Abstract
Abstract X-ray and EUV pictures from space experiments (e.g. SKYLAB ) have revealed that the corona of the Sun consists of a variety of discrete structures - involving a range of timescales - which appear to outline the magnetic field lines emerging from the convection zone below the photosphere. Among the brightest regions in X-rays and EUV are those in which the field lines close back to the surface and which confine the hot emitting plasma in loop structures. Simple scaling laws have been developed for the static model of a single magnetic loop relating average loop temperature, pressure and length and these have been applied more or less successfully to solar observations. For many other cool stars with convective envelopes X rays have been detected from hot plasmas with temperatures ranging from ∼0.5 to ∼30 MK. The strong correlation between X-ray luminosity and stellar rotational velocity suggests a surface magnetic activity associated with an internal dynamo such as has been assumed for the Sun. The detailed spatial structure of stellar coronae is not yet known, although by analogy with the Sun it is widely assumed that stellar coronae - both quiescent and flaring - are heated by magnetohydrodynamic processes, with much of the plasma confined in loop-like structures connecting opposite magnetic polarities in the photosphere. In this paper I consider a few results from solar and stellar X-ray observations that constrain basic properties of magnetic loops.
Published Version
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