Detalles de publicación
PP 011077
Center-to-limb variation of the area covered by magnetic bright points in the quiet Sun
((1) Instituto de Astrofisica de Canarias, Tenerife,Spain,
(2) Departamento de Astrofisica, Universidad de La Laguna, Tenerife, Spain
(3) Image Processing Laboratory, Universidad de Valencia, Spain)
CONTEXT: The quiet Sun magnetic fields produce ubiquitous bright points (BPs) that
cover a significant fraction of the solar surface. Their contribution to the total solar
irradiance (TSI) is so-far unknown.
AIMS: To measure the center-to-limb variation (CLV) of the fraction of solar surface
covered by quiet Sun magnetic bright points. The fraction is referred to as 'fraction of
covered surface', or FCS.
METHODS: Counting of the area covered by BPs in $G$-band images obtained at
various heliocentric angles with the 1-m Swedish Solar Telescope on La Palma. Through
restoration, the images are close to the diffraction limit of the instrument (~0.1 arcsec).
RESULTS: The FCS is largest at disk center (~1 %), and then drops down to become 0.2 %
at 'mu'= 0.3 (with 'mu' the cosine of the heliocentric angle. The relationship has large scatter,
which we evaluate comparing different subfields within our FOVs. We work out a toy-model
to describe the observed CLV, which considers the BPs to be depressions in the mean solar
photosphere characterized by a depth, a width, and a spread of inclinations. Although the model
is poorly constrained by observations, it shows the BPs to be shallow structures (depth < width)
with a large range of inclinations. We also estimate how different parts of the solar disk
may contribute to TSI variations, finding that 90 % is contributed by BPs having 'mu' > 0.5,
and half of it is due to BPs with 'mu' > 0.8.
cover a significant fraction of the solar surface. Their contribution to the total solar
irradiance (TSI) is so-far unknown.
AIMS: To measure the center-to-limb variation (CLV) of the fraction of solar surface
covered by quiet Sun magnetic bright points. The fraction is referred to as 'fraction of
covered surface', or FCS.
METHODS: Counting of the area covered by BPs in $G$-band images obtained at
various heliocentric angles with the 1-m Swedish Solar Telescope on La Palma. Through
restoration, the images are close to the diffraction limit of the instrument (~0.1 arcsec).
RESULTS: The FCS is largest at disk center (~1 %), and then drops down to become 0.2 %
at 'mu'= 0.3 (with 'mu' the cosine of the heliocentric angle. The relationship has large scatter,
which we evaluate comparing different subfields within our FOVs. We work out a toy-model
to describe the observed CLV, which considers the BPs to be depressions in the mean solar
photosphere characterized by a depth, a width, and a spread of inclinations. Although the model
is poorly constrained by observations, it shows the BPs to be shallow structures (depth < width)
with a large range of inclinations. We also estimate how different parts of the solar disk
may contribute to TSI variations, finding that 90 % is contributed by BPs having 'mu' > 0.5,
and half of it is due to BPs with 'mu' > 0.8.