Interstellar Flow Longitude From the Symmetry of the Pickup Ion Cutoff at 1 Au

Möbius, E.; Lee, M. A.; Drews, C.

doi:10.1088/0004-637x/815/1/20

Cited by 26 publications

(35 citation statements)

References 44 publications

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“…Another method for using PUIs as a diagnostic tool to derive the interstellar flow longitude, λ flow , was recently proposed by Möbius et al (2015). As shown in Möbius et al (1999) the injection speed of PUIs into the solar wind depends on ecliptic longitude because of the longitude-dependant relative motion of the neutral interstellar wind particles and the radially outward streaming solar wind.…”

Section: Contextmentioning

confidence: 99%

“…In this paper we revisit the method presented as a proof-ofconcept study by Möbius et al (2015) using He + PUI data from the PLAsma and SupraThermal Ion Composition instrument (PLASTIC; Galvin et al (2008)) on board the Solar TErrestrial RElations Observatory Ahead spacecraft (STEREO A). We extend this method by analyzing its weaknesses and proposing ways to circumvent these disadvantages.…”

Section: Motivation and Goalsmentioning

confidence: 99%

“…Second, we provide an overview of the PUI physics that enables the determination of the interstellar flow longitude from PUI VDFs, which was performed in Möbius et al (2015). We summarize the individual steps of the revisited analysis and describe the improvements implemented in each step.…”

Section: Motivation and Goalsmentioning

confidence: 99%

“…As in Möbius et al (2015) we perform the PUI analysis in the solar wind frame. This has the advantage that the injection speed of PUIs is solely a function of the solar wind speed, |u sw | = v sw , and the local interstellar neutral flow velocity, V n .…”

Section: Motivation and Goalsmentioning

confidence: 99%

“…Accordingly, all PUIs of the torus VDF move at solar wind speed in the solar wind frame in this case. Möbius et al (2015) perform their analysis of the PUI distribution in terms of the normalized PUI speed w He + = v He + v sw , where v He + = |u He + − u sw | is the PUI speed in the solar wind frame. In contrast, we transform the measured PUI speeds into another data product, V r , which eliminates the influence of the ambient solar wind speed on the cutoff speed determination.…”

Section: Motivation and Goalsmentioning

confidence: 99%

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Challenges in the determination of the interstellar flow longitude from the pickup ion cutoff

Taut

Berger

Möbius

et al. 2018

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Context. The interstellar flow longitude corresponds to the Sun's direction of movement relative to the local interstellar medium. Thus, it constitutes a fundamental parameter for our understanding of the heliosphere and, in particular, its interaction with its surroundings, which is currently investigated by the Interstellar Boundary EXplorer (IBEX). One possibility to derive this parameter is based on pickup ions (PUIs) that are former neutral ions that have been ionized in the inner heliosphere. The neutrals enter the heliosphere as an interstellar wind from the direction of the Sun's movement against the partially ionized interstellar medium. PUIs carry information about the spatial variation of their neutral parent population (density and flow vector field) in their velocity distribution function. From the symmetry of the longitudinal flow velocity distribution, the interstellar flow longitude can be derived. Aims. The aim of this paper is to identify and eliminate systematic errors that are connected to this approach of measuring the interstellar flow longitude; we want to minimize any systematic influences on the result of this analysis and give a reasonable estimate for the uncertainty. Methods. We use He + data measured by the PLAsma and SupraThermal Ion Composition (PLASTIC) sensor on the Solar TErrestrial RElations Observatory Ahead (STEREO A) spacecraft. We analyze a recent approach, identify sources of systematic errors, and propose solutions to eliminate them. Furthermore, a method is introduced to estimate the error associated with this approach. Additionally, we investigate how the selection of interplanetary magnetic field angles, which is closely connected to the pickup ion velocity distribution function, affects the result for the interstellar flow longitude. Results. We find that the revised analysis used to address part of the expected systematic effects obtains significantly different results than presented in the previous study. In particular, the derived uncertainties are considerably larger. Furthermore, an unexpected systematic trend of the resulting interstellar flow longitude with the selection of interplanetary magnetic field orientation is uncovered.

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Section: Contextmentioning

confidence: 99%

Section: Motivation and Goalsmentioning

confidence: 99%

Section: Motivation and Goalsmentioning

confidence: 99%

Section: Motivation and Goalsmentioning

confidence: 99%

Section: Motivation and Goalsmentioning

confidence: 99%

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Challenges in the determination of the interstellar flow longitude from the pickup ion cutoff

Taut

Berger

Möbius

et al. 2018

A&A

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Interstellar Mapping and Acceleration Probe (IMAP): A New NASA Mission

et al. 2018

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In Situ Observations of Interstellar Pickup Ions from 1 au to the Outer Heliosphere

et al. 2022

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Interstellar pickup ions are an ubiquitous and thermodynamically important component of the solar wind plasma in the heliosphere. These PUIs are born from the ionization of the interstellar neutral gas, consisting of hydrogen, helium, and trace amounts of heavier elements, in the solar wind as the heliosphere moves through the local interstellar medium. As cold interstellar neutral atoms become ionized, they form an energetic ring beam distribution comoving with the solar wind. Subsequent scattering in pitch angle by intrinsic and self-generated turbulence and their advection with the radially expanding solar wind leads to the formation of a filled-shell PUI distribution, whose density and pressure relative to the thermal solar wind ions grows with distance from the Sun.This paper reviews the history of in situ measurements of interstellar PUIs in the heliosphere. Starting with the first detection in the 1980s, interstellar PUIs were identified by their highly nonthermal distribution with a cutoff at twice the solar wind speed. Measurements of the PUI distribution shell cutoff and the He focusing cone, a downwind region of increased density formed by the solar gravity, have helped characterize the properties of the interstellar gas from near-Earth vantage points. The preferential heating of interstellar PUIs compared to the core solar wind has become evident in the existence of suprathermal PUI tails, the nonadiabatic cooling index of the PUI distribution, and PUIs’ mediation of interplanetary shocks. Unlike the Voyager and Pioneer spacecraft, New Horizon’s Solar Wind Around Pluto (SWAP) instrument is taking the only direct measurements of interstellar PUIs in the outer heliosphere, currently out to $\sim47~\text{au}$ ∼ 47 au from the Sun or halfway to the heliospheric termination shock.

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Interstellar Flow Longitude From the Symmetry of the Pickup Ion Cutoff at 1 Au

Cited by 26 publications

References 44 publications

Challenges in the determination of the interstellar flow longitude from the pickup ion cutoff

Challenges in the determination of the interstellar flow longitude from the pickup ion cutoff

Interstellar Mapping and Acceleration Probe (IMAP): A New NASA Mission

In Situ Observations of Interstellar Pickup Ions from 1 au to the Outer Heliosphere

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