Author name code: heinzel ADS astronomy entries on 2022-09-14 author:"Heinzel, Petr" ------------------------------------------------------------------------ Title: Coronal mass ejection followed by a prominence eruption and a plasma blob as observed by Solar Orbiter Authors: Bemporad, A.; Andretta, V.; Susino, R.; Mancuso, S.; Spadaro, D.; Mierla, M.; Berghmans, D.; D'Huys, E.; Zhukov, A. N.; Talpeanu, D. -C.; Colaninno, R.; Hess, P.; Koza, J.; Jejčič, S.; Heinzel, P.; Antonucci, E.; Da Deppo, V.; Fineschi, S.; Frassati, F.; Jerse, G.; Landini, F.; Naletto, G.; Nicolini, G.; Pancrazzi, M.; Romoli, M.; Sasso, C.; Slemer, A.; Stangalini, M.; Teriaca, L. Bibcode: 2022A&A...665A...7B Altcode: 2022arXiv220210294B Context. On 2021 February 12, two subsequent eruptions occurred above the western limb of the Sun, as seen along the Sun-Earth line. The first event was a typical slow coronal mass ejection (CME), followed ∼7 h later by a smaller and collimated prominence eruption, originating south of the CME, followed by a plasma blob. These events were observed not only by the SOHO and STEREO-A missions, but also by the suite of remote-sensing instruments on board Solar Orbiter.
Aims: We show how data acquired by the Full Sun Imager (FSI), the Metis coronagraph, and the Heliospheric Imager (HI) from the Solar Orbiter perspective can be combined to study the eruptions and different source regions. Moreover, we show how Metis data can be analyzed to provide new information about solar eruptions.
Methods: Different 3D reconstruction methods were applied to the data acquired by different spacecraft, including remote-sensing instruments on board Solar Orbiter. Images acquired by the two Metis channels in the visible light (VL) and H I Ly-α line (UV) were combined to derive physical information about the expanding plasma. The polarization ratio technique was also applied for the first time to Metis images acquired in the VL channel.
Results: The two eruptions were followed in 3D from their source region to their expansion in the intermediate corona. By combining VL and UV Metis data, the formation of a post-CME current sheet (CS) was followed for the first time in the intermediate corona. The plasma temperature gradient across a post-CME blob propagating along the CS was also measured for the first time. Application of the polarization ratio technique to Metis data shows that by combining four different polarization measurements, the errors are reduced by ∼5 − 7%. This constrains the 3D plasma distribution better.

Movies associated to Figs. 4-7 are available at https://www.aanda.org Title: Linking Small-scale Solar Wind Properties with Large-scale Coronal Source Regions through Joint Parker Solar Probe-Metis/Solar Orbiter Observations Authors: Telloni, Daniele; Zank, Gary P.; Sorriso-Valvo, Luca; D'Amicis, Raffaella; Panasenco, Olga; Susino, Roberto; Bruno, Roberto; Perrone, Denise; Adhikari, Laxman; Liang, Haoming; Nakanotani, Masaru; Zhao, Lingling; Hadid, Lina Z.; Sánchez-Cano, Beatriz; Verscharen, Daniel; Velli, Marco; Grimani, Catia; Marino, Raffaele; Carbone, Francesco; Mancuso, Salvatore; Biondo, Ruggero; Pagano, Paolo; Reale, Fabio; Bale, Stuart D.; Kasper, Justin C.; Case, Anthony W.; de Wit, Thierry Dudok; Goetz, Keith; Harvey, Peter R.; Korreck, Kelly E.; Larson, Davin; Livi, Roberto; MacDowall, Robert J.; Malaspina, David M.; Pulupa, Marc; Stevens, Michael L.; Whittlesey, Phyllis; Romoli, Marco; Andretta, Vincenzo; Deppo, Vania Da; Fineschi, Silvano; Heinzel, Petr; Moses, John D.; Naletto, Giampiero; Nicolini, Gianalfredo; Spadaro, Daniele; Stangalini, Marco; Teriaca, Luca; Capobianco, Gerardo; Capuano, Giuseppe E.; Casini, Chiara; Casti, Marta; Chioetto, Paolo; Corso, Alain J.; Leo, Yara De; Fabi, Michele; Frassati, Federica; Frassetto, Fabio; Giordano, Silvio; Guglielmino, Salvo L.; Jerse, Giovanna; Landini, Federico; Liberatore, Alessandro; Magli, Enrico; Massone, Giuseppe; Messerotti, Mauro; Pancrazzi, Maurizio; Pelizzo, Maria G.; Romano, Paolo; Sasso, Clementina; Schühle, Udo; Slemer, Alessandra; Straus, Thomas; Uslenghi, Michela; Volpicelli, Cosimo A.; Zangrilli, Luca; Zuppella, Paola; Abbo, Lucia; Auchère, Frédéric; Cuadrado, Regina Aznar; Berlicki, Arkadiusz; Ciaravella, Angela; Lamy, Philippe; Lanzafame, Alessandro; Malvezzi, Marco; Nicolosi, Piergiorgio; Nisticò, Giuseppe; Peter, Hardi; Solanki, Sami K.; Strachan, Leonard; Tsinganos, Kanaris; Ventura, Rita; Vial, Jean-Claude; Woch, Joachim; Zimbardo, Gaetano Bibcode: 2022ApJ...935..112T Altcode: The solar wind measured in situ by Parker Solar Probe in the very inner heliosphere is studied in combination with the remote-sensing observation of the coronal source region provided by the METIS coronagraph aboard Solar Orbiter. The coronal outflows observed near the ecliptic by Metis on 2021 January 17 at 16:30 UT, between 3.5 and 6.3 R ⊙ above the eastern solar limb, can be associated with the streams sampled by PSP at 0.11 and 0.26 au from the Sun, in two time intervals almost 5 days apart. The two plasma flows come from two distinct source regions, characterized by different magnetic field polarity and intensity at the coronal base. It follows that both the global and local properties of the two streams are different. Specifically, the solar wind emanating from the stronger magnetic field region has a lower bulk flux density, as expected, and is in a state of well-developed Alfvénic turbulence, with low intermittency. This is interpreted in terms of slab turbulence in the context of nearly incompressible magnetohydrodynamics. Conversely, the highly intermittent and poorly developed turbulent behavior of the solar wind from the weaker magnetic field region is presumably due to large magnetic deflections most likely attributed to the presence of switchbacks of interchange reconnection origin. Title: Dark off-limb gap: manifestation of temperature minimum and dynamic nature of the chromosphere Authors: Kuridze, D.; Heinzel, P.; Koza, J.; Oliver, R. Bibcode: 2022arXiv220814134K Altcode: We study off-limb emission of the lower solar atmosphere using high-resolution imaging spectroscopy in the H$\beta$ and Ca II 8542 Å lines obtained with the CHROMospheric Imaging Spectrometer (CHROMIS) and the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m Solar Telescope. The H$\beta$ line wing images show the dark intensity gap between the photospheric limb and chromosphere which is absent in the Ca II images. We calculate synthetic spectra of the off-limb emissions with the RH code in the one-dimension spherical geometry and find good agreement with the observations. The analysis of synthetic line profiles shows that the gap in the H$\beta$ line wing images maps the temperature minimum region between the photosphere and chromosphere due to the well known opacity and emissivity gap of Balmer lines in this layer. However, observed gap is detected farther from the line core in the outer line wing positions than in the synthetic profiles. We found that an increased microturbulence in the model chromosphere is needed to reproduce the dark gap in the outer line wing, suggesting that observed H$\beta$ gap is the manifestation of the temperature minimum and the dynamic nature of the solar chromosphere. The temperature minimum produces a small enhancement in synthetic Ca II line-wing intensities. Observed off-limb Ca II line-wing emissions show similar enhancement below temperature minimum layer near the edge of the photospheric limb. 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: A first comparison of FLARIX flare simulations with the MSDP H-alpha spectral observations on very short time scales Authors: Heinzel, Petr; Kasparova, Jana; Berlicki, Arkadiusz; Radziszewski, Krzysztof; Rudawy, Pawel Bibcode: 2022cosp...44.2560H Altcode: We present first results of a comparative analysis of high temporal resolution MSDP H$\alpha$ observations of a compact solar flare with results of radiation-hydrodynamical simulations performed using the FLARIX code. X-ray spectral observations of a compact C1 GOES-class flare obtained from RHESSI satellite were used to estimate physical parameters of the electron beams transporting the energy from the reconnection site down to the chromosphere. These parameters are then used for data-driven FLARIX simulations. A small size of the flare and its simple structure allowed us to assume a single-loop geometry which significantly simplified the modelling and analysis of the whole event. Using the MSDP imaging spectrograph at Bia{\l}k\'{o}w observatory, it was possible to compare the recorded H$\alpha$ line emission with that obtained from FLARIX simulations, on short time-scales down to 50 ms. Title: Geometry and dynamics of cool flare loops observed by IRIS Authors: Mikuła, Katarzyna; Heinzel, Petr; Berlicki, Arkadiusz Bibcode: 2022cosp...44.2414M Altcode: Flare loops represent a well-known, inseparable part of solar flares. They are observed mainly during the gradual phase of the flares, being rooted in flare ribbons. They can form an entire arcade which evolves in the corona, sometimes for hours. The loops are visible in a wide range of temperature bands, from X-rays (hot flare loops) to temperatures of the cool chromospheric-type plasma seen in the ultraviolet and optical spectrum (cool flare loops). We present results of our analysis of cool flare loops observed during the gradual phase of M6.5 solar flare on June 22, 2015 based on the ultraviolet observations obtained by Interface Region Imaging Spectrograph (IRIS). Detailed investigation of these loops, made on the basis of Mg II line profiles, was presented in Mikuła et al. (2017). Mg II line profiles were modelled using the standard cloud model method that allowed us obtaining simultaneously the physical parameters characteridsing the moving plasma inside selected loops, i.e. the velocity along the line-of-sight, microturbulent velocity, optical thickness, and the line source function. Here we present a next step of the work — reconstruction of the true shape of flare loops based on the geometric method of Loughhead, Wang and Blows (1983). Based on two-dimensional images of a given loop structure located on the solar disk or at the limb, we can obtain its true orientation and its size. The shape of the analysed loops was determined mainly from IRIS slit-jaw images at 1330, 1400 and 2796 \AA{}, supplemented with SDO/AIA 171 \AA{} images in some cases. Using basic geometry, we reconstructed the shape of selected loops in the three-dimensional space. Based on the method presented in Loughhead and Bray (1984) we were able to derive the so-called true velocity of the plasma flows, i.e. the velocity along the loop axis. The results obtained for each loop were then compared with the free fall velocities. Title: New Insight into UV Compact Bursts - Statistical Analysis of IRIS Data Authors: Berlicki, Arkadiusz; Heinzel, Petr; Schmieder, Brigitte; Michalina Litwicka, M. Bibcode: 2022cosp...44.2532B Altcode: UV small-scale brightenings have been frequently observed by IRIS in both NUV and FUV channels. They appear as compact and intense, but short lived bursts visible within the solar active regions. Some of them seem to be closely connected with the well-known Ellerman bombs and so-called IRIS bombs. Based on the IRIS observations of many compact bursts obtained in chromospheric Mg II h and k lines, Mg II triplet and FUV lines we present detailed statistical analysis of these phenomena. In the work of Grubecka et al. (2016), five different compact bursts (CBs) were selected and analysed in detail. NLTE semi-empirical models of them were constructed based on their spectral characteristics in the Mg II h and k lines. In addition, they were preliminarily categorised into three types. In present work we extend previous analysis and investigate statistical diversity of Mg II lines of UV bursts and their visibility in FUV lines such as Si IV or C II. IRIS database from 2013-2018 was searched for dense rasters of active and emerging flux regions containing spectra in Mg II, C II and Si IV. A next step was to reconstruct full rasters in which we were looking for compact brightenings with size of the order of one arcsec. We found more than two thousands CBs using criteria based on specific parameters of the Mg II k line profile. In addition, we analysed also the emission of Mg II UV triplet and some parameters of Si IV and C II lines. This database allowed us to make a novel statistical analysis of all bursts and we categorised them in previously defined three types, depending on their Mg II line profiles shapes. We also investigated the correlations between the emission of Mg II lines, "hotter" Si IV lines, and C II lines in order to find which of these events are linked with IRIS bombs (Peter et al. 2014). Finally, we analysed some observables of those UV bursts, which can be defined as candidates for Ellerman bombs. 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: Spectral line asymmetries observed during stellar flares Authors: Wollmann, Jiří; Heinzel, Petr; Kabath, Petr; Karjalainen, Raine; Skarka, Marek; Špoková, Magdalena Bibcode: 2022cosp...44.2468W Altcode: Stellar flares are highly energetic events occuring in stellar atmospheres. This solar-like activity has been observed on G, K and M stars. Red dwarfs usually have vast and strong magnetic fields which often reconnect and produce strong flares, sometimes classified as the so-called superflares. From spectroscopic observations we see, apart from typical enhancements of the line intensities, clearly asymmetrical line profiles. In analogy with solar flares, one would interpret them as due to flows in the flaring chromosphere. However, some stellar observations indicate a peculiar behaviour of such asymmetries and their nature is not well understood. In this work we present recent spectroscopic observations of flares on AD Leo star obtained with the Ondrejov Echelle Spectrograph. We analyze detected asymmetries using the non-LTE radiative-transfer modeling and demonstrate the importance of flare dynamics. Our interpretation is based on a close analogy with solar flares. Title: Mini solar flare and jet due to small scale surface motions Authors: Joshi, Reetika; Vilmer, Nicole; Chandra, Ramesh; Heinzel, Petr; Bommier, Veronique; Schmieder, Brigitte; Aulanier, Guillaume; Tomin, James Bibcode: 2022cosp...44.2535J Altcode: Here we present the study of the fine structure and dynamics of the plasma at a jet base forming a mini-flare between two emerging magnetic fluxes (EMFs) observed with Interface Region Imaging Spectrograph (IRIS) and the Solar Dynamics Observatory instruments. This active region is an outcome of the collapse of two EMFs overlaid by arch filament systems. We observed that, before the jet an extension of the flux rope was present and a part of it was detached and formed a small bipole with a bald patch region, which dynamically became an X-current sheet over the dome of one EMF where the reconnection took place. At the time in the site of reconnection, the IRIS C II, Si IV, and Mg II line profiles present bi directional flows in a tiny region. These types of spectra are typically associated with twist, rotation, or the presence of plasma in helical structures. The tilt observed in our spectra can be explained by the presence of a helical structure at the jet base during the reconnection process due to a transfer of the twist from a flux rope in the vicinity of the jet. We also combined the observations of the Balmer continuum obtained with the IRIS (spectra and SJIs 2832 Å). The calibrated Balmer continuum was compared to non-local thermodynamic equilibrium radiative transfer flare models and the radiated energy was estimated. Assuming thick target HXR emission, we calculated the energy of the non thermal electrons detected by the Fermi/GBM and compared it to the radiated energy. The electron-beam flux estimated from Fermi/GBM between 10$ ^{9}$ and 10$ ^{10}$ erg s$ ^{-1}$ cm$ ^{-2}$ is consistent with the beam flux required in non-LTE radiative transfer models to obtain the excess of Balmer continuum emission observed in this IRIS spectra. We conclude that the bombardment of electrons could be in a region smaller than the IRIS spatial resolution. 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: Doppler-velocity Drifts Detected in a Solar Prominence Authors: Zapiór, Maciej; Heinzel, Petr; Khomenko, Elena Bibcode: 2022ApJ...934...16Z Altcode: We analyzed multiline observations of a quiescent prominence from the slit spectrograph located at the Ondřejov Observatory. Dopplergrams and integrated intensity maps of the whole prominence were obtained from observations in six spectral lines: Ca II H, Hϵ, Hβ, He I D3, Hα, and Ca II IR. By combining integrated intensity maps with non-LTE radiative-transfer modeling, we carefully identified areas in an optically thin regime. The comparison of the Doppler-velocity maps and scatterplots from different lines shows the existence of differences in the velocity of ions and neutrals called velocity drift. The drift is of a local nature, present mostly at prominence edges in the area with a large velocity gradient, as can be tentatively expected based on multifluid MHD models. We could not explore the time evolution of the drift, since our data set consists of a single scan only. Our paper brings another contribution to a rather controversial problem of the detection of multifluid effects in solar prominences. Title: Modeling Balmer line signatures of stellar CMEs Authors: Leitzinger, M.; Odert, P.; Heinzel, P. Bibcode: 2022MNRAS.513.6058L Altcode: 2022MNRAS.tmp.1287L; 2022arXiv220503110L From the Sun, we know that coronal mass ejections (CMEs) are a transient phenomenon, often correlated with flares. They have an impact on solar mass- and angular momentum loss, and therefore solar evolution, and make a significant part of space weather. The same is true for stars, but stellar CMEs are still not well constrained, although new methodologies have been established, and new detections presented in the recent past. So far, probable detections of stellar CMEs have been presented, but their physical parameters which are not directly accessible from observations, such as electron density, optical thickness, temperature, etc., have been so far not determined for the majority of known events. We apply cloud modeling, as commonly used on the Sun, to a known event from the literature, detected on the young dMe star V374 Peg. This event manifests itself in extra emission on the blue side of the Balmer lines. By determining the line source function from 1D NLTE modeling together with the cloud model formulation, we present distributions of physical parameters of this event. We find that except for temperature and area all parameters are at the upper range of typical solar prominence parameters. The temperature and the area of the event were found to be higher than for typical solar prominences observed in Balmer lines. We find more solutions for the filament than for the prominence geometry. Moreover, we show that filaments can appear in emission on dMe stars contrary to the solar case. Title: Prominence eruption observed in He II 304 Å up to >6 R⊙ by EUI/FSI aboard Solar Orbiter Authors: Mierla, M.; Zhukov, A. N.; Berghmans, D.; Parenti, S.; Auchère, F.; Heinzel, P.; Seaton, D. B.; Palmerio, E.; Jejčič, S.; Janssens, J.; Kraaikamp, E.; Nicula, B.; Long, D. M.; Hayes, L. A.; Jebaraj, I. C.; Talpeanu, D. -C.; D'Huys, E.; Dolla, L.; Gissot, S.; Magdalenić, J.; Rodriguez, L.; Shestov, S.; Stegen, K.; Verbeeck, C.; Sasso, C.; Romoli, M.; Andretta, V. Bibcode: 2022A&A...662L...5M Altcode: 2022arXiv220515214M
Aims: We report observations of a unique, large prominence eruption that was observed in the He II 304 Å passband of the Extreme Ultraviolet Imager/Full Sun Imager telescope aboard Solar Orbiter on 15-16 February 2022.
