Gunár et al. 2010, A&A 514, A43

Statistical comparison of the observed and synthetic hydrogen
Lyman line profiles in solar prominences

S. Gunár, P. Schwartz, B. Schmieder, P. Heinzel, & U. Anzer

pdf: Gunár et al. 2010, Astonomy & Astrophysic 514, A43

Aims: We analyse a unique set of prominence SOHO/SUMER Lyman spectra by comparing it with synthetic spectra obtained by 2D multi-thread prominence fine-structure models.

Methods: We employed a novel statistical approach to the analysis of the observed and synthetic Lyman spectra. We compared the statistical distributions of the line properties of the observed and synthetic Lyman spectra using a set of four statistical criteria.

Results: We demonstrate the very good agreement between the observed Lyman spectra and synthetic spectra obtained by modelling.
Conclusions: Our set of statistical criteria is well-suited to analyses of the prominence Lyman spectra because of its sensitivity to a number of different parameters governing the conditions in the prominence fine structures.

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Gunár et al. 2009, Boulder, CO

2D Radiative Transfer in Heterogeneous
Atmospheric Structures

2D Radiative Transfer in Heterogeneous Atmospheric Structures

S. Gunár, P. Heinzel & U. Anzer

From the RECENT DIRECTIONS IN ASTROPHYSICAL QUANTITATIVE SPECTROSCOPY AND RADIATION HYDRODYNAMICS conference, March 30 – April 3, 2009, Boulder, CO.

Abstract: In stellar atmospheres we observe highly heterogeneous structures, such as the solar chromosphere, solar prominences, stellar winds, etc. We have developed a 2D radiative transfer code which solves a multi-level non-LTE problem for hydrogen within an externally irradiated heterogeneous medium. Mutual radiative interaction between individual fine structures is consistently taken into account for the case of solar prominences.

Poster:poster_Boulder

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Gunár et al. 2008, A&A 490, 307

On Lyman-line asymmetries in quiescent prominences

S. Gunár, P. Heinzel, U. Anzer & B. Schmieder

pdf: Gunár et al. 2008, Astronomy & Astrophysics 490, 307

Aims: We study the asymmetries of the synthetic hydrogen Lyman lines and the process of their formation.

Methods: To obtain the synthetic Lyman line profiles, we use a multi-thread prominence finestructure model consisting of identical 2D threads. The 2D thread models are in MHS equilibrium, include an empirical PCTR and consistently solve the 2D non-LTE radiative transfer. Each thread of the multi-thread model has a randomly assigned LOS velocity.

Results: The synthetic Lyman spectrum obtained by multi-thread modelling exhibits substantial asymmetries of the line profiles even thought the LOS velocities of individual threads are only of the order of 10 km/s. Moreover, our results show that the synthetic Lyman- alpha profiles may exhibit an opposite asymmetry as compared to higher Lyman lines.

Conclusions: The presence and the behaviour of the asymmetrical profiles of the synthetic Lyman spectrum is in agreement with observed profiles taken by SOHO/SUMER.

of identical 2D threads. The 2D thread models are in MHS equilibrium, include an empirical prominence-corona transition region, and
solve consistently 2D non-LTE radiative transfer. Each thread of the multi-thread model
has a randomly assigned LOS velocity.}
{The synthetic Lyman spectrum obtained by multi-thread modelling exhibits substantial asymmetries of the line
profiles,
even though the LOS velocities of individual threads are only of the order of 10 km
s$^{-1}$. Moreover, our results indicate that the synthetic Lyman-$\alpha$ profiles may exhibit an opposite asymmetry
to that of the higher Lyman lines.}{The presence and behaviour of the asymmetrical profiles of the synthetic Lyman
lines agree with observed profiles acquired by SUMER
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Gunár et al. 2007b, A&A 472, 929

Properties of prominence fine-structure threads derived
from SOHO/SUMER hydrogen Lyman lines

Properties of prominence fine-structure threads derived from SOHO/SUMER hydrogen Lyman lines

S. Gunár, P. Heinzel, B. Schmieder, P. Schwartz, & U. Anzer

pdf: Gunár et al. 2007b, Astronomy & Astrophysics 472, 929 

Context: The SOHO/SUMER observations provide us for the first time with the prominence spectra in the Lyman-α line outside the attenuator together with the higher members of the hydrogen Lyman series.

Aims: We derive the prominence fine-structure thread properties by comparing the SOHO/SUMER hydrogen Lyman series observations with the synthetic Lyman lines.

Methods: To obtain the synthetic profiles of the Lyman lines, we used 2D prominence fine-structure thread models with a PCTR and consistently solved the 2D non-LTE multilevel radiative transfer. The trial-and-error method was applied to find the model with the best agreement between the synthetic Lyman line profiles and the observed ones.

Results: The properties of the resulting model with the best match of the synthetic and observed line profiles are central (minimum) temperature T_{0} = 7000 K, maximum column mass in the centre of the thread M0 = 1.1 × 10^{−4} g cm^{−2}, horizontal field strength in the middle of the thread Bx(0) = 6 Gauss and the boundary pressure p0 = 0.015 dyn cm^{−2}.

Conclusions: The Lyman line profiles observed by SOHO/SUMER can be better reproduced by using multi-thread models consisting of a set of the 2D prominence fine-structure threads placed perpendicularly to the line-of-sight, rather than with the single-thread model.

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Gunár et al. 2007a, A&A 463, 737

Prominence fine structures in a magnetic equilibrium:
III. Lyman continuum in 2D configurations

Prominence fine structures in a magnetic equilibrium: III. Lyman continuum in 2D configurations

S. Gunár, P. Heinzel, & U. Anzer

pdf: Gunár et al. 2007a, Astronomy & Astrophysics 463, 737

Aims: We discuss the behavior of the Lyman continuum profiles studied on the grid of 2D vertical-thread models for prominence fine structures.

Methods: Multilevel non-LTE transfer calculations for a 12-level plus continuum hydrogen model atom are used.

Results: Since the Lyman continuum is formed in regions with different temperatures for different orientations between the magnetic field direction and the line-of-sight, our Lyman continuum modeling, together with additional information from Lyman lines, represents a very useful tool for the determination of the thread structure.

Conclusions: A comparison between our theoretical Lyman continuum models between 800 Å and 911 Å with the observed values shows that such a modeling can give interesting new constraints on the temperature structure in prominence threads.

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