Cosmic ray production and transport in astrospheres

• Applicant: Dr. Klaus Scherer
• Subject Area: Astrophysics and Astronomy
• Term: from 2012 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 232615537

• Final Report Year: 2019

Final Report Abstract

In this project we have simulated the astrospheres around hot and cool stars, where the focus was on the hot stars. The astrospheres include the interaction zones between the “supersonic” stellar wind and the interstellar medium which has a supersonic relative speed with respect to the star. These interaction zones include the termination shock, where the stellar wind becomes subsonic as well as the bow shock where the interstellar flow becomes sub sonic and the tangential discontinuity inbetween. This interaction was the first time modelled with a 3D MHD code including heating and cooling functions. These models can be rotated at the origin (the star) and then shifted to some distance (ca 600 pc for λ Cephei) and projected on a sky map. We used this projection to model some of the observed quantities, like the Hα flux or the synchroton radiation. We also used the standard analytic MHD Rankine-Hugoniot equations to compare those values in inflow direction with those of the model. Furthermore we showed that the analytic determination of the termination shock distances is not always applicable in MHD. We then started to discuss the cosmic ray flux of astrospheres and their imprints on Earth (cosmic ray anisotropy). It turned out that we need a non-equilibrium distribution function to model the corresponding diffusion coefficients. We used the standard κ-distribution to do so, but recognized that this leads to problems because this distribution is not well posed. We then started to develop a new κ-distribution (the regularized one) and are still exploring its characteristic. We had to overcome the problems with the standard κ-distribution. That are too high pressure values when κ approaches 3/2. We could overcome these difficulties and extend the range to κ > 0 by introducing the regularised κ-distribution.

Publications

• Ionization rates in the heliosheath and in astrosheaths. Spatial dependence and dynamical relevance, Astron. & Astrophys., 2014, 563
  K. Scherer, H. Fichtner, H. J. Fahr, M. Bzowski, M. and S. E. S.Ferreira
  
• On the radial evolution of κ distributions of pickup protons in the supersonic solar wind, J. Geophys. Res., 2014, 119
  H. J. Fahr, H. Fichtner, K. Scherer
  
• The IBEX ribbon as a signature of the inhomogeneity of the local interstellar medium, Astron. & Astrophys., 2014, 561
  H. Fichtner, K. Scherer, F. Effenberger, J. Zønnchen, N. Schwadron, and D. J. McComas, David J.
  
• The Return of the Bow Shock, Astrophys. J. , 2014, 1
  K. Scherer, and H. Fichtner
  
• Cosmic rays in astrospheres, Astron. & Astrophys., 2015, 576
  K. Scherer, A. van der Schyff, D. J. Bomans, S. E. S. Ferreira, H. Fichtner, J. Kleimann, R. D. Strauss, K. Weis, T. Wiengarten, and T. Wodzinski, T.
  
• Lyman-alpha Radiation Pressure in the Heliosphere: Results from a 3D Monte Carlo Radiative Transfer Simulation, J. Phys. Conf. Ser., 642, 2015
  B. Fayock, G. P. Zank, J. Heerikhuisen, C. R. Gilbert and K. Scherer
  
• A Generalized Two-component Model of Solar Wind Turbulence and ab initio Diffusion Mean-Free Paths and Drift Lengthscales of Cosmic Rays, Astrophys. J. , 833 (2016), p. 17
  T. Wiengarten, S. Oughton, N. E. Engelbrecht, H. Fichtner, J. Kleimann, and K. Scherer
  
• Comic ray flux anisotropies caused by astrospheres, Astroparticle Physics, 82 (2016), pp. 93–98
  K. Scherer, R. D. Strauss, S. E. S. Ferreira, and H. Fichtner
  
• Generalized Multi-polytropic Rankine- Hugoniot Relations and the Entropy Condition, Astrophys. J. , 833 (2016), p. 38
  K. Scherer, H. Fichtner, H. J. Fahr, C. Röken, and J. Kleimann
  
• On the evolution of the κ distribution of protons in the inner heliosheath, Journal of Geophysical Research (Space Physics), 121 (2016), pp. 8203–8214
  H.-J. Fahr, A. Sylla, H. Fichtner, and K. Scherer
  
• Shock structures of astrospheres, Astron. & Astrophys., 586 (2016), p. A111
  K. Scherer, H. Fichtner, J. Kleimann, T. Wiengarten, D. J. Bomans, and K. Weis
  
• Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields, Space Sci. Rev., 212 (2017), pp. 193–248
  N. V. Pogorelov, H. Fichtner, A. Czechowski, A. Lazarian, B. Lembege, J. A. le Roux, M. S. Potgieter, K. Scherer, E. C. Stone, R. D. Strauss, T. Wiengarten, P. Wurz, G. P. Zank, and M. Zhang
  
• Origin of the Differential Fluxes of Low-energy Electrons in the Inner Heliosheath, Astrophys. J. Lett., 848 (2017), p. L3
  H. J. Fahr, S. M. Krimigis, H. Fichtner, K. Scherer, A. Sylla, S. E. S. Ferreira, and M. S. Potgieter
  
• Regularized κ-distributions with non-diverging moments, EPL (Europhysics Letters), 120 (2017), p. 50002
  K. Scherer, H. Fichtner, and M. Lazar
  
• Entropy of plasmas described with regularized κ distributions, Phys. Rev. E, 98 (2018), p. 053205
  H. Fichtner, K. Scherer, M. Lazar, H. J. Fahr, and Z. Vörös
  
• Modified κ-distribution of Solar Wind Electrons and Steady-state Langmuir Turbulence, Astrophys. J. , 868 (2018), p. 131
  P. H. Yoon, M. Lazar, K. Scherer, H. Fichtner, and R. Schlickeiser
  
• On the applicability of κ-distributions, Astrophys. J. , 881, (2018), p. 93
  K. Scherer, H. Fichtner, H.-J. Fahr, and M. Lazar
  
• The interaction of multiple stellar winds in stellar clusters: potential flow, Astron. & Astrophys., 616 (2018), p. A115
  K. Scherer, A. Noack, J. Kleimann, H. Fichtner, and K. Weis
  
• Uncertainties in the heliosheath ion temperatures, Annales Geophysicae, 36 (2018), pp. 37–46
  K. Scherer, H. J. Fahr, H. Fichtner, A. Sylla, J. D. Richardson, and M. Lazar
  
• Moments of the anisotropic regularized κ-distributions, Astrophys. J. , 880, (2019), p. 93
  K. Scherer, M. Lazar,E. Husidic and H. Fichtner