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Science 24 February 1984:
Vol. 223. no. 4638, pp. 777 - 784
DOI: 10.1126/science.223.4638.777
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Articles

Chromospheres, Transition Regions, and Coronas

Erika Böhm-Vitense

The increase in temperature outward from the surface of a stellar photosphere can be understood by looking at the local energy balance. The relatively high-density stellar photosphere is cooled effectively by radiative energy loss penetrating the optically thin corona. For the low-density chromosphere and corona, if the energy input cannot be balanced by radiative energy losses, the temperature will rise steeply, possibly up to 1 million degrees or more. Coronal heating and emission appear to be strongly influenced by magnetic fields, leading to large differences in x-ray emission for otherwise similar stars. Comparatively small variations are seen in the overall chromospheric emission of stars. Chromospheres are probably mainly heated by shock-wave energy dissipation, modified by magnetic fields.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)