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Astron. Astrophys. 350, 1071-1078 (1999)


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Neutral interstellar gas atoms reducing the solar wind Mach number and fractionally neutralizing the solar wind

Hans J. Fahr 1 and Daniel Ruciski 2

1 Institut für Astrophysik und Extraterrestrische Forschung der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany (UNF308@ibm.rhrz.uni-bonn.de)
2 Space Research Centre of the Polish Academy of Sciences, Bartycka 18 A, PL-00-716 Warsaw, Poland (rucinski@cbk.waw.pl)

Received 6 October 1998 / Accepted 24 February 1999

Abstract

Many stars are known to drive stellar winds of the solar wind type. Thus when moving through the ambient interstellar medium these stars not simply ionize this medium but also interact as moving stellar wind systems. Only neutral interstellar gas components can directly enter the inner stellar wind region and there undergo charge exchange reactions with the supersonic stellar wind protons. Thereby the dynamical identities of plasma and gas components are partially exchanged. The net effect is that energy is extracted from the wind plasma and transferred to newly created energetic neutral atoms (ENA) transporting the former wind energy over large distances into the distant interstellar medium. As example for stellar wind systems in general, in the following we study quantitatively the effect of a loading of the initial solar wind plasma with transcharged neutral atoms connected with the incorporation of suprathermal pick-up ions and an associated reduction of the effective solar wind sonic Mach number. In addition the removal of kinetic solar wind energy by neutralized solar wind protons leads to a nonclassical reduction of the solar wind ram pressure and thereby a reduction of the location of the heliospheric termination shock. Our results indicate that a substantial percentage of the original solar wind energy is converted into a global flow of energetic neutral atoms and that the effective solar wind Mach numbers in the outer heliosphere are drastically reduced if presently quoted neutral H-atom densities in the outer heliosphere of [FORMULA] [cm-3] are in fact prevailing.

Key words: inteplanetary medium – solar system: general – Sun: solar wind – plasmas

Send offprint requests to: H.J. Fahr (UNF308@ibm.rhrz.uni-bonn.de)

© European Southern Observatory (ESO) 1999

Online publication: October 14, 1999

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