Methods: Observations from several vantage points - Solar Orbiter, the Solar-Terrestrial Relations Observatory, the Solar and Heliospheric Observatory, and Earth-orbiting satellites - were used to measure the kinematics of the erupting prominence and the associated coronal mass ejection. Three-dimensional reconstruction was used to calculate the deprojected positions and speeds of different parts of the prominence. Observations in several passbands allowed us to analyse the radiative properties of the erupting prominence.
Results: The leading parts of the erupting prominence and the leading edge of the corresponding coronal mass ejection propagate at speeds of around 1700 km s−1 and 2200 km s−1, respectively, while the trailing parts of the prominence are significantly slower (around 500 km s−1). Parts of the prominence are tracked up to heights of over 6 R⊙. The He II emission is probably produced via collisional excitation rather than scattering. Surprisingly, the brightness of a trailing feature increases with height.
Conclusions: The reported prominence is the first observed in He II 304 Å emission at such a great height (above 6 R⊙).

Movies are available at https://www.aanda.org Title: Observation of Magnetic Switchback in the Solar Corona Authors: Telloni, Daniele; Zank, Gary P.; Stangalini, Marco; Downs, Cooper; Liang, Haoming; Nakanotani, Masaru; Andretta, Vincenzo; Antonucci, Ester; Sorriso-Valvo, Luca; Adhikari, Laxman; Zhao, Lingling; Marino, Raffaele; Susino, Roberto; Grimani, Catia; Fabi, Michele; D'Amicis, Raffaella; Perrone, Denise; Bruno, Roberto; Carbone, Francesco; Mancuso, Salvatore; Romoli, Marco; Da Deppo, Vania; Fineschi, Silvano; Heinzel, Petr; Moses, John D.; Naletto, Giampiero; Nicolini, Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Frassati, Federica; Jerse, Giovanna; Landini, Federico; Pancrazzi, Maurizio; Russano, Giuliana; Sasso, Clementina; Berghmans, David; Auchère, Frédéric; Aznar Cuadrado, Regina; Chitta, Lakshmi P.; Harra, Louise; Kraaikamp, Emil; Long, David M.; Mandal, Sudip; Parenti, Susanna; Pelouze, Gabriel; Peter, Hardi; Rodriguez, Luciano; Schühle, Udo; Schwanitz, Conrad; Smith, Phil J.; Verbeeck, Cis; Zhukov, Andrei N. Bibcode: 2022arXiv220603090T Altcode: Switchbacks are sudden, large radial deflections of the solar wind magnetic field, widely revealed in interplanetary space by the Parker Solar Probe. The switchbacks' formation mechanism and sources are still unresolved, although candidate mechanisms include Alfvénic turbulence, shear-driven Kelvin-Helmholtz instabilities, interchange reconnection, and geometrical effects related to the Parker spiral. This Letter presents observations from the Metis coronagraph onboard Solar Orbiter of a single large propagating S-shaped vortex, interpreted as first evidence of a switchback in the solar corona. It originated above an active region with the related loop system bounded by open-field regions to the East and West. Observations, modeling, and theory provide strong arguments in favor of the interchange reconnection origin of switchbacks. Metis measurements suggest that the initiation of the switchback may also be an indicator of the origin of slow solar wind. 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: Constraining stellar CMEs by solar observations Authors: Leitzinger, Martin; Odert, Petra; Leka, K. D.; Heinzel, Petr; Dissauer, Karin Bibcode: 2021AGUFM.U43B..06L Altcode: Stellar coronal mass ejections (CMEs) may play an important role in star-planet interactions, such as planetary atmospheric escape, and in stellar mass- and angular momentum loss, influencing stellar evolution. In the last decades much effort has been put into determining parameters of stellar CMEs. New detection methods have been developed, but still the number of convincing events is low and far from enabling statistical analyses. So far the methods of detections comprise the direct signature of ejected plasma, namely Doppler shifted emission/absorption visible in spectra (optical, UV, X-ray), absorptions seen during flares in X-rays interpreted as obscuring events, and CME-associated signatures known from the Sun, like radio type II bursts and coronal dimmings, the latter being only recently established. The first method (Doppler shifted emission/absorption lines) has been used since decades on stars (especially in H which well probes the eruptive filament/prominence in the CME core) and provides a few convincing detections and a large number of candidate events with projected velocities significantly below the stars' escape velocities. Such events could be CMEs seen in projection but it has been proposed that these signatures could be caused by flare related plasma dynamics. As there is a large pool of candidate events which cannot be unambiguously interpreted as CMEs, we propose a new approach to distinguish between flare and CME related signtures to increase the number of convincing CME events. What we observe from stars are disk integrated signals, in contrast to solar observations. To constrain stellar CMEs by solar observations, solar 2D imaging spectroscopy is required from which spatially integrated spectra can be created for a sufficiently large number of events (flares and CMEs). These aspects are fulfilled by MEES CCD (MCCD) optical observations at Mees Solar Observatory (MSO). Therefore we propose the analysis of a sample of solar flares and filaments/prominences from MCCD/MSO and their spatially integrated spectra which allows to separate contributions from flares and filaments/prominences. We present preliminary results of a few selected solar events from MCCD demonstrating how to characterize flare and CME related signatures in stellar observations. Title: Empirical atmosphere model in a mini flare during magnetic reconnection Authors: Schmieder, Brigitte; Joshi, Reetika; Chandra, Ramesh; Aulanier, Guillaume; Tei, Akiko; Heinzel, Petr; Tomin, James; Vilmer, Nicole; Bommier, Veronique Bibcode: 2021arXiv211206790S Altcode: A spatio-temporal analysis of IRIS spectra of MgII, CII, and SiIV ions allows us to study the dynamics and the stratification of the flare atmosphere along the line of sight during the magnetic reconnection phase at the jet base. Strong asymmetric MgII and CII line profiles with extended blue wings observed at the reconnection site are interpreted by the presence of two chromospheric temperature clouds: one explosive cloud with blueshifts at 290 km/s and one cloud with smaller Doppler shift (around 36 km/s). Simultaneously at the same location a mini flare was observed with strong emission in multi temperatures (AIA), in several spectral IRIS lines (e.g. Oiv and Siiv, Mgii), absorption of identified chromospheric lines in Siiv line profile, enhancement of the Balmer continuum and X-ray emission by FERMI/GBM. With the standard thick-target flare model we calculate the energy of non thermal electrons observed by FERMI and compare it to the energy radiated by the Balmer continuum emission. We show that the low energy input by non thermal electrons above 20 keV was still sufficient to produce the excess of Balmer continuum. Title: The first coronal mass ejection observed in both visible-light and UV H I Ly-α channels of the Metis coronagraph on board Solar Orbiter Authors: Andretta, V.; Bemporad, A.; De Leo, Y.; Jerse, G.; Landini, F.; Mierla, M.; Naletto, G.; Romoli, M.; Sasso, C.; Slemer, A.; Spadaro, D.; Susino, R.; Talpeanu, D. -C.; Telloni, D.; Teriaca, L.; Uslenghi, M.; Antonucci, E.; Auchère, F.; Berghmans, D.; Berlicki, A.; Capobianco, G.; Capuano, G. E.; Casini, C.; Casti, M.; Chioetto, P.; Da Deppo, V.; Fabi, M.; Fineschi, S.; Frassati, F.; Frassetto, F.; Giordano, S.; Grimani, C.; Heinzel, P.; Liberatore, A.; Magli, E.; Massone, G.; Messerotti, M.; Moses, D.; Nicolini, G.; Pancrazzi, M.; Pelizzo, M. -G.; Romano, P.; Schühle, U.; Stangalini, M.; Straus, Th.; Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Aznar Cuadrado, R.; Bruno, R.; Ciaravella, A.; D'Amicis, R.; Lamy, P.; Lanzafame, A.; Malvezzi, A. M.; Nicolosi, P.; Nisticò, G.; Peter, H.; Plainaki, C.; Poletto, L.; Reale, F.; Solanki, S. K.; Strachan, L.; Tondello, G.; Tsinganos, K.; Velli, M.; Ventura, R.; Vial, J. -C.; Woch, J.; Zimbardo, G. Bibcode: 2021A&A...656L..14A Altcode: Context. The Metis coronagraph on board Solar Orbiter offers a new view of coronal mass ejections (CMEs), observing them for the first time with simultaneous images acquired with a broad-band filter in the visible-light interval and with a narrow-band filter around the H I Ly-α line at 121.567 nm, the so-called Metis UV channel.
Aims: We show the first Metis observations of a CME, obtained on 16 and 17 January 2021. The event was also observed by the EUI/FSI imager on board Solar Orbiter, as well as by other space-based coronagraphs, such as STEREO-A/COR2 and SOHO/LASCO/C2, whose images are combined here with Metis data.
Methods: Different images are analysed here to reconstruct the 3D orientation of the expanding CME flux rope using the graduated cylindrical shell model. This also allows us to identify the possible location of the source region. Measurements of the CME kinematics allow us to quantify the expected Doppler dimming in the Ly-α channel.
Results: Observations show that most CME features seen in the visible-light images are also seen in the Ly-α images, although some features in the latter channel appear more structured than their visible-light counterparts. We estimated the expansion velocity of this event to be below 140 km s−1. Hence, these observations can be understood by assuming that Doppler dimming effects do not strongly reduce the Ly-α emission from the CME. These velocities are comparable with or smaller than the radial velocities inferred from the same data in a similar coronal structure on the east side of the Sun.
Conclusions: The first observations by Metis of a CME demonstrate the capability of the instrument to provide valuable and novel information on the structure and dynamics of these coronal events. Considering also its diagnostics capabilities regarding the conditions of the ambient corona, Metis promises to significantly advance our knowledge of such phenomena.

Movies are available at https://www.aanda.org Title: Cosmic-ray flux predictions and observations for and with Metis on board Solar Orbiter Authors: Grimani, C.; Andretta, V.; Chioetto, P.; Da Deppo, V.; Fabi, M.; Gissot, S.; Naletto, G.; Persici, A.; Plainaki, C.; Romoli, M.; Sabbatini, F.; Spadaro, D.; Stangalini, M.; Telloni, D.; Uslenghi, M.; Antonucci, E.; Bemporad, A.; Capobianco, G.; Capuano, G.; Casti, M.; De Leo, Y.; Fineschi, S.; Frassati, F.; Frassetto, F.; Heinzel, P.; Jerse, G.; Landini, F.; Liberatore, A.; Magli, E.; Messerotti, M.; Moses, D.; Nicolini, G.; Pancrazzi, M.; Pelizzo, M. G.; Romano, P.; Sasso, C.; Schühle, U.; Slemer, A.; Straus, T.; Susino, R.; Teriaca, L.; Volpicelli, C. A.; Freiherr von Forstner, J. L.; Zuppella, P. Bibcode: 2021A&A...656A..15G Altcode: 2021arXiv210413700G Context. The Metis coronagraph is one of the remote sensing instruments hosted on board the ESA/NASA Solar Orbiter mission. Metis is devoted to carry out the first simultaneous imaging of the solar corona in both visible light (VL) and ultraviolet (UV). High-energy particles can penetrate spacecraft materials and may limit the performance of the on-board instruments. A study of the galactic cosmic-ray (GCR) tracks observed in the first VL images gathered by Metis during the commissioning phase is presented here. A similar analysis is planned for the UV channel.
Aims: We aim to formulate a prediction of the GCR flux up to hundreds of GeV for the first part of the Solar Orbiter mission to study the performance of the Metis coronagraph.
Methods: The GCR model predictions are compared to observations gathered on board Solar Orbiter by the High-Energy Telescope in the range between 10 MeV and 100 MeV in the summer of 2020 as well as with the previous measurements. Estimated cosmic-ray fluxes above 70 MeV n−1 have been also parameterized and used for Monte Carlo simulations aimed at reproducing the cosmic-ray track observations in the Metis coronagraph VL images. The same parameterizations can also be used to study the performance of other detectors.
