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Stellar model chromospheres. III - Arcturus /K2 III/Models are constructed for the upper photosphere and chromosphere of Arcturus based on the H, K, and IR triplet lines of Ca II and the h and k lines of Mg II. The chromosphere model is derived from complete redistribution solutions for a five-level Ca II ion and a two-level Mg II ion. A photospheric model is derived from the Ca II wings using first the 'traditional' complete-redistribution limit and then the more realistic partial-redistribution approximation. The temperature and mass column densities for the temperature-minimum region and the chromosphere-transition region boundary are computed, and the pressure in the transition region and corona are estimated. It is found that the ratio of minimum temperature to effective temperature is approximately 0.77 for Arcturus, Procyon, and the sun, and that mass tends to increase at the temperature minimum with decreasing gravity. The pressure is found to be about 1 percent of the solar value, and the surface brightness of the Arcturus transition region and coronal spectrum is estimated to be much less than for the sun. The partial-redistribution calculation for the Ca II K line indicates that the emission width is at least partially determined by damping rather than Doppler broadening, suggesting a reexamination of previous explanations for the Wilson-Bappu effect.
Document ID
19750062741
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Ayres, T. R.
Linsky, J. L.
(Joint Institute for Laboratory Astrophysics Boulder, Colo., United States)
Date Acquired
August 8, 2013
Publication Date
September 15, 1975
Publication Information
Publication: Astrophysical Journal
Volume: 200
Subject Category
Astrophysics
Accession Number
75A46813
Funding Number(s)
CONTRACT_GRANT: NAS5-23274
CONTRACT_GRANT: NGR-06-003-057
Distribution Limits
Public
Copyright
Other

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