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Astron. Astrophys. 320, 1001-1012 (1997)

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Bisectors and line-parameter variations over granular and intergranular regions in 2-D artificial granulation

A.S. Gadun 1, A. Hanslmeier 2 and K. N. Pikalov 1

1 Main Astronomical Observatory of Ukrainian NAS, Goloseevo, 252650 Kiev-22, Ukraine
2 Institut für Astronomie, Universitätsplatz 5, A-8010 Graz, Austria

Received 17 June 1996 / Accepted 13 September 1996

Abstract

Two sets of two-dimensional models of the solar granulation have been used to interpret the published observations of spectral lines of Fe I 4911.54, 4911.78, and 6494.99 Å obtained with high spectral and spatial resolution over selected granular and intergranular regions. The models differ by the horizontal size of the modeling region and treatment of thermal convection.

We study the variations of continuum intensity, residual intensity in the line cores, Doppler velocities, line asymmetries over granular and intergranular areas in the center of the solar disk and compare the correlation between these parameters obtained from models with observational ones.

A good reproduction of the observational results can be found only by applying 2-D models that treat the solar thermal convection as a fully non-stationary system with interacting flows. Such models also take into account the important role of secondary motions that influence the middle and upper photosphere. As essential perturbing factors there appear photospheric flows with supersonic velocities which can change the photometric profiles of granules, create regions with inversion of temperature distribution and impact onto the velocity field.

Variations of line parameters strongly depend on limitations in spatial resolution (spatial smearing). This was simulated in the models by applying different Gaussian smearing functions. Seeing was found to affect variations of equivalent widths, full widths at half maxima, and bisectors of the lines most strongly.

Key words: hydrodynamics – line: formation – Sun: granulation – Sun: photosphere

Send offprint requests to: A. Hanslmeier

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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