Results: By comparing observations of cosmic-ray tracks in the Metis VL images with FLUKA Monte Carlo simulations of cosmic-ray interactions in the VL detector, we find that cosmic rays fire only a fraction, on the order of 10−4, of the whole image pixel sample. We also find that the overall efficiency for cosmic-ray identification in the Metis VL images is approximately equal to the contribution of Z ≥ 2 GCR particles. A similar study will be carried out during the whole of the Solar Orbiter's mission duration for the purposes of instrument diagnostics and to verify whether the Metis data and Monte Carlo simulations would allow for a long-term monitoring of the GCR proton flux. Title: First light observations of the solar wind in the outer corona with the Metis coronagraph Authors: Romoli, M.; Antonucci, E.; Andretta, V.; Capuano, G. E.; Da Deppo, V.; De Leo, Y.; Downs, C.; Fineschi, S.; Heinzel, P.; Landini, F.; Liberatore, A.; Naletto, G.; Nicolini, G.; Pancrazzi, M.; Sasso, C.; Spadaro, D.; Susino, R.; Telloni, D.; Teriaca, L.; Uslenghi, M.; Wang, Y. -M.; Bemporad, A.; Capobianco, G.; Casti, M.; Fabi, M.; Frassati, F.; Frassetto, F.; Giordano, S.; Grimani, C.; Jerse, G.; Magli, E.; Massone, G.; Messerotti, M.; Moses, D.; Pelizzo, M. -G.; Romano, P.; Schühle, U.; Slemer, A.; Stangalini, M.; Straus, T.; Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Auchère, F.; Aznar Cuadrado, R.; Berlicki, A.; Bruno, R.; Ciaravella, A.; D'Amicis, R.; Lamy, P.; Lanzafame, A.; Malvezzi, A. M.; Nicolosi, P.; Nisticò, G.; Peter, H.; Plainaki, C.; Poletto, L.; Reale, F.; Solanki, S. K.; Strachan, L.; Tondello, G.; Tsinganos, K.; Velli, M.; Ventura, R.; Vial, J. -C.; Woch, J.; Zimbardo, G. Bibcode: 2021A&A...656A..32R Altcode: 2021arXiv210613344R In this work, we present an investigation of the wind in the solar corona that has been initiated by observations of the resonantly scattered ultraviolet emission of the coronal plasma obtained with UVCS-SOHO, designed to measure the wind outflow speed by applying Doppler dimming diagnostics. Metis on Solar Orbiter complements the UVCS spectroscopic observations that were performed during solar activity cycle 23 by simultaneously imaging the polarized visible light and the H I Lyman-α corona in order to obtain high spatial and temporal resolution maps of the outward velocity of the continuously expanding solar atmosphere. The Metis observations, taken on May 15, 2020, provide the first H I Lyman-α images of the extended corona and the first instantaneous map of the speed of the coronal plasma outflows during the minimum of solar activity and allow us to identify the layer where the slow wind flow is observed. The polarized visible light (580-640 nm) and the ultraviolet H I Lyα (121.6 nm) coronal emissions, obtained with the two Metis channels, were combined in order to measure the dimming of the UV emission relative to a static corona. This effect is caused by the outward motion of the coronal plasma along the direction of incidence of the chromospheric photons on the coronal neutral hydrogen. The plasma outflow velocity was then derived as a function of the measured Doppler dimming. The static corona UV emission was simulated on the basis of the plasma electron density inferred from the polarized visible light. This study leads to the identification, in the velocity maps of the solar corona, of the high-density layer about ±10° wide, centered on the extension of a quiet equatorial streamer present at the east limb - the coronal origin of the heliospheric current sheet - where the slowest wind flows at about 160 ± 18 km s−1 from 4 R⊙ to 6 R⊙. Beyond the boundaries of the high-density layer, the wind velocity rapidly increases, marking the transition between slow and fast wind in the corona. Title: Analysis and modeling of the dynamics of the glow of calcium and hydrogen lines in solar and stellar flares Authors: Kupryakov, Yurij Alekseevich; Bychkov, Konstantin Veniaminovich; Belova, Oksana Mikhailovna; Gorshkov, Alexey Borisovich; Heinzel, Petr; Kotrč, Pavel Bibcode: 2021OAst...30...91K Altcode: We present intensity curves of solar flares obtained in the Hα hydrogen line and CaII H, CaIR 8542Å lines using multichannel spectrographs of Ondřejov Observatory (Czech Republic) for the period 2000-2012. The general behavior of observed intensity curves is practically the same for all flares and is consistent with temporal variations of X-ray emission. However, our results differ significantly from those obtained by other authors for selected flare stars, for example, AD Leo; EV Lac; YZ CMi. We tried to explain the difference in the behavior of Ca II and Hα radiation flux by appearance of a shock wave during a flare and slow heating of the plasma. Title: Balmer continuum enhancement detected in a mini flare observed with IRIS Authors: Joshi, Reetika; Schmieder, Brigitte; Heinzel, Petr; Tomin, James; Chandra, Ramesh; Vilmer, Nicole Bibcode: 2021A&A...654A..31J Altcode: 2021arXiv210711651J Context. Optical and near-UV continuum emissions in flares contribute substantially to the flare energy budget. Two mechanisms play an important role for continuum emission in flares: hydrogen recombination after sudden ionization at chromospheric layers, and transportation of the energy radiatively from the chromosphere to lower layers in the atmosphere, the so-called back-warming.
Aims: The aim of the paper is to distinguish between these two mechanisms for the excess of the Balmer continuum observed in a flare.
Methods: We combined the observations of the Balmer continuum obtained with the Interface Region Imaging Spectrograph (IRIS) (spectra and slit-jaw images (SJIs) 2832 Å) and hard X-ray (HXR) emission detected by the Fermi/Gamma Burst Monitor (GBM) during a mini flare. The calibrated Balmer continuum was compared to non-local thermodynamic equilibrium (LTE) radiative transfer flare models, and the radiated energy was estimated. Assuming thick target HXR emission, we calculated the energy of the nonthermal electrons detected by the Fermi/GBM and compared it to the radiated energy.
Results: The favorable argument of a relation between the Balmer continuum excess and the HXR emission is that there is a good time coincidence between them. In addition, the shape of the maximum brightness in the 2832 SJIs, which is mainly due to this Balmer continuum excess, is similar to that of the Fermi/GBM light curve. The electron-beam flux estimated from Fermi/GBM between 109 and 1010 erg s−1 cm−2 is consistent with the beam flux required in non-LTE radiative transfer models to obtain the excess of Balmer continuum emission observed in this IRIS spectra.
Conclusions: The low-energy input by nonthermal electrons above 20 keV is sufficient to produce the enhancement in the Balmer continuum emission. This could be explained by the topology of the reconnection site. The reconnection starts in a tiny bald-patch region, which is transformed dynamically into an X-point current sheet. The size of the interacting region would be below the spatial resolution of the instrument. Title: On the importance of Ca II photoionization by the hydrogen lyman transitions in solar flare models Authors: Osborne, C. M. J.; Heinzel, P.; Kašparová, J.; Fletcher, L. Bibcode: 2021MNRAS.507.1972O Altcode: 2021MNRAS.tmp.1947O; 2021arXiv210711145O The forward fitting of solar flare observations with radiation-hydrodynamic simulations is a common technique for learning about energy deposition and atmospheric evolution during these explosive events. A frequent spectral line choice for this process is Ca II 854.2 nm due to its formation in the chromosphere and substantial variability. It is important to ensure that this line is accurately modelled to obtain the correct interpretation of observations. Here, we investigate the importance of photoionization of Ca II to Ca III by the hydrogen Lyman transitions, whilst the Lyman continuum is typically considered in this context in simulations, the associated bound-bound transitions are not. This investigation uses two RADYN flare simulations and reprocesses the radiative transfer using the Lightweaver framework which accounts for the overlapping of all active transitions. The Ca II 854.2 nm line profiles are found to vary significantly due to photoionization by the Lyman lines, showing notably different shapes and even reversed asymmetries. Finally, we investigate to what extent these effects modify the energy balance of the simulation and the implications on future radiation-hydrodynamic simulations. There is found to be a 10-15 per cent change in detailed optically thick radiative losses from considering these photoionization effects on the calcium lines in the two simulations presented, demonstrating the importance of considering these effects in a self-consistent way. 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: Exploring the Solar Wind from Its Source on the Corona into the Inner Heliosphere during the First Solar Orbiter-Parker Solar Probe Quadrature Authors: Telloni, Daniele; Andretta, Vincenzo; Antonucci, Ester; Bemporad, Alessandro; Capuano, Giuseppe E.; Fineschi, Silvano; Giordano, Silvio; Habbal, Shadia; Perrone, Denise; Pinto, Rui F.; Sorriso-Valvo, Luca; Spadaro, Daniele; Susino, Roberto; Woodham, Lloyd D.; Zank, Gary P.; Romoli, Marco; Bale, Stuart D.; Kasper, Justin C.; Auchère, Frédéric; Bruno, Roberto; Capobianco, Gerardo; Case, Anthony W.; Casini, Chiara; Casti, Marta; Chioetto, Paolo; Corso, Alain J.; Da Deppo, Vania; De Leo, Yara; Dudok de Wit, Thierry; Frassati, Federica; Frassetto, Fabio; Goetz, Keith; Guglielmino, Salvo L.; Harvey, Peter R.; Heinzel, Petr; Jerse, Giovanna; Korreck, Kelly E.; Landini, Federico; Larson, Davin; Liberatore, Alessandro; Livi, Roberto; MacDowall, Robert J.; Magli, Enrico; Malaspina, David M.; Massone, Giuseppe; Messerotti, Mauro; Moses, John D.; Naletto, Giampiero; Nicolini, Gianalfredo; Nisticò, Giuseppe; Panasenco, Olga; Pancrazzi, Maurizio; Pelizzo, Maria G.; Pulupa, Marc; Reale, Fabio; Romano, Paolo; Sasso, Clementina; Schühle, Udo; Stangalini, Marco; Stevens, Michael L.; Strachan, Leonard; Straus, Thomas; Teriaca, Luca; Uslenghi, Michela; Velli, Marco; Verscharen, Daniel; Volpicelli, Cosimo A.; Whittlesey, Phyllis; Zangrilli, Luca; Zimbardo, Gaetano; Zuppella, Paola Bibcode: 2021ApJ...920L..14T Altcode: 2021arXiv211011031T This Letter addresses the first Solar Orbiter (SO)-Parker Solar Probe (PSP) quadrature, occurring on 2021 January 18 to investigate the evolution of solar wind from the extended corona to the inner heliosphere. Assuming ballistic propagation, the same plasma volume observed remotely in the corona at altitudes between 3.5 and 6.3 solar radii above the solar limb with the Metis coronagraph on SO can be tracked to PSP, orbiting at 0.1 au, thus allowing the local properties of the solar wind to be linked to the coronal source region from where it originated. Thanks to the close approach of PSP to the Sun and the simultaneous Metis observation of the solar corona, the flow-aligned magnetic field and the bulk kinetic energy flux density can be empirically inferred along the coronal current sheet with an unprecedented accuracy, allowing in particular estimation of the Alfvén radius at 8.7 solar radii during the time of this event. This is thus the very first study of the same solar wind plasma as it expands from the sub-Alfvénic solar corona to just above the Alfvén surface. 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: In-flight optical performance assessment for the Metis solar coronagraph Authors: Da Deppo, Vania; Chioetto, Paolo; Andretta, Vincenzo; Casini, Chiara; Frassetto, Fabio; Slemer, Alessandra; Zuppella, Paola; Romoli, Marco; Fineschi, Silvano; Heinzel, Petr; Naletto, Giampiero; Nicolini, Gianalfredo; Spadaro, Daniele; Stangalini, Marco; Teriaca, Luca; Bemporad, Alessandro; Casti, Marta; Fabi, Michele; Grimani, Catia; Heerlein, Klaus; Jerse, Giovanna; Landini, Federico; Liberatore, Alessandro; Magli, Enrico; Melich, Radek; Pancrazzi, Maurizio; Pelizzo, Maria-G.; Romano, Paolo; Sasso, Clementina; Straus, Thomas; Susino, Roberto; Uslenghi, Michela; Volpicelli, Cosimo Antonio Bibcode: 2021SPIE11852E..10D Altcode: Metis is a multi-wavelength coronagraph onboard the European Space Agency (ESA) Solar Orbiter mission. The instrument features an innovative instrument design conceived for simultaneously imaging the Sun's corona in the visible and ultraviolet range. The Metis visible channel employs broad-band, polarized imaging of the visible K-corona, while the UV one uses narrow-band imaging at the HI Ly 􀄮, i.e. 121.6 nm. During the commissioning different acquisitions and activities, performed with both the Metis channels, have been carried out with the aim to check the functioning and the performance of the instrument. In particular, specific observations of stars have been devised to assess the optical alignment of the telescope and to derive the instrument optical parameters such as focal length, PSF and possibly check the optical distortion and the vignetting function. In this paper, the preliminary results obtained for the PSF of both channels and the determination of the scale for the visible channel will be described and discussed. The in-flight obtained data will be compared to those obtained on-ground during the calibration campaign. Title: On-ground flat-field calibration of the Metis coronagraph onboard the Solar Orbiter ESA mission Authors: Casini, C.; Da Deppo, V.; Zuppella, P.; Chioetto, P.; Slemer, A.; Frassetto, F.; Romoli, M.; Landini, F.; Pancrazzi, M.; Andretta, V.; De Leo, Y.; Bemporad, A.; Fabi, M.; Fineschi, S.; Frassati, F.; Grimani, C.; Jerse, G.; Heerlein, K.; Liberatore, A.; Magli, E.; Naletto, G.; Nicolini, G.; Pelizzo, M. G.; Romano, P.; Sasso, C.; Spadaro, D.; Stangalini, M.; Straus, T.; Susino, R.; Teriaca, L.; Uslenghi, M.; Casti, M.; Heinzel, P.; Volpicelli, A. Bibcode: 2021SPIE11852E..5BC Altcode: Solar Orbiter, launched on February 9th 2020, is an ESA/NASA mission conceived to study the Sun. This work presents the embedded Metis coronagraph and its on-ground calibration in the 580-640 nm wavelength range using a flat field panel. It provides a uniform illumination to evaluate the response of each pixel of the detector; and to characterize the Field of View (FoV) of the coronagraph. Different images with different exposure times were acquired during the on-ground calibration campaign. They were analyzed to verify the linearity response of the instrument and the requirements for the FoV: the maximum area of the sky that Metis can acquire. Title: Challenges during Metis-Solar Orbiter commissioning phase Authors: Romoli, Marco; Andretta, Vincenzo; Bemporad, Alessandro; Casti, Marta; Da Deppo, Vania; De Leo, Yara; Fabi, Michele; Fineschi, Silvano; Frassetto, Fabio; Grimani, Catia; Heerlein, Klaus; Heinzel, Petr; Jerse, Giovanna; Landini, Federico; Liberatore, Alessandro; Magli, Enrico; Naletto, Giampiero; Nicolini, Gianalfredo; Pancrazzi, Maurizio; Pelizzo, Maria Guglielmina; Romano, Paolo; Sasso, Clementina; Schühle, Udo; Slemer, Alessandra; Spadaro, Daniele; Straus, Thomas; Susino, Roberto; Teriaca, Luca; Uslenghi, Michela; Volpicelli, Cosimo Antonio; Zupella, Paola Bibcode: 2021SPIE11852E..5AR Altcode: Metis is the visible light and UV light imaging coronagraph on board the ESA-NASA mission Solar Orbiter that has been launched February 10th, 2020, from Cape Canaveral. Scope of the mission is to study the Sun up close, taking high-resolution images of the Sun's poles for the first time, and understanding the Sun-Earth connection. Metis coronagraph will image the solar corona in the linearly polarized broadband visible radiation and in the UV HI Ly-α line from 1.6 to 3 solar radii when at Solar Orbiter perihelion, providing a diagnostics, with unprecedented temporal coverage and spatial resolution, of the structures and dynamics of the full corona. Solar Orbiter commissioning phase big challenge was Covid-19 social distancing phase that affected the way commissioning of a spacecraft and its payload is typically done. Metis coronagraph on-board Solar Orbiter had its additional challenges: to wake up and check the performance of the optical, electrical and thermal subsystems, most of them unchecked since Metis delivery to spacecraft prime, Airbus, in May 2017. The roadmap to the fully commissioned coronagraph is here described throughout the steps from the software functional test, the switch on of the detectors of the two channels, UV and visible, to the optimization of the occulting system and the characterization of the instrumental stray light, one of the most challenging features in a coronagraph. Title: In-flight calibration of Metis coronagraph on board of Solar Orbiter Authors: Liberatore, A.; Fineschi, S.; Casti, M.; Capobianco, G.; Romoli, M.; Andretta, V.; Bemporad, A.; Da Deppo, V.; De Leo, Y.; Fabi, M.; Frassetto, F.; Grimani, C.; Heerlein, K.; Heinzel, P.; Jerse, G.; Landini, F.; Magli, E.; Naletto, G.; Nicolini, G.; Pancrazzi, M.; Pelizzo, M. G.; Romano, P.; Sasso, C.; Slemer, A.; Spadaro, D.; Straus, T.; Susino, R.; Teriaca, L.; Uslenghi, M.; Volpicelli, C. A.; Zuppella, P. Bibcode: 2021SPIE11852E..48L Altcode: Metis coronagraph is one of the remote-sensing instruments of the Solar Orbiter mission launched at the begin of 2020. The mission profile will allow for the first time the remote-sensing observation of the Sun from a very close distance and increasing the latitude with respect to the ecliptic plane. In particular, Metis is aimed at the overall characterization and study of the solar corona and solar wind. Metis instrument acquires images of the solar corona in two different wavelengths simultaneously; ultraviolet (UV) and visible-light (VL). The VL channel includes a polarimeter with an electro-optically modulating Liquid Crystal Variable Retarder (LCVR) to measure the linearly polarized brighness pB) of the K-corona. This paper presents part of the in-flight calibration results for both wavelength channels together with a comparison with on-ground calibrations. The orientation of the K-corona linear polarization was used for the in-flight calibration of the Metis polarimeter. This paper describes the correction of the on-ground VL vignetting function after the in-flight adjustment of the internal occulter. The same vignetting function was adaptated to the UV channel. Title: IRIS observations of chromospheric heating by acoustic waves in solar quiet and active regions Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.; Liu, W.; Mravcová, L. Bibcode: 2021A&A...648A..28A Altcode: 2021arXiv210208678A
Aims: To study the heating of solar chromospheric magnetic and nonmagnetic regions by acoustic and magnetoacoustic waves, the deposited acoustic-energy flux derived from observations of strong chromospheric lines is compared with the total integrated radiative losses.
