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.

中文翻译：

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太阳和恒星日冕的FIP和FIP逆效应

我们回顾了我们在太阳和恒星中冠状元素丰度异常的知识状态。我们专注于在太阳日冕和慢速风以及类似太阳的矮星的日冕中观察到的第一个电离势（FIP）效应，以及在较晚光谱类型的恒星的日冕中观察到的“反向FIP”效应; 特别是M矮人。这些效应分别与相对于FIP低于约10 eV的元素的光球值的冠状丰度的增加或减少有关。它们是根据磁动力流在色球层中的传播和/或反射所产生的动磁力来解释的。这会作用于色球离子，但不会作用于中性离子，因此会导致离子中性分离。适用于闭合磁环的模型的详细说明，给出了开阔地带的区域，这解释了慢风和快风之间太阳FIP分馏中观察到的差异。结果表明，这种模型也可以解释太阳风中氦的消耗。氦的耗竭对发生离子中性分离的色球层高度敏感，并且在闭合磁环中氦丰度的行为强烈表明这些波具有冠状起源。可以预料到这一点和其他类似的推论对太阳日冕加热理论有很大的影响。随着声波模式的转换，源自下方的热层波（主要是快速模式波）也会引起离子中性分离。根据磁场的几何形状，这可能会导致FIP或Inverse FIP效应。我们认为，这种构型更可能发生在后来的恒星中（已知在任何情况下都具有更强的视场），这解释了M型矮星发生反向FIP效应的原因。最后，我们讨论了未来工作的可能方向。