Proceedings of Solar Wind 9 Conference, ed. Shadia Habbal, AIP, 1999

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## Heliospheric Interface Filtration of the Interstellar Hydrogen

V.V. Izmodenov  *  1,2, R. Lallement 1 and J. Malama  3

1 Service d'Aeronomie, CNRS, F-91371 Verrieres le Buisson, France (Vlad.Izmodenov; Rosine.Lallement@aerov.jussieu.fr)
2 Departament of Aeromechanics and Gas Dynamics, Faculty of Mechanics and Mathematics, Moscow State University (izmod@ipmnet.ru)
3 Institute for Problems in Mechanics, Moscow, Russia

Abstract

In this paper we have used a kinetic model of the flow of interstellar atoms with updated values of velocity, temperature and density of the circumsolar interstellar cloud, and calculated how quantities which are directly associated to the observations vary as a function of the interstellar proton  number density $n_{p,LIC}$. These quantities are the degree of filtration, the temperature and the velocity of the interstellar H-atoms in the inner heliosphere, the distances to the bow shock (BS), heliopause (HP) and termination shock (TS), and the plasma frequencies in the LIC, at the BS and in the maximum compression region around the heliosphere
which constitutes the "barrier" for radio waves formed in the interstellar medium. Comparing the model results with pick up ion data, $Ly- \alpha$ measurements, and low-frequencies radio emissions, we have searched for a number density of protons in the LIC
compartible with all observations.

We find it difficult in the frame of this model without interstellar magnetic field to reconcile the distance to the shock and the heliopause deduced from time-delay of the radio emissions with other diagnostics and discuss possible explanations for these discrepancies. We also conclude that, on the basis of this model, the most likely value for the proton density in the LIC is in the range $0.04 cm^{-3} < n_{p,LIC} < 0.07 cm^{-3}$.