Methods: A set of 23 quiet-Sun and weak-plage regions were observed in the Mg II k and h lines with the Interface Region Imaging Spectrograph (IRIS). The deposited acoustic-energy flux was derived from Doppler velocities observed at two different geometrical heights corresponding to the middle and upper chromosphere. A set of scaled nonlocal thermodynamic equilibrium 1D hydrostatic semi-empirical models - obtained by fitting synthetic to observed line profiles - was applied to compute the radiative losses. The characteristics of observed waves were studied by means of a wavelet analysis.
Results: Observed waves propagate upward at supersonic speed. In the quiet chromosphere, the deposited acoustic flux is sufficient to balance the radiative losses and maintain the semi-empirical temperatures in the layers under study. In the active-region chromosphere, the comparison shows that the contribution of acoustic-energy flux to the radiative losses is only 10−30%.
Conclusions: Acoustic and magnetoacoustic waves play an important role in the chromospheric heating, depositing a main part of their energy in the chromosphere. Acoustic waves compensate for a substantial fraction of the chromospheric radiative losses in quiet regions. In active regions, their contribution is too small to balance the radiative losses and the chromosphere has to be heated by other mechanisms. Title: Constraining stellar CME occurrence with optical spectroscopy Authors: Odert, Petra; Leitzinger, Martin; Guenther, Eike W.; Heinzel, Petr Bibcode: 2021csss.confE..96O Altcode: Our knowledge on coronal mass ejections (CMEs) on stars other than the Sun is still sparse. Spectroscopic observations in the optical sometimes show asymmetrically broadened wings and/or transient extra-emissions in chromospheric lines during or shortly after flare events. These may be interpreted as signatures of prominence eruptions, which are closely related to CMEs on the Sun. Dedicated searches for these signatures have, however, mostly yielded non-detections. Here we present a semi-empirical model which combines predictions of intrinsic stellar CME rates with simple radiative transfer calculations in the Balmer lines. We find that typical observations have most likely been too short and/or they had a too low signal-to-noise ratio to detect CMEs. We predict the minimum observing time needed to detect CMEs in the Balmer lines for stars with different spectral types and activity levels. Title: Multi-thermal atmosphere of a mini-solar flare during magnetic reconnection observed with IRIS Authors: Joshi, Reetika; Schmieder, Brigitte; Tei, Akiko; Aulanier, Guillaume; Lörinčík, Juraj; Chandra, Ramesh; Heinzel, Petr Bibcode: 2021A&A...645A..80J Altcode: 2020arXiv201015401J Context. The Interface Region Imaging Spectrograph (IRIS) with its high spatial and temporal resolution facilitates exceptional plasma diagnostics of solar chromospheric and coronal activity during magnetic reconnection.
Aims: The aim of this work is to study the fine structure and dynamics of the plasma at a jet base forming a mini-flare between two emerging magnetic fluxes (EMFs) observed with IRIS and the Solar Dynamics Observatory instruments.
Methods: We proceed to a spatio-temporal analysis of IRIS spectra observed in the spectral ranges of Mg II, C II, and Si IV ions. Doppler velocities from Mg II lines were computed using a cloud model technique.
Results: Strong asymmetric Mg II and C II line profiles with extended blue wings observed at the reconnection site (jet base) are interpreted by the presence of two chromospheric temperature clouds: one explosive cloud with blueshifts at 290 km s-1 and one cloud with smaller Doppler shift (around 36 km s-1). Simultaneously at the same location (jet base), strong emission of several transition region lines (e.g. O IV and Si IV), emission of the Mg II triplet lines, and absorption of identified chromospheric lines in Si IV broad profiles have been observed and analysed.
Conclusions: Such observations of IRIS line and continuum emissions allow us to propose a stratification model for the white light, mini-flare atmosphere with multiple layers of different temperatures along the line of sight in a reconnection current sheet. It is the first time that we could quantify the fast speed (possibly Alfvénic flows) of cool clouds ejected perpendicularly to the jet direction via the cloud model technique. We conjecture that the ejected clouds come from plasma which was trapped between the two EMFs before reconnection or be caused by chromospheric-temperature (cool) upflow material similar to a surge during reconnection.

Movies are available at https://www.aanda.org 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: Cool flare loops in solar and stellar coronae Authors: Heinzel, Petr Bibcode: 2021cosp...43E.969H Altcode: Cool structures in solar and stellar coronae may take various forms like prominences, cores of CMEs or cool flare loops which often exhibit the so-called coronal rain. In this talk we will focus on the latter structures which recently attracted a great attention in relation with largest solar flares observed during the 24th solar cycle. We will summarise the multi-wavelength observations of giant off-limb post-flare loops from September 10, 2017 and show the principally new results concerning their magnetic fields and overall densities. High densities obtained certainly require a strong magnetic field to keep the loops stably confined in the corona. Downflows consistent with the coronal rain and high non-thermal motions (the so-called microturbulence) have been detected. Moreover, SDO/HMI data also indicate high densities which would be compatible with those predicted in loops expected on other cool stars. These conditions are favourable for explanation of the continuum emission enhancements during superflares, in terms of the loop-arcade component. However, in order to explain the superflare behaviour, large loop-arcade areas are required as suggested in Heinzel and Shibata 2018. Finally, we will show the effect of cool stellar loops on the spectral line emission variations during a flare which seems to be an unresolved mixture of ribbon and loop emission. 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: Metis - Solar Orbiter Topical Team on "Modelling of CME propagation/evolution in corona and solar wind in connection with Space Weather" Authors: Bemporad, A.; Banerjee, D.; Berlicki, A.; Biondo, R.; Boe, B.; Calchetti, D.; Capuano, G.; De Leo, Y.; Del Moro, D.; Feng, L.; Foldes, R.; Frassati, F.; Frazin, R. A.; Giovannelli, L.; Giunta, A. S.; Heinzel, P.; Ippolito, A.; Janvier, M.; Jerse, G.; Kilpua, K. E. J.; Laurenza, M.; Lloveras, D.; Magdalenic, J.; Mancuso, S.; Messerotti, M.; Mierla, M.; Nandy, D.; Napoletano, G.; Nuevo, F.; Pagano, P.; Pinto, R.; Plainaki, C.; Reale, F.; Romoli, M.; Rodriguez, L.; Slemer, A.; Spadaro, D.; Susino, R.; Stangalini, M.; Vainio, R. O.; Valori, G.; Vásquez, A. M.; West, M. J. Bibcode: 2020AGUFMSH0360027B Altcode: Despite the current availability of multi-spacecraft observations of Coronal Mass Ejections (CMEs) and their interplanetary counterpart (ICMEs), at present we still don't understand which physical phenomena are driving their expansion and propagation phases. This also limits our understanding on how CMEs (observed with remote sensing data) become ICMEs (observed in situ), how they interact with the background solar wind, and how their final geo-effectiveness can be modified during their interplanetary evolution. Such problems match some of the scientific objectives of the Solar Orbiter Science Activity Plan and of the Metis coronagraph. Thanks to its multi-channel capability, Metis (acquiring images in the visible light and at the same time in the UV HI Lyman-alpha emission) will really provide an unprecedented view of CMEs and in particular of their thermodynamic evolution. At closest approaches to the Sun (in the nominal mission), Metis will acquire high spatial resolution and/or temporal cadence multi-channel images of CMEs. Farther from the Sun, Metis will shed light on the early Interplanetary propagation of CMEs. Later on (in the extended mission) Metis will observe for the first time the CME/ICME propagation out-of-ecliptic. These novelties will be combined with the unique vantage point that will be offered by the Solar Orbiter spacecraft, and supported with valuable data acquired by other on-board remote sensing (e.g. SPICE, EUI, SoloHI) and in situ (e.g. EPD, MAG, SWA, RPW) instruments. In this contribution we present the ongoing activities of the Metis Topical Team on "CME/ICME propagation", (http://metis.oato.inaf.it/topical_teams.html), an international working group recently established and gathering scientists from different countries, experts of both in-situ and remote sensing observations, as well as numerical simulations, and we summarize the main science objectives discussed during the last months. Title: Solar Orbiter: connecting remote sensing and in situ measurements Authors: Horbury, T. S.; Auchere, F.; Antonucci, E.; Berghmans, D.; Bruno, R.; Carlsson, M.; del Toro Iniesta, J. C.; Fludra, A.; Harra, L.; Hassler, D.; Heinzel, P.; Howard, R. A.; Krucker, S.; Livi, S. A.; Long, D.; Louarn, P.; Maksimovic, M.; Mueller, D.; Owen, C. J.; Peter, H.; Rochus, P. L.; Rodriguez-Pacheco, J.; Romoli, M.; Schühle, U.; Solanki, S. K.; Teriaca, L.; Wimmer-Schweingruber, R. F.; Zouganelis, Y.; Laker, R. Bibcode: 2020AGUFMSH038..10H Altcode: A key science goal of the Solar Orbiter mission is to make connections between phenomena on the Sun and their manifestations in interplanetary space. To that end, the spacecraft carries a carefully tailored payload of six remote sensing instruments and four making in situ measurements. During June 2020, while the spacecraft was around 0.5 AU from the Sun, the remote sensing instruments operated for several days. While this was primarily an engineering activity, the resulting observations provided outstanding measurements and represent the ideal first opportunity to investigate the potential for making connections between the remote sensing and in situ payloads on Solar Orbiter.

We present a preliminary analysis of the available remote sensing and in situ observations, showing how connections can be made, and discuss the potential for further, more precise mapping to be performed as the mission progresses. Title: Observational study of chromospheric heating by acoustic waves Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.; García-Rivas, M.; Denker, C.; Balthasar, H.; Verma, M.; Kontogiannis, I.; Koza, J.; Korda, D.; Kuckein, C. Bibcode: 2020A&A...642A..52A Altcode: 2020arXiv200802688A
Aims: Our aim is to investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere. Observations in strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses.
Methods: Quiet-Sun and weak-plage regions were observed in the Ca II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph (FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and in the Hα and Hβ lines with the echelle spectrograph attached to the Vacuum Tower Telescope on 2018 December 11 and 2019 June 6. The deposited acoustic energy flux at frequencies up to 20 mHz was derived from Doppler velocities observed in line centers and wings. Radiative losses were computed by means of a set of scaled non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models obtained by fitting synthetic to observed line profiles.
Results: In the middle chromosphere (h = 1000-1400 km), the radiative losses can be fully balanced by the deposited acoustic energy flux in a quiet-Sun region. In the upper chromosphere (h > 1400 km), the deposited acoustic flux is small compared to the radiative losses in quiet as well as in plage regions. The crucial parameter determining the amount of deposited acoustic flux is the gas density at a given height.
Conclusions: The acoustic energy flux is efficiently deposited in the middle chromosphere, where the density of gas is sufficiently high. About 90% of the available acoustic energy flux in the quiet-Sun region is deposited in these layers, and thus it is a major contributor to the radiative losses of the middle chromosphere. In the upper chromosphere, the deposited acoustic flux is too low, so that other heating mechanisms have to act to balance the radiative cooling. 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: Metis: the Solar Orbiter visible light and ultraviolet coronal imager Authors: Antonucci, Ester; Romoli, Marco; Andretta, Vincenzo; Fineschi, Silvano; Heinzel, Petr; Moses, J. Daniel; Naletto, Giampiero; Nicolini, Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Berlicki, Arkadiusz; Capobianco, Gerardo; Crescenzio, Giuseppe; Da Deppo, Vania; Focardi, Mauro; Frassetto, Fabio; Heerlein, Klaus; Landini, Federico; Magli, Enrico; Marco Malvezzi, Andrea; Massone, Giuseppe; Melich, Radek; Nicolosi, Piergiorgio; Noci, Giancarlo; Pancrazzi, Maurizio; Pelizzo, Maria G.; Poletto, Luca; Sasso, Clementina; Schühle, Udo; Solanki, Sami K.; Strachan, Leonard; Susino, Roberto; Tondello, Giuseppe; Uslenghi, Michela; Woch, Joachim; Abbo, Lucia; Bemporad, Alessandro; Casti, Marta; Dolei, Sergio; Grimani, Catia; Messerotti, Mauro; Ricci, Marco; Straus, Thomas; Telloni, Daniele; Zuppella, Paola; Auchère, Frederic; Bruno, Roberto; Ciaravella, Angela; Corso, Alain J.; Alvarez Copano, Miguel; Aznar Cuadrado, Regina; D'Amicis, Raffaella; Enge, Reiner; Gravina, Alessio; Jejčič, Sonja; Lamy, Philippe; Lanzafame, Alessandro; Meierdierks, Thimo; Papagiannaki, Ioanna; Peter, Hardi; Fernandez Rico, German; Giday Sertsu, Mewael; Staub, Jan; Tsinganos, Kanaris; Velli, Marco; Ventura, Rita; Verroi, Enrico; Vial, Jean-Claude; Vives, Sebastien; Volpicelli, Antonio; Werner, Stephan; Zerr, Andreas; Negri, Barbara; Castronuovo, Marco; Gabrielli, Alessandro; Bertacin, Roberto; Carpentiero, Rita; Natalucci, Silvia; Marliani, Filippo; Cesa, Marco; Laget, Philippe; Morea, Danilo; Pieraccini, Stefano; Radaelli, Paolo; Sandri, Paolo; Sarra, Paolo; Cesare, Stefano; Del Forno, Felice; Massa, Ernesto; Montabone, Mauro; Mottini, Sergio; Quattropani, Daniele; Schillaci, Tiziano; Boccardo, Roberto; Brando, Rosario; Pandi, Arianna; Baietto, Cristian; Bertone, Riccardo; Alvarez-Herrero, Alberto; García Parejo, Pilar; Cebollero, María; Amoruso, Mauro; Centonze, Vito Bibcode: 2020A&A...642A..10A Altcode: 2019arXiv191108462A
Aims: Metis is the first solar coronagraph designed for a space mission and is capable of performing simultaneous imaging of the off-limb solar corona in both visible and UV light. The observations obtained with Metis aboard the Solar Orbiter ESA-NASA observatory will enable us to diagnose, with unprecedented temporal coverage and spatial resolution, the structures and dynamics of the full corona in a square field of view (FoV) of ±2.9° in width, with an inner circular FoV at 1.6°, thus spanning the solar atmosphere from 1.7 R⊙ to about 9 R⊙, owing to the eccentricity of the spacecraft orbit. Due to the uniqueness of the Solar Orbiter mission profile, Metis will be able to observe the solar corona from a close (0.28 AU, at the closest perihelion) vantage point, achieving increasing out-of-ecliptic views with the increase of the orbit inclination over time. Moreover, observations near perihelion, during the phase of lower rotational velocity of the solar surface relative to the spacecraft, allow longer-term studies of the off-limb coronal features, thus finally disentangling their intrinsic evolution from effects due to solar rotation.
Methods: Thanks to a novel occultation design and a combination of a UV interference coating of the mirrors and a spectral bandpass filter, Metis images the solar corona simultaneously in the visible light band, between 580 and 640 nm, and in the UV H I Lyman-α line at 121.6 nm. The visible light channel also includes a broadband polarimeter able to observe the linearly polarised component of the K corona. The coronal images in both the UV H I Lyman-α and polarised visible light are obtained at high spatial resolution with a spatial scale down to about 2000 km and 15 000 km at perihelion, in the cases of the visible and UV light, respectively. A temporal resolution down to 1 s can be achieved when observing coronal fluctuations in visible light.
