Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...476..366w&link_type=abstract
Astrophysical Journal v.476, p.366
Astronomy and Astrophysics
Astronomy
38
Atomic Processes, Hydrodynamics, Ism: Clouds, Sun: Solar Wind
Scientific paper
We investigate the self-consistent interaction of the local interstellar cloud (LIC) and solar wind, focusing on its manifestations in the heliospheric hydrogen (H) distribution. This system is modeled hydrodynamically as a fluid proton-electron plasma and three H fluids, each arising from charge exchange production within three distinct plasma environments. Perhaps our most significant finding is that, based on the Dalgarno cross section, thermalizing H-H collisions are crucial to determining the heliospheric H distribution. Hot secondary H atoms produced from charge exchange with the solar wind will be thermalized with the bulk of the cooler LIC H distribution. This thermalization should be complete for the postheliospheric H beyond ~108 downstream from the Sun. Observed along nearby downstream interstellar sightlines, we may expect to see temperatures of order 105 K in the bulk of the postheliospheric-traversal H distribution. Recent observations along the Sirius sightline by Bertin et al. may be explainable in these terms. Based on the Dalgarno cross section for thermalizing H-proton collisions without charge transfer, this interaction should be important as well. This implies that previous charge exchange--only models have underestimated the degree of H-proton coupling and thereby the efficiency of heliospheric filtration of LIC H. The variation among published values of the charge exchange cross section is 40% at 1 eV. We find that this variation will affect predictions of the H density at 50 AU by a similar factor. We performed calculations using the larger of the charge exchange cross sections to conclude that the proton density in the LIC is not likely greater than a few x10-2 cm-3. We show densities, temperatures, and radial velocities of the three H fluids along the sight lines of some nearby stars for one of these calculations, using an LIC proton density of 0.1 cm-3. Results from a first crude model of the effects of H-H collisions are given in an appendix.
Hall Doyle T.
Pauls Louis H.
Williams Lance Lee
Zank Gary P.
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