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The Measurement of Stellar Photospheric Magnetic Fields

Published online by Cambridge University Press:  30 March 2016

R D Robinson
R D Robinson*
Affiliation:
Anglo-Australian Observatory, P 0 Box 296, Epping N S W 2121, Australia

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The credit for the first detection of magnetic fields on a star belongs to Hale who, in 1908, spectroscopically examined sunspots and determined their Zeeman splitting. Routine measurements of fields, however, did not come until the late 1940’s, with the development of the magnetograph by Babcock. This measurement technique relied on the fact that the split components of a magnetically sensitive line profile had opposite senses of circular polarization. Since the displacement of these components from the central wavelength was directly proportional to the strength of the magnetic field, it was found that the degree of circular polarization measured in the wings of an appropriate spectral line could be directly related to the magnetic flux present within the resolution element, provided the degree of magnetic splitting did not exceed the Doppler width of the line. The technique was applied to the Sun with highly successful results. It was possible to show that the magnetic fields were influential in nearly every form of solar activity. They structured the atmosphere and affected the energy transport, cooling some areas (sunspots) and heating others (e.g., plages and the corona). It was also found that the fields could act as resevoirs of energy. This energy can be explosively released, resulting in flare and mass ejection events.

Type
Joint Discussions
Information
Highlights of Astronomy , Volume 7: Highlights of Astronomy. As presented at the XIXth General Assembly of the IAU, 1985 , 1986 , pp. 417 - 424
Copyright
Copyright © Reidel 1986

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