Woitke , P & Aresu , G 2017 , ' Stellar energetic particle ionization in protoplanetary disks around T Tauri stars ' , Astronomy & Astrophysics , vol. 603 , A96 . https://doi.org/10.1051/0004-6361/201630241
Astronomy & Astrophysics
Copyright © ESO, 2017. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at: https://doi.org/10.1051/0004-6361/201630241
DescriptionThe research leading to these results has received funding from the European Union Seventh Framework Programme FP7-2011 under grant agreement No. 284405. R.CH. acknowledges funding by the Austrian Science Fund (FWF): project number P24790. M.P. acknowledges funding from the European Unions Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 664931. The computational results presented have been achieved using the Vienna Scientific Cluster (VSC). This publication was supported by the Austrian Science Fund (FWF).
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