Author name code: gunar ADS astronomy entries on 2022-09-14 author:"Gunar, Stanislav" ------------------------------------------------------------------------ Title: Data-driven Model of Temporal Evolution of Solar Mg II h and k Profiles over the Solar Cycle Authors: Koza, Július; Gunár, Stanislav; Schwartz, Pavol; Heinzel, Petr; Liu, Wenjuan Bibcode: 2022ApJS..261...17K Altcode: The solar radiation in the cores of the Mg II h and k spectral lines plays a significant role in the illumination of prominences, coronal mass ejections (CMEs), spicules, flare loops, and surges. Moreover, the radiation in these lines strongly correlates with solar magnetic activity and the ultraviolet solar spectral irradiance affecting the photochemistry, especially of oxygen and nitrogen, in the middle atmosphere of the Earth. This work provides a data-driven model of temporal evolution of the solar full-disk Mg II h and k profiles over the solar cycle. The capability of the model to reproduce the Mg II h and k profiles for an arbitrary date is statistically assessed. Based on selected 76 IRIS near-UV full-Sun mosaics covering almost the full solar cycle 24, we find the parameters of double-Gaussian fits of the disk-averaged Mg II h and k profiles and a model of their temporal evolution parameterized by the Bremen composite Mg II index. The model yields intensities within the uncertainties of the observed data in more than 90% of the reconstructed profiles assuming a statistically representative set of Bremen Mg II index values in the range of 0.150-0.165. The relevant full-disk Mg II h and k calibrated profiles with uncertainties and spectral irradiances are provided as an online machine-readable table. The model yields Mg II h and k profiles representing the disk incident radiation for the radiative-transfer modeling of prominences, CMEs, spicules, flare loops, and surges observed at arbitrary time. Title: Large Impact of the Mg II h and k Incident Radiation Change on Results of Radiative Transfer Models and the Importance of Dynamics Authors: Gunár, Stanislav; Heinzel, Petr; Koza, Július; Schwartz, Pavol Bibcode: 2022ApJ...934..133G Altcode: We demonstrate that changes in the incident radiation in Mg II h and k lines have a significant impact on the results of radiative transfer modeling of prominence-like plasmas. To uncover the extent of this impact and allow easy comparison, here we study two cases, one representing the minimum of the solar activity and the other corresponding to the typical conditions during solar maxima. To represent well the properties of the prominence plasma, we use the 2D non-LTE (i.e., departures from local thermodynamic equilibrium) model of prominence fine structures in both the single-thread configuration and the multithread configuration incorporating prominence dynamics. We show that in the modeled environment of prominence fine structures, the change in the central, integrated, and peak intensities of the synthetic Mg II h and k profiles can be as large as the change in the incident radiation itself. This means that the Mg II h and k spectra of observed prominences can be affected by tens of percent because the illumination from the solar disk can change by such a degree over the solar cycle. That makes the knowledge and use of event-specific incident radiation data very important for the diagnostics of prominences and other chromospheric and coronal structures when using Mg II h and k spectral observations. In addition, the observed Mg II h and k spectra are strongly influenced by the line-of-sight dynamics, as the multithread configuration of the 2D model allows us to reveal. The effect of dynamics is, unsurprisingly, most pronounced in the line widths and integrated intensities. Title: Science with the ASPIICS coronagraph onboard PROBA-3 Authors: Gunár, Stanislav; Fineschi, Silvano; Inhester, Bernd; Zhukov, Andrei; Mierla, Marilena; Tsinganos, Kanaris; Lamy, Philippe; Rudawy, Pawel Bibcode: 2022cosp...44.1326G Altcode: The giant distributed coronagraph ASPIICS onboard the formation-flying mission PROBA-3 of ESA will investigate hitherto practically unexplored inner depths of the solar corona. This region lies above the reach of disk imagers such as SDO and below the inner limit of other coronagraphs. Although difficult to observe, the inner corona is a place of great interest. This is where the fast solar wind gets accelerated to supersonic velocities and where CMEs also reach their maximum accelerations. It is also the place where the transition between the regions of the closed and open magnetic field often happens and the slow solar wind originates. Thanks to its field of view (2048 x 2048 pixels) reaching from 1.098 to 3 Rsun, good spatial resolution (2.8 arcsec per pixel) and minimized straylight, ASPIICS will be able to follow the connectivity of magnetic structures in corona down to the solar surface. When coupled with regular (every week) long duration (up to 6 hours) observations, it will allow us to comprehensively compare and validate the MHD models of the large-scale coronal magnetic field configuration and its evolution. The inner field-of-view limit reaching very close to the solar surface will also enable us to study the onset and early evolution of CMEs or to follow erupting prominences beyond the reaches of the disk imagers. Thanks to the high cadence (up to 2 seconds) we can start to investigate the manifestation of small-scale solar dynamic processes within the inner corona. Moreover, together with the DARA instrument measuring the total solar irradiance onboard the occulting spacecraft of PROBA-3, ASPIICS will help us to understand the partition of the magnetic free energy into the radiative energy and the kinetic energy during solar eruptions. The pursuit of these science goals will happen in coordination with Solar Orbiter, Parker Solar Probe, Aditya-L1, and ASO-S. The synergies stemming from these collaborations are promising to lead us into a golden age of space coronagraphy. Title: Co-located Data Relay and Storage Spacecraft as a data-downlink solution for small satellites and their constellations Authors: Gunár, Stanislav Bibcode: 2022cosp...44.1993G Altcode: We explore the potential of the use of co-located Data Relay and Storage Spacecraft (DRS S/C) as data-handling hubs providing enhanced downlink and data storage capabilities for research satellites and their constellations. Why should we search for such a solution? Because the volumes of data produced by research satellites continue to rise and will do so in future. However, the data-transfer bottlenecks, and the trade-offs that they pose, impact both large and small scientific missions already today. Indeed, the constraints imposed by the current data-downlink technologies affect the small satellites the hardest, making the entry of smaller players into space research difficult. On the other hand, at the time when the research satellites grapple with limited throughput, vast volumes of data are routinely relayed via telecommunication satellites every day. These advanced spacecraft produced by commercial companies are being built in series which continually drives down their cost and increases their capabilities. This contrast between the scientific and commercial worlds highlights the need for the exploration of new, innovative data-downlink technologies. One of such enabler technologies could be the co-located DRS S/C. These infrastructure-building platforms would open new possibilities for small research and technology demonstration satellites and might lead to a change of paradigm of space research from the use of single, all-purpose satellites to constellations of large and small spacecraft anchored by DRS S/C hubs. Title: Diagnostics of The Prominence Plasma Based on IRIS, H-alpha and ALMA Observations Authors: Berlicki, Arkadiusz; Bárta, Miroslav; Gunár, Stanislav; Heinzel, Petr; Jejcic, Sonja; Radziszewski, Krzysztof; Rudawy, Pawel Bibcode: 2022cosp...44.2543B Altcode: Solar prominences are now commonly observed above the solar limb in different spectral bands and recent developments of new observing techniques allow us to detect them from radio to far-UV ranges. In addition to often used spectral observations in optical and UV, ALMA interferometer obtained high-resolution images of a quiescent solar prominence at 3 millimeters (Band 3) during the coordinated space and ground-based observing campaign. For the first time high-resolution observations of such structures in the millimeter radio domain are available. The fine structures of this prominence was also observed in the UV with IRIS and in the H$\alpha$ line with the MSDP of Wroc{\l}aw Observatory. Both UV and H$\alpha$ data contains not only images, but also spectra which makes the available dataset extremely valuable. Moreover, all UV, H$\alpha$ and ALMA observations are co-temporal which gives an unprecedented opportunity for a novel diagnostic, not available so far. In this work we present analysis of the prominence spectral characteristics in H$\alpha$ and UV Mg II lines, looking for the statistical dependence between different parameters (metrics) in the line profiles. This combined data is then used for determination of plasma parameters in the prominence fine structures. In addition, UV and H$\alpha$ spectral maps are compared with the brightness temperature mosaics from ALMA, providing an additional constraint on the plasma kinetic temperature. Detailed diagnostics is then based on extensive NLTE numerical simulations of the radiative transfer inside heterogeneous prominence structures. Title: The European Solar Telescope Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.; Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein, C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados, M.; the EST team Bibcode: 2022arXiv220710905Q Altcode: The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR, the French Télescope Héliographique pour l'Étude du Magnétisme et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope (DOT). With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems. Title: Variability of solar Lyman-alpha and Mg II h&k lines throughout the solar cycle and its impact on the diagnostics of chromospheric and coronal structures Authors: Gunár, Stanislav; Schwartz, Pavol; Heinzel, Petr; Liu, Wenjuan; Koza, Julius Bibcode: 2022cosp...44.1553G Altcode: The solar radiation in the Lyman-alpha and Mg II h&k spectral lines plays a crucial role in the illumination of chromospheric and coronal structures, such as prominences/filaments, spicules, chromospheric fibrils, cores of coronal mass ejections, or solar wind. Moreover, it is important for the investigation of the heliosphere, Earth ionosphere, and the atmospheres of planets, moons, and comets. However, the emissivity of the Sun is not constant in these lines but changes considerably throughout the solar cycle. To study these changes and their impact, we first had to set the baseline representing the radiation from the solar disk during a minimum of solar activity. We thus derived new sets of quiet-Sun reference profiles of Lyman-alpha and Mg II h&k lines. For the Lyman-alpha line, we used SOHO/SUMER raster scans obtained without the use of the SUMER attenuator (Gunár et al. 2020) and for the Mg II h&k lines we used the broad catalogue of IRIS full-Sun mosaics (Gunár et al. 2021). To quantify the variability with the solar cycle, we used the LISIRD Composite Lyman-alpha index to adapt the Lyman lines to any specific date (Gunár et al. 2020). For the Mg II h&k lines, we used a data-driven model based on the Bremen Composite Mg II index (Koza et al. 2022). These long-term measures then allowed us to investigate how the changing irradiation from the solar surface influences the synthetic spectra produced by the radiative transfer modelling. As we showed in Gunár et al. (2020, 2022), both changes in the Lyman lines and the Mg II h&k lines affect the resulting synthetic spectra significantly, even up to 50 % depending on the strength of individual solar cycles. That, however, has a strong impact on the diagnostics of the observed chromospheric and coronal structures, making up-to-date information about the solar activity a critical input for their precise modelling. Title: Non-LTE Inversion of Prominence Spectroscopic Observations in Hα and Mg II h&k lines Authors: Jejčič, Sonja; Heinzel, Petr; Schmieder, Brigitte; Gunár, Stanislav; Mein, Pierre; Mein, Nicole; Ruan, Guiping Bibcode: 2022ApJ...932....3J Altcode: We continued our investigation of the plasma characteristics of a quiescent prominence that occurred on 2017 March 30. The prominence was observed simultaneously by several instruments, including the Interface Region Imaging Spectrograph (IRIS) and the Multichannel Subtractive Double Pass (MSDP) spectrograph operating at the Meudon solar tower. We focused on IRIS Mg II h&k and MSDP Hα spectra, selecting 55 well-coaligned points within the prominence. We computed an extensive grid of 63,000 isothermal and isobaric 1D-slab prominence models with a non-LTE (i.e., departures from the local thermodynamic equilibrium) radiative transfer code. We then performed a 1.5D spectral inversion searching for an optimal model that best fits five parameters of the observed profiles (observables), namely, the integrated intensity of the Hα and Mg II k lines, the FWHM of both lines, and the ratio of intensities of the Mg II k and Mg II h lines. The latter is sensitive to temperature. Our results show that the prominence is a low-temperature structure, mostly below 10,000 K, with some excursions to higher values (up to 18,000 K) but also rather low temperatures (around 5000 K). The microturbulent velocity is typically low, peaking around 8 km s-1, and electron density values are of the order of 1010 cm-3. The peak effective thickness is 500 km, although the values range up to 5000 km. The studied prominence is rather optically thin in the Hα line and optically thick in the Mg II h&k lines. Title: Subarcsecond Imaging of a Solar Active Region Filament With ALMA and IRIS Authors: da Silva Santos, J. M.; White, S. M.; Reardon, K.; Cauzzi, G.; Gunár, S.; Heinzel, P.; Leenaarts, J. Bibcode: 2022FrASS...9.8115D Altcode: 2022arXiv220413178D Quiescent filaments appear as absorption features on the solar disk when observed in chromospheric lines and at continuum wavelengths in the millimeter (mm) range. Active region (AR) filaments are their small-scale, low-altitude analogues, but they could not be resolved in previous mm observations. This spectral diagnostic can provide insight into the details of the formation and physical properties of their fine threads, which are still not fully understood. Here, we shed light on the thermal structure of an AR filament using high-resolution brightness temperature (Tb) maps taken with ALMA Band 6 complemented by simultaneous IRIS near-UV spectra, Hinode/SOT photospheric magnetograms, and SDO/AIA extreme-UV images. Some of the dark threads visible in the AIA 304 Å passband and in the core of Mg ii resonance lines have dark (Tb < 5,000 K) counterparts in the 1.25 mm maps, but their visibility significantly varies across the filament spine and in time. These opacity changes are possibly related to variations in temperature and electron density in filament fine structures. The coolest Tb values (< 5,000 K) coincide with regions of low integrated intensity in the Mg ii h and k lines. ALMA Band 3 maps taken after the Band 6 ones do not clearly show the filament structure, contrary to the expectation that the contrast should increase at longer wavelengths based on previous observations of quiescent filaments. The ALMA maps are not consistent with isothermal conditions, but the temporal evolution of the filament may partly account for this. Title: ALMA as a Prominence Thermometer: First Observations Authors: Heinzel, Petr; Berlicki, Arkadiusz; Bárta, Miroslav; Rudawy, Paweł; Gunár, Stanislav; Labrosse, Nicolas; Radziszewski, Krzysztof Bibcode: 2022ApJ...927L..29H Altcode: 2022arXiv220212761H We present first prominence observations obtained with Atacama Large Millimeter Array (ALMA) in Band 3 at the wavelength of 3 mm. High-resolution observations have been coaligned with the MSDP Hα data from Wrocław-Białków large coronagraph at similar spatial resolution. We analyze one particular cotemporal snapshot, first calibrating both ALMA and MSDP data and then demonstrating a reasonable correlation between both. In particular, we can see quite similar fine-structure patterns in both ALMA brightness-temperature maps and MSDP maps of Hα intensities. Using ALMA, we intend to derive the prominence kinetic temperatures. However, having current observations only in one band, we use an independent diagnostic constraint, which is the Hα line integrated intensity. We develop an inversion code and show that it can provide realistic temperatures for brighter parts of the prominence where one gets a unique solution, while within faint structures, such inversion is ill conditioned. In brighter parts, ALMA serves as a prominence thermometer, provided that the optical thickness in Band 3 is large enough. In order to find a relation between brightness and kinetic temperatures for a given observed Hα intensity, we constructed an extended grid of non-LTE prominence models covering a broad range of prominence parameters. We also show the effect of the plane-of-sky filling factor on our results. Title: VizieR Online Data Catalog: Quiet-Sun MgII h & k line profiles from IRIS (Gunar+, 2021) Authors: Gunar, S.; Koza, J.; Schwartz, P.; Heinzel, P.; Liu, W. Bibcode: 2021yCat..22550016G Altcode: Since its launch, the Interface Region Imaging Spectrograph (IRIS) commenced a quasi-regular acquisition of maps of the entire solar disk in both NUV and FUV spectral ranges. At the time of writing, the archive of the IRIS full-Sun mosaics contained 91 observations spanning the period from 2013 September 30 to 2020 October 19 which cover two spectral windows of +/-1.75Å centered at 2803.53Å (MgII h) and 2796.35Å (MgII k).

