Heliospheric conditions that affect the interstellar gas inside the heliosphere

¹ Space Sciences Center, University of Southern California, Los Angeles, CA 90089, USA Praxis, Inc., Alexandria, VA, USA e-mail: mcmullind@pxi.com
² Space Research Centre PAS, Bratycka 18A, 00-716 Warsaw, Poland
³ Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824, USA
⁴ International Space Science Institute, 3012 Bern, Switzerland
⁵ Los Alamos National Laboratory, Los Alamos, NM 87545, USA
⁶ Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁷ Max-Planck-Institut für Aeronomie, 37191 Katlenburg-Lindau, Germany
⁸ Space Sciences Center, University of Southern California, Los Angeles, CA 90089, USA
⁹ Service d'Aéronomie du CNRS, BP 3, 91371, Verrières-le-Buisson, France

Received: 26 January 2004
Accepted: 23 June 2004

Abstract

The interstellar gas that flows through the heliosphere is strongly affected by ionization close to the Sun, in particular solar photoionization, electron impact, and charge exchange. Therefore, the interpretation of any observation of interstellar gas in the inner heliosphere hinges upon the accurate knowledge of these effects and their variations. In addition, the irradiance and line profile of the relevant solar spectral line are needed to properly interpret resonant backscattering observations of the interstellar neutral gas. With instrumentation on ACE, SOHO and Wind, continuous monitoring of these important environmental conditions simultaneously with a multitude of interstellar gas observations has become possible for the first time. In this paper we present a compilation of the processes and parameters that affect the distribution of interstellar helium inside the heliosphere and their observation, including the irradiance and line profile of the He 58.4 nm line. We also make the connection to proxies for these parameters and evaluate their accuracy in order to expand the time period of coverage wherever possible.