The influence of electron impact ionization on the distribution of interstellar helium in the inner heliosphere - Possible consequences for determination of interstellar helium parameters
Abstract
The modification of the classical 'hot' model describing the helium density distribution with inclusion of the process of electron impact ionization of He atoms is discussed. Assuming a bi-Maxwellian representation of the solar wind electron velocity distribution, a quasi-analytical relation for the electron impact ionization rate of neutral interstellar helium is obtained and evaluated as a function of heliocentric distance. The resulting ionization rate is compared to the photoionization and charge-exchange reaction rates. It is shown that at the earth's orbit the electron impact ionization contributes 10-20 percent to the total helium ionization frequency, and the relative importance of this ionizing process increases significantly with the decrease of the distance from the sun. The incorporation of electron impact ionization into the model leads to noticeable modifications of the predicted helium density distribution for distances less than 2 AU.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 1989
- Bibcode:
- 1989A&A...224..290R
- Keywords:
-
- Electron Impact;
- Gas Ionization;
- Helium Atoms;
- Helium Ions;
- Interstellar Gas;
- Solar Wind;
- Heliosphere;
- Velocity Distribution;
- Solar Physics