D. Rucinski

Observations of the helium focusing cone with pickup ions

The helium gravitational focusing cone has been observed using pickup He + , first during the solar minimum in 1984–1985 with the AMPTE/IRM spacecraft, and again in more detail from 1998 to 2002 with ACE and in 2000 with Nozomi. Five traversals of the cone allow us to obtain an accurate determination of the ecliptic longitude of the interstellar wind flow direction,

Heliospheric conditions that affect the interstellar gas inside the heliosphere

lambda = 74.43 degr, pm, 0.33 degr

Modification of Properties and Dynamics of Distant Solar Wind Due to Its Interaction with Neutral Interstellar Gas

, while observations of pickup He ++ with Ulysses give us an estimate, relatively free of instrumental systematic uncertainties, of the neutral He density,

Expected Fluxes of H+ Pickup Ions in the Inner Heliosphere during Various Phases of Solar Cycle

n_{rm He} = 0.0151, pm, 0.0015

On the Asymmetry of the Distribution of the Anomalous Cosmic-Ray Component in the Heliosphere

cm -3 , in the Local Interstellar Cloud. From best fits to the measured velocity distributions of pickup He + using time-stationary models we deduce the radial dependence and magnitude of electron-impact ionization rates that cannot presently be measured, and find this to be an important ionization process in the inner (

On the Possibility of Detection of Small Comets in Ly-α

la

Broadening of the Interplanetary Helium Cone Structure Due to Elastic Collisions of LISM Helium Atoms with Solar Wind Ions

0.5xa0AU) heliosphere. We obtain excellent model fits to the 1998 cone profile using measured or deduced rates and known interstellar He parameters, and from this conclude that cross-field diffusion of pickup He + is small. Furthermore, we find no evidence for extra sources of He in or near the cone region. Best fits to the velocity distributions of He + are obtained assuming isotropic solar-wind-frame distributions, and we conclude from this that the scattering mean free path for pickup He + in the turbulent slow solar wind is small, probably less than 0.1xa0AU. We argue that application of 3D, time-dependent models for computation of the spatial distribution of interstellar neutral helium in the inner heliosphere may lead to excellent fits of short-term averaged pickup He + data without assuming loss rates that are significantly different from production rates.

Imprints from the solar cycle on the helium atom and helium pickup ion distributions

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.

Modulation of interplanetary hydrogen density distribution during the solar cycle.

Neutral interstellar H atoms penetrate into the inner heliosphere and after ionization are converted into pickup ions (PUIS). The main loss process of these atoms is resonant charge transfer with solar wind (SW) protons. The appropriate method to describe this interaction is a kinetic approach based on the Boltzmann—Vlasov integro-differential equation (see, e.g., Ripken and Fahr, 1983; Fahr, 1991; Osterbart and Fahr, 1992; Baranov and Malama, 1993). Charge-exchange removal of keV-particles from SW connected with mass loading by new ions (nearly at rest) significantly affects the solar wind momentum flow. Incorporation of the new ions as suprathermal PUI’s into the SW bulk flow leads also to a non-adiabatic plasma behaviour recognized first by Fahr (1973), and Holzer and Leer (1973).

Modulation of the interstellar oxygen-to-hydrogen ratio by the heliospheric interface plasma

The objective of our work was to study latitudinal and time dependent effects in H+ pickup ion fluxes, potentially interesting with respect to Ulysses data analysis. Assuming models of radiation pressure and hydrogen ionisation rates based on long-term, multispacecraft observations (Bzowski, 2001a, b; and references therein), we calculate a time- and latitude-dependent distribution of interstellar neutral hydrogen in a plane perpendicular to the gas inflow direction. Based on this density model we compute expected fluxes of H+ pickup ions (H+ PUI) during various phases of recent solar cycles at various heliographic latitudes to check the amplitude of both types of variations at heliocentric distances relevant for Ulysses/SWICS observations (Gloeckler et al., 1993; Gloeckler, 1996a).