太阳和恒星日冕中的FIP和逆FIP效应

IF 20.9 1区 物理与天体物理
J. Martin Laming
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引用次数: 213

摘要

我们回顾了我们对太阳和恒星中日冕元素丰度异常的认识状态。我们重点研究了在太阳日冕和慢速风以及类太阳矮星日冕中观测到的第一电离势(FIP)效应,以及在后期光谱型恒星日冕中观测到的“逆FIP”效应;特别是M个矮星。这些影响分别与相对于FIP低于约10 eV的元素的光球值的日冕丰度的增强或耗尽有关。它们被解释为由于磁流体动力波在色球中的传播和/或反射而产生的质动势。这作用于色球离子,而不是中性离子,因此可以导致离子中性分馏。考虑到观测到的太阳慢风和快风的FIP分值的差异,给出了该模型应用于闭合磁环和开放磁场区域的详细描述。结果表明,这种模型也可以解释观测到的太阳风中氦的耗尽。氦耗尽对离子中性分离发生的色球高度敏感,封闭磁环中氦丰度的行为强烈表明波具有日冕起源。这个和其他类似的推论可能会对太阳日冕加热理论产生强烈的影响。从下面发出的色球波作为声波模式转换,主要是快速模式波,也可以引起离子中性分离。根据磁场的几何形状,这可能导致FIP或逆FIP效应。我们认为,这种结构更可能发生在较晚类型的恒星(无论如何都有更强的场),这解释了M矮星中出现逆FIP效应的原因。最后,我们讨论了未来工作的可能方向。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

The FIP and Inverse FIP Effects in Solar and Stellar Coronae

The FIP and Inverse FIP Effects in Solar and Stellar Coronae

We review our state of knowledge of coronal element abundance anomalies in the Sun and stars. We concentrate on the first ionization potential (FIP) effect observed in the solar corona and slow-speed wind, and in the coronae of solar-like dwarf stars, and the “inverse FIP” effect seen in the corona of stars of later spectral type; specifically M dwarfs. These effects relate to the enhancement or depletion, respectively, in coronal abundance with respect to photospheric values of elements with FIP below about 10 eV. They are interpreted in terms of the ponderomotive force due to the propagation and/or reflection of magnetohydrodynamic waves in the chromosphere. This acts on chromospheric ions, but not neutrals, and so can lead to ion-neutral fractionation.

A detailed description of the model applied to closed magnetic loops, and to open field regions is given, accounting for the observed difference in solar FIP fractionation between the slow and fast wind. It is shown that such a model can also account for the observed depletion of helium in the solar wind. The helium depletion is sensitive to the chromospheric altitude where ion-neutral separation occurs, and the behavior of the helium abundance in the closed magnetic loop strongly suggests that the waves have a coronal origin. This, and other similar inferences may be expected to have a strong bearing on theories of solar coronal heating.

Chromospheric waves originating from below as acoustic waves mode convert, mainly to fast-mode waves, can also give rise to ion-neutral separation. Depending on the geometry of the magnetic field, this can result in FIP or Inverse FIP effects. We argue that such configurations are more likely to occur in later-type stars (known to have stronger field in any case), and that this explains the occurrence of the Inverse FIP effect in M dwarfs. We conclude with a discussion of possible directions for future work.

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来源期刊
Living Reviews in Solar Physics
Living Reviews in Solar Physics ASTRONOMY & ASTROPHYSICS-
自引率
1.40%
发文量
3
期刊介绍: Living Reviews in Solar Physics, a platinum open-access journal, publishes invited reviews covering research across all areas of solar and heliospheric physics. It distinguishes itself by maintaining a collection of high-quality reviews regularly updated by the authors. Established in 2004, it was founded by the Max Planck Institute for Solar System Research (MPS). "Living Reviews®" is a registered trademark of Springer International Publishing AG.
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