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
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DOI：
10.1051/0004-6361/201731796
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发表时间：
2018-03
影响因子：
6.5
通讯作者：
A. Taut;L. Berger;E. Möbius;C. Drews;V. Heidrich-Meisner;D. Keilbach;M. Lee;R. Wimmer–Schweingruber
中科院分区：
文献类型：
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作者：
A. Taut;L. Berger;E. Möbius;C. Drews;V. Heidrich-Meisner;D. Keilbach;M. Lee;R. Wimmer–Schweingruber
上下文星际流经度对应于太阳相对于当地星际介质的运动方向。因此，它构成了我们理解日光层的基本参数，特别是它与周围环境的相互作用，目前正在由星际边界探测器（IBEX）进行研究。导出该参数的一种可能性是基于拾取离子（PUI），其是已经在内日光层中电离的前中性离子。中性粒子以星际风的形式从太阳运动的方向进入日球层，与部分电离的星际介质相碰撞。PUI在其速度分布函数中携带有关其中性母体种群（密度和流矢量场）空间变化的信息。从纵向流速分布的对称性，可以推导出星际流经度。瞄准！本文的目的是识别和消除与测量星际流经度的方法有关的系统误差;我们希望最大限度地减少任何系统对分析结果的影响，并对不确定性进行合理的估计。方法.我们使用He +数据测量的等离子体和超热离子成分（塑料）传感器上的日地关系天文台前方（STEREO A）航天器。我们分析了最近的方法，确定系统误差的来源，并提出解决方案，以消除它们。此外，介绍了一种方法来估计与这种方法相关的误差。此外，我们研究了行星际磁场角度的选择，这是密切相关的拾取离子速度分布函数，影响星际流经度的结果。结果我们发现，用于解决部分预期系统效应的修订分析获得了与先前研究中呈现的结果显著不同的结果。特别是，衍生的不确定性要大得多。此外，一个意想不到的系统趋势，所产生的星际流经度与行星际磁场方向的选择被发现。
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. Aim. 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.