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On the structure of solar and stellar coronae - Loops and loop heat transport
Litwin, Christof; Rosner, Robert
AA(Chicago Univ., IL), AB(Chicago Univ., IL)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 412, no. 1, p. 375-385. (ApJ Homepage)
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NASA/STI Keywords:
Computational Astrophysics, Coronal Loops, Heat Transfer, Stellar Coronas, Atmospheric Heating, Energy Transfer, Magnetic Field Reconnection, Photosphere, Stellar Atmospheres, Stellar Magnetic Fields
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We discuss the principal constraints on mechanisms for structuring and heating the outer atmospheres - the coronae - of stars. We argue that the essential cause of highly localized heating in the coronae of stars like the sun is the spatially intermittent nature of stellar surface magnetic fields, and that the spatial scale of the resulting coronal structures is related to the spatial structure of the photospheric fields. We show that significant constraints on coronal heating mechanisms derive from the observed variations in coronal emission, and, in addition, show that the observed structuring perpendicular to coronal magnetic fields imposes severe constraints on mechanisms for heat dispersal in the low-beta atmosphere. In particular, we find that most of commonly considered mechanisms for heat dispersal, such as anomalous diffusion due to plasma turbulence or magnetic field line stochasticity, are much too slow to account for the observed rapid heating of coronal loops. The most plausible mechanism appears to be reconnection at the interface between two adjacent coronal flux bundles. Based on a model invoking hyperresistivity, we show that such a mechanism naturally leads to dominance of isolated single bright coronal loops and to bright coronal plasma structures whose spatial scale transverse to the local magnetic field is comparable to observed dimensions of coronal X-ray loops.

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Database: Astronomy
arXiv e-prints