Stokes profile analysis and vector magnetic fields. III. Extended temperature minima of sunspot umbrae as inferred from Stokes profiles of Mg I 4571 A

Journal Article · Wed Jul 01 04:00:00 EDT 1987 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/165425· OSTI ID:6364307

Lites, B W; Skumanich, A; Rees, D E; Murphy, G A; Carlsson, M

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. 35 references.

• Research Organization: High Altitude Observatory, Boulder, CO; Sydney Univ., Australia; Oslo Universitetet, Norway
• OSTI ID: 6364307
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 318; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALKALINE EARTH METALS
ATMOSPHERES
CHROMOSPHERE
ELEMENTS
EQUILIBRIUM
HEATING
LTE
MAGNESIUM
MAGNETIC FIELD CONFIGURATIONS
METALS
SOLAR ACTIVITY
SOLAR ATMOSPHERE
STARSPOTS
STELLAR ACTIVITY
SUNSPOTS
TEMPERATURE DISTRIBUTION