(4 data files). Title: Quiet-Sun Mg II h and k Line Profiles Derived from IRIS Full-Sun Mosaics. I. Reference Profiles and Center-to-limb Variation Authors: Gunár, Stanislav; Koza, Július; Schwartz, Pavol; Heinzel, Petr; Liu, Wenjuan Bibcode: 2021ApJS..255...16G Altcode: We derived high-precision reference profiles of the Mg II h and k lines that represent the quiet Sun during a minimum of the solar activity. To do so, we used the broad catalog of full-Sun mosaics obtained by the Interface Region Imaging Spectrograph (IRIS). To minimize the influence of the local variations due to the on-disk solar features and to achieve low levels of uncertainties, we used 12 IRIS full-Sun mosaics without sunspots or other significant signs of solar activity. These mosaics were obtained between 2019 April and 2020 September in the near-ultraviolet spectral range. In this paper, we present the disk-averaged reference profiles of Mg II h and Mg II k lines, together with a series of reference profiles spanning the distance between the disk center and the solar limb. These series of profiles offer a detailed representation of the center-to-limb variation of both Mg II h and Mg II k lines. The reference Mg II h and k line profiles provided in this paper can be used as the incident radiation boundary condition for radiative-transfer modeling of prominences, spicules, and other coronal and chromospheric structures. Title: Spectral inversion of H-alpha and MgII lines in quiescent prominences Authors: Heinzel, Petr; Schmieder, Brigitte; Ruan, Guiping; Mein, Pierre; Gunár, Stanislav; Jejcic, Sonja; Mein, Nicole Bibcode: 2021cosp...43E1764H Altcode: Recent spectral analysis of simultaneous H-alpha (MSDP) and MgII lines (IRIS) (Guiping et al. 2019) has revealed certain bifurcation in resulting models. Two solutions were found from the line inversions using the non-LTE modeling: relatively high kinetic temperature and low non-thermal motions or temperatures mostly compatible with standard ones plus non-thermal motions of the order of 16 km/sec. Here we will present an improved spectral line inversion technique which clearly prefers the latter solution. Strong non-thermal motions are then interpreted as a mixture of microturbulence and the line-of-sight dynamics of prominence fine-structure threads. A detailed multithread modeling with the 2D non-LTE code and stochastic distributions of threads (position, dynamics) is now in progress and we will show our preliminary results. Title: Magnetic support of the solar filaments Authors: Schmieder, Brigitte; Aulanier, Guillaume; Gunár, Stanislav; Dudik, Jaroslav; Heinzel, Petr Bibcode: 2021cosp...43E1766S Altcode: The scale height in prominence is 500 km at maximum. However, non activated prominences can reach an altitude of 50000 km or more. Hanging filaments observed over the limb give the impression of quasi vertical structures. It was already the view in the past but reactivated by the movies of Hinode in Ca II line showing fuzzing vertical structures. In the corona it is not possible to measure the magnetic field supporting prominences. Only extrapolations of the photospheric magnetic field explain how cool plasma embedded in the dips of the magnetic field lines can be supported in the hot corona. I will review a few papers showing the distribution of the cool plasma dips and the observations of filaments on the disk visible in H$\alpha$ and in UV. A recent paper shows how a 3D extrapolation model and a radiative-transfer based H$\alpha$ visualization method leads to H$\alpha$ prominence fine structures. Finally, I will discuss the perspective effects on the perceived morphology of observed and modeled prominences. Title: Links between prominence/filament magnetic field and plasma: What can 3D WPFS models teach us? Authors: Gunár, Stanislav; Schmieder, Brigitte; Aulanier, Guillaume; Heinzel, Petr; Mackay, Duncan; Dudik, Jaroslav Bibcode: 2021cosp...43E1769G Altcode: The magnetic field constitutes the skeleton and the driving force of prominences/filaments. It supports the dense prominence plasma against gravity and insulates it from the hot, coronal environment. The magnetic field is also responsible for the prominence stability, evolution and eruptions which affect the heliosphere and ultimately the Earth. However, a strong imbalance exists between the numerous efforts in detailed modelling of prominence magnetic field and its understanding from observations. That is due to the complex nature of the direct (and indirect) observations of solar magnetic fields which are challenging at the best of times and even more so in prominences or filaments. The direct observations of the prominence magnetic field require high-precision spectro-polarimetric measurements and realistic assumptions about the plasma structure which allow us to infer the field configuration from its effect on the polarized light emergent from the observed structures. The indirect observations rely on the perceived location, shape and dynamics of the prominence or filament plasma, often using moving small-scale plasma structures as tracers guided by the field lines. Both methods thus rely on the presence of observable plasma in the magnetic field configuration, and on the radiation which carries the information about the in-situ conditions to the observer. No prominence/filament magnetic field measurements are made without these two additional components, which are sometimes an afterthought in the magnetic field models. We have developed 3D Whole-Prominence Fine Structure (WPFS) models to illuminate the links between the prominence magnetic field, its plasma distributed among numerous fine structures and the radiation which carries the information about the prominence physical conditions to the observer. What can we learn from these 3D models? For example, we can see that a small change of the magnetic field configuration can have a large effect on the perceived structure of prominences and filaments visible in the H-alpha line. Consequently, this means that significant changes observed in prominences or filaments do not need to suggest that equally large changes in the underlying magnetic field configuration had to occur. In another example, we see that seemingly incomparable differences in the morphological look of prominences (long horizontal fine structures versus small blobs of plasma arranged into more-less vertical features) may not need to imply the existence of radically different magnetic field configurations. Rather, they might simply be manifestations of projection effects that can differ greatly depending on the viewing angle under which we observe the naturally three-dimensional prominences/filaments. Title: Quiet-Sun hydrogen Lyman-α line profile derived from SOHO/SUMER solar-disk observations Authors: Gunár, S.; Schwartz, P.; Koza, J.; Heinzel, P. Bibcode: 2020A&A...644A.109G Altcode: 2020arXiv201101299G Context. The solar radiation in the Lyman-α spectral line of hydrogen plays a significant role in the illumination of chromospheric and coronal structures, such as prominences, spicules, chromospheric fibrils, cores of coronal mass ejections, and solar wind. Moreover, it is important for the investigation of the heliosphere, Earth's ionosphere, and the atmospheres of planets, moons, and comets.
Aims: We derive a reference quiet-Sun Lyman-α spectral profile that is representative of the Lyman-α radiation from the solar disk during a minimum of solar activity. This profile can serve as an incident radiation boundary condition for the radiative transfer modelling of chromospheric and coronal structures. Because the solar radiation in the Lyman lines is not constant over time but varies significantly with the solar cycle, we provide a method for the adaptation of the incident radiation Lyman line profiles (Lyman-α and higher lines) to a specific date. Moreover, we analyse how the change in the incident radiation influences the synthetic spectra produced by the radiative transfer modelling.
Methods: We used SOHO/SUMER Lyman-α raster scans obtained without the use of the attenuator in various quiet-Sun regions on the solar disk. The observations were performed on three consecutive days (June 24, 25, and 26, 2008) during a period of minimum solar activity. The reference Lyman-α profile was obtained as a spatial average over eight available raster scans. To take into account the Lyman-α variation with the solar cycle, we used the LISIRD composite Lyman-α index. To estimate the influence of the change in the incident radiation in the Lyman lines on the results of radiative transfer models, we used a 2D prominence fine structure model.
Results: We present the reference quiet-Sun Lyman-α profile and a table of coefficients describing the variation of the Lyman lines with the solar cycle throughout the lifetime of SOHO. The analysis of the influence of the change in the incident radiation shows that the synthetic spectra are strongly affected by the modification of the incident radiation boundary condition. The most pronounced impact is on the central and integrated intensities of the Lyman lines. There, the change in the synthetic spectra can often have the same amplitude as the change in the incident radiation itself. The impact on the specific intensities in the peaks of reversed Lyman-line profiles is smaller but still significant. The hydrogen Hα line can also be considerably affected, despite the fact that the Hα radiation from the solar disk does not vary with the solar cycle.

