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Astron. Astrophys. 324, 1179-1182

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Research Note

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
2Institut d'Astrophysique CNRS, 98bis Bvd. d'Arago, F-75014 Paris, France
3Universitäts-Sternwarte, Geismarlandstr.11, D-37083 Göttingen, 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

Send offprint requests to: E. Wiehr

© European Southern Observatory (ESO) 1997