In summary, we can conclude that the contributions of the different ionization processes to the total ionization rate for the most abundant interstellar species are basically known. The ionization of the noble gases He and Ne is almost completely dominated by photoionization, whereas for H charge-exchange with the solar wind is most important. For other species, such as 0 and Ar, both processes contribute significantly. Electron impact ionization can typically contribute by '" 10% to the total rate in the inner Solar System. Because direct measurements of the solar EUV flux are not yet continuously available, the variation of the ionization rate over the solar cycle still contains a relatively large uncertainty. The recent measurements of pickup ion distributions and of the neutral helium gas provide an independent tool to determine the total ionization rate that can be used to cross calibrate with the results obtained for the individual ionization processes. Acknowledgements The authors are grateful to M. Allen for supplying us with new data on photoioniza tion cross-sections compiled by him. We thank also M. Gruntman for drawing our attention to and support in collecting the most recent data on charge-exchange cross-sections. D. R. was supported by grant No. 2 P03C. 004. 09 from the Com mittee for Scientific Research (Poland). This work was also supported in part through NASA contract NAS7-918, NSF Grant INT-911637, NASA Grant NAGW- 2579.
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Springer Book Archives
Science as an Adventure.- The Heliosphere.- The Heliosphere.- The
Heliospheric Magnetic Field.- The Solar Wind: A Turbulent Magnetohydrodynamic
Medium.- Voyager Observations of the Magnetic Field, Interstellar Pickup Ions
and Solar Wind in the Distant Heliosphere.- Origin of C+ Ions in the
Heliosphere.- Radio Emissions from the Outer Heliosphere.- A Summary of Solar
Wind Observations at High Latitudes: Ulysses.- Ionization Processes in the
Heliosphere Rates and Methods of Their Determination.- 3-D Magnetic Field
and Current System in the Heliosphere.- Modelling the Heliosphere.- The
Termination Shock.- The Termination Shock of the Solar Wind.- Composition of
Anomalous Cosmic Rays and Implications for the Heliosphere.- Implications of
a Weak Termination Shock.- The Acceleration of Pickup Ions.- The Isotopic
Composition of Anomalous Cosmic Rays from SAMPEX.- The Local Interstellar
Medium.- GHRS Observations of the LISM.- In Situ Measurements of Interstellar
Dust with the Ulysses and Galileo Spaceprobes.- The Local Bubble, Current
State of Observations and Models.- The Local Bubble, Origin and Evolution.-
The Interstellar Gas Flow Through the Heliospheric Interface Region.- LISM
Structure Fragmented Superbubble Shell?.- Relative Ionizations in the
Nearest Interstellar Gas.- Properties of the Interstellar Gas Inside the
Heliosphere.- Local Clouds: Distribution, Density and Kinematics Through
Ground-Based and HST Spectroscopy.- Possible Shock Wave in the Local
Interstellar Plasma, Very Close to the Heliosphere.- Interstellar Grains in
the Solar System: Requirements for an Analysis.- Modelling of the
Interstellar Hydrogen Distribution in the Heliosphere.- Observations of the
Local Interstellar Medium with the Extreme Ultraviolet Explorer.- Recent
Results on theParameters of the Interstellar Helium from the Ulysses/GAS
Experiment.- Interaction Between HS And Lism.- Physical and Chemical
Characteristics of the ISM Inside and Outside the Heliosphere.- Axisymmetric
Self-Consistent Model of the Solar Wind Interaction with the LISM: Basic
Results and Possible Ways of Development.- UV Studies and the Solar Wind.-
Quasilinear Relaxation of Interstellar Pickup Ions.- The Abundance of Atomic
1H, 4He, and 3He in the Local Interstellar Cloud from Pickup Ion Observations
with SWICS on Ulysses.- Physics of Interplanetary and Interstellar Dust.-
Relations Between ISM Inside and Outside the Heliosphere.- The Local
Interstellar Medium Viewed Through Pickup Ions, Recent Results and Future
Perspectives.- Moment Equation Description of Interstellar Hydrogen.- Pickup
Protons in the Heliosphere.- Author index.