Data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/644/A109 Title: IRIS Mg II Observations and Non-LTE Modeling of Off-limb Spicules Authors: Tei, A.; Gunár, S.; Heinzel, P.; Okamoto, T. J.; Štěpán, J.; Jejčič, S.; Shibata, K. Bibcode: 2020AGUFMSH0010008T Altcode: We investigated the off-limb spicules observed in the Mg II h and k spectral lines by Interface Region Imaging Spectrograph (IRIS) in a solar polar coronal hole. We analyzed the large data set of obtained spectra to extract quantitative information about the line intensities, line shifts, and line widths. The observed Mg II line profiles are broad and double peaked at lower altitudes, broad but flat topped at middle altitudes, and narrow and single peaked with the largest Doppler shifts at higher altitudes. We used one-dimensional non-LTE vertical slab models (i.e., models that consider departures from local thermodynamic equilibrium) in single-slab and multi-slab configurations to interpret the observations and to investigate how a superposition of spicules along a line of sight (LOS) affects the synthetic Mg II line profiles. The employed multi-slab models are either static, i.e., without any LOS velocities, or assume randomly assigned LOS velocities of individual slabs, representing the spicule dynamics. We performed such single-slab and multi-slab modeling for a broad set of model input parameters and examined the dependence of the Mg II line profiles on these parameters. In this presentation, we demonstrate that the observed line widths of the Mg h and k line profiles are strongly affected by the presence of multiple spicules along the LOS. We also show that the profiles obtained at higher altitudes can be reproduced by single-slab models representing individual spicules. We found that the multi-slab model with a random distribution of the LOS velocities ranging from −25 to 25 km/s can well reproduce the width and the shape of the Mg II profiles observed at middle altitudes. Title: VizieR Online Data Catalog: Quiet-sun hydrogen Lyman-alpha line profile (Gunar+, 2020) Authors: Gunar, S.; Schwartz, P.; Koza, J.; Heinzel, P. Bibcode: 2020yCat..36440109G Altcode: The reference quiet-Sun Lyman-alpha profile obtained as an average over eight SOHO/SUMER raster scans obtained between 2008/06/24 and 2008/06/26. The central wavelength lambda0 of the Lyman-alpha line is 1215.67Å (121.567nm).

The symmetrized reference quiet-Sun Lyman-alpha profile obtained by symmetrization of the full profile from Table A1. Only the right half of the profile is provided. The central wavelength lambda0 of the Lyman-alpha line is 1215.67Å (121.567nm).

table B1 ~List of coefficients describing the variation of the solar radiation in the Lyman-alpha and higher Lyman lines. The coefficients were derived from 400-day averaged LISIRD Lyman-alpha composite index (Machol et al., 2019E&SS....6.2263M). We provide coefficients for selected dates throughout the lifetime of SOHO. Coefficients for the Lyman-alpha line are computed with respect to the date 2008/06/25. Coefficients for the higher Lyman lines are computed with respect to the date 1996/05/15 used in Warren et al. (1998ApJS..119..105W).

(3 data files). Title: IRIS Mg II Observations and Non-LTE Modeling of Off-limb Spicules in a Solar Polar Coronal Hole Authors: Tei, Akiko; Gunár, Stanislav; Heinzel, Petr; Okamoto, Takenori J.; Štěpán, Jiří; Jejčič, Sonja; Shibata, Kazunari Bibcode: 2020ApJ...888...42T Altcode: 2019arXiv191112243T We investigated the off-limb spicules observed in the Mg II h and k lines by IRIS in a solar polar coronal hole. We analyzed the large data set of obtained spectra to extract quantitative information about the line intensities, shifts, and widths. The observed Mg II line profiles are broad and double peaked at lower altitudes, broad but flat topped at middle altitudes, and narrow and single peaked with the largest Doppler shifts at higher altitudes. We use one-dimensional non-LTE vertical slab models (I.e., models that consider departures from local thermodynamic equilibrium) in single-slab and multi-slab configurations to interpret the observations and to investigate how a superposition of spicules along the line of sight (LOS) affects the synthetic Mg II line profiles. The used multi-slab models either are static, I.e., without any LOS velocities, or assume randomly assigned LOS velocities of individual slabs, representing the spicule dynamics. We conducted such single-slab and multi-slab modeling for a broad set of model input parameters and showed the dependence of the Mg II line profiles on these parameters. We demonstrated that the observed line widths of the h and k line profiles are strongly affected by the presence of multiple spicules along the LOS. We later showed that the profiles obtained at higher altitudes can be reproduced by single-slab models representing individual spicules. We found that the multi-slab model with a random distribution of the LOS velocities ranging from -25 to 25 km s-1 can well reproduce the width and the shape of Mg II profiles observed at middle altitudes. Title: Diagnostics of the Prominence Plasma from Hα and Mg II Spectral Observations Authors: Ruan, Guiping; Jejčič, Sonja; Schmieder, Brigitte; Mein, Pierre; Mein, Nicole; Heinzel, Petr; Gunár, Stanislav; Chen, Yao Bibcode: 2019ApJ...886..134R Altcode: The goal of this paper is to derive the physical conditions of the prominence observed on 2017 March 30. To do so, we use a unique set of data in Mg II lines obtained with the space-borne Interface Region Imaging Spectrograph (IRIS) and in Hα line with the ground-based Multi-Channel Subtractive Double Pass spectrograph operating at the Meudon solar tower. Here, we analyze the prominence spectra of Mg II h and k lines, and the Hα line in the part of the prominence which is visible in both sets of lines. We compute a grid of 1D NLTE (i.e., departures from the local thermodynamical equilibrium) models providing synthetic spectra of Mg II k and h, and Hα lines in a large space of model input parameters (temperature, density, pressure, and microturbulent velocity). We compare Mg II and Hα line profiles observed in 75 positions of the prominence with the synthetic profiles from the grid of models. These models allow us to compute the relationships between the integrated intensities and between the optical thickness in Hα and Mg II k lines. The optical thickness τ is between 0.05 and 2, and {τ }Mg{{II}}{{k}}} is between 3 and 200. We show that the relationship of the observed integrated intensities agrees well with the synthetic integrated intensities for models with a higher microturbulence (16 km s-1) and T around 8000 K, ne = 1.5 × 1010 cm-3, p = 0.05 dyne. In this case, large microturbulence values could be a way to take into account the large mixed velocities existing in the observed prominence. Title: 2D non-LTE modelling of a filament observed in the Hα line with the DST/IBIS spectropolarimeter Authors: Schwartz, P.; Gunár, S.; Jenkins, J. M.; Long, D. M.; Heinzel, P.; Choudhary, D. P. Bibcode: 2019A&A...631A.146S Altcode: 2019arXiv191003607S Context. We study a fragment of a large quiescent filament observed on May 29, 2017 by the Interferometric BIdimensional Spectropolarimeter (IBIS) mounted at the Dunn Solar Telescope. We focus on its quiescent stage prior to its eruption.
Aims: We analyse the spectral observations obtained in the Hα line to derive the thermodynamic properties of the plasma of the observed fragment of the filament.
Methods: We used a 2D filament model employing radiative transfer computations under conditions that depart from the local thermodynamic equilibrium. We employed a forward modelling technique in which we used the 2D model to produce synthetic Hα line profiles that we compared with the observations. We then found the set of model input parameters, which produces synthetic spectra with the best agreement with observations.
Results: Our analysis shows that one part of the observed fragment of the filament is cooler, denser, and more dynamic than its other part that is hotter, less dense, and more quiescent. The derived temperatures in the first part range from 6000 K to 10 000 K and in the latter part from 11 000 K to 14 000 K. The gas pressure is 0.2-0.4 dyn cm-2 in the first part and around 0.15 dyn cm-2 in the latter part. The more dynamic nature of the first part is characterised by the line-of-sight velocities with absolute values of 6-7 km s-1 and microturbulent velocities of 8-9 km s-1. On the other hand, the latter part exhibits line-of-sight velocities with absolute values 0-2.5 km s-1 and microturbulent velocities of 4-6 km s-1. Title: The influence of Hinode/SOT NFI instrumental effects on the visibility of simulated prominence fine structures in Hα Authors: Gunár, S.; Jurčák, J.; Ichimoto, K. Bibcode: 2019A&A...629A.118G Altcode: Context. Models of entire prominences with their numerous fine structures distributed within the prominence magnetic field use approximate radiative transfer techniques to visualize the simulated prominences. However, to accurately compare synthetic images of prominences obtained in this way with observations and to precisely analyze the visibility of even the faintest prominence features, it is important to take into account the influence of instrumental properties on the synthetic spectra and images.
Aims: In the present work, we investigate how synthetic Hα images of simulated prominences are impacted by the instrumental effects induced by the Narrowband Filter Imager (NFI) of the Solar Optical Telescope (SOT) onboard the Hinode satellite.
Methods: To process the synthetic Hα images provided by 3D Whole-Prominence Fine Structure (WPFS) models into SOT-like synthetic Hα images, we take into account the effects of the integration over the theoretical narrow-band transmission profile of NFI Lyot filter, the influence of the stray-light and point spread function (PSF) of Hinode/SOT, and the observed noise level. This allows us to compare the visibility of the prominence fine structures in the SOT-like synthetic Hα images with the synthetic Hα line-center images used by the 3D models and with a pair of Hinode/SOT NFI observations of quiescent prominences.
Results: The comparison between the SOT-like synthetic Hα images and the synthetic Hα line-center images shows that all large and small-scale features are very similar in both visualizations and that the same very faint prominence fine structures can be discerned in both. This demonstrates that the computationally efficient Hα line-center visualization technique can be reliably used for the purpose of visualization of complex 3D prominence models. In addition, the qualitative comparison between the SOT-like synthetic images and prominence observations shows that the 3D WPFS models can reproduce large-scale prominence features rather well. However, the distribution of the prominence fine structures is significantly more diffuse in the observations than in the models and the diffuse intensity areas surrounding the observed prominences are also not present in the synthetic images. We also found that the maximum intensities reached in the models are about twice as high as those present in the observations-an indication that the mass-loading assumed in the present 3D WPFS models might be too large. Title: Modeling the Scattering Polarization of the Hydrogen Lyα Line Observed by CLASP in a Filament Channel Authors: Štěpán, J.; Trujillo Bueno, J.; Gunár, S.; Heinzel, P.; del Pino Alemán, T.; Kano, R.; Ishikawa, R.; Narukage, N.; Bando, T.; Winebarger, A.; Kobayashi, K.; Auchère, F. Bibcode: 2019ASPC..526..165S Altcode: The 400 arcsec spectrograph slit of CLASP crossed mainly quiet regions of the solar chromosphere, from the limb towards the solar disk center. Interestingly, in the CLASP slit-jaw images and in the SDO images of the He II line at 304 Å, we can identify a filament channel (FC) extending over more than 60 arcsec crossing the slit of the spectrograph. In order to interpret the peculiar spatial variation of the Q/I and U/I signals observed by CLASP in the hydrogen Lyα line (1216 Å), we perform multi-dimensional radiative transfer modeling in given filament models. In this contribution, we show the first results of the two-dimensional calculations we have carried out, with the aim of determining the filament thermal and magnetic structure by comparing the theoretical and the observed polarization signals. Our results suggest that the temperature gradients in the filament observed by CLASP are significantly larger than previously thought. Title: 3D Whole-Prominence Fine Structure Model as a Test Case for Verification and Development of Magnetic Field Inversion Techniques Authors: Gunár, S.; Mackay, D. H.; Štěpán, J.; Heinzel, P.; Trujillo Bueno, J. Bibcode: 2019ASPC..526..159G Altcode: We show the potential of a new 3D whole-prominence fine structure model to serve as a well-controlled yet complex environment for testing inversion techniques for the magnetic field inference. The realistic 3D magnetic field and plasma environment provided by the model can be used for the direct synthesis of spectro-polarimetric data. Such synthetic data can be analyzed by advanced inversion tools and their results compared with the known properties provided by the model. Title: Importance of the Hα Visibility and Projection Effects for the Interpretation of Prominence Fine-structure Observations Authors: Gunár, Stanislav; Dudík, Jaroslav; Aulanier, Guillaume; Schmieder, Brigitte; Heinzel, Petr Bibcode: 2018ApJ...867..115G Altcode: We construct a new 3D Whole-prominence Fine-structure (WPFS) model based on a prominence magnetic field configuration designed to qualitatively approximate the morphology of a quiescent prominence observed on 2010 June 22. The model represents an entire prominence with its numerous fine structures formed by a prominence plasma located in dips in the prominence magnetic field. We use the constructed 3D model and employ a radiative-transfer-based Hα visualization method to analyze the Hα visibility of prominence fine structures and its effect on the perceived morphology of observed and modeled prominences. We qualitatively compare three techniques used for visualization of modeled prominences—visualizations drawing magnetic dips up to a height of 1 pressure scale height, drawing the full extent of magnetic dips, and the synthetic Hα visualization—and discuss their suitability for direct comparison between models and observations of prominences and filaments. We also discuss the role of visibility of the prominence fine structures in the estimation of the total height of prominences, which may indicate the height of pre-erupting flux ropes. This parameter is critical for the observational determination of the flux-rope stability. In addition, we employ the WPFS model to assess the effects caused by a projection of the naturally three-dimensional and heterogeneous prominences onto a two-dimensional plane of the sky. We discuss here how the morphological structures of prominences differ when observed in projections from different viewing angles. We also discuss the shapes of the dipped magnetic field lines and the perceived projection of motions of prominence fine structures along such field lines. Title: Statistical analysis of UV spectra of a quiescent prominence observed by IRIS Authors: Jejčič, S.; Schwartz, P.; Heinzel, P.; Zapiór, M.; Gunár, S. Bibcode: 2018A&A...618A..88J Altcode: 2018arXiv180705767J Context. The paper analyzes the structure and dynamics of a quiescent prominence that occurred on October 22, 2013 and was observed by several instruments including the Interface Region Imaging Spectrograph (IRIS).
Aims: We aim to determine the physical characteristics of the observed prominence using Mg II k and h (2796 and 2803 Å), C II (1334 and 1336 Å), and Si IV (1394 Å) lines observed by IRIS. In addition we study the dynamical behavior of the prominence.
Methods: We employed the one-dimensional non-LTE (departures from the local thermodynamic equilibrium - LTE) modeling of Mg II lines assuming static isothermal-isobaric slabs. We selected a large grid of models with realistic input parameters expected for quiescent prominences (temperature, gas pressure, effective thickness, microturbulent velocity, height above the solar surface) and computed synthetic Mg II lines. The method of Scargle periodograms was used to detect possible prominence oscillations.
Results: We analyzed 2160 points of the observed prominence in five different sections along the slit averaged over ten pixels due to low signal to noise ratio in the C II and Si IV lines. We computed the integrated intensity for all studied lines, while the central intensity and reversal ratio was determined only for both Mg II and C II 1334 lines. We plotted several correlations: time evolution of the integrated intensities and central intensities, scatter plots between all combinations of line integrated intensities, and reversal ratio as a function of integrated intensity. We also compared Mg II observations with the models. Results show that more than two-thirds of Mg II profiles and about one-half of C II 1334 profiles are reversed. Profiles of Si IV are generally unreversed. The Mg II and C II lines are optically thick, while the Si IV line is optically thin.
Conclusions: The studied prominence shows no global oscillations in the Mg II and C II lines. Therefore, the observed time variations are caused by random motions of fine structures with velocities up to 10 km s-1. The observed average ratio of Mg II k to Mg II h line intensities can be used to determine the prominence's characteristic temperature. Certain disagreements between observed and synthetic line intensities of Mg II lines point to the necessity of using more complex two-dimensional multi-thread modeling in the future.

