Vv. Izmodenov et al., Filtration of interstellar hydrogen in the two-shock heliospheric interface: Inferences on the local interstellar cloud electron density, J GEO R-S P, 104(A3), 1999, pp. 4731-4741
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).