Results: The Metis measurements, obtained from different latitudes, will allow for complete characterisation of the main physical parameters and dynamics of the electron and neutral hydrogen/proton plasma components of the corona in the region where the solar wind undergoes the acceleration process and where the onset and initial propagation of coronal mass ejections (CMEs) take place. The near-Sun multi-wavelength coronal imaging performed with Metis, combined with the unique opportunities offered by the Solar Orbiter mission, can effectively address crucial issues of solar physics such as: the origin and heating/acceleration of the fast and slow solar wind streams; the origin, acceleration, and transport of the solar energetic particles; and the transient ejection of coronal mass and its evolution in the inner heliosphere, thus significantly improving our understanding of the region connecting the Sun to the heliosphere and of the processes generating and driving the solar wind and coronal mass ejections.
Conclusions: This paper presents the scientific objectives and requirements, the overall optical design of the Metis instrument, the thermo-mechanical design, and the processing and power unit; reports on the results of the campaigns dedicated to integration, alignment, and tests, and to the characterisation of the instrument performance; describes the operation concept, data handling, and software tools; and, finally, the diagnostic techniques to be applied to the data, as well as a brief description of the expected scientific products. The performance of the instrument measured during calibrations ensures that the scientific objectives of Metis can be pursued with success.

Metis website: http://metis.oato.inaf.it Title: On the Possibility of Detecting Helium D3 Line Polarization with Metis Authors: Heinzel, Petr; Štěpán, Jiři; Bemporad, Alessandro; Fineschi, Silvano; Jejčič, Sonja; Labrosse, Nicolas; Susino, Roberto Bibcode: 2020ApJ...900....8H Altcode: 2020arXiv200708940H Metis, the space coronagraph on board the Solar Orbiter, offers us new capabilities for studying eruptive prominences and coronal mass ejections (CMEs). Its two spectral channels, hydrogen Lα and visible light (VL), will provide for the first time coaligned and cotemporal images to study dynamics and plasma properties of CMEs. Moreover, with the VL channel (580-640 nm) we find an exciting possibility to detect the helium D3 line (587.73 nm) and its linear polarization. The aim of this study is to predict the diagnostic potential of this line regarding the CME thermal and magnetic structure. For a grid of models we first compute the intensity of the D3 line together with VL continuum intensity due to Thomson scattering on core electrons. We show that the Metis VL channel will detect a mixture of both, with predominance of the helium emission at intermediate temperatures between 30 and 50,000 K. Then we use the code HAZEL to compute the degree of linear polarization detectable in the VL channel. This is a mixture of D3 scattering polarization and continuum polarization. The former one is lowered in the presence of a magnetic field and the polarization axis is rotated (Hanle effect). Metis has the capability of measuring Q/I and U/I polarization degrees and we show their dependence on temperature and magnetic field. At T = 30,000 K we find a significant lowering of Q/I which is due to strongly enhanced D3 line emission, while depolarization at 10 G amounts roughly to 10%. Title: Spectral Characteristics and Formation Height of Off-limb Flare Ribbons Authors: Kuridze, David; Mathioudakis, Mihalis; Heinzel, Petr; Koza, Július; Morgan, Huw; Oliver, Ramon; Kowalski, Adam F.; Allred, Joel C. Bibcode: 2020ApJ...896..120K Altcode: 2020arXiv200510924K Flare ribbons are bright manifestations of flare energy dissipation in the lower solar atmosphere. For the first time, we report on high-resolution imaging spectroscopy observations of flare ribbons situated off limb in the Hβ and Ca II 8542 Å lines and make a detailed comparison with radiative hydrodynamic simulations. Observations of the X8.2 class solar flare SOL 2017-09-10T16:06 UT obtained with the Swedish Solar Telescope reveal bright horizontal emission layers in Hβ line-wing images located near the footpoints of the flare loops. The apparent separation between the ribbon observed in the Hβ wing and the nominal photospheric limb is about 300-500 km. The Ca II 8542 Å line-wing images show much fainter ribbon emissions located right on the edge of the limb, without clear separation from the limb. RADYN models are used to investigate synthetic spectral line profiles for the flaring atmosphere, and good agreement is found with the observations. The simulations show that, toward the limb, where the line of sight is substantially oblique with respect to the vertical direction, the flaring atmosphere model reproduces the high contrast of the off-limb Hβ ribbons and their significant elevation above the photosphere. The ribbons in the Ca II 8542 Å line-wing images are located deeper in the lower solar atmosphere with a lower contrast. A comparison of the height deposition of electron beam energy and the intensity contribution function shows that the Hβ line-wing intensities can be a useful tracer of flare energy deposition in the lower solar atmosphere. Title: Signatures of Helium Continuum in Cool Flare Loops Observed by SDO/AIA Authors: Heinzel, Petr; Schwartz, Pavol; Lörinčík, Juraj; Koza, Július; Jejčič, Sonja; Kuridze, David Bibcode: 2020ApJ...896L..35H Altcode: 2020arXiv200600574H We present an analysis of off-limb cool flare loops observed by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) during the gradual phase of SOL2017-09-10T16:06 X8.2-class flare. In the extreme-ultraviolet (EUV) channels starting from the 335 Å one, cool loops appear as dark structures against the bright loop arcade. These dark structures were precisely coaligned (spatially and temporally) with loops observed by Swedish Solar Telescope (SST) in emission lines of hydrogen and ionized calcium. A recently published semi-empirical model of cool loops based on SST observations serves to predict the level of hydrogen and helium recombination continua. The continua were synthesized using an approximate non-LTE (I.e., departures from local thermodynamic equilibrium) approach and theoretical spectra were then transformed to AIA signals. Comparison with signals detected inside the dark loops shows that only in AIA 211 Å channel the computed level of recombination continua is consistent with observations for some models, while in all other channels that are more distant from the continua edges the synthetic continuum is far too low. In analogy with on-disk observations of flares we interpret the surplus emission as due to numerous EUV lines emitted from hot but faint loops in front of the cool ones. Finally we briefly comment on failure of the standard absorption model when used for analysis of the dark-loop brightness. Title: Optical design of the multi-wavelength imaging coronagraph Metis for the solar orbiter mission Authors: Fineschi, S.; Naletto, G.; Romoli, M.; Da Deppo, V.; Antonucci, E.; Moses, D.; Malvezzi, A. M.; Nicolini, G.; Spadaro, D.; Teriaca, L.; Andretta, V.; Capobianco, G.; Crescenzio, G.; Focardi, M.; Frassetto, F.; Landini, F.; Massone, G.; Melich, R.; Nicolosi, P.; Pancrazzi, M.; Pelizzo, M. G.; Poletto, L.; Schühle, U.; Uslenghi, M.; Vives, S.; Solanki, S. K.; Heinzel, P.; Berlicki, A.; Cesare, S.; Morea, D.; Mottini, S.; Sandri, P.; Alvarez-Herrero, A.; Castronuovo, M. Bibcode: 2020ExA....49..239F Altcode: 2020ExA...tmp...14F This paper describes the innovative optical design of the Metis coronagraph for the Solar Orbiter ESA-NASA mission. Metis is a multi-wavelength, externally occulted telescope for the imaging of the solar corona in both the visible and ultraviolet wavelength ranges. Metis adopts a novel occultation scheme for the solar disk, that we named "inverse external occulter", for reducing the extremely high thermal load on the instrument at the spacecraft perihelion. The core of the Metis optical design is an aplanatic Gregorian telescope common to both the visible and ultraviolet channels. A suitable dichroic beam-splitter, optimized for transmitting a narrow-band in the ultraviolet (121.6 nm, HI Lyman-α) and reflecting a broadband in the visible (580-640 nm) spectral range, is used to separate the two optical paths. Along the visible light optical path, a liquid crystal electro-optical modulator, used for the first time in space, allows making polarimetric measurements. Title: Stellar coronal mass ejections - II. Constraints from spectroscopic observations Authors: Odert, P.; Leitzinger, M.; Guenther, E. W.; Heinzel, P. Bibcode: 2020MNRAS.494.3766O Altcode: 2020MNRAS.tmp.1176O; 2020arXiv200404063O Detections of stellar coronal mass ejections (CMEs) are still rare. Observations of strong Balmer line asymmetries during flare events have been interpreted as being caused by CMEs. Here, we aim to estimate the maximum possible Balmer line fluxes expected from CMEs to infer their detectability in spectroscopic observations. Moreover, we use these results together with a model of intrinsic CME rates to infer the potentially observable CME rates for stars of different spectral types under various observing conditions, as well as the minimum required observing time to detect stellar CMEs in Balmer lines. We find that generally CME detection is favoured for mid- to late-type M dwarfs, as they require the lowest signal-to-noise ratio for CME detection, and the fraction of observable-to-intrinsic CMEs is largest. They may require, however, longer observing times than stars of earlier spectral types at the same activity level, as their predicted intrinsic CME rates are lower. CME detections are generally favoured for stars close to the saturation regime, because they are expected to have the highest intrinsic rates; the predicted minimum observing time to detect CMEs on just moderately active stars is already >100 h. By comparison with spectroscopic data sets including detections as well as non-detections of CMEs, we find that our modelled maximum observable CME rates are generally consistent with these observations on adopting parameters within the ranges determined by observations of solar and stellar prominences. Title: Chromospheric Heating by Acoustic Waves Compared to Radiative Cooling. II. Revised Grid of Models Authors: Abbasvand, Vahid; Sobotka, Michal; Heinzel, Petr; Švanda, Michal; Jurčák, Jan; del Moro, Dario; Berrilli, Francesco Bibcode: 2020ApJ...890...22A Altcode: 2020arXiv200103413A Acoustic and magnetoacoustic waves are considered to be possible agents of chromospheric heating. We present a comparison of deposited acoustic energy flux with total integrated radiative losses in the middle chromosphere of the quiet Sun and a weak plage. The comparison is based on a consistent set of high-resolution observations acquired by the Interferometric Bidimensional Spectrometer instrument in the Ca II 854.2 nm line. The deposited acoustic-flux energy is derived from Doppler velocities observed in the line core and a set of 1737 non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models, which also provide the radiative losses. The models are obtained by scaling the temperature and column mass of five initial models by Vernazza et al. (1981; VAL) B-F to get the best fit of synthetic to observed profiles. We find that the deposited acoustic-flux energy in the quiet-Sun chromosphere balances 30%-50% of the energy released by radiation. In the plage, it contributes by 50%-60% in locations with vertical magnetic field and 70%-90% in regions where the magnetic field is inclined more than 50° to the solar surface normal. 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: Analysis of the Quasi-Periodic Pulsations in the X9.3 and X8.3 Flares on 6 and 10 September 2017 Observed by SDO/EVE, PROBA2/LYRA and MAVEN/EUVM Authors: Dominique, M.; Zhukov, A.; Thiemann, E.; Dolla, L.; Heinzel, P.; Wauters, L.; Dammasch, I. E. Bibcode: 2019AGUFMSH13D3422D Altcode: Quasi-periodic pulsations (QPPs) refer to nearly-periodic oscillations that are often observed in irradiance time series during most solar flares and have also been reported in several stellar flares. Two families of mechanisms are usually invoked to explain QPPs: MHD waves and quasi-periodic particle acceleration. In both cases, QPPs could inform us on the conditions in which flares happen. The two strongest flares of the current solar cycle, i.e. the X9.3 flare on 6 September 2017 and the off-limb X8.3 flare that occurred four days later, have been observed by two SXR-to-UV radiometers: SDO/EVE and PROBA2/LYRA. These two flares were produced in similar conditions by the same active region. However, if QPPs with periods between 1 and 100 s were clearly detected in the LYRA and EVE time series during the first event, this was not the case during the second event. To understand what causes this difference between the two flares, we involve the observations by a third instrument: MAVEN/EUVM orbiting Mars. We will compare the observations by the three instruments and see how this can shed some light on the QPP phenomenon. 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 Hα 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: Spectral Diagnostics of Cool Flare Loops Observed by the SST. I. Inversion of the Ca II 8542 Å and Hβ Lines Authors: Koza, Július; Kuridze, David; Heinzel, Petr; Jejčič, Sonja; Morgan, Huw; Zapiór, Maciej Bibcode: 2019ApJ...885..154K Altcode: 2019arXiv190907356K Flare loops form an integral part of eruptive events, being detected in the range of temperatures from X-rays down to cool chromospheric-like plasmas. While hot loops are routinely observed by the Solar Dynamics Observatory’s Atmospheric Imaging Assembly, cool loops seen off-limb are rare. In this paper we employ unique observations of the SOL2017-09-10T16:06 X8.2-class flare which produced an extended arcade of loops. The Swedish 1 m Solar Telescope made a series of spectral images of the cool off-limb loops in the Ca II 8542 Å and the hydrogen Hβ lines. Our focus is on the loop apices. Non-local thermal equilibrium (non-LTE; i.e., departures from LTE) spectral inversion is achieved through the construction of extended grids of models covering a realistic range of plasma parameters. The Multilevel Accelerated Lambda Iterations code solves the non-LTE radiative-transfer problem in a 1D externally illuminated slab, approximating the studied loop segment. Inversion of the Ca II 8542 Å and Hβ lines yields two similar solutions, both indicating high electron densities around 2 × 1012 cm-3 and relatively large microturbulence around 25 km s-1. These are in reasonable agreement with other independent studies of the same or similar events. In particular, the high electron densities in the range 1012-1013 cm-3 are consistent with those derived from the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager white-light observations. The presence of such high densities in solar eruptive flares supports the loop interpretation of the optical continuum emission of stars which manifest superflares. Title: Modelling of Flare Processes: A Comparison of the Two RHD Codes FLARIX and RADYN Authors: Kašparová, Jana; Carlsson, Mats; Heinzel, Petr; Varady, Michal Bibcode: 2019ASPC..519..141K Altcode: We present a comparison of two autonomous, methodologically different radiation hydrodynamic codes, FLARIX and RADYN, and their use to model the solar flare processes. Both codes can model the time evolution of a 1D atmosphere heated by a specified process, e.g. by electron beams propagating from the injection site in the corona down to the lower atmosphere. In such a scenario time scales can be rather short and lead to fast heating on even sub-second time scales. Our aim is to compare the FLARIX and RADYN codes using exactly the same setup and model conditions. Although such a comparison has never been done successfully before for this type of codes, we will present a close agreement between the time evolution of the modelled atmospheric structure for a test case of electron beam heating. Title: Solar and Stellar Chromospheres Authors: Heinzel, Petr; Štěpán, Jiří Bibcode: 2019ASPC..519...59H Altcode: RADCOSMOS conference was largely devoted to many aspects of stellar photospheric modeling, and namely a great success of Ivan's code <tt>TLUSTY</tt> was emphasized. In this short contribution we focus on models of solar and stellar chromospheres which are not in radiative equilibrium and thus require the knowledge of various non-radiative heating mechanisms. We desrcibe both semiempirical, as well as fully 3D RMHD models and mention the importance of partial redistribution for a proper line diagnostics. Finally, since RADCOSMOS was also covering topic of the polarized line transfer, we present here some of the latests achievements related to the solar chromosphere. 