The movies associated to Figs. 1 and 7 are available at https://www.aanda.org Title: On the Dynamic Nature of a Quiescent Prominence Observed by IRIS and MSDP Spectrographs Authors: Ruan, Guiping; Schmieder, Brigitte; Mein, Pierre; Mein, Nicole; Labrosse, Nicolas; Gunár, Stanislav; Chen, Yao Bibcode: 2018ApJ...865..123R Altcode: Quiescent solar prominences are generally considered to have a stable large-scale structure. However, they consist of multiple small-scale structures that are often significantly dynamic. To understand the nature of prominence plasma dynamics we use the high spatial, temporal, and spectral resolution observations obtained by Interface Region Imaging Spectrograph (IRIS) during a coordinated campaign with the Multichannel Subtractive Double Pass spectrograph at the Meudon Solar Tower. Detailed analysis of the IRIS observations of Mg II lines, including the analysis of Dopplershift and line width obtained with two different methods (quantile method and Gaussian-fit method) are discussed in the frame of the dynamic nature of the structures. Large-scale coherent blueshift and redshift features are observed in Mg II lines and Hα exhibiting a slow evolution during 1:40 hr of observations. We explain the presence of several significantly asymmetric peaks in the observed Mg II line profiles by the presence of several prominence fine structures moving with different velocities located along the line of sight (LOS). In such a case, the decrease of the intensity of individual components of the observed spectra with the distance from the central wavelength can be explained by the Doppler dimming effect. We show that C II line profiles may be used to confirm the existence of multi-components along the LOS. Title: 3D modelling of magnetic field and plasma structure of entire prominences Authors: Gunár, Stanislav; Anzer, Ulrich; Heinzel, Petr; Mackay, Duncan Bibcode: 2018cosp...42E1315G Altcode: The 3D Whole-Prominence Fine Structure (WPFS) model allows us for the first time to simulate entire prominences/filaments including their numerous fine structures. This model combines a 3D magnetic field configuration of an entire prominence obtained from non-linear force-free field simulations, with a detailed description of the prominence plasma. The plasma is located in magnetic dips in hydrostatic equilibrium and is distributed along hundreds of fine structures within the 3D magnetic model. The prominence plasma has realistic density and temperature distributions including the prominence-corona transition region. This allows us to produce synthetic H-alpha images of simulated prominences both in emission on the solar limb and in absorption against the solar disk (viewed as filaments) using a single model.Such 3D WPFS model provides us with consistent information about the prominence magnetic field configuration, prominence fine structure plasma and its radiative output. Moreover, we are able to follow the evolution of modeled prominences caused by changes of the underlying photospheric magnetic flux distribution. Thanks to these capabilities we can study links between the photospheric flux distribution, prominence magnetic field configuration, distribution and composition of the prominence plasma and its observable signatures. These relationships are important for interpretation of the observed imaging and spectral/spectropolarimetric data and for inference of the properties of the prominence magnetic field. Title: Dynamics in quiescent prominences observed by the IRIS and MSDP spectrographs Authors: Gunár, Stanislav; Schmieder, Brigitte; Ruan, Guiping; Mein, Pierre; Heinzel, Petr Bibcode: 2018cosp...42E1314G Altcode: Quiescent solar prominences are generally considered to be stable. However, these prominences consist of a multitude of small-scale structures or threads that are often significantly dynamic. To understand the nature of the plasma dynamics we use the high spatial, temporal and spectral resolution observations obtained by IRIS during coordinated campaign with the MSDP spectrograph at the Meudon Solar Tower. Mg II h and k lines observed by IRIS represent a good diagnostic tool for investigation of the prominence fine structure dynamics, as they are optically thick under the prominence conditions. We will present detailed IRIS observations of Mg II lines. We explain significant asymmetries in the observed Mg II spectra by the presence of several threads located along the line of sight with different velocities. In such a case, the decrease of the intensity of individual components of the observed spectra with the distance from the central wavelength can be explained by the Doppler dimming effect. To interpret the observed Mg II profiles in terms of dynamics we use 1D or 2D radiative transfer models including a prominence-corona transition region. We also show that the H-alpha line which is optically thinner than the Mg II doublet is an important constrain for the radiative transfer radiation modelling. Title: Can 3D whole-prominence fine structure models be used for assessment of the prominence plasma mass and distribution prior to the onset of CMEs? Authors: Gunár, Stanislav; Schmieder, Brigitte; Aulanier, Guillaume; Anzer, Ulrich; Heinzel, Petr; Mackay, Duncan; Dudik, Jaroslav Bibcode: 2018cosp...42E1316G Altcode: Two complex 3D models of entire prominences including their numerous fine structures were recently developed. The first 3D Whole-Prominence Fine Structure (WPFS) model was developed by Gunár and Mackay. The second 3D WPFS model was put forward by Gunár, Aulanier, Dudík, Heinzel, and Schmieder. These 3D prominence models combine simulations of the 3D magnetic field configuration of an entire prominence with a detailed description of the prominence plasma. The plasma is located in magnetic dips in hydrostatic equilibrium and is distributed along hundreds of fine structures. The assumed prominence plasma has realistic density and temperature distributions including the prominence-corona transition region.These 3D WPFS models allow us to study the distribution and the mass of the prominence plasma contained in prominence magnetic field configurations. These can be crucial during the onset and early evolution of CMEs. Moreover, prominence plasma represents a bulk of the material ejected by CMEs into the interplanetary space. Here, we investigate the potential of using the 3D WPFS models for assessment of the role the prominence plasma plays in the initiation and evolution of CMEs. Title: Visibility of Prominences Using the He I D3 Line Filter on the PROBA-3/ASPIICS Coronagraph Authors: Jejčič, S.; Heinzel, P.; Labrosse, N.; Zhukov, A. N.; Bemporad, A.; Fineschi, S.; Gunár, S. Bibcode: 2018SoPh..293...33J Altcode: 2018arXiv180700155J We determine the optimal width and shape of the narrow-band filter centered on the He I D3 line for prominence and coronal mass ejection (CME) observations with the ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun) coronagraph onboard the PROBA-3 (Project for On-board Autonomy) satellite, to be launched in 2020. We analyze He I D3 line intensities for three representative non-local thermal equilibrium prominence models at temperatures 8, 30, and 100 kK computed with a radiative transfer code and the prominence visible-light (VL) emission due to Thomson scattering on the prominence electrons. We compute various useful relations at prominence line-of-sight velocities of 0, 100, and 300 km s−1 for 20 Å wide flat filter and three Gaussian filters with a full-width at half-maximum (FWHM) equal to 5, 10, and 20 Å to show the relative brightness contribution of the He I D3 line and the prominence VL to the visibility in a given narrow-band filter. We also discuss possible signal contamination by Na I D1 and D2 lines, which otherwise may be useful to detect comets. Our results mainly show that i) an optimal narrow-band filter should be flat or somewhere between flat and Gaussian with an FWHM of 20 Å in order to detect fast-moving prominence structures, ii) the maximum emission in the He I D3 line is at 30 kK and the minimal at 100 kK, and iii) the ratio of emission in the He I D3 line to the VL emission can provide a useful diagnostic for the temperature of prominence structures. This ratio is up to 10 for hot prominence structures, up to 100 for cool structures, and up to 1000 for warm structures. Title: Quiescent Prominences in the Era of ALMA. II. Kinetic Temperature Diagnostics Authors: Gunár, Stanislav; Heinzel, Petr; Anzer, Ulrich; Mackay, Duncan H. Bibcode: 2018ApJ...853...21G Altcode: We provide the theoretical background for diagnostics of the thermal properties of solar prominences observed by the Atacama Large Millimeter/submillimeter Array (ALMA). To do this, we employ the 3D Whole-Prominence Fine Structure (WPFS) model that produces synthetic ALMA-like observations of a complex simulated prominence. We use synthetic observations derived at two different submillimeter/millimeter (SMM) wavelengths—one at a wavelength at which the simulated prominence is completely optically thin and another at a wavelength at which a significant portion of the simulated prominence is optically thick—as if these were the actual ALMA observations. This allows us to develop a technique for an analysis of the prominence plasma thermal properties from such a pair of simultaneous high-resolution ALMA observations. The 3D WPFS model also provides detailed information about the distribution of the kinetic temperature and the optical thickness along any line of sight. We can thus assess whether the measure of the kinetic temperature derived from observations accurately represents the actual kinetic temperature properties of the observed plasma. We demonstrate here that in a given pixel the optical thickness at the wavelength at which the prominence plasma is optically thick needs to be above unity or even larger to achieve a sufficient accuracy of the derived information about the kinetic temperature of the analyzed plasma. Information about the optical thickness cannot be directly discerned from observations at the SMM wavelengths alone. However, we show that a criterion that can identify those pixels in which the derived kinetic temperature values correspond well to the actual thermal properties in which the observed prominence can be established. Title: Quiescent Prominences in the Era of ALMA: Simulated Observations Using the 3D Whole-prominence Fine Structure Model Authors: Gunár, Stanislav; Heinzel, Petr; Mackay, Duncan H.; Anzer, Ulrich Bibcode: 2016ApJ...833..141G Altcode: We use the detailed 3D whole-prominence fine structure model to produce the first simulated high-resolution ALMA observations of a modeled quiescent solar prominence. The maps of synthetic brightness temperature and optical thickness shown in the present paper are produced using a visualization method for synthesis of the submillimeter/millimeter radio continua. We have obtained the simulated observations of both the prominence at the limb and the filament on the disk at wavelengths covering a broad range that encompasses the full potential of ALMA. We demonstrate here extent to which the small-scale and large-scale prominence and filament structures will be visible in the ALMA observations spanning both the optically thin and thick regimes. We analyze the relationship between the brightness and kinetic temperature of the prominence plasma. We also illustrate the opportunities ALMA will provide for studying the thermal structure of the prominence plasma from the cores of the cool prominence fine structure to the prominence-corona transition region. In addition, we show that detailed 3D modeling of entire prominences with their numerous fine structures will be important for the correct interpretation of future ALMA observations of prominences. Title: Properties of the prominence magnetic field and plasma distributions as obtained from 3D whole-prominence fine structure modeling Authors: Gunár, S.; Mackay, D. H. Bibcode: 2016A&A...592A..60G Altcode:
Aims: We analyze distributions of the magnetic field strength and prominence plasma (temperature, pressure, plasma β, and mass) using the 3D whole-prominence fine structure model.
Methods: The model combines a 3D magnetic field configuration of an entire prominence, obtained from non-linear force-free field simulations, with a detailed semi-empirically derived description of the prominence plasma. The plasma is located in magnetic dips in hydrostatic equilibrium and is distributed along multiple fine structures within the 3D magnetic model.
Results: We show that in the modeled prominence, the variations of the magnetic field strength and its orientation are insignificant on scales comparable to the smallest dimensions of the observed prominence fine structures. We also show the ability of the 3D whole-prominence fine structure model to reveal the distribution of the prominence plasma with respect to its temperature within the prominence volume. This provides new insights into the composition of the prominence-corona transition region. We further demonstrate that the values of the plasma β are small throughout the majority of the modeled prominences when realistic photospheric magnetic flux distributions and prominence plasma parameters are assumed. While this is generally true, we also find that in the region with the deepest magnetic dips, the plasma β may increase towards unity. Finally, we show that the mass of the modeled prominence plasma is in good agreement with the mass of observed non-eruptive prominences. Title: Solar Science with the Atacama Large Millimeter/Submillimeter Array—A New View of Our Sun Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu, B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin, P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz, A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.; Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary, D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.; Selhorst, C. L.; Barta, M. Bibcode: 2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere—a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases. Title: ALMA Observations of the Sun in Cycle 4 and Beyond Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.; Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.; Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson, M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.; Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov, V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões, P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig, A.; White, S.; Yagoubov, P.; Zaqarashvili, T. Bibcode: 2016arXiv160100587W Altcode: This document was created by the Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) in preparation of the first regular observations of the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA), which are anticipated to start in ALMA Cycle 4 in October 2016. The science cases presented here demonstrate that a large number of scientifically highly interesting observations could be made already with the still limited solar observing modes foreseen for Cycle 4 and that ALMA has the potential to make important contributions to answering long-standing scientific questions in solar physics. With the proposal deadline for ALMA Cycle 4 in April 2016 and the Commissioning and Science Verification campaign in December 2015 in sight, several of the SSALMON Expert Teams composed strategic documents in which they outlined potential solar observations that could be feasible given the anticipated technical capabilities in Cycle 4. These documents have been combined and supplemented with an analysis, resulting in recommendations for solar observing with ALMA in Cycle 4. In addition, the detailed