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Title:
Stokes profile analysis and vector magnetic fields. III - Extended temperature minima of sunspot umbrae as inferred from Stokes profiles of MG I 4571 A
Authors:
Lites, B. W.; Skumanich, A.; Rees, D. E.; Murphy, G. A.; Carlsson, M.
Affiliation:
AA(High Altitude Observatory, Boulder, CO), AB(High Altitude Observatory, Boulder, CO), AC(Sydney, University, Australia), AD(Sydney, University, Australia), AE(Oslo, Universitetet, Norway)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 318, July 15, 1987, p. 930-939. (ApJ Homepage)
Publication Date:
07/1987
Category:
Solar Physics
Origin:
STI
NASA/STI Keywords:
LINE SHAPE, SOLAR MAGNETIC FIELD, STOKES LAW OF RADIATION, SUNSPOTS, TEMPERATURE DISTRIBUTION, ATOMIC INTERACTIONS, MAGNESIUM, MAGNETIC FIELD CONFIGURATIONS, RADIATIVE HEAT TRANSFER, UMBRAS
DOI:
10.1086/165425
Bibliographic Code:
1987ApJ...318..930L

Abstract

Observed Stokes profiles of Mg I 4571 A are analyzed as a diagnostic of the magnetic field and thermal structure at the temperature minimum of sunspot umbrae. Multilevel non-LTE transfer calculations of the Mg I-II-III excitation and ionization balance in model umbral atmospheres show: (1) Mg I to be far less ionized in sunspot umbrae than in the quiet sun, leading to greatly enhanced opacity in 4571 A, and (2) LTE excitation of 4571 A. Existing umbral models predict emission cores of the Stokes I profile due to the chromospheric temperature rise. This feature is not present in observed umbral profiles. Moreover, such an emission reversal causes similar anomalous features in the Stokes Q, U, V profiles, which are also not observed. Umbral atmospheres with extended temperature minima are suggested. Implications for chromospheric heating mechanisms and the utility of this line for solar vector magnetic field measurements are discussed.

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