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: Determination of the physical properties of an erupting prominence from SOHO/LASCO and UVCS observations Authors: Susino, R.; Bemporad, A.; Heinzel, P.; Jejčič, S.; Anzer, , U.; Dzifčáková, E. Bibcode: 2019NCimC..42...37S Altcode: We studied the physical conditions of an erupting prominence observed in the core of a coronal mass ejection, using combination of SOHO/LASCO-C2 visible-light images and SOHO/UVCS ultraviolet data. Measured intensities and profiles of the neutral-hydrogen Lyman- α and Lyman- β lines and the 977 Å C III line were used together with the visible-light brightness to derive the geometrical and physical parameters of the prominence, such as the line-of-sight apparent thickness, electron column density, kinetic temperature, and microturbolent velocity. These parameters were used to constrain a non-LTE ( i.e., out of local thermodynamic equilibrium) radiative-transfer model of the prominence that provides the effective thickness, electron density, and flow velocity, in a sample of points selected along the prominence. The prominence can be described as a hot structure with low electron density and very low gas pressure compared to typical quiescent prominences. Intensities of the hydrogen lines were also used for a detailed determination of the plasma line-of-sight filling factor, in the two prominence points where simultaneous and cospatial LASCO-C2 and UVCS observations were available. Title: Chapter 5.2 - Models of Solar and Stellar Atmospheres Authors: Heinzel, Petr Bibcode: 2019sgsp.book..157H Altcode: This chapter addresses the basic principles of the radiative transfer theory and nonequilibrium plasma physics, which were developed during the past century and are now widely used to model solar and stellar atmospheres. Many key results have been obtained and new numerical methods developed by solar physicists; they serve as a guide for stellar astrophysics. We start with the basics of radiation transport and demonstrate the classical ideas of the nonequilibrium line formation using a two-level atom example. Then we summarize the equations used to construct standard plane-parallel models of atmospheres in hydrostatic and radiative equilibrium and show examples of models with different levels of complexity. Although such models are well-suited for modeling photospheres, solar and stellar chromospheres require even more advanced approaches. The simplest is represented by so-called semiempirical models; we show some classical examples for the Sun and cool stars. A specific class of problems concerns isolated atmospheric structures illuminated by solar or stellar disk radiation. Based on various atmospheric models, we discuss how model spectra are synthesized and spectral lines are actually formed. Finally, we briefly introduce the topic of radiation hydrodynamics as the most sophisticated tool for solar and stellar atmospheric modeling. Title: Blue-wing enhancement of the chromospheric Mg II h and k lines in a solar flare Authors: Tei, Akiko; Sakaue, Takahito; Okamoto, Takenori J.; Kawate, Tomoko; Heinzel, Petr; UeNo, Satoru; Asai, Ayumi; Ichimoto, Kiyoshi; Shibata, Kazunari Bibcode: 2018PASJ...70..100T Altcode: 2018PASJ..tmp...61T; 2018arXiv180305237T We performed coordinated observations of AR 12205, which showed a C-class flare on 2014 November 11, with the Interface Region Imaging Spectrograph (IRIS) and the Domeless Solar Telescope (DST) at Hida Observatory. Using spectral data in the Si IV 1403 Å, C II 1335 Å, and Mg II h and k lines from IRIS and the Ca II K, Ca II 8542 Å, and Hα lines from DST, we investigated a moving flare kernel during the flare. In the Mg II h line, the leading edge of the flare kernel showed an intensity enhancement in the blue wing and a smaller intensity of the blue-side peak (h2v) than that of the red-side one (h2r). The blueshift lasted for 9-48 s with a typical speed of 10.1 ± 2.6 km s-1, which was followed by a high intensity and a large redshift with a speed of up to 51 km s-1 detected in the Mg II h line. The large redshift was a common property for all six lines, but the blueshift prior to it was found only in the Mg II lines. Cloud modeling of the Mg II h line suggests that the blue-wing enhancement with such a peak difference could have been caused by a chromospheric-temperature (cool) upflow. We discuss a scenario in which an upflow of cool plasma is lifted up by expanding hot plasma owing to the deep penetration of non-thermal electrons into the chromosphere. Furthermore, we found that the blueshift persisted without any subsequent redshift in the leading edge of the flare kernel during its decaying phase. The cause of such a long-lasting blueshift is also discussed. Title: Solar Ultraviolet Bursts Authors: Young, Peter R.; Tian, Hui; Peter, Hardi; Rutten, Robert J.; Nelson, Chris J.; Huang, Zhenghua; Schmieder, Brigitte; Vissers, Gregal J. M.; Toriumi, Shin; Rouppe van der Voort, Luc H. M.; Madjarska, Maria S.; Danilovic, Sanja; Berlicki, Arkadiusz; Chitta, L. P.; Cheung, Mark C. M.; Madsen, Chad; Reardon, Kevin P.; Katsukawa, Yukio; Heinzel, Petr Bibcode: 2018SSRv..214..120Y Altcode: 2018arXiv180505850Y The term "ultraviolet (UV) burst" is introduced to describe small, intense, transient brightenings in ultraviolet images of solar active regions. We inventorize their properties and provide a definition based on image sequences in transition-region lines. Coronal signatures are rare, and most bursts are associated with small-scale, canceling opposite-polarity fields in the photosphere that occur in emerging flux regions, moving magnetic features in sunspot moats, and sunspot light bridges. We also compare UV bursts with similar transition-region phenomena found previously in solar ultraviolet spectrometry and with similar phenomena at optical wavelengths, in particular Ellerman bombs. Akin to the latter, UV bursts are probably small-scale magnetic reconnection events occurring in the low atmosphere, at photospheric and/or chromospheric heights. Their intense emission in lines with optically thin formation gives unique diagnostic opportunities for studying the physics of magnetic reconnection in the low solar atmosphere. This paper is a review report from an International Space Science Institute team that met in 2016-2017. Title: High-density Off-limb Flare Loops Observed by SDO Authors: Jejčič, S.; Kleint, L.; Heinzel, P. Bibcode: 2018ApJ...867..134J Altcode: 2018arXiv181002431J The density distribution of flare loops and the mechanisms of their emission in the continuum are still open questions. On 2017 September 10, a prominent loop system appeared during the gradual phase of an X8.2 flare (SOL2017-09-10), visible in all passbands of SDO/AIA and in the white-light continuum of SDO/HMI. We investigate its electron density by taking into account all radiation processes in the flare loops, i.e., the Thomson continuum, hydrogen Paschen and Brackett recombination continua, as well as free-free continuum emission. We derive a quadratic function of the electron density for a given temperature and effective loop thickness. By absolutely calibrating SDO/HMI intensities, we convert the measured intensities into electron density at each pixel in the loops. For a grid of plausible temperatures between cool (6000 K) and hot (106 K) structures, the electron density is computed for representative effective thicknesses between 200 and 20,000 km. We obtain a relatively high maximum electron density, about 1013 cm-3. At such high electron densities, the Thomson continuum is negligible and therefore one would not expect a significant polarization degree in dense loops. We conclude that the Paschen and Brackett recombination continua are dominant in cool flare loops, while the free-free continuum emission is dominant for warmer and hot loops. 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: First Detection of Solar Flare Emission in Mid-ultraviolet Balmer Continuum Authors: Dominique, Marie; Zhukov, Andrei N.; Heinzel, Petr; Dammasch, Ingolf E.; Wauters, Laurence; Dolla, Laurent; Shestov, Sergei; Kretzschmar, Matthieu; Machol, Janet; Lapenta, Giovanni; Schmutz, Werner Bibcode: 2018ApJ...867L..24D Altcode: 2018arXiv181009835D We present the first detection of solar flare emission at mid-ultraviolet wavelengths around 2000 Å by the channel 2 of the Large-Yield RAdiometer (LYRA) on board the PRoject for OnBoard Autonomy 2 mission. The flare (SOL20170906) was also observed in the channel 1 of LYRA centered at the H I Lyα line at 1216 Å, showing a clear non-thermal profile in both channels. The flare radiation in channel 2 is consistent with the hydrogen Balmer continuum emission produced by an optically thin chromospheric slab heated up to 10,000 K. Simultaneous observations in channels 1 and 2 allow the separation of the line emission (primarily from the Lyα line) from the Balmer continuum emission. Together with the recent detection of the Balmer continuum emission in the near-ultraviolet by the Interface Region Imaging Spectrometer, the LYRA observations strengthen the interpretation of broadband flare emission as the hydrogen recombination continua originating in the chromosphere. 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: Hot prominence detected in the core of a coronal mass ejection. III. Plasma filling factor from UVCS Lyman-α and Lyman-β observations Authors: Susino, R.; Bemporad, A.; Jejčič, S.; Heinzel, P. Bibcode: 2018A&A...617A..21S Altcode: 2018arXiv180512465S Context. We study an erupting prominence embedded in the core of a coronal mass ejection that occurred on August 2, 2000, and focus on deriving the plasma filling factor of the prominence.
Aims: We explore two methods for measuring this factor along the line of sight. They are based on a combination of visible-light and ultraviolet spectroscopic observations.
Methods: Theoretical relationships for resonant scattering and collisional excitation were used to evaluate the intensity of the neutral hydrogen Lyman-α and Lyman-β lines in two prominence points where simultaneous and cospatial LASCO-C2 and UVCS data were available. Thermodynamic and geometrical parameters assumed for the calculation (i.e., electron column density, kinetic temperature, flow velocity, chromospheric Lyα and Lyβ intensities and profiles, and thickness of the prominence along the line of sight) are provided by both observations and the results of a detailed 1D non-local thermal equilibrium (non-LTE) radiative-transfer model of the prominence, developed in our previous work. The geometrical filling factor was derived from comparing the calculated and measured intensities of the two lines. The results were then checked against the non-LTE model in order to verify the reliability of the methods.
Results: The resulting filling factors are consistent with the model in both prominence points when the radiative and collisional components of the total intensity of the hydrogen lines are separated using the Lyα and Lyβ line intensities, which is required to estimate the filling factor. The exploration of the parameter space shows that the results are weakly sensitive to the plasma flow velocity, but depend more strongly on the assumed kinetic temperatures.
Conclusions: The combination of visible-light and ultraviolet Lyα and Lyβ data can be used to approximately estimate the line-of-sight geometrical filling factor in erupting prominences, but the proposed technique, which is model dependent, is reliable only for emission that is optically thin in the lines considered, a condition that is not in general representative of prominence plasma. 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: Plasma physical parameters of a prominence embedded in the core of a Coronal Mass Ejection Authors: Bemporad, Alessandro; Anzer, Ulrich; Heinzel, Petr; Jejcic, Sonja; Susino, Roberto Bibcode: 2018cosp...42E.267B Altcode: We determine the plasma physical parameters of an erupting prominence embedded in the core of a CME, combininging visible light coronagraphic images from SOHO/LASCO with UV spectra acquired by SOHO/UVCS. Strong UV emissions were detected in the hydrogen Lyman-α and Lyman-β lines and C III line. Visible light and UV intensities have been used to estimate the projected thickness and velocity of the prominence, together with the effective plasma temperature, microturbolent velocity, and column density. These parameters have been used to constrain 1D NLTE modeling of the erupting plasma, taking into account the effects of large flow velocities (Doppler dimming). Roughly one-half of considered points in the prominence body show a non-negligible Lyman-α optical thickness. Comparison between the calculated and the measured intensities of the two Lyman lines was also used to derive the geometrical filling factor. Results show that the erupting prominence plasma is relatively hot, with a low electron density, a wide range of effective thicknesses, a rather narrow range of radial flow velocities, and a microturbulence of about 25 km/s. This analysis provides a basis for future diagnostics of prominences using the METIS coronagraph on board the Solar Orbiter mission. 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: Hot Erupting Prominences in Cores of Cme's Authors: Heinzel, Petr; Bemporad, Alessandro; Anzer, Ulrich; Jejcic, Sonja; Susino, Roberto; Dzifcakova, Elena Bibcode: 2018cosp...42E1421H Altcode: Coronal mass ejections (CME) associated with prominence eruptions exhibit relatively coolmaterial in their cores. Such prominence plasmas were frequently detected in various spectrallines by SOHO/UVCS coronagraph and in the visible light by SOHO/LASCO as well as bySTEREO coronagraphs. UVCS provided excellent spectra of CME-core prominences and anextended catalogue of these data is available. We will present recent results of a hot prominence diagnostics using the hydrogen Lyman lines and the CIII line . The erupting prominence parameters are further constrained by the visible light observations from LASCO-C2. A novel non-LTE modeling based on such observations will be presented and we will highlight the diagnostic potential of the UV and visible light for future space coronagraphs like Metis on board the ESA Solar Orbiter mission. The plasma parameters of such hot prominences are compared with those obtained from numerical MHD simulations of erupting flux ropes surrounded by CMEs. Finally, we will also mention synergies with stellar analogues. 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: IRIS Observations and Modeling of MGII Flare Loops Authors: Heinzel, Petr; Berlicki, Arkadiusz; Mikula, Katarzyna; Liu, Wenjuan Bibcode: 2018cosp...42E1423H Altcode: Solar chromospheric flares are often associated with cool loops which are rooted in the ribbons. These loops extend into coronal altitudes and usually are modelled as prominence-like structures illuminated from the solar disk. The loops exhibit large down-flows (coronal rain) and they evolve in time in accordance with the characteristic cooling times of the loop plasmas. Cool loops are visible in various spectral lines formed at chromospheric temperatures. We exploit novel observations of such loops in MgII h and k lines obtained by the IRIS satellite, analyse selected observations where the cool loops are well visible and studytheir temporal evolution. Our spectroscopic diagnostics is based on 2D non-LTE modelling ofMgII lines in flare loops taking into account the flows along the loops. From these models wedetermine various plasma parameters and the rates of radiation cooling. These results allow usto better understand the structure, dynamics and evolution of cool flare loops. Title: Blue wing enhancement of the chromospheric Mg II h and k lines in a solar flare Authors: Tei, Akiko; Shibata, Kazunari; Asai, Ayumi; Ichimoto, Kiyoshi; Heinzel, Petr; Ueno, Satoru; Okamoto, Joten; Sakaue, Takahito; Kawate, Tomoko Bibcode: 2018cosp...42E3350T Altcode: We performed coordinated observations of NOAA AR 12205, which produced a C-class flare on 2014 November 11, with the Interface Region Imaging Spectrograph (IRIS) and the Domeless Solar Telescope (DST) at Hida Observatory.Using spectral data in the Si IV 1403 Å, C II 1335 Å, and Mg II h and k lines from IRIS and the Ca II K, Ca II 8542 Å, and Hα lines from DST, we investigated the temporal and spatial evolution around a moving flare kernel.In the Mg II h line, the leading edge of the kernel showed intensity enhancement in the blue wing and difference between the blue-side peak and red-side one (I_{h2v} < I_{h2r}).Then, the drastic change of the intensity in the red wing occurred.The blueshift lasted for 9-48 s with a speed of 10.1 ± 2.6 km s^{-1} and it was followed by the strong redshift with a speed of up to 51 km s^{-1} detected in the Mg II h line.The strong redshift was a common property for all six lines but the blueshift prior to it was found only in the Mg II lines.A cloud modeling of the Mg II h line suggests that the blue wing enhancement with such peak difference can be caused by a chromospheric-temperature (cool) upflow.We discuss a scenario in which an upflow of cool plasma is lifted up by expanding (hot) plasma owing to the deep penetration of non-thermal electrons into the chromosphere.In addition, at the leading edge of the final flare footpoints, the blueshift persisted in the Mg II h line, which was not followed by any large redshift and intensity enhancement.Such long-lasting blueshift can be explained by cool upflow caused by small energy flux into the lower atmosphere. Title: Cool Loops on Cool Stars Authors: Heinzel, Petr Bibcode: 2018cosp...42E1422H Altcode: Recently a significant effort has been devoted to systematic modelling of solar and stellar chromospheric flares which are typically manifested by bright ribbons embedded in the lower atmospheric layers. However, apart from ribbons detectable in a broad range of the electromagnetic spectrum, overlying loops are also frequently observed on the Sun. They appear in various spectral lines and can be well resolved in the so-called eruptive flares. We will show how their appearance depends on the loop plasma conditions and parameters. We will also briefly review the efforts to model the radiation properties of such loops and namely of those which cooled down to chromospheric temperatures. Light curves of the flaring ribbons may differ from time evolution of the loop brightness and this can be easily detected on the Sun. However, on cool stars the measured light curves may contain an unresolved information about the temporal evolution of both ribbons and cool loops and we will demonstrate how this can be modelled. Title: Can Flare Loops Contribute to the White-light Emission of Stellar Superflares? Authors: Heinzel, P.; Shibata, K. Bibcode: 2018ApJ...859..143H Altcode: 2018arXiv180409656H Since the discovery of stellar superflares by the Kepler satellite, these extremely energetic events have been studied in analogy to solar flares. Their white-light (WL) continuum emission has been interpreted as being produced by heated ribbons. In this paper, we compute the WL emission from overlying flare loops depending on their density and temperature and show that, under conditions expected during superflares, the continuum brightening due to extended loop arcades can significantly contribute to stellar flux detected by Kepler. This requires electron densities in the loops of 1012-1013 cm-3 or higher. We show that such densities, exceeding those typically present in solar-flare loops, can be reached on M-dwarf and solar-type superflare stars with large starspots and much stronger magnetic fields. Quite importantly, the WL radiation of loops is not very sensitive to their temperature and thus both cool as well as hot loops may contribute. We show that the WL intensity emergent from optically thin loops is lower than the blackbody radiation from flare ribbons, but the contribution of loops to total stellar flux can be quite important due to their significant emitting areas. This new scenario for interpreting superflare emission suggests that the observed WL flux is due to a mixture of the ribbon and loop radiation and can be even loop-dominated during the gradual phase of superflares. Title: Observation of the X9.3 flare of September 6 2017 in UV/EUV by PROBA2/LYRA Authors: Dominique, Marie; Zhukov, Andrei; Heinzel, Petr; Dammasch, Ingolf E.; Wauters, Laurence; Dolla, Laurent; Shestov, Sergei Bibcode: 2018tess.conf31903D Altcode: After several months of relative quietness, a sudden burst of solar activity was observed starting on September 4 2017, when the NOAA AR 12673 started to develop quickly. This region remained active until it disappeared behind the west limb on September 10. It produced multiple strong flares (27 M-class flares and 4 X-class flares). Among them, there were the two strongest flare observed so far during the solar cycle 24: the X9.3 flare of September 6 and the off-limb X8.3 flare of September 10.