science cases also demonstrate the scientific priorities of the solar physics community and which capabilities are wanted for the next observing cycles. The work on this White Paper effort was coordinated in close cooperation with the two international solar ALMA development studies led by T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be further updated until the beginning of Cycle 4 in October 2016. In particular, we plan to adjust the technical capabilities of the solar observing modes once finally decided and to further demonstrate the feasibility and scientific potential of the included science cases by means of numerical simulations of the solar atmosphere and corresponding simulated ALMA observations. Title: SSALMON - The Solar Simulations for the Atacama Large Millimeter Observatory Network Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu, B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.; Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.; Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier, A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M. Bibcode: 2015AdSpR..56.2679W Altcode: 2015arXiv150205601W The Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) was initiated in 2014 in connection with two ALMA development studies. The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful new tool, which can also observe the Sun at high spatial, temporal, and spectral resolution. The international SSALMONetwork aims at co-ordinating the further development of solar observing modes for ALMA and at promoting scientific opportunities for solar physics with particular focus on numerical simulations, which can provide important constraints for the observing modes and can aid the interpretation of future observations. The radiation detected by ALMA originates mostly in the solar chromosphere - a complex and dynamic layer between the photosphere and corona, which plays an important role in the transport of energy and matter and the heating of the outer layers of the solar atmosphere. Potential targets include active regions, prominences, quiet Sun regions, flares. Here, we give a brief overview over the network and potential science cases for future solar observations with ALMA. Title: 3D Whole-prominence Fine Structure Modeling. II. Prominence Evolution Authors: Gunár, Stanislav; Mackay, Duncan H. Bibcode: 2015ApJ...812...93G Altcode: We use the new three-dimensional (3D) whole-prominence fine structure model to study the evolution of prominences and their fine structures in response to changes in the underlying photospheric magnetic flux distribution. The applied model combines a detailed 3D prominence magnetic field configuration with a realistic description of the prominence plasma distributed along multiple fine structures. In addition, we utilize an approximate Hα visualization technique to study the evolution of the visible cool prominence plasma both in emission (prominence) and absorption (filament). We show that the initial magnetic field configuration of the modeled prominence is significantly disturbed by the changing position of a single polarity of a magnetic bipole as the bipole is advected toward the main body of the filament. This leads to the creation of a barb, which becomes the dominant feature visible in the synthetic Hα images of both the prominence and filament views. The evolution of the bipole also creates conditions that lead to the disappearance and reappearance of large portions of the main body. We also show that an arch-like region containing a dark void (a bubble) can be naturally produced in the synthetic prominence Hα images. While not visible in terms of the magnetic field lines, it is due to a lack of Hα emission from low-pressure, low-density plasma located in shallow magnetic dips lying along the lines of sight intersecting the dark void. In addition, a quasi-vertical small-scale feature consisting of short and deep dips, piled one above the other, is produced. Title: High-resolution fine-structure synthetic imaging of an entire prominence using 3D whole-prominence fine structure modelling Authors: Gunar, Stanislav; Mackay, Duncan; Heinzel, Petr; Anzer, Ulrich Bibcode: 2015IAUGA..2251323G Altcode: The newly developed 3D whole-prominence fine structure (WPFS) model (Gunár & Mackay 2015) allows us for the first time to simulate entire prominences/filaments including their numerous fine structures. This model combines a 3D magnetic field configuration of an entire prominence obtained from non-linear force-free field simulations, with a detailed description of the prominence plasma. The plasma is located in magnetic dips in hydrostatic equilibrium and is distributed along hundreds of fine structures within the 3D magnetic model. The prominence plasma has realistic density and temperature distributions including the prominence-corona transition region.To produce the high-resolution synthetic H-alpha images of the WPFS model we use a novel fast approximate radiative transfer visualization technique (Heinzel et al. 2015). This allows us for the first time to produce images of the prominences in emission on the solar limb and filaments in absorption against the solar disk using a single model. The prominence plasma and magnetic field are described in the WPFS model on scales that allow us to produce synthetic images with resolution matching that of the state-of-the-art observations, or indeed that of the upcoming solar observatories, such as DKIST or Solar-C. Moreover, to complement the prominence/filament synthetic images we have consistent information about the magnetic field and plasma parameters everywhere in the modeled prominences. This allows us to investigate the apparent puzzling nature of the observed prominence and filament fine structures. We can also study the connections between the local configuration of the magnetic field and the observable structure of the finest prominence/filament features. In addition, we are able to investigate the prominence evolution. We can consistently study the influence of the varying photospheric flux distribution on the prominence magnetic field configuration and its effect on the observable prominence plasma. Title: Multi-wavelength synthetic flare loops from 2D simulations with FLASH Authors: none Heinzel, Petr; Gunar, Stanislav; Falewicz, Robert; Rudawy, Pawel Bibcode: 2015IAUGA..2258400N Altcode: MHD code FLASH has been used to simulate the temporal evolution of the flare-loop system. Our 2D approach assumes a long arcade of flare loops anchored in the chromospheric ribbons. As the result of a gradual reconnection, the loop system is growing and the flare ribbons are being more and more separated in agreement with typical observations. Simultaneously, hot flare loops cool down and new hot loops appear next to them. We simulate the temporal evolution of the whole arcade of loops and synthesize the visibility of loops at various stages of cooling. The coolest loops finally appear in the hydrogen H-alpha line and are visualized using our new approximate method. The resulting evolution demonstrates well both the spatial and temporal behavior of multi-temperature loops, including their dynamics. Title: Fast approximate radiative transfer method for visualizing the fine structure of prominences in the hydrogen Hα line Authors: Heinzel, P.; Gunár, S.; Anzer, U. Bibcode: 2015A&A...579A..16H Altcode:
Aims: We present a novel approximate radiative transfer method developed to visualize 3D whole-prominence models with multiple fine structures using the hydrogen Hα spectral line.
Methods: This method employs a fast line-of-sight synthesis of the Hα line profiles through the whole 3D prominence volume and realistically reflects the basic properties of the Hα line formation in the cool and low-density prominence medium. The method can be applied both to prominences seen above the limb and filaments seen against the disk.
Results: We provide recipes for the use of this method for visualizing the prominence or filament models that have multiple fine structures. We also perform tests of the method that demonstrate its accuracy under prominence conditions.
Conclusions: We demonstrate that this fast approximate radiative transfer method provides realistic synthetic Hα intensities useful for a reliable visualization of prominences and filaments. Such synthetic high-resolution images of modeled prominences/filaments can be used for a direct comparison with high-resolution observations. Title: Non-LTE modelling of prominence fine structures using hydrogen Lyman-line profiles Authors: Schwartz, P.; Gunár, S.; Curdt, W. Bibcode: 2015A&A...577A..92S Altcode:
Aims: We perform a detailed statistical analysis of the spectral Lyman-line observations of the quiescent prominence observed on May 18, 2005.
Methods: We used a profile-to-profile comparison of the synthetic Lyman spectra obtained by 2D single-thread prominence fine-structure model as a starting point for a full statistical analysis of the observed Lyman spectra. We employed 2D multi-thread fine-structure models with random positions and line-of-sight velocities of each thread to obtain a statistically significant set of synthetic Lyman-line profiles. We used for the first time multi-thread models composed of non-identical threads and viewed at line-of-sight angles different from perpendicular to the magnetic field.
Results: We investigated the plasma properties of the prominence observed with the SoHO/SUMER spectrograph on May 18, 2005 by comparing the histograms of three statistical parameters characterizing the properties of the synthetic and observed line profiles. In this way, the integrated intensity, Lyman decrement ratio, and the ratio of intensity at the central reversal to the average intensity of peaks provided insight into the column mass and the central temperature of the prominence fine structures. Title: 3D Whole-Prominence Fine Structure Modeling Authors: Gunár, Stanislav; Mackay, Duncan H. Bibcode: 2015ApJ...803...64G Altcode: We present the first 3D whole-prominence fine structure model. The model combines a 3D magnetic field configuration of an entire prominence obtained from nonlinear force-free field simulations, with a detailed description of the prominence plasma. The plasma is located in magnetic dips in hydrostatic equilibrium and is distributed along multiple fine structures within the 3D magnetic model. Through the use of a novel radiative transfer visualization technique for the Hα line such plasma-loaded magnetic field model produces synthetic images of the modeled prominence comparable with high-resolution observations. This allows us for the first time to use a single technique to consistently study, in both emission on the limb and absorption against the solar disk, the fine structures of prominences/filaments produced by a magnetic field model. Title: Understanding the Mg II and Hα Spectra in a Highly Dynamical Solar Prominence Authors: Heinzel, P.; Schmieder, B.; Mein, N.; Gunár, S. Bibcode: 2015ApJ...800L..13H Altcode: Mg ii h and k and Hα spectra in a dynamical prominence have been obtained along the slit of the Interface Region Imaging Spectrograph (IRIS) and with the Meudon Multi-channel Subtractive Double Pass spectrograph on 2013 September 24, respectively. Single Mg ii line profiles are not much reversed, while at some positions along the IRIS slit the profiles show several discrete peaks that are Doppler-shifted. The intensity of these peaks is generally decreasing with their increasing Doppler shift. We interpret this unusual behavior as being due to the Doppler dimming effect. We discuss the possibility to interpret the unreversed single profiles by using a two-dimensional (2D) model of the entire prominence body with specific radiative boundary conditions. We have performed new 2D isothermal-isobaric modeling of both Hα and Mg ii lines and show the ability of such models to account for the line profile variations as observed. However, the Mg ii line-center intensities require the model with a temperature increase toward the prominence boundary. We show that even simple one-dimensional (1D) models with a prominence-to-corona transition region (PCTR) fit the observed Mg ii and Hα lines quite well, while the isothermal-isobaric models (1D or 2D) are inconsistent with simultaneous observations in the Mg ii h and k and Hα lines, meaning that the Hα line provides a strong additional constraint on the modeling. IRIS far-UV detection of the C ii lines in this prominence seems to provide a direct constraint on the PCTR part of the model. Title: Multi-Wavelength Eclipse Observations of a Quiescent Prominence Authors: Jejčič, S.; Heinzel, P.; Zapiór, M.; Druckmüller, M.; Gunár, S.; Kotrč, P. Bibcode: 2014SoPh..289.2487J Altcode: 2014SoPh..tmp...30J We construct the maps of temperatures, geometrical thicknesses, electron densities and gas pressures in a quiescent prominence. For this we use the RGB signal of the prominence visible-light emission detected during the total solar eclipse of 1 August 2008 in Mongolia and quasi-simultaneous Hα spectra taken at Ondřejov Observatory. The method of disentangling the electron density and geometrical (effective) thickness was described by Jejčič and Heinzel (Solar Phys.254, 89 - 100, 2009) and is used here for the first time to analyse the spatial variations of prominence parameters. For the studied prominence we obtained the following range of parameters: temperature 6000 - 15 000 K, effective thickness 200 - 15000 km, electron density 5×109 - 1011 cm−3 and gas pressure 0.02 - 0.2 dyn cm−2 (assuming a fixed ionisation degree np/nH=0.5). The electron density increases towards the bottom of the prominence, which we explain by an enhanced photoionisation due to the incident solar radiation. To confirm this, we construct a two-dimensional radiative-transfer model with realistic prominence illumination. Title: Magnetic field and radiative transfer modelling of a quiescent prominence Authors: Gunár, S.; Schwartz, P.; Dudík, J.; Schmieder, B.; Heinzel, P.; Jurčák, J. Bibcode: 2014A&A...567A.123G Altcode:
Aims: The aim of this work is to analyse the multi-instrument observations of the June 22, 2010 prominence to study its structure in detail, including the prominence-corona transition region and the dark bubble located below the prominence body.
Methods: We combined results of the 3D magnetic field modelling with 2D prominence fine structure radiative transfer models to fully exploit the available observations.
Results: The 3D linear force-free field model with the unsheared bipole reproduces the morphology of the analysed prominence reasonably well, thus providing useful information about its magnetic field configuration and the location of the magnetic dips. The 2D models of the prominence fine structures provide a good representation of the local plasma configuration in the region dominated by the quasi-vertical threads. However, the low observed Lyman-α central intensities and the morphology of the analysed prominence suggest that its upper central part is not directly illuminated from the solar surface.
Conclusions: This multi-disciplinary prominence study allows us to argue that a large part of the prominence-corona transition region plasma can be located inside the magnetic dips in small-scale features that surround the cool prominence material located in the dip centre. We also argue that the dark prominence bubbles can be formed because of perturbations of the prominence magnetic field by parasitic bipoles, causing them to be devoid of the magnetic dips. Magnetic dips, however, form thin layers that surround these bubbles, which might explain the occurrence of the cool prominence material in the lines of sight intersecting the prominence bubbles.

