Warm Breeze from the starboard bow: a new population of neutral helium in the heliosphere

Abstract

We investigate the signals from neutral He atoms observed from Earth orbit in 2010 by IBEX. The full He signal observed during the 2010 observation season can be explained as a superposition of pristine neutral interstellar He gas and an additional population of neutral He that we call the Warm Breeze. The Warm Breeze is approximately two-fold slower and 2.5 times warmer than the primary interstellar He population, and its density in front of the heliosphere is ~7% that of the neutral interstellar helium. The inflow direction of the Warm Breeze differs by ~19deg from the inflow direction of interstellar gas. The Warm Breeze seems a long-term feature of the heliospheric environment. It has not been detected earlier because it is strongly ionized inside the heliosphere, which brings it below the threshold of detection via pickup ion and heliospheric backscatter glow observations, as well as by the direct sampling of GAS/Ulysses. Possible sources for the Warm Breeze include (1) the secondary population of interstellar helium, created via charge exchange and perhaps elastic scattering of neutral interstellar He atoms on interstellar He+ ions in the outer heliosheath, or (2) a gust of interstellar He originating from a hypothetic wave train in the Local Interstellar Cloud. A secondary population is expected from models, but the characteristics of the Warm Breeze do not fully conform to modeling results. If, nevertheless, this is the explanation, IBEX-Lo observations of the Warm Breeze provide key insights into the physical state of plasma in the outer heliosheath. If the second hypothesis is true, the source is likely to be located within a few thousand of AU from the Sun, which is the propagation range of possible gusts of interstellar neutral helium with the Warm Breeze characteristics against dissipation via elastic scattering in the Local Cloud.

arXiv commentsubmitted to ApJS

References in corpus (15)

• The Structure of the Local Interstellar Medium V: Electron Densities
• The Boundary Conditions of the Heliosphere: Photoionization Models Constrained by Interstellar and In Situ Data
• Density of neutral interstellar hydrogen at the termination shock from Ulysses pickup ion observations
• Solar parameters for modeling interplanetary background
• Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX
• Effects of interstellar and solar wind ionized helium on the interaction of the solar wind with the local interstellar medium
• Heliospheric, Astrospheric, and Insterstellar Lyman-alpha Absorption Toward 36 Oph
• Local Interstellar Neutral Hydrogen sampled in-situ by IBEX
• A possible generation mechanism for the IBEX ribbon from outside the heliosphere
• Microstructure of the Local Interstellar Cloud and the Identification of the Hyades Cloud
• Ionization rates in the heliosheath and in astrosheaths
• Precision Pointing of IBEX-Lo Observations
• Effect of the heliospheric interface on the distribution of interstellar hydrogen atom inside the heliosphere
• Uncovering the magnetic environment of our solar system
• Assessment of detectability of neutral interstellar deuterium by IBEX observations

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