Effects of interstellar and solar wind ionized helium on the interaction of the solar wind with the local interstellar medium

Abstract

The Sun is moving through a warm ($\sim$6500 K) and partly ionized local interstellar cloud (LIC) with a velocity of $\sim$26 km/s. Recent measurements of the ionization of the LIC (Wolff et al., 1999) suggest that interstellar helium in the vicinity of the Sun is 30-40 % ionized, while 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 paper we present results of a new model of the solar wind interaction with the interstellar medium, which takes into account interstellar helium ions. Using results of this model we find that the heliopause, termination and bow shocks are closer to the Sun when compared to 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, we apply our new model to place constraints on the plausible location of the termination shock.