Movie and Appendix A are available in electronic form at http://www.aanda.org Title: Modelling of quiescent prominence fine structures Authors: Gunár, S. Bibcode: 2014IAUS..300...59G Altcode: We review here the current status and the latest results of the modelling of quiescent prominence fine structures. We begin with the simulations of the prominence magnetic field configurations, through an overview of the modelling of the fine structure formation and dynamics, and with the emphasis on the radiative transfer modelling of the realistic prominence fine structures. We also illuminate the future directions of the field that lie in the combining of the existing approaches into more complex multi-disciplinary models. Title: Mapping prominence plasma parameters from eclipse observations Authors: Jejčič, Sonja; Heinzel, Petr; Zapiór, Maciej; Druckmüller, Miloslav; Gunár, Stanislav; Kotrč, Pavel Bibcode: 2014IAUS..300..420J Altcode: Using the eclipse observations, we construct the maps of quiescent prominence temperatures, electron densities, pressures and geometrical thicknesses. For this we use the RGB signal of prominence visible-light emission detected during the total solar eclipse on August 1, 2008 in Mongolia, and quasi-simultaneous Hα spectra taken at Ondřejov observatory. The method of disentangling the electron density and effective geometrical thickness was described by Jejčič & Heinzel (2009) and is used here for the first time to analyse the spatial variations of various prominence parameters. Title: Puzzling nature of the fine structure of quiescent prominences and filaments Authors: Gunár, Stanislav; Heinzel, Petr; Anzer, Ulrich; Mackay, Duncan H. Bibcode: 2013JPhCS.440a2035G Altcode: Even after more than 160 years of observations and modelling of solar prominences their true nature contains many open questions. In this work we argue that current 2D prominence fine structure models can help us to understand the puzzling connection between quasi-vertical fine structures often seen in quiescent prominences observed on the solar limb and horizontally aligned dark fibrils representing the fine structures of prominences observed in absorption against the solar disk (filaments). Title: Non-linear force-free magnetic dip models of quiescent prominence fine structures Authors: Gunár, S.; Mackay, D. H.; Anzer, U.; Heinzel, P. Bibcode: 2013A&A...551A...3G Altcode:
Aims: We use 3D non-linear force-free magnetic field modeling of prominence/filament magnetic fields to develop the first 2D models of individual prominence fine structures based on the 3D configuration of the magnetic field of the whole prominence.
Methods: We use an iterative technique to fill the magnetic dips produced by the 3D modeling with realistic prominence plasma in hydrostatic equilibrium and with a temperature structure that contains the prominence-corona transition region. With this well-defined plasma structure the radiative transfer can be treated in detail in 2D and the resulting synthetic emission can be compared with prominence/filament observations.
Results: Newly developed non-linear force-free magnetic dip models are able to produce synthetic hydrogen Lyman spectra in a qualitative agreement with a range of quiescent prominence observations. Moreover, the plasma structure of these models agrees with the gravity induced prominence fine structure models which have already been shown to produce synthetic spectra in good qualitative agreement with several observed prominences.
Conclusions: We describe in detail the iterative technique which can be used to produce realistic plasma models of prominence fine structures located in prominence magnetic field configurations containing dips, obtained using any kind of magnetic field modeling. Title: Prominence fine-structure dynamics as inferred from 2D non-LTE models Authors: Gunar, Stanislav; Schmieder, Brigitte; Mein, Pierre; Heinzel, Petr Bibcode: 2012cosp...39..683G Altcode: 2012cosp.meet..683G 2D multi-thread prominence fine structure models are able to produce synthetic Lyman spectra in very good agreement with spectral observations by SOHO/SUMER including the spectral line asymmetries. The synthetic differential emission measure curves derived from these models are also in a good agreement with observations. Now we show that these models are also able to produce synthetic H-alpha line profiles in very good agreement with observations which allows us to analyze not only the physical parameters of the prominence fine-structure plasma but also some aspects of its dynamical behaviour. We compare the synthetic H-alpha spectra with the observed spectra of the April 26, 2007 prominence using three statistical parameters: the line integrated intensity, the line full-width at the half-maximum (FWHM), and the Doppler velocity derived from shifts of the line profiles. This statistical analysis allows us to conclude that the overall statistical distribution of the LOS velocities in the April 26, 2007 prominence at the time of the observations was below +/-15 km/s and in the prominence core was close to +/-10 km/s. In combination with the analysis of the Lyman spectra we determine several physical parameters of the observed prominence fine structures which show that the April 26, 2007 prominence was relatively less massive. We are also able to put some constrains on the prominence core temperature that might be relatively low, reaching values below 6000 K. Title: Dynamics of quiescent prominence fine structures analyzed by 2D non-LTE modelling of the Hα line Authors: Gunár, S.; Mein, P.; Schmieder, B.; Heinzel, P.; Mein, N. Bibcode: 2012A&A...543A..93G Altcode:
Aims: We analyze the dynamics of the prominence fine structures of a quiescent prominence observed on April 26, 2007 during a coordinated campaign of several spaceborne and ground-based instruments. We use Lyman spectra observed by SOHO/SUMER and the Hα line spectra obtained by MSDP spectrograph working at the Meudon Solar Tower.
Methods: We employ the 2D multi-thread prominence fine-structure modelling that includes randomly distributed line-of-sight (LOS) velocities of individual threads to derive models producing synthetic Lyman lines in good agreement with the SOHO/SUMER observations. We then use these models to produce synthetic Hα line spectra that we compare with the observed spectra using three statistical parameters: the line integrated intensity, the line full-width at half-maximum (FWHM), and the Doppler velocity derived from shifts of the line profiles.
Results: We demonstrate that the 2D multi-thread models that produce synthetic Lyman spectra in agreement with observations also generate synthetic Hα spectra in good agreement with the observed ones. The statistical analysis of the FWHM and Doppler velocities of the synthetic Hα line profiles show that the overall LOS velocities in the April 26, 2007 prominence at the time of the observations were below 15 km s-1 and in the prominence core were close to 10 km s-1. In combination with the analysis of the Lyman spectra, we determine several physical parameters of the observed prominence fine-structures that show that the April 26, 2007 prominence had a relatively low-mass weakly magnetized structure. We are also able to impose some constraints on the prominence core temperature, which may be relatively low, with values below 6000 K.
Conclusions: The combination of 2D non-LTE prominence fine-structure modelling with the statistical analysis of the observed and synthetic Lyman and Hα spectra allows us to analyze the influence of the model input parameters and the velocity fields on the synthetic Hα line profiles, thus determine the overall dynamics of the observed prominence as well as the physical parameters of its plasma.

