PROPERTIES OF THE INTERSTELLAR GAS INSIDE THE HELIOSPHERE

Methods and results of investigations of the interstellar gas inside t he heliosphere are summarized and discussed. Flow parameters of H and He and the relative abundances of H, He, N, O, and Ne in the distant h eliosphere are given. Charge exchange processes in front of the helios phere affect the flow of hydrogen and oxygen through the heliopause. T he speed of hydrogen is reduced by similar to 6 km/s, and screening le ads to a reduction of the O/He and H/He ratios in the neutral gas ente ring the heliosphere. When the screening effect and the acceleration p rocesses leading to the anomalous cosmic rays (ACR) are sufficiently u nderstood, abundances in the LIC can be derived from measurements insi de the heliosphere. Since isotopic ratios are virtually not changed by screening or by EUV and solar wind ionisation, relative abundances of isotopes in the gaseous phase of the LIC can be determined with no or minor correction from investigations of the neutral gas, pickup ions and ACR particles.