Bibcode
Bello González, N.; Yelles Chaouche, L.; Okunev, O.; Kneer, F.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 494, Issue 3, 2009, pp.1091-1106
Fecha de publicación:
2
2009
Revista
Número de citas
31
Número de citas referidas
27
Descripción
Context: Small-scale magnetic fields play an important role in the
structure and the dynamics of the solar atmosphere. Aims: This
study aims at revealing the evolution of magnetic fields, together with
granular convection in the quiet Sun by means of observations with high
spatial, spectral, and temporal resolution and of numerical MHD
simulations. Methods: Time sequences from quiet Sun disc centre
were obtained with the upgraded “Göttingen” Fabry-Perot
spectropolarimeter at the Vacuum Tower Telescope, Observatorio del
Teide/Tenerife, in the Fe I 6173 Å line. The data were
reconstructed with speckle methods. For comparison with the
observations, numerical simulations of granular magnetoconvection were
carried out with the MURaM code. The intensities and Stokes vectors
emerging from the simulation box were degraded in wavelength, spatial
co-ordinates, and noise to the quality of the observations. Results: The noise in the observed magnetograms from the
centre-of-gravity method is σ_B≈2 G, yielding a polarimetric
sensitivity of 3 × 1015 Mx, at a cadence of 23 s with
0.33 arcsec spatial resolution in a field of view of ˜33
arcsec× 25 arcsec. Many of the observed V profiles in network and
internetwork (IN) areas exhibit strong asymmetries that indicate strong
magnetoconvection. The temporal evolutions of IN structures and of a
bright point (BP), as seen in broadband and line-minimum images, in
Dopplergrams, and in magnetograms, are presented. The magnetic field
structure in the numerical MHD simulations is even more complex than
seen in the observations. Correspondingly, the emergent Stokes profiles
are often very abnormal. The degradation yields a reduction of the
intrinsic field strength to the “observed” one by a factor
4-5. The spectral resolution of the spectrometer is adequate, yet the
limitation in spatial resolution and by noise filtering swamps the
details seen in the non-degraded simulations. A BP was not found in the
simulations, presumably because BP's are not so common and the simulated
box is quiet small: only 6 Mm wide in both horizontal directions. Conclusions: The combination of high-resolution observations with
numerical simulation is a highly valuable means for studying small-scale
magnetic fields on the Sun. Two-dimensional, low-noise data with
spectral resolution as good as achieved here and with spatial resolution
of 0.1 arcsec and better are needed to better understand this important
part of the solar magnetism.
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