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Paper: Photospheric Magnetic Field Measurements on Late-Type Stars and Brown Dwarfs
Volume: 384, 14th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun
Page: 145
Authors: Johns-Krull, C.M.
Abstract: Magnetic fields produce activity on the Sun and cool stars. Activity itself involves both the dynamo production of magnetic fields and the magnetic heating of the outer atmosphere of stars, and in some cases brown dwarfs, which produces the radiative signatures of activity. In the past several years, measurements of the photospheric magnetic field strength have become available for a number of low mass stars and brown dwarfs, allowing us to separate the study of field production from the study of non-radiative heating. Much of the recent observational effort has centered on T Tauri stars, due to the importance of strong stellar fields in explaining this stage of star formation, and on very low mass stars and brown dwarfs where measurements of traditional activity indicators suggest sharp differences in field production and/or heating efficiency compared to what is observed in slightly higer mass stars. Somewhat surprisingly, measurements on these two classes of fully convective objects reveals mean magnetic field strengths of 2-3 kG in many cases. Here, I will review the techniques for measuring the photospheric magnetic field by looking for effects caused by Zeeman broadening of spectral lines. I will discuss the implications of the latest field measurements for dynamo theories. Finally, I will suggest some avenues likely to be fruitful for future research in the field.
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