What are "Faculae"?
Thomas Berger (1), Alan Title (1), Ted Tarbell (1),
Luc Rouppe van der Voort (2),
Mats Lofdahl, Goran Scharmer (3)
(1) Lockheed Martin Solar and Astrophysics Lab, Palo Alto, CA, USA
(2) Institute of Theoretical Astrophysics, University of Oslo, Norway
(3) Royal Swedish Academy of Sciences, Stockholm, Sweden
We present very high resolution filtergram and magnetogram observations
of solar faculae taken at the Swedish 1-meter Solar Telescope on La
Palma. The data clearly show the three-dimensional structure of faculae
seen near the limb of the sun. Three datasets with line-of-sight angles
of 16, 34, and 53 degrees are analyzed to show that the contrast versus
magnetic flux density function of faculae is constant, in stark
distinction from that of "magnetic bright points" identified in
near-disk-center images which show a strong change in brightness as a
function of magnetic flux density. It is clear that "faculae" are not
"flux tubes" - they are granules seen through the transparency caused
by groups of flux tubes in front of the granules. The results are
compared to recent numerical simulations that arrive at essentially the
same conclusion. Previous results which show a strong dependency of
facular contrast on magnetic flux density were caused by insufficient
spatial resolution leading to a mixture of the signal from bright
facular walls and the dark micropores immediately in front of them. The
findings are relevant to studies of total solar irradiance (TSI) that
use facular contrast as a function of disk position and magnetic field
in order to model the increase in TSI with increasing sunspot activity.
Correspondence
Thomas Berger (berger@lmsal.com), LMSAL
presentation
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