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Title: The solar BaII 4554 angstrom line as a Doppler diagnostic: NLTE analysis in 3D hydrodynamical model
Authors: Shchukina, N. G ×
Olshevsky, Vyacheslav
Khomenko, Elena #
Issue Date: 2009
Publisher: EDP Sciences
Series Title: Astronomy & Astrophysics vol:506 issue:3 pages:1393-1404
Abstract: Aims. The aim of this paper is to analyse the validity of the Dopplergram and λ-meter techniques for the Doppler diagnostics of solar
photospheric velocities using the Ba ii 4554 Å line.
Methods. Both techniques are evaluated by means of NLTE radiative transfer calculations of the Ba ii 4554 Å line in a threedimensional
hydrodynamical model of solar convection.We consider the cases of spatially unsmeared profiles and the profiles smeared
to the resolution of ground-based observations.
Results. We find that: (i) speckle-reconstructed Dopplergram velocities reproduce the “true” velocities well at heights around 300 km,
except for intergranular lanes with strong downflows where the velocity can be overestimated; (ii) the λ-meter velocities give a good
representation of the “true” velocities through the whole photosphere, both under the original and reduced spatial resolutions. The
velocities derived from the inner wing of smeared Ba ii 4554 Å line profiles are more reliable than those for the outer wing. Only
under high spatial resolution does the inner wing velocities calculated in intergranular regions give an underestimate (or even a sign
reversal) compared with the model velocities; (iii) NLTE effects should be taken into account in modelling the Ba ii 4554 Å line
profiles. Such effects are more pronounced in intergranular regions.
Conclusions. Our analysis supports the opinion that the Dopplergram technique applied to the Ba ii 4554 Å line is a valuable tool
for the Doppler diagnostics of the middle photosphere around 300 km. The λ-meter technique applied to this line gives us a good
opportunity to “trace” the non-thermal motions along the whole photosphere up to the temperature minimum and lower chromosphere.
ISSN: 0004-6361
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Non-KU Leuven Association publications
× corresponding author
# (joint) last author

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