2D radiative-magnetohydrostatic model of a prominence observed by Hinode, SoHO/SUMER and Meudon/MSDP

Abstract

Aims. Prominences observed by Hinode show very dynamical and intriguing structures. To understand the mechanisms that are responsible for these moving structures, it is important to know the physical conditions that prevail in fine-structure threads. In the present work we analyse a quiescent prominence with fine structures, which exhibits dynamic behaviour, which was observed in the hydrogen Hα line with Hinode/SOT, Meudon/MSDP and Ondřejov/HSFA2, and simultaneously in hydrogen Lyman lines with SoHO/SUMER during a coordinated campaign. We derive the fine-structure physical parameters of this prominence and also address the questions of the role of the magnetic dips and of the interpretation of the flows. Methods. We calibrate the SoHO/SUMER and Meudon/MSDP data and obtain the line profiles of the hydrogen Lyman series (Lβ to L6), the Ciii (977.03 Å) and Svi (933.40 Å), and Hα along the slit of SoHO/SUMER that crosses the Hinode/SOT prominence. We employ a complex 2D radiation-magnetohydrostatic (RMHS) modelling technique to properly interpret the observed spectral lines and derive the physical parameters of interest. The model was constrained not only with integrated intensities of the lines, but also with the hydrogen line profiles. Results. The slit of SoHO/SUMER is crossing different prominence structures: threads and dark bubbles. Comparing the observed integrated intensities, the depressions of Hα bubbles are clearly identified in the Lyman, Ciii, and Svi lines. To fit the observations, we propose a new 2D model with the following parameters: T = 8000 K, p cen = 0.035 dyn cm −2 , B = 5 Gauss, n e = 10 10 cm −3 , 40 threads each 1000 km wide, plasma β is 3.5 × 10 −2 . Conclusions. The analysis of Ciii and Svi emission in dark Hα bubbles allows us to conclude that there is no excess of a hotter plasma in these bubbles. The new 2D model allows us to diagnose the orientation of the magnetic field versus the LOS. The 40 threads are integrated along the LOS. We demonstrate that integrated intensities alone are not sufficient to derive the realistic physical parameters of the prominence. The profiles of the Lyman lines and also those of the Hα line are necessary to constrain 2D RMHS models. The magnetic field in threads is horizontal, perpendicular to the LOS, and in the form of shallow dips. With this geometry the dynamics of fine structures in prominences could be interpreted by a shrinkage of the quasi-horizontal magnetic field lines and apparently is not caused by the quasi-vertical bulk flows of the plasma, as Hinode/SOT movies seemingly suggest.

Dynamics of quiescent prominence fine structures analyzed by 2D non-LTE modelling of the Hα line

“…We start our investigation with the Model2, which was found by Berlicki et al (2011) to produce synthetic Lyman spectra in good agreement with observations (see Fig. 9).…”

“…This appears to be in conflict to the findings of Schmieder et al (2007), who showed that the Lyman line profiles obtained with the LOS perpendicular to the magnetic field exhibit a central reversal, while those obtained with a LOS parallel to the field show the nonreversed profile shape. However, as discussed by Berlicki et al (2011) and Gunár et al (2011b), this dependance of the Lyman line profile shape on the orientation of the LOS is valid only for models of sufficiently high mass. In the case of low-mass, lowpressure models such as Model2 or Model_DEM (Gunár et al 2011b), even the Lyman lines obtained with LOS perpendicular to the magnetic field exhibit non-reversed profiles.…”

“…In the present study, we use multi-thread configurations of the 2D prominence fine-structure models, which are more realistic than single-thread models and can produce synthetic Lyman and Balmer (Hα) spectra in better agreement with observations (see Gunár et al 2007Gunár et al , 2008Gunár et al , 2010Berlicki et al 2011). Individual threads of these multi-thread models are randomly shifted with respect to the foremost thread (see Fig.…”

“…The prominence studied in this work was previously investigated by Berlicki et al (2011) who analysed the UV spectra obtained by SOHO/SUMER together with Hα observations acquired using the Meudon/MSDP spectrograph and HSFA2 (HorizontalSonnen-Forschungs-Anlage) spectrograph in Ondřejov (Kotrč 2009). However, these authors used for this investigation the Hα spectra only from a very narrow region of the prominence corresponding to the position and the dimensions of the SUMER slit.…”

“…9). The synthetic Lyman spectra produced by Model2 exhibit non-reversed line profiles (apart from the Lyman-α profiles that are always reversed), regardless of the orientation of the LOS with respect to the magnetic field (see Berlicki et al 2011). This appears to be in conflict to the findings of Schmieder et al (2007), who showed that the Lyman line profiles obtained with the LOS perpendicular to the magnetic field exhibit a central reversal, while those obtained with a LOS parallel to the field show the nonreversed profile shape.…”