Angular Scattering in Charge Exchange: Issues and Implications for Secondary Interstellar Hydrogen

Abstract

Interstellar neutral atoms provide a remote diagnostic of plasma in the outer heliosheath and the very local interstellar medium via charge exchange collisions that convert ions into atoms and vice versa. So far, most studies of interstellar atoms assumed that daughter hydrogen atoms directly inherit the kinetic properties of parent protons. This assumption neglects angular scattering of the interacting particles. However, for low relative velocities, as expected for charge exchanges in the outer heliosheath, this scattering is significant. In this study, we present how the parameters of daughter populations depend on the relative velocity and temperatures of parent populations. For this purpose, we numerically compute collision terms with and without this scattering. We find that the secondary population of interstellar hydrogen atoms, for the parent populations with the relative bulk velocity of 20 km s${}^{-1}$ and equal temperatures of 7500 K, has ~2 km s${}^{-1}$ higher bulk velocity if the scattering is taken into account. Additionally, temperatures are higher by ~2400 K and ~1200 K in parallel and perpendicular direction to the relative motion of parent populations, respectively. Moreover, a significant departure of secondary atoms from the Maxwell-Boltzmann distribution is expected for high relative velocities of parent populations. This process affects the distribution and density of interstellar atoms in the heliosphere and production of pickup ions. Thus, we show that angular scattering in charge exchange collisions is important to include in analyses of interstellar neutral atoms and pickup ions observed at 1 au and in the outer heliosphere.

22 pages, 13 figures, to appear in the Astrophysical Journal

References in corpus (21)

• The Solar Wind Around Pluto (SWAP) Instrument Aboard New Horizons
• Interstellar neutral helium in the heliosphere from IBEX observations. III. Mach number of the flow, velocity vector, and temperature from the first six years of measurements
• Warm Breeze from the starboard bow: a new population of neutral helium in the heliosphere
• Revisiting Ulysses Observations of Interstellar Helium
• Interstellar Pickup Ion Observations to 38 AU
• Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields
• Interstellar neutral helium in the heliosphere from IBEX observations. IV. Flow vector, Mach number, and abundance of the Warm Breeze
• Local Interstellar Neutral Hydrogen sampled in-situ by IBEX
• Comparing various multi-component global heliosphere models
• Neutral interstellar He parameters in front of the heliosphere 1994--2007
• Interstellar neutral helium in the heliosphere from IBEX observations. VI. The He${}^{+}$ density and the ionization state in the Very Local Interstellar Matter
• In Situ Observations of Preferential Pickup Ion Heating at an Interplanetary Shock
• Interstellar Neutral Gas Species And Their Pickup Ions Inside The Heliospheric Termination Shock. Ionization Rates For H, O, Ne, And He
• The helium Warm Breeze in IBEX observations as a result of charge exchange collisions in the outer heliosheath
• Evolution of the Solar Lyman-Alpha line profile during the solar cycle
• Interstellar neutral helium in the heliosphere from IBEX observations. V. Observations in IBEX-Lo ESA steps 1, 2, & 3
• Interstellar hydrogen fluxes measured by IBEX-Lo in 2009: numerical modeling and comparison with the data
• Evolution of the solar Ly-$\alpha$ line profile during the solar cycle. II. How accurate is the present radiation pressure paradigm for interstellar neutral H in the heliosphere?
• Evidence for Asymmetry in the Velocity Distribution of the Interstellar Neutral Helium Flow Observed by IBEX and Ulysses
• A Ulysses Detection of Secondary Helium Neutrals
• Synthesis of the distribution function of ISN He

Cited by in corpus (5)

• Very Local Interstellar Medium Revealed by Complete Solar Cycle of Interstellar Neutral Helium Observations with IBEX
• Slowdown and Heating of Interstellar Neutral Helium by Elastic Collisions Beyond the Heliopause
• Interstellar Neutral Hydrogen in the Heliosphere: New Horizons Observations in the Context of Models
• Production and Loss Processes of Hydrogen Energetic Neutral Atoms in the Heliosphere from 5 eV to 500 keV
• Effects of angular scattering and H+p, H+H collisions on the properties of interstellar atoms in the heliosphere