Appendix A is available in electronic form at http://www.aanda.org Title: Synthetic differential emission measure curves of prominence fine structures. II. The SoHO/SUMER prominence of 8 June 2004 Authors: Gunár, S.; Parenti, S.; Anzer, U.; Heinzel, P.; Vial, J. -C. Bibcode: 2011A&A...535A.122G Altcode:
Aims: This study is the first attempt to combine the prominence observations in Lyman, UV, and EUV lines with the determination of the prominence differential emission measure derived using two different techniques, one based on the inversion of the observed UV and EUV lines and the other employing 2D non-LTE prominence fine-structure modeling of the Lyman spectra.
Methods: We use a trial-and-error method to derive the 2D multi-thread prominence fine-structure model producing synthetic Lyman spectra in good agreement with the observations. We then employ a numerical method to perform the forward determination of the DEM from 2D multi-thread models and compare the synthetic DEM curves with those derived from observations using inversion techniques.
Results: A set of available observations of the June 8, 2004 prominence allows us to determine the range of input parameters, which contains models producing synthetic Lyman spectra in good agreement with the observations. We select three models, which represent this parametric-space area well and compute the synthetic DEM curves for multi-thread realizations of these models. The synthetic DEM curves of selected models are in good agreement with the DEM curves derived from the observations.
Conclusions: We show that the evaluation of the prominence fine-structure DEM complements the analysis of the prominence hydrogen Lyman spectra and that its combination with the detailed radiative-transfer modeling of prominence fine structures provides a useful tool for investigating the prominence temperature structure from the cool core to the prominence-corona transition region. Title: 2D radiative-magnetohydrostatic model of a prominence observed by Hinode, SoHO/SUMER and Meudon/MSDP Authors: Berlicki, A.; Gunar, S.; Heinzel, P.; Schmieder, B.; Schwartz, P. Bibcode: 2011A&A...530A.143B Altcode:
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, pcen = 0.035 dyn cm-2, B = 5 Gauss, ne = 1010 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. Title: Synthetic differential emission measure curves of prominence fine structures Authors: Gunár, S.; Heinzel, P.; Anzer, U. Bibcode: 2011A&A...528A..47G Altcode:
Aims: We use 2D single and multi-thread prominence fine-structure models to obtain the synthetic DEM curves. These are then compared with the DEM curves derived from observations.
Methods: We use the temperature and electron density structure resulting from the 2D models and numerically compute the average synthetic DEM curves for different orientations of the threads with respect to the line of sight.
Results: We show that the synthetic DEM curves obtained by 2D modelling are similar to the DEM curves derived from observations of quiescent prominences.
Conclusions: The DEM curves derived from observations, which are most reliable above temperatures of 20 000 K, can be extended towards cool prominence-core temperatures by supplementing them with synthetic DEM values obtained by modelling hydrogen Lyman spectra originating mainly at temperatures below 20 000 K. On the other hand, the observed DEM can constrain the temperature structure of the prominence fine structures above the formation temperatures of the Lyman spectrum. Title: Statistical comparison of the observed and synthetic hydrogen Lyman line profiles in solar prominences Authors: Gunár, S.; Schwartz, P.; Schmieder, B.; Heinzel, P.; Anzer, U. Bibcode: 2010A&A...514A..43G Altcode:
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. Title: Physics of Solar Prominences: I—Spectral Diagnostics and Non-LTE Modelling Authors: Labrosse, N.; Heinzel, P.; Vial, J. -C.; Kucera, T.; Parenti, S.; Gunár, S.; Schmieder, B.; Kilper, G. Bibcode: 2010SSRv..151..243L Altcode: 2010SSRv..tmp...34L; 2010arXiv1001.1620L This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE ( i.e. when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences. Title: How do unresolved motions affect the prominence hydrogen Lyman spectrum. Authors: Gunar, Stanislav; Schwartz, Pavol; Schmieder, Brigitte; Heinzel, Petr; Anzer, Ulrich Bibcode: 2010cosp...38.2830G Altcode: 2010cosp.meet.2830G Space-born observations of quiescent prominences in the hydrogen Lyman line series provide a considerable amount of information about their structure and physical properties. Lyman line series thus represents a focus of several detailed studies. However, the substantial asymmetries exhibited by considerable number of observed Lyman line profiles present a strong indication for the existence of hidden fine-structure dynamics. If attributed merely to the Doppler shift effect, these asymmetries would correspond to radial velocities of the order of 100 km/s. Such high velocities, however, were never observed in quiescent prominences. Typical fine-structure velocities are of the order of 10 km/s. To tackle this problem, we have modified our 2D multi-thread prominence models and randomly assigned line-of-sight (LOS) velocities of the order of 10 km/s to each thread. The obtained synthetic Lyman spectrum exhibits substantial asymme-tries of the line profiles comparable with SOHO/SUMER observations. Moreover, our results do indicate that the synthetic Lyman-α profiles may exhibit an opposite asymmetry to that of the higher Lyman lines. This is consistent with observations which often show opposite asym-metries of these lines at the same prominence location. We have demonstrated the agreement of synthetic and observed spectra not only by comparing asymmetries of individual profiles but also by exploiting statistically significant sets of the observed and synthetic data. These results represent an important step in our understanding of hidden fine-structure dynamics of quiescent prominences. Title: Title: Can purely emissive Ly_beta prominence spectra be caused by the line of sight oriented parallelly to the magnetic field? Authors: Schwartz, Pavol; Gunar, Stanislav; Heinzel, Petr; Schmieder, Brigitte Bibcode: 2010cosp...38.2852S Altcode: 2010cosp.meet.2852S Small bright prominence was observed on the SW limb on April 26, 2007 between 13:01 and 23:50 UT by SUMER spectrograph on-board SoHO in hydrogen Lyman line series except the Lyα line. Profiles of the Lyβ line are peculiar for a prominence because they do not exhibit any central reversals (dips in cores of the lines). This could be explained by the fact that the line of sight is parallel with the direction of the magnetic field in the prominence. We can investigate this fact by a statistical comparison of observed profiles with the synthetic ones computed using the 2D multi-thread model of the prominence. We use synthetic profiles obtained for various orientations of the line of sight with respect to the magnetic field, ranging from perpendicular to parallel. Profiles are compared statistically using their characteristics such as integral intensities, so-called Lyman decrement (ratio of integral intensity of the line to integral intensity of the Lyβ line, etc.). Title: Relations between theoretical and observational plasma parameters and the radiation of the prominence Authors: Berlicki, Arkadiusz; Schwartz, Pavol; Schmieder, Brigitte; Heinzel, Petr; Gunar, Stanislav Bibcode: 2010cosp...38.2945B Altcode: 2010cosp.meet.2945B On April 26, 2007 the quiescent prominence was observed during the coordinated campaign of prominence studies icluding SOT, XRT, and EIS on Hinode, MDI, EIT, SUMER, and CDS on SOHO, TRACE, and several ground-based observatories. This was the first Hinode-SUMER ob-serving campaign. In this analysis we use the data obtained with Hinode/SOT, SOHO/SUMER and Multichannel Spectrograph MSDP (Meudon, France). The SUMER instrument provide us the UV spectra of the prominence in several spectral lines along the 120 arcsec slit crossing the prominence. We used the following lines: Lβ, Lγ, Lδ, L , C III and S VI. Using these spectra we calculated the integrated intensities along the slit for all these lines. We also calculated the integrated intensity of the Hα line from the spectroscopic ground-based MSDP observations for the same parts of the prominence observed at the same time. These intensities were used to calibrate the Hinode/SOT data. Next, we analyzed the relations between different observed intensities in these lines and compared them with the values obtained from the theoretical simulations. We analyzed the correlations between observations and theoretical modeling and as a results we estimated the different physical parameters of the prominence plasma. Title: Prominence fine structures and corresponding differential emission measures Authors: Gunar, Stanislav; Heinzel, Petr; Anzer, Ulrich Bibcode: 2010cosp...38.2845G Altcode: 2010cosp.meet.2845G We use the temperature and density structure resulting from multi-thread prominence fine-structure models (consisting of individual 2D vertical threads) to compute the differential emission measures (DEM). We derive the DEM at various positions along the length of the foremost thread of the multi-thread model and also for various angles between the line-of-sight and the magnetic field. We compare the calculated DEM values with those obtained by in-versions from the observed intensities of the transition-region UV lines. We show that the unresolved fine-structuring of quiescent prominences along a particular line-of-sight has consid-erable effect on shape of the DEM curve due to fracturing of the prominence-corona transition region into many thin layers corresponding to individual prominence fine structures. Title: Solar quiescent prominences. Filamentary structure and energetics Authors: Heinzel, P.; Anzer, U.; Gunár, S. Bibcode: 2010MmSAI..81..654H Altcode: We present a first attempt to solve the non-LTE radiative-transfer problem within a 2D numerical domain consisting of several randomly distributed vertical threads. This represents a starting point to simulate mutual radiative interaction between such prominence threads. The second part of the paper presents our new results which concern the radiative equilibrium in prominences and in their fine structure. We show that adding the non-hydrogenic radiative losses significantly lowers the central equilibrium temperatures. To match the observed temperatures, an additional heating seems to be unavoidable. Title: On Lyman-line asymmetries in quiescent prominences Authors: Gunár, S.; Heinzel, P.; Anzer, U.; Schmieder, B. Bibcode: 2008A&A...490..307G Altcode: Aims: We study the asymmetries of the synthetic hydrogen Lyman lines and the process responsible for their formation.
Methods: To obtain the synthetic Lyman line profiles, we use a multi-thread prominence fine-structure model consisting 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 line-of-sight (LOS) velocity.
Results: 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-α profiles may exhibit an opposite asymmetry to that of the higher Lyman lines.
Conclusions: The presence and behaviour of the asymmetrical profiles of the synthetic Lyman lines agree with observed profiles acquired by SUMER.

