Astron. Astrophys. 324, 1179-1182
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Three colour photometry of solar limb faculae
C.R. de Boer1, G. Stellmacher2, and E. Wiehr3
1Max-Planck-Institut für Aeronomie,
D-37191 Katlenburg-Lindau, Germany
Received 3 December 1996 / Accepted 26 February 1997
The contrasts of limb faculae at various heliocentric angles are observed in three continuum windows largely free of absorption lines. Observations with interference filters show a contrast decrease with wavelength which is not found when using an `UBF' to select the shortest continuum window. Limb faculae in speckle-reconstructed images yield contrasts being typically 1.2 times higher than those deduced from the `best images' of the corresponding bursts.
The fit of the wavelength dependence (`colour index') to a black-body law is significantly better for the contrasts deduced from the reconstructed images than for the contrasts from the best images. The uncorrected contrasts yield a mean facular temperature excess of 200-300 K; those from the reconstructed images yield about 470 K. The center-to-limb variation is found to be much smaller than the fluctuations between individual faculae.
Key words: Sun: faculae, plages
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© European Southern Observatory (ESO) 1997