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On the Variability of He+ Suprathermal Tails

机译:论他+上海尾尾的可变性

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Interstellar neutral helium penetrates to well within 1 AU where it is ionized predominantly by UV from the Sun. These freshly created He+ pickup ions (PUI) are convected outward with the solar wind and subject to acceleration processes, for example in compression regions, corotating interaction regions, or CME-driven interplanetary shocks. These acceleration processes result in the formation of suprathermal tails in the PUI velocity distribution. The PLASTIC instruments on the STEREO spacecraft cover for pickup He the energy range of ~1-20 keV/nuc. They allow the determination of PUI velocity distribution functions from the source distribution to suprathermal energies. In this paper we study the suprathermal tails of He pickup ions during the period January to December 2008 that featured many corotating interaction regions. The PLASTIC observations for the He+ suprathermal tail show a large variability of the spectral index γ of the distribution function f(w)~wγ, with w = V/V_(sw), where V and Vsw are the particle velocity and the solar wind velocity, respectively. Incorporating a transformation from the spacecraft frame to the solar wind frame, the spectral index at velocities 1.5 ≤ w ≤ 5 (in the solar wind frame) ranges from γ ~-5.7 at a forward shock to γ =-9 in the slow solar wind.
机译:星际中性氦气渗透到1个AU内,其中它来自太阳的UV主要被电离。这些新建的HE +拾取离子(PUI)与太阳风向外与加速过程一起传达,例如在压缩区域,卡托基相互作区或CME驱动的行星际冲击中。这些加速度过程导致PUI速度分布中的Suprathermal尾部。立体声宇宙飞船上的塑料仪器用于拾取何种〜20 kev / nuc的能量范围。它们允许确定从源分布到超级能量的PUI速度分布函数。在本文中,我们在2008年1月至12月期间的拾取离子的Suprathermal尾部研究了许多Corotate互动区域。 HE +上级尾部的塑料观察显示了分布函数f(w)〜wγ的分布函数f(w)〜wγ的尺寸变化,W = v / v_(SW),其中V和VSW是颗粒速度和太阳风速度分别。将从航天器框架的变换纳入太阳风框架,速度为1.5≤W≤5(在太阳风框架中)的光谱折射率从γ〜-5.7处的慢太阳风中的γ= -9处的γ〜-5.7。 。

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