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Relations between the photospheric magnetic field and the emission from the outer atmospheres of cool stars. I - The solar CA II K line core emission
Schrijver, C. J.; Cote, J.; Zwaan, C.; Saar, S. H.
AA(Joint Institute for Laboratory Astrophysics, Boulder, CO), AB(SRON, Laboratorium voor Ruimteonderzoek; Utrecht, Rijksuniversiteit, Netherlands), AC(Utrecht, Rijksuniversiteit, Netherlands), AD(Joint Institute for Laboratory Astrophysics, Boulder, CO; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 337, Feb. 15, 1989, p. 964-976. (ApJ Homepage)
Publication Date:
Solar Physics
NASA/STI Keywords:
Cool Stars, Photosphere, Solar Spectra, Stellar Atmospheres, Stellar Magnetic Fields, Calcium, Emission Spectra, Magnetic Flux, Radiant Flux Density, Solar Activity, Stellar Cores
Bibliographic Code:


Observations of a solar active region complex and its surroundings are used to establish a quantitative relation between the Ca II K line core intensity and magnetic flux density. The Ca II K line core intensity is transformed to a Ca II H + K line core flux density to facilitate a comparison of solar and stellar data. A new absolute calibration for the Mount Wilson Ca II H + K fluxes for G-type dwarfs is derived. The minimum Ca II K flux, found in the centers of supergranulation cells in quiet regions on the sun, is identical to the minimum flux that is observed for solar-type stars. An expression is presented for the nonlinear trend between the Ca II H + K line core excess flux density and the absolute value of the magnetic flux density. Models that explain the nonlinearity of the mean trend and the large intrinsic scatter about it are discussed. The solar data define a relation that is similar to the relation between stellar hemisphere-average magnetic flux densities and Ca II H + K excess flux densities.

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