Infrared Photometry of Solar Photospheric Structures. II. Center-to-Limb Variation of Active Regions

Details Infrared Photometry of Solar Photospheric Structures. II. Center-to-Limb Variation of Active Regions Infrared Photometry of Solar Photospheric Structures. II. Center-to-Limb Variation of Active Regions

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002apj...570..886s&link_type=abstract

The Astrophysical Journal, Volume 570, Issue 2, pp. 886-899.

Astronomy and Astrophysics

Astronomy

13

Sun: Faculae, Plages, Sun: Granulation, Sun: Photosphere

Scientific paper

Simultaneous broadband single images and time series of images have been obtained at λ0.8 and λ1.55 μm, which are at the extremes of the continuum absorption coefficient of the solar atmosphere. Active regions have been observed for different heliocentric angles. Weighted difference images between the two wavelength bands have been used to identify faculae. Center-to-limb variations of facular relative intensity distribution, facular size distribution, and facular size-intensity relations have been obtained. At the spatial resolution of the observations, faculae show no contrast at the disk center at λ0.8 μm, while dark faculae are observed at λ1.55 μm. The transition from dark to bright faculae occurs between μ=0.6 and 0.5 in λ1.55 μm images. The maximum of the mean facular relative intensity is found at μ=0.3 for both wavelengths. However, the peak of the facular relative intensity is greater and appears closer to the limb the larger the faculae are. Brightness temperature maps have been computed for the best pairs of images, and temperature difference images have been derived. The temperature difference Tb(1.55μm)-Tb(0.8μm) in pores is larger than that in the quiet photosphere at the disk center, but smaller near the limb. Faculae show smaller temperature differences than the quiet photosphere at the disk center, but the temperature differences near the limb are almost equal. Pores are surrounded by ringlike structures of low temperature difference at the disk center. Near the limb these ringlike structures appear bright in the brightness temperature maps and show a temperature difference similar to that of the quiet photosphere.

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