4 research outputs found
Effects of interstellar and solar wind ionized helium on the interaction of the solar wind with the local interstellar medium
The Sun is moving through a warm (6500 K) and partly ionized local
interstellar cloud (LIC) with a velocity of 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 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.Comment: accepted for publication in Astrophys. J. Letter
Lyman-alpha Absorption from Heliosheath Neutrals
We assess what information HST observations of stellar Ly-alpha lines can
provide on the heliosheath, the region of the heliosphere between the
termination shock and heliopause. To search for evidence of heliosheath
absorption, we conduct a systematic inspection of stellar Ly-alpha lines
reconstructed after correcting for ISM absorption (and
heliospheric/astrospheric absorption, if present). Most of the stellar lines
are well centered on the stellar radial velocity, as expected, but the three
lines of sight with the most downwind orientations relative to the ISM flow
(Chi1 Ori, HD 28205, and HD 28568) have significantly blueshifted Ly-alpha
lines. Since it is in downwind directions where heliosheath absorption should
be strongest, the blueshifts are almost certainly caused by previously
undetected heliosheath absorption. We make an initial comparison between the
heliosheath absorption and the predictions of a pair of heliospheric models. A
model with a complex multi-component treatment of plasma within the heliosphere
predicts less absorption than a model with a simple single-fluid treatment,
which leads to better agreement with the data. Finally, we find that
nonplanetary energetic neutral atom (ENA) fluxes measured by the ASPERA-3
instrument on board Mars Express, which have been interpreted as being from the
heliosheath, are probably too high to be consistent with the relative lack of
heliosheath absorption seen by HST. This would argue for a local interplanetary
source for these ENAs instead of a heliosheath source.Comment: 27 pages, 7 figures, AASTEX v5.0, accepted by Ap