IBEX Observations of Elastic Scattering of Interstellar Helium by Solar Wind Particles

arXiv - PHYS - Solar and Stellar Astrophysics Pub Date : 2024-09-18 DOI:arxiv-2409.11784

H. Islam, N. Schwadron, E. Moebius, F. Rahmanifard, J. M. Sokol, A. Galli, D. J. McComas, P. Wurz, S. A. Fuselier, K. Fairchild, D. Heirtzler

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Abstract

The IBEX-Lo instrument on the Interstellar Boundary Explorer (IBEX) mission observes primary and secondary interstellar helium in its 4 lowest energy steps. Observations of these helium populations have been systematically analyzed and compared to simulations using the analytic full integration of neutrals model (aFINM). A systematic difference is observed between the simulations and observations of secondary helium during solar cycle (SC) 24. We show that elastic scattering of primary helium by solar wind protons, which redistributes atoms from the core of the flux distribution, provides an explanation of the observed divergence from simulations. We verify that elastic scattering forms a halo in the wings of the primary He distribution in the spin-angle direction. Correcting the simulation for the effects of elastic scattering requires an increase of the estimated density of primary helium compared to previous estimates by Ulysses/GAS. Thus, based on our analysis of IBEX observations and $\chi ^2$ minimization of simulation data that include the effects of elastic scattering, any estimation of neutral interstellar helium density at 1 AU by direct detection of the peak flux of neutral helium needs to be adjusted by $~\sim$ 10%

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IBEX 观测太阳风粒子对星际氦的弹性散射

星际边界探测器（IBEX）任务上的 IBEX-Lo 仪器观测了 4 个最低能量级的原生和次生星际氦。对这些氦种群的观测结果进行了系统分析，并与使用中性分析全积分模型（aFINM）进行的模拟结果进行了比较。模拟结果与太阳周期（SC）24 期间观测到的二次氦之间存在系统性差异。我们发现，太阳风质子对原生氦的弹性散射，使原子从通量分布的核心位置分散开来，从而解释了所观测到的与模拟结果之间的差异。我们验证了弹性散射在原生氦分布的两翼形成了一个自旋角方向的光环。修正模拟中的弹性散射效应，需要增加原生氦的估计密度，而不是像以前用Ulysses/GAS估计的那样。因此，根据我们对IBEX观测数据的分析，以及对包含弹性散射影响的模拟数据的$\chi ^2$最小化，任何通过直接探测中性氦的峰值通量来估算1AU处的中性星际氦密度，都需要调整$~\sim$ 10%。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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arXiv - PHYS - Solar and Stellar Astrophysics

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