At the time of these two events, the Large-Yield Radiometer (LYRA) onboard PROBA2 was performing a special flare observation campaign, involving one of its spare units that is normally only used for calibration purposes. As this unit was only sporadically opened over the mission lifetime, it is relatively preserved from the ageing processes that otherwise affect the instrument, and it delivered very clear observations of both flares. In particular, the X9.3 flare produced a signature in the four channels of the instrument, of which two observe the EUV range, one the hydrogen Lyman-alpha line, and the last one the continuum around 2000 Angstroms. As flare observations are relatively rare in Lyman-alpha and almost non-existing in the continuum around 2000 Angstroms, this constitutes a rather unique set of observations. In contrast, the X8.3 flare only produced signatures in the two EUV channels.

This presentation will describe the LYRA observations, compare both flares, and discuss the origin of the emitted signal in the four channels. Title: Václav Bumba (1925 - 2018) Authors: Kotrč, Pavel; Heinzel, Petr; Sobotka, Michal; Ambrož, Pavel; van Driel-Gesztelyi, Lidia Bibcode: 2018SoPh..293...40K Altcode: No abstract at ADS 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: ASPIICS: a giant, white light and emission line coronagraph for the ESA proba-3 formation flight mission Authors: Lamy, P. L.; Vivès, S.; Curdt, W.; Damé, L.; Davila, J.; Defise, J. -M.; Fineschi, S.; Heinzel, P.; Howard, Russel; Kuzin, S.; Schmutz, W.; Tsinganos, K.; Zhukov, A. Bibcode: 2017SPIE10565E..0TL Altcode: Classical externally-occulted coronagraphs are presently limited in their performances by the distance between the external occulter and the front objective. The diffraction fringe from the occulter and the vignetted pupil which degrades the spatial resolution prevent useful observations of the white light corona inside typically 2-2.5 solar radii (Rsun). Formation flying offers and elegant solution to these limitations and allows conceiving giant, externally-occulted coronagraphs using a two-component space system with the external occulter on one spacecraft and the optical instrument on the other spacecraft at a distance of hundred meters [1, 2]. Such an instrument ASPIICS (Association de Satellites Pour l'Imagerie et l'Interférométrie de la Couronne Solaire) has been selected by the European Space Agency (ESA) to fly on its PROBA-3 mission of formation flying demonstration which is presently in phase B (Fig. 1). The classical design of an externally-occulted coronagraph is adapted to the formation flying configuration allowing the detection of the very inner corona as close as 0.04 solar radii from the solar limb. By tuning the position of the occulter spacecraft, it may even be possible to reach the chromosphere and the upper part of the spicules [3]. ASPIICS will perform (i) high spatial resolution imaging of the continuum K+F corona in photometric and polarimetric modes, (ii) high spatial resolution imaging of the E-corona in two coronal emission lines (CEL): Fe XIV and He I D3, and (iii) two-dimensional spectrophotometry of the Fe XIV emission line. ASPIICS will address the question of the coronal heating and the role of waves by characterizing propagating fluctuations (waves and turbulence) in the solar wind acceleration region and by looking for oscillations in the intensity and Doppler shift of spectral lines. The combined imaging and spectral diagnostics capabilities available with ASPIICS will allow mapping the velocity field of the corona both in the sky plane (directly on the images) and along the line-of-sight by measuring the Doppler shifts of emission lines in an effort to determine how the different components of the solar wind, slow and fast are accelerated. With a possible launch in 2014, ASPIICS will observe the corona during the maximum of solar activity, insuring the detection of many Coronal Mass Ejections (CMEs). By rapidly alternating high-resolution imaging and spectroscopy, CMEs will be thoroughly characterized. Title: Hot prominence detected in the core of a coronal mass ejection. II. Analysis of the C III line detected by SOHO/UVCS Authors: Jejčič, S.; Susino, R.; Heinzel, P.; Dzifčáková, E.; Bemporad, A.; Anzer, U. Bibcode: 2017A&A...607A..80J Altcode: Context. We study the physics of erupting prominences in the core of coronal mass ejections (CMEs) and present a continuation of a previous analysis.
Aims: We determine the kinetic temperature and microturbulent velocity of an erupting prominence embedded in the core of a CME that occurred on August 2, 2000 using the Ultraviolet Coronagraph and Spectrometer observations (UVCS) on board the Solar and Heliospheric Observatory (SOHO) simultaneously in the hydrogen Lα and C III lines. We develop the non-LTE (departures from the local thermodynamic equilibrium - LTE) spectral diagnostics based on Lα and Lβ measured integrated intensities to derive other physical quantities of the hot erupting prominence. Based on this, we synthesize the C III line intensity to compare it with observations.
Methods: Our method is based on non-LTE modeling of eruptive prominences. We used a general non-LTE radiative-transfer code only for optically thin prominence points because optically thick points do not allow the direct determination of the kinetic temperature and microturbulence from the line profiles. The input parameters of the code were the kinetic temperature and microturbulent velocity derived from the Lα and C III line widths, as well as the integrated intensity of the Lα and Lβ lines. The code runs in three loops to compute the radial flow velocity, electron density, and effective thickness as the best fit to the Lα and Lβ integrated intensities within the accuracy defined by the absolute radiometric calibration of UVCS data.
Results: We analyzed 39 observational points along the whole erupting prominence because for these points we found a solution for the kinetic temperature and microturbulent velocity. For these points we ran the non-LTE code to determine best-fit models. All models with τ0(Lα) ≤ 0.3 and τ0(C III) ≤ 0.3 were analyzed further, for which we computed the integrated intensity of the C III line using a two-level atom. The best agreement between computed and observed integrated intensity led to 30 optically thin points along the prominence. The results are presented as histograms of the kinetic temperature, microturbulent velocity, effective thickness, radial flow velocity, electron density, and gas pressure. We also show the relation between the microturbulence and kinetic temperature together with a scatter plot of computed versus observed C III integrated intensities and the ratio of the computed to observed C III integrated intensities versus kinetic temperature.
Conclusions: The erupting prominence embedded in the CME is relatively hot with a low electron density, a wide range of effective thicknesses, a rather narrow range of radial flow velocities, and a microturbulence of about 25 km s-1. This analysis shows a disagreement between observed and synthetic intensities of the C III line, the reason for which most probably is that photoionization is neglected in calculations of the ionization equilibrium. Alternatively, the disagreement might be due to non-equilibrium processes. Title: On the Nature of Off-limb Flare Continuum Sources Detected by SDO/HMI Authors: Heinzel, P.; Kleint, L.; Kašparová, J.; Krucker, S. Bibcode: 2017ApJ...847...48H Altcode: 2017arXiv170906377H The Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory has provided unique observations of off-limb flare emission. White-light continuum enhancements were detected in the “continuum” channel of the Fe 6173 Å line during the impulsive phase of the observed flares. In this paper we aim to determine which radiation mechanism is responsible for such enhancement being seen above the limb, at chromospheric heights around or below 1000 km. Using a simple analytical approach, we compare two candidate mechanisms, the hydrogen recombination continuum (Paschen) and the Thomson continuum due to scattering of disk radiation on flare electrons. Both mechanisms depend on the electron density, which is typically enhanced during the impulsive phase of a flare as the result of collisional ionization (both thermal and also non-thermal due to electron beams). We conclude that for electron densities higher than 1012 cm-3, the Paschen recombination continuum significantly dominates the Thomson scattering continuum and there is some contribution from the hydrogen free-free emission. This is further supported by detailed radiation-hydrodynamical (RHD) simulations of the flare chromosphere heated by the electron beams. We use the RHD code FLARIX to compute the temporal evolution of the flare-heating in a semi-circular loop. The synthesized continuum structure above the limb resembles the off-limb flare structures detected by HMI, namely their height above the limb, as well as the radiation intensity. These results are consistent with recent findings related to hydrogen Balmer continuum enhancements, which were clearly detected in disk flares by the IRIS near-ultraviolet spectrometer. Title: Structure and Dynamics of Cool Flare Loops Observed by the Interface Region Imaging Spectrograph Authors: Mikuła, K.; Heinzel, P.; Liu, W.; Berlicki, A. Bibcode: 2017ApJ...845...30M Altcode: Flare loops were well observed with the Interface Region Imaging Spectrograph (IRIS) during the gradual phase of two solar flares on 2014 March 29 and 2015 June 22. Cool flare loops are visible in various spectral lines formed at chromospheric and transition-region temperatures and exhibit large downflows which correspond to the standard scenario. The principal aim of this work is to analyze the structure and dynamics of cool flare loops observed in Mg II lines. Synthetic profiles of the Mg II h line are computed using the classical cloud model and assuming a uniform background intensity. In this paper, we study novel IRIS NUV observations of such loops in Mg II h and k lines and also show the behavior of hotter lines detected in the FUV channel. We obtained the spatial evolution of the velocities: near the loop top, the flow velocities are small and they are increasing toward the loop legs. Moreover, from slit-jaw image (SJI) movies, we observe some plasma upflows into the loops, which are also detectable in Mg II spectra. The brightness of the loops systematically decreases with increasing flow velocity, and we ascribe this to the effect of Doppler dimming, which works for Mg II lines. Emission profiles of Mg II were found to be extremely broad, and we explain this through the large unresolved non-thermal motions. Title: On the Origin of the Flare Emission in IRIS’ SJI 2832 Filter:Balmer Continuum or Spectral Lines? Authors: Kleint, Lucia; Heinzel, Petr; Krucker, Säm Bibcode: 2017ApJ...837..160K Altcode: 2017arXiv170207167K Continuum (“white-light,” WL) emission dominates the energetics of flares. Filter-based observations, such as the IRIS SJI 2832 filter, show WL-like brightenings during flares, but it is unclear whether the emission arises from real continuum emission or enhanced spectral lines, possibly turning into emission. The difficulty in filter-based observations, contrary to spectral observations, is to determine which processes contribute to the observed brightening during flares. Here we determine the contribution of the Balmer continuum and the spectral line emission to IRIS’ SJI 2832 emission by analyzing the appropriate passband in simultaneous IRIS NUV spectra. We find that spectral line emission can contribute up to 100% to the observed slitjaw images (SJI) emission, that the relative contributions usually temporally vary, and that the highest SJI enhancements that are observed are most likely because of the Balmer continuum. We conclude that care should be taken when calling SJI 2832 a continuum filter during flares, because the influence of the lines on the emission can be significant. Title: Extreme Space Weather in Extra-Solar Systems - a Flare Alert Program Authors: Hanslmeier, A.; Leitzinger, M.; Greimel, R.; Odert, P.; Ratzka, T.; Brajša, R.; Guenther, E. W.; Korhonen, H.; Pribulla, T.; Šlechta, M.; Vida, K.; Güdel, M.; Heinzel, P.; Lammer, H.; Ribas, I. Bibcode: 2017CEAB...41...67H Altcode: Highly energetic stellar activity phenomena, such as outbreaks of radiations (flares) and mass expulsions into the helio-/astro-sphere (coronal mass ejections/CMEs), may have a severe impact on the atmospheric evolution of planets. Stellar flare have been studied for decades now and their typical parameters are determined statistically. However, observations of stellar CMEs are rare, yielding only a handful of detections so far. The detection of CMEs on stars demands more observational effort than the detection flares, because the circumstellar environment cannot be spatially resolved like in the Solar System. The most convincing detections up to now were found as Doppler-shifted Balmer line extra-emission/absorption features emerging close to flare events, indicating the rise end ejection of prominence material embedded in the CME core. Dedicated programs aiming for a statistical determination of occurrence rates and the parameters of stellar CMEs are still lacking. Therefore, we propose an innovative and efficient observational approach to search for and characterize CMEs on Sun-like and late-type pre-main sequence and main sequence stars to determine stellar CME parameters and their occurrence rates as a function of stellar spectral type and age, as well as establish a stellar flare/CME association rate, for the first time ever. 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: NLTE modeling of a small active region filament observed with the VTT Authors: Schwartz, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Gömöry, P.; Rybák, J.; Heinzel, P.; Kučera, A. Bibcode: 2016AN....337.1045S Altcode: An active region mini-discretionary-filament was observed with the Vacuum Tower Telescope (VTT) in Tenerife simultaneously in the He I infrared triplet using the Tenerife Infrared Polarimeter 1 (TIP 1), in Hα with the TESOS Fabry-Pérot interferometer, and in Ca II 8542 Å with the VTT spectrograph. The spectropolarimetric data were inverted using the HAZEL code and Hα profiles were modelled by solving a NLTE radiative transfer in a simple isobaric and isothermal 2D slab irradiated both from its bottom and sides from the solar surface. It was found that the mini-discretionary-filament is composed of horizontal fluxtubes, along which the cool plasma of T∼10 000 K can flow with very large, even supersonic, velocities. Title: On measurements of the Balmer continuum flux in a solar flare: Analysis of pre-flare and flare pulsations Authors: Zapiór, M.; Kotrč, P.; Oliver, R.; Procházka, O.; Heinzel, P. Bibcode: 2016AN....337.1078Z Altcode: A new ground based device for the measurement of the Balmer continuum flux in solar flares was recently developed and installed at the Ondřejov Observatory. We observed an X1 solar flare on 2014 June 11 during its pre-flare and impulsive phases using a wide band spectrometer with a cadence of 1 s. The Ensemble Empirical Mode Decomposition (EEMD) of the registered signal was performed. We found damped oscillations with a period of 609 s and damping time of 1478 s. Shorter periods of about 30-120 s were found during the pre-flare and impulsive phases, but they might be of non-flare origin. Title: Height formation of bright points observed by IRIS in Mg II line wings during flux emergence Authors: Grubecka, M.; Schmieder, B.; Berlicki, A.; Heinzel, P.; Dalmasse, K.; Mein, P. Bibcode: 2016A&A...593A..32G Altcode: Context. A flux emergence in the active region AR 111850 was observed on September 24, 2013 with the Interface Region Imaging Spectrograph (IRIS). Many bright points are associated with the new emerging flux and show enhancement brightening in the UV spectra.
Aims: The aim of this work is to compute the altitude formation of the compact bright points (CBs) observed in Mg II lines in the context of searching Ellerman bombs (EBs).
Methods: IRIS provided two large dense rasters of spectra in Mg II h and k lines, Mg II triplet, C II and Si IV lines covering all the active region and slit jaws in the two bandpasses (1400 Å and 2796 Å) starting at 11:44 UT and 15:39 UT, and lasting 20 min each. Synthetic profiles of Mg II and Hα lines are computed with non-local thermodynamic equlibrium (NLTE) radiative transfer treatment in 1D solar atmosphere model including a hotspot region defined by three parameters: temperature, altitude, and width.
Results: Within the two IRIS rasters, 74 CBs are detected in the far wings of the Mg II lines (at +/-1 Å and 3.5 Å). Around 10% of CBs have a signature in Si IV and CII. NLTE models with a hotspot located in the low atmosphere were found to fit a sample of Mg II profiles in CBs. The Hα profiles computed with these Mg II CB models are consistent with typical EB profiles observed from ground based telescopes e.g. THEMIS. A 2D NLTE modelling of fibrils (canopy) demonstrates that the Mg II line centres can be significantly affected but not the peaks and the wings of Mg II lines.
