Decompounding: an estimation problem for Poisson random sums

The Sun is moving through a warm (~6500 K) and partly ionized local interstellar cloud (LIC) with a velocity of ~26 km s-1. Recent measurements of the ionization of the LIC (Wolff, Koester, & Lallement) suggest that interstellar helium in the vicinity of the Sun is 30%-40% ionized and that interstellar hydrogen is less ionized. Consequently, interstellar helium ions contribute up to 50% of the total dynamic pressure of the ionized interstellar component. Up to now, interstellar helium ions have been ignored in existing models of the heliospheric interface. In this Letter, we present results of a new model of the interaction of the solar wind with the interstellar medium; this model takes into account interstellar helium ions. Using the results of this model, we find that the heliopause, termination, and bow shocks are closer to the Sun than the model results that ignore He ions. The influence of interstellar helium ions is partially compensated by solar wind (alpha)-particles, which are taken into account in our new model as well. Finally, with our new model, we place constraints on the plausible location of the termination shock.