Filtration of interstellar hydrogen in the two-shock heliospheric interface: Inferences on the local interstellar cloud electron density

The solar system is moving through the partially ionized local interstellar cloud (LIC). The ionized matter of the LIC interacts with the expanding so lar wind forming the heliospheric interface. The neutral component (interst ellar atoms) penetrates through the heliospheric interface into the heliosp here, where it is measured directly "in situ" as pick-up ions and neutral a toms land as anomalous cosmic rays) or indirectly through resonant scatteri ng of solar Ly alpha. When crossing the heliospheric interface, interstella r atoms interact with the plasma component through charge exchange. This in teraction leads to changes of both neutral gas and plasma properties. The h eliospheric interface is also the source of radio emissions which have been detected by the Voyager since 1983. In this paper, we have used a kinetic model of the flow of the interstellar atoms with updated values of velocity , temperature, and density of the circumsolar interstellar hydrogen and cal culated how all quantities which are directly associated to the observation s vary as a function of the interstellar proton number density n(p,LIC) The se quantities are the degree of filtration, the temperature and the velocit y of the interstellar H atoms in the inner heliosphere, the distances to th e bow shock (BS), heliopause, and termination shock, and the plasma frequen cies 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 recent pickup ion dat a, Ly alpha measurements, and low-frequencies radio emissions, we have sear ched for a number density of protons in the local interstellar cloud compat ible with all observations. We find it difficult in the frame of this model without interstellar magnet ic field to reconcile the distance to the shock and heliopause deduced from the time delay of the radio emissions with other diagnostics and discuss p ossible explanations for these discrepancies, as the existence of an additi onal interstellar magnetic pressure (2.1 mu G < B < 4 mu G for a perpendicu lar magnetic field). We also conclude that on the basis of this model the m ost likely value for the proton density in the local interstellar cloud is in the range 0.04 cm(-3) < n(p,LIC) < 0.07 cm(-3).