Appendix A is only available in electronic form at http://www.aanda.org Title: Prominence and its Coronal Cavity Observed by Hinode, TRACE and SOHO Authors: Schmieder, B.; Heinzel, P.; Schwartz, P.; Gunar, S. Bibcode: 2008ESPM...12.2.95S Altcode: We will first give a definition of what is a prominence according to the glossary of Solar Physicists. A prominence is a filament observed at the limb. A filament lies over the inversion line of photospheric longitudinal magnetic field and is supported in dips of horizontal magnetic field lines. Recent models of flux tubes prove that fine structures of prominences could be represented by vertical structures embedded in dips of horizontal field lines.

Observations of a prominence observed in H? by Hinode/SOT and the solar tower of Meudon show a very high dynamic nature. SUMER spectra in Lyman series show no reverse profiles indicating a large prominence corona transition region.

This prominence is surrounded by a large coronal cavity as show spatial telescopes (TRACE, XRT).

These results will be discussed in term of different formation models. Title: On Lyman-line Asymmetries in Quiescent Prominences Authors: Gunár, S.; Heinzel, P.; Anzer, U.; Schmieder, B. Bibcode: 2008ESPM...12.3.18G Altcode: We present a new study of the asymmetries of synthetic hydrogen Lyman line profiles and suggest the mechanism of their formation.

In order to obtain the synthetic Lyman line profiles, we use multi-thread prominence fine-structure model consisting of identical vertical 2D threads. The 2D thread models are in magnetohydrostatic (MHS) equilibrium, include an empirical prominence-corona transition region (PCTR) and consistently solve the 2D non-LTE radiative transfer. Individual threads of the multi-thread fine-structure model have a randomly assigned LOS velocities.

The synthetic Lyman spectrum obtained by our 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-1. Moreover, our results show that the synthetic Lyman-? profiles may exhibit an opposite asymmetry as compared to higher Lyman lines. These results are in agreement with the observed Lyman line profiles from SOHO/SUMER.

The presence and the behaviour of the asymmetrical profiles of the synthetic Lyman spectrum is in agreement with observed profiles taken by SUMER. Title: Solar Prominence Diagnostic with Hinode/EIS Authors: Labrosse, N.; Schmieder, B.; Heinzel, P.; Gunar, S. Bibcode: 2008ESPM...12.2.21L Altcode: We report here on observations of a solar prominence obtained on 26 April 2007 using the Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. Selected profiles for lines with formation temperatures between log(T)=4.7 and log(T)=6.3 are given and are used to explain the existence of dark features in the raster images. We estimate the contribution of the He II 256.32 Å line in the raster image at 256 Å in the prominence region. We compare the observed prominence profiles with theoretical profiles from non-LTE radiative transfer models and deduce the contribution of resonant scattering in the He II 256 Å emission. Title: Properties of prominence fine-structure threads derived from SOHO/SUMER hydrogen Lyman lines Authors: Gunár, S.; Heinzel, P.; Schmieder, B.; Schwartz, P.; Anzer, U. Bibcode: 2007A&A...472..929G Altcode: 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 T0 = 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. Title: Prominence Parameters from 2D Modeling of Lyman Lines Measured with SUMER Authors: Gunár, S.; Heinzel, P.; Schmieder, B.; Anzer, U. Bibcode: 2007ASPC..368..317G Altcode: We present SOHO/SUMER observations of a solar prominence in the hydrogen Lyman series lines and compare the line profiles with the synthetic ones obtained using our 2D prominence modeling. The observations contain the Ly-β, Ly-γ, and Ly-δ lines on 25 May 2005.

In order to derive the prominence parameters we used our 2D fine structure models of vertical threads in magnetohydrostatic (MHS) equilibrium. By varying the input model parameters (central temperature, boundary pressure, magnetic field, central column mass and turbulent velocity) we obtained a model having the synthetic Lyman line profiles in good agreement with the observed ones. In this way we are able to determine the structure of the magnetic dip and the thermodynamical parameters in the observed prominence. Title: Spectral Diagnostics of the Magnetic Field Orientation in a Prominence Observed with SOHO/SUMER Authors: Schmieder, B.; Gunár, S.; Heinzel, P.; Anzer, U. Bibcode: 2007SoPh..241...53S Altcode: During several campaigns focused on prominences we have obtained coordinated spectral observations from the ground and from space. The SOHO/SUMER spectrometer allows us to observe, among others, the whole Lyman series of hydrogen, while the Hα line was observed by the MSDP spectrograph at the VTT. For the Lyman lines, non-LTE radiative-transfer computations have shown the importance of the optical thickness of the prominence - corona transition region (PCTR) and its relation to the magnetic field orientation for the explanation of the observed line profiles. Moreover, Heinzel, Anzer, and Gunár (2005, Astron. Astrophys.442, 331) developed a 2D magnetostatic model of prominence fine structures that demonstrates how the shapes of Lyman lines vary, depending on the orientation of the magnetic field with respect to the line of sight. To support this result observationally, we focus here on a round-shaped filament observed during three days as it was crossing the limb. The Lyman profiles observed on the limb are different from day to day. We interpret these differences as being due to the change of orientation of the prominence axis (and therefore the magnetic field direction) with respect to the line of sight. The Lyman lines are more reversed if the line of sight is across the prominence axis as compared to the case when it is aligned along its axis. Title: Prominence fine structures in a magnetic equilibrium. III. Lyman continuum in 2D configurations Authors: Gunár, S.; Heinzel, P.; Anzer, U. Bibcode: 2007A&A...463..737G Altcode: 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. Title: Prominence Parameters Derived from Hydrogen Lyman-α Spectral Profiles Measured by SOHO/SUMER Authors: Gunár, S.; Teriaca, L.; Heinzel, P.; Schühle, U. Bibcode: 2006ESASP.617E..63G Altcode: 2006soho...17E..63G No abstract at ADS Title: Prominence Fine Structures in Amagnetic Equilibrium: a Grid Oftwo-Dimensional Models Authors: Gunár, S.; Heinzel, P.; Anzer, U. Bibcode: 2005ESASP.600E..85G Altcode: 2005dysu.confE..85G; 2005ESPM...11...85G No abstract at ADS Title: Prominence fine structures in a magnetic equilibrium. II. A grid of two-dimensional models Authors: Heinzel, P.; Anzer, U.; Gunár, S. Bibcode: 2005A&A...442..331H Altcode: We construct a grid of 2D vertical-thread models for prominence fine structures which are in magnetohydrostatic (MHS) equilibrium. Such thread models have been described in a previous paper by Heinzel & Anzer (2001), but here we use a modified 2D transfer code with an adaptive MHS grid. Multilevel non-LTE transfer calculations are now performed for a 12-level plus continuum hydrogen model atom, in order to study the behaviour of the Lyman-series lines observed by SOHO/SUMER. Our grid consists of 18 models which cover a range of central column masses, magnetic-field intensities and two parameters characterising the 2D temperature structure of the thread. Since different Lyman lines and their parts (line center, peak, wings) are formed at different places within the thread, the Lyman series may serve as a good diagnostic tool for thermodynamic conditions varying from central cool parts to a prominence-corona transition region. We demonstrate this behaviour for various lines, showing their synthetic profiles as seen from two perpendicular directions along and across the magnetic field lines, respectively, and displaying the respective contribution functions. This study confirms our earlier conclusion that the Lyman line profiles are much more reversed when seen across the field lines, compared to those seen along the lines. The latter can be even unreversed. We also show the geometrical cross-section (shape) of all 18 models. Their thread-like shape with a considerable aspect ratio resembles recent high-resolution Hα images. Finally, we discuss the relation of our thread models to the vertical threads studied by Fontenla et al. (1996, ApJ, 466, 496).