Interstellar hydrogen ionization in the heliosheath

Gruntman, M.

doi:10.1002/2015ja021539

Cited by 9 publications

(4 citation statements)

References 79 publications

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“…Observations of the F-corona continuum in the near-infrared show a sharp drop off in brightness that scale between r −1.9 to r −2.5 for the equatorial and r −2.3 to r −2.8 for the polar solar regions below 10R which correspond to freeze-in distances in our simulations (Koutchmy & Lamy 1985;MacQueen & Greeley 1995;Leinert & Jackson 1998). In Gruntman (1994Gruntman ( , 1996, both n H and n H2 were estimated as ∝ r −1.15 below 1AU. However neutrals in the heliosphere are highly uncertain and remain relatively unknown in the vicinity of the Sun.…”

Section: Modeling Of Solar He + Ionssupporting

confidence: 50%

On the production of He$^+$ of solar origin in the solar wind

Rivera,

Landi,

Lepri

et al. 2020

Preprint

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Solar wind measurements in the heliosphere are predominantly comprised of protons, alphas, and minor elements in a highly ionized state. The majority of low charge states, such as He + , measured in situ are often attributed to pick up ions of non-solar origin. However, through inspection of the velocity distribution functions of near Earth measurements, we find a small but significant population of He + ions in the normal solar wind whose properties indicate that it originated from the Sun and has evolved as part of the normal solar wind. Current ionization models, largely governed by electron impact and radiative ionization and recombination processes, underestimate this population by several orders of magnitude. Therefore, to reconcile the singly ionized He observed, we investigate recombination of solar He 2+ through charge exchange with neutrals from circumsolar dust as a possible formation mechanism of solar He + . We present an empirical profile of neutrals necessary for charge exchange to become an effective vehicle to recombine He 2+ to He + such that it meets observational He + values. We find the formation of He + is not only sensitive to the density of neutrals but also to the inner boundary of the neutral distribution encountered along the solar wind path. However, further observational constraints are necessary to confirm that the interaction between solar α particles and dust neutrals is the primary source of the He + observations.

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Section: Modeling Of Solar He + Ionssupporting

confidence: 50%

On the production of He$^+$ of solar origin in the solar wind

Rivera,

Landi,

Lepri

et al. 2020

Preprint

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“…In most self-consistent models of heliospheric dynamics, so far, only the influence of neutral hydrogen is considered by taking into account its charge exchange with solar wind protons and its ionization by the solar radiation (e.g., [153,91,154] and references therein). The dynamical relevance of both the electron impact ionization of hydrogen, although recognized by [155], [36] as well as [156], and the photo-ionization of helium, although recognized as being filtered in the inner heliosheath [157,158], have not yet been explored in detail. There is only one attempt to include helium self-consistently in the heliospheric modeling [36], in which the emphasis is on the additional ram pressure due to the charged helium ions.…”

Section: The Effect Of Helium Charge Exchangementioning

confidence: 99%

Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields

et al. 2017

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Publication resulting from an International ISSI Team of the same name. Submitted to Space Science ReviewsInternational audienceThis paper summarizes the results obtained by the team "Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields" supported by the International Space Science Institute in Bern, Switzerland. We focus on the physical processes occurring in the outer heliosphere, especially at its boundary called the heliopause (HP), and in the LISM. The importance of magnetic field, charge exchange between atoms and ions, and solar cycle on the heliopause topology and observed heliocentric distances to different heliospheric discontinuities are discussed. It is shown that time-dependent boundary conditions are necessary to describe the heliospheric asymmetries detected by the Voyager spacecraft. We also discuss the structure of the HP, especially due to its instability and magnetic reconnection. It is demonstrated that the Rayleigh-Taylor instability of the nose of the HP creates consecutive layers of the interstellar and heliospheric plasma which are magnetically connected to different sources. This may be a possible explanation of abrupt changes in the galactic and anomalous cosmic ray fluxes observed by Voyager 1 when it was crossing the HP structure for a period of about one month in the summer of 2012. This paper also discusses the plausibility of fitting simulation results to a number of observational data sets obtained by in situ and remote measurements. The distribution of magnetic field in the vicinity of the HP is discussed in the context of Voyager measurements. We discuss the transport of energetic particles in the inner and outer heliosheath, concentrating on the anisotropic spatial diffusion diffusion tensor and the pitch-angle dependence of perpendicular diffusion and demonstrate that the latter can explain the observed pitch-angle anisotropies of both the anomalous and galactic cosmic rays in the outer heliosheath

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“…The second term in Equation (1) describes the advection with the solar wind with velocity u , p the third term describes diffusion of particles in velocity space, the fourth term describes adiabatic heating/cooling, and the last term describes a source (or sink) for the distribution due to, for example, charge-exchange with interstellar neutral atoms. Other ionization processes are ignored, such as photoionization (which is negligible at large distances from the Sun) and electron-impact ionization (the distribution of electrons in the IHS is not known, even though it has had recent attention, see e.g., Chalov & Fahr 2013;Chashei & Fahr 2013;Scherer et al 2014;Fahr et al 2015;Gruntman 2015).…”

Section: Pui Transportmentioning

confidence: 99%

Using Kappa Functions to Characterize Outer Heliosphere Proton Distributions in the Presence of Charge-Exchange

Zirnstein

McComas

2015

ApJ

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Kappa functions have long been used in the analysis and modeling of suprathermal particles in various space plasmas. In situ observations of the supersonic solar wind show its distribution contains a cold ion core and powerlaw tail, which is well-represented by a kappa function. In situ plasma observations by Voyager, as well as observations of energetic neutral atom (ENA) spectra by the Interstellar Boundary Explorer (IBEX), showed that the compressed and heated inner heliosheath (IHS) plasma beyond the termination shock can also be represented by a kappa function. IBEX exposes the IHS plasma properties through the detection of ENAs generated by chargeexchange in the IHS. However, charge-exchange modifies the plasma as it flows through the IHS, and makes it difficult to ascertain the parent proton distribution. In this paper we investigate the evolution of proton distributions, initially represented by a kappa function, that experience losses due to charge-exchange in the IHS. In the absence of other processes, it is no longer representable by a single kappa function due to the energydependent, charge-exchange process. While one can still fit a kappa function to the evolving proton distribution over limited energy ranges, this yields fitting parameters (pseudo-density, pseudo-temperature, pseudo-kappa index) that depend on the energy range of the fit. We discuss the effects of fitting a kappa function to the IHS proton distribution over limited energy ranges, its dependence on the initial proton distribution properties at the termination shock, and implications for understanding the observations.

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Interstellar hydrogen ionization in the heliosheath

Cited by 9 publications

References 79 publications

On the production of He$^+$ of solar origin in the solar wind

On the production of He$^+$ of solar origin in the solar wind

Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields

Using Kappa Functions to Characterize Outer Heliosphere Proton Distributions in the Presence of Charge-Exchange

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