HR: 0830h
AN: SP41B-05    [Abstracts]
TI: Calcium Circumfacules: New Findings About a Neglected Phenomenon
AU: * Harvey, J W
EM: jharvey@noao.edu
AF: National Solar Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 United States
AB: In 1903, Hale and Ellerman noted faint, elliptical dark regions surrounding CaII K₂₃₂ plages. Deslandres in 1910 showed these features to be more prominent in CaII K₃ spectroheliograms and named them circumfacules. In 1930, d'Azambuja found them to be strikingly prominent in CaII 8542 Å spectroheliograms. Bumba and Howard in 1965 suggested that the calcium circumfacules are composed of broad dark features corresponding to dark Hα fibrils. They noted that the visibility is greatest at the time of maximum K plage brightness. The small handful of available descriptions of this phenomenon leave one with the impression that the calcium circumfacules are manifestations of dark fibrils fanning out from the edges of plages to form the outermost chromospheric boundaries of active regions. Many questions remain: Why are they most prominent in 8542 Å? Are they really fuzzy dark fibrils or something different? Are they associated with the diffuse, mainly horizontal chromospheric magnetic field surrounding some plages? What is their effect on sun-as-a-star spectral irradiance measurements? Daily full disk observations of the 8542 Å line have been made at NSO since 1996. Using these data, and new SOLIS vector spectromagnetograph 8542 Å observations of Stokes I and V line profiles, these and other questions are addressed. The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation.
DE: 7507 Chromosphere
DE: 7524 Magnetic fields
SC: Solar Physics Division - AAS [SP]
MN: 2005 Joint Assembly