Conclusions: We conclude that the bright points observed in Mg II lines can be formed in an extended domain of altitudes in the photosphere and/or the chromosphere (400 to 750 km). Our results are consistent with the theory of heating by Joule dissipation in the atmosphere produced by magnetic field reconnection during flux emergence. Title: Synthetic Hydrogen Spectra of Oscillating Prominence Slabs Immersed in the Solar Corona Authors: Zapiór, M.; Oliver, R.; Ballester, J. L.; Heinzel, P. Bibcode: 2016ApJ...827..131Z Altcode: We study the behavior of Hα and Hβ spectral lines and their spectral indicators in an oscillating solar prominence slab surrounded by the solar corona, using an MHD model combined with a 1D radiative transfer code taken in the line of sight perpendicular to the slab. We calculate the time variation of the Doppler shift, half-width, and maximum intensity of the Hα and Hβ spectral lines for different modes of oscillation. We find a non-sinusoidal time dependence of some spectral parameters with time. Because Hα and Hβ spectral indicators have different behavior for different modes, caused by differing optical depths of formation and different plasma parameter variations in time and along the slab, they may be used for prominence seismology, especially to derive the internal velocity field in prominences. Title: Flares In Time-Domain Surveys Authors: Kowalski, Adam; Hawley, Suzanne; Davenport, James; Berlicki, Arkadiusz; Cauzzi, Gianna; Fletcher, Lyndsay; Heinzel, Petr; Notsu, Yuta; Loyd, Parke; Martinez Oliveros, Juan Carlos; Pugh, Chloe; Schmidt, Sarah Jane; Karmakar, Subhajeet; Pye, John; Flaccomio, Ettore Bibcode: 2016csss.confE.126K Altcode: Proceedings for the splinter session "Flares in Time-Domain Surveys" convened at Cool Stars 19 on June 07, 2016 in Uppsala, Sweden. Contains a two page summary of the splinter session, links to YouTube talks, and a PDF copy of the slides from the presenters. Title: Chromospheric Heating by Acoustic Waves Compared to Radiative Cooling Authors: Sobotka, M.; Heinzel, P.; Švanda, M.; Jurčák, J.; del Moro, D.; Berrilli, F. Bibcode: 2016ApJ...826...49S Altcode: 2016arXiv160504794S Acoustic and magnetoacoustic waves are among the possible candidate mechanisms that heat the upper layers of the solar atmosphere. A weak chromospheric plage near the large solar pore NOAA 11005 was observed on 2008 October 15, in the Fe I 617.3 nm and Ca II 853.2 nm lines of the Interferometric Bidimemsional Spectrometer attached to the Dunn Solar Telescope. In analyzing the Ca II observations (with spatial and temporal resolutions of 0.″4 and 52 s) the energy deposited by acoustic waves is compared to that released by radiative losses. The deposited acoustic flux is estimated from the power spectra of Doppler oscillations measured in the Ca II line core. The radiative losses are calculated using a grid of seven one-dimensional hydrostatic semi-empirical model atmospheres. The comparison shows that the spatial correlation of the maps of radiative losses and acoustic flux is 72%. In a quiet chromosphere, the contribution of acoustic energy flux to radiative losses is small, only about 15%. In active areas with a photospheric magnetic-field strength between 300 and 1300 G and an inclination of 20°-60°, the contribution increases from 23% (chromospheric network) to 54% (a plage). However, these values have to be considered as lower limits and it might be possible that the acoustic energy flux is the main contributor to the heating of bright chromospheric network and plages. Title: Hot prominence detected in the core of a coronal mass ejection: Analysis of SOHO/UVCS Lα and SOHO/LASCO visible-light observations Authors: Heinzel, P.; Susino, R.; Jejčič, S.; Bemporad, A.; Anzer, U. Bibcode: 2016A&A...589A.128H Altcode: Context. The paper deals with the physics of erupting prominences in the core of coronal mass ejections (CME).
Aims: We determine the physical parameters of an erupting prominence embedded in the core of a CME using SOHO/UVCS hydrogen Lα and Lβ lines and SOHO/LASCO visible light observations. In particular we analyze the CME event observed on August 2, 2000. We develop the non-LTE (NLTE; I.e. considering departures from the local thermodynamic equilibrium - LTE) spectral diagnostics based on Lα and visible light observations.
Methods: Our method is based on 1D NLTE modeling of eruptive prominences and takes into account the effect of large flow velocities, which reach up to 300 km s-1 for the studied event (the so-called Doppler dimming). The NLTE radiative-transfer method can be used for both optically thin and thick prominence structures. We combine spectroscopic UVCS observations of an erupting prominence in the core of a CME with visible light images from LASCO-C2 in order to derive the geometrical parameters like projected thickness and velocity, together with the effective temperature and column density of electrons. These are then used to constrain our NLTE radiative transfer modeling which provides the kinetic temperature, microturbulent velocity, gas pressure, ionization degree, the line opacities, and the prominence effective thickness (geometrical filling factor).
Results: Analysis was made for 69 observational points (spatial pixels) inside the whole erupting prominence. Roughly one-half of them show a non-negligible Lα optical thickness for flow velocity 300 km s-1 and about one-third for flow velocity 150 km s-1. All pixels with Lατ0 ≤ 0.3 have been considered for further analysis, which is presented in the form of statistical distributions (histograms) of various physical quantities such as the kinetic temperature, gas pressure, and electron density for two representative flow velocities (150 and 300 km s-1) and non-zero microturbulence. For two pixels co-temporal LASCO visible-light data are also available, which further constrains the diagnostics of the electron density and effective thickness. Detailed NLTE modeling is presented for various sets of input parameters.
Conclusions: The studied CME event shows that the erupting prominence expands to large volumes, meaning that it is a low-pressure structure with low electron densities and high temperatures. This analysis provides a basis for future diagnostics using the METIS coronagraph on board the Solar Orbiter mission. Title: The dynamics and magnetism of the X1 flare on 2014-03-29 Authors: Kleint, Lucia; Heinzel, Petr; Philip, Judge; Krucker, Sam Bibcode: 2016SPD....47.0613K Altcode: The X1 flare on 2014-03-29 was observed with an unprecedented number of instruments including chromospheric polarimetry and spectroscopy from the UV to the IR. By combining data from these instruments, we can answer several open questions: Where is the observed continuum emission during flares formed and through which physical processes? How does the magnetic field structure in the photosphere and in the chromosphere change during a flare? We discuss the implications of our findings on standard flare models. Title: Is it Possible to Use the Green Coronal Line Instead of X rays to Cancel an Effect of the Coronal Emissivity Deficit in Estimation of the Prominence Total Mass from Decrease of the EUV-corona Intensities? Authors: Schwartz, P.; Heinzel, P.; Jejčič, S.; Rybák, J.; Kotrč, P.; Fárník, F.; Kupryakov, Yu. A.; Deluca, E. E.; Golub, L.; Jibben, P. R.; Anzer, U.; Tlatov, A. G. .; Guseva, S. A. Bibcode: 2016ASPC..504...89S Altcode: Total masses of six quiescent prominences observed from April through June 2011 were estimated using multi-spectral observations (in EUV, X-rays, Hα, and Ca <small>II</small> H). The method for the total mass estimation is based on the fact that the intensity of the EUV solar corona at wavelengths below 912 Å is reduced at a prominence by the absorption in resonance continua (photoionisation) of hydrogen and possibly by helium and subsequently an amount of absorbed radiation is proportional to the column density of hydrogen and helium plasma. Moreover, the deficit of the coronal emissivity in volume occupied by the cool prominence plasma also contributes to the intensity decrease. The observations in X-rays which are not absorbed by the prominence plasma, allow us to separate these two mechanisms from each other. The X-ray observations of XRT onboard the Hinode satellite made with the Al-mesh focal filter were used because the X-ray coronal radiation formed in plasma of temperatures of the order of 106 K was registered and EUV spectral lines occurring in the 193, 211 and 335 Å channels of the Atmospheric Imaging Assembly of the Solar Dynamics Observatory satellite are also formed at such temperatures. Unfortunately, the Al-mesh filter has a secondary peak of the transmittance at around 171 Å which causes a contribution from the EUV corona to the measured data of up to 11 % in the quiet corona. Thus, absorption in prominence plasma influences XRT X-ray data when using the Al-mesh filter. On the other hand, other X-ray XRT filters are more sensitive to plasma of much higher temperatures (log T of the order of 7), thus observations using these filters cannot be used together with the AIA observations in the method for mass estimations. This problem could be solved using observations in the green coronal line instead of X-rays. Absorption of the green coronal line by a prominence plasma is negligible and this line is formed at temperatures of the order of 106 K. We compare values of the total mass of the prominence observed on 20 October 2012 on the SE limb estimated when using XRT X-ray observations and observations in the green coronal line obtained at Kislovodsk Mountain Astronomical Station of the Pulkovo observatory (Russia). Title: Magnetic Field and Plasma Diagnostics from Coordinated Prominence Observations Authors: Schmieder, B.; Levens, P.; Dalmasse, K.; Mein, N.; Mein, P.; Lopez-Ariste, A.; Labrosse, N.; Heinzel, P. Bibcode: 2016ASPC..504..119S Altcode: We study the magnetic field in prominences from a statistical point of view, by using THEMIS in the MTR mode, performing spectropolarimetry of the He I D3 line. Combining these measurements with spectroscopic data from IRIS, Hinode/EIS as well as ground-based telescopes, such as the Meudon Solar Tower, we infer the temperature, density, and flow velocities of the plasma. There are a number of open questions that we aim to answer: - What is the general direction of the magnetic field in prominences? Is the model using a single orientation of magnetic field always valid for atypical prominences? %- Does this depend on the location of the filament on the disk (visible in Hα, in He II 304 Å) over an inversion line between weak or strong network ? - Are prominences in a weak environment field dominated by gas pressure? - Measuring the Doppler shifts in Mg II lines (with IRIS) and in Hα can tell us if there are substantial velocities to maintain vertical rotating structures, as has been suggested for tornado-like prominences. We present here some results obtained with different ground-based and space-based instruments in this framework. Title: Measurements of Continuum Flux in Solar Flares Authors: Kotrč, P.; Heinzel, P.; Procházka, O. Bibcode: 2016ASPC..504...49K Altcode: A broad-band diagnostics of chromospheric flare plasma needs to analyze spectra covering many spectral lines and various continuum features. The flare spectra are well detected on the background of the solar disk, but the detection of flare line emission from the Sun-as-a-star in optical is much more difficult due to a strong background radiation. When the flare/background radiation contrast is strong enough to be detected, we need a device for measuring the flux from a selected part of the flaring region. Here we present technical demands for such an instrument and its brief description. This device denoted as Image Selector is a post-focus instrument installed at the horizontal solar telescope HSFA2 of the Ondřejov observatory, described by Kotrč (2009). Its core consists of a system of diaphragms, imaging Hα telescope and a fast spectrometer with dispersion of 3 px per Å but with cadency reaching up to 50 frames per second. The first solar flares observed recently by this novel technique provide quite interesting results. Our analysis of the data proves that the described device is sufficiently sensitive to detect variations in the Balmer continuum during solar flares. 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: Non-LTE Inversion of Spectropolarimetric and Spectroscopic Observations of a Small Active-region Filament Observed at the VTT Authors: Schwartz, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Gömöry, P.; Rybák, J.; Kučera, A.; Heinzel, P. Bibcode: 2016ASPC..504..205S Altcode: An active region mini-filament was observed by VTT simultaneously in the He<small>I</small> 10 830 Å triplet by the TIP 1 spectropolarimeter, in Hα by the TESOS Fabry-Pérot interferometer, and in Ca <small>II</small> 8542 Å by the VTT spectrograph. The spectropolarimetric data were inverted using the HAZEL code and Hα profiles were modelled solving a NLTE radiative transfer in a simple isobaric and isothermal 2D slab irradiated both from bottom and sides. It was found that the mini-filament is composed of horizontal fluxtubes, along which the cool plasma of T∼10 000 K can flow by very large - even supersonic - velocities. Title: New Observations of Balmer Continuum Flux in Solar Flares. Instrument Description and First Results Authors: Kotrč, P.; Procházka, O.; Heinzel, P. Bibcode: 2016SoPh..291..779K Altcode: 2016SoPh..tmp...17K; 2016arXiv160104610K Increase in the Balmer continuum radiation during solar flares was predicted by various authors, but has never been firmly confirmed observationally using ground-based slit spectrographs. Here we describe a new post-focal instrument, the image selector, with which the Balmer continuum flux can be measured from the whole flare area, in analogy to successful detections of flaring dMe stars. The system was developed and put into operation at the horizontal solar telescope HSFA2 of the Ondřejov Observatory. We measure the total flux by a fast spectrometer from a limited but well-defined region on the solar disk. Using a system of diaphragms, the disturbing contribution of a bright solar disk can be eliminated as much as possible. Light curves of the measured flux in the spectral range 350 - 440 nm are processed, together with the H α images of the flaring area delimited by the appropriate diaphragm. The spectral flux data are flat-fielded, calibrated, and processed to be compared with model predictions. Our analysis of the data proves that the described device is sufficiently sensitive to detect variations in the Balmer continuum during solar flares. Assuming that the Balmer-continuum kernels have at least a similar size as those visible in H α , we find the flux increase in the Balmer continuum to reach 230 - 550 % of the quiet continuum during the observed X-class flare. We also found temporal changes in the Balmer continuum flux starting well before the onset of the flare in H α. Title: Observations and modeling of the ultraviolet emission of solar flares Authors: Mikuła, Katarzyna; Berlicki, Arkadiusz; Heinzel, Petr Bibcode: 2016IAUS..320...57M Altcode: In this paper we present the method of using far UV spectra of the flare observed by Interface Region Imaging Spectrograph (IRIS) for determination of the contribution of the continuum emission to the total UV radiation observed e.g. by SDO in 1600 Å channel. In our method the Si IV (1402.77 Å) line observed by IRIS is used as a proxy of C IV line emission contained in SDO/AIA UV images. Determined intensity of the flare continuum emission can be used to study the physics of the flare heated chromosphere and for better understanding of the emission mechanisms. Title: White-light continuum emission from a solar flare and plage Authors: Berlicki, Arkadiusz; Awasthi, Arun Kumar; Heinzel, Petr; Sobotka, Michal Bibcode: 2016IAUS..320..268B Altcode: 2016arXiv160404186B Observations of flare emissions in the optical continuum are very rare. Therefore, the analysis of such observations is useful and may contribute to our understanding of the flaring chromosphere and photosphere. We study the white light continuum emission observed during the X6.9 flare. This emission comes not only from the flare ribbons but also form the nearby plage area. The main aim of this work is to disentangle the flare and plage (facula) emission. We analyzed the spatial, spectral and temporal evolution of the flare and plage properties by analyzing multi-wavelength observations. We study the morphological correlation of the white-light continuum emission observed with different instruments. We found that some active region areas which produce the continuum emission correspond rather to plages than to the flare kernels. We showed that in some cases the continuum emission from the WL flare kernels is very similar to the continuum emission of faculae. Title: Numerical RHD simulations of flaring chromosphere with Flarix Authors: Heinzel, Petr; Kašparová, Jana; Varady, Michal; Karlický, Marian; Moravec, Zdeněk Bibcode: 2016IAUS..320..233H Altcode: 2016arXiv160200016H Flarix is a radiation-hydrodynamical (RHD) code for modeling of the response of the chromosphere to a beam bombardment during solar flares. It solves the set of hydrodynamic conservation equations coupled with NLTE equations of radiative transfer. The simulations are driven by high energy electron beams. We present results of the Flarix simulations of a flaring loop relevant to the problem of continuum radiation during flares. In particular we focus on properties of the hydrogen Balmer continuum which was recently detected by IRIS. Title: Continuum Enhancements in the Ultraviolet, the Visible and the Infrared during the X1 Flare on 2014 March 29 Authors: Kleint, Lucia; Heinzel, Petr; Judge, Phil; Krucker, Säm Bibcode: 2016ApJ...816...88K Altcode: 2015arXiv151104161K Enhanced continuum brightness is observed in many flares (“white light flares”), yet it is still unclear which processes contribute to the emission. To understand the transport of energy needed to account for this emission, we must first identify both the emission processