Infrared Photometry of Solar Photospheric Structures. I. Active Regions at the Center of the Disk

Sobotka, M.; Vázquez, M.; Sánchez Cuberes, M.; Bonet, J. A.; Hanslmeier, A.
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The Astrophysical Journal, Volume 544, Issue 2, pp. 1155-1168.

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Simultaneous time series of broadband images of two active regions close to the disk center were acquired at the Swedish Vacuum Solar Telescope, La Palma, in the infrared bands at 1.55 and 0.80 μm, corresponding to the minimum and maximum continuum opacities, respectively. Dark faculae are detected in images obtained as weighted intensity differences between both wavelength bands. Maps of brightness temperatures Tb (1.55 μm) and Tb (0.80 μm) were computed for the best pairs of images. In the scatter plots Tb (1.55) versus Tb (0.80), the elements of quiet regions can be clearly distinguished from those of faculae and pores, while the transition between faculae and pores is smooth. The temperature difference Tb(1.55)-Tb(0.80) in faculae is lower than that in the quiet photosphere but increases with decreasing Tb and is higher inside pores. Most of the pores are surrounded by ringlike regions of low temperature difference. The minimum intensity of pores at both wavelengths decreases with increasing diameter. Maps of horizontal motions of dark faculae and pores were derived from time series of intensity-difference images, using the local correlation tracking technique. Velocities corresponding to large-scale separation of polarities, an emergence of magnetic flux, twist and contraction related to a pore formation, shear motions, and a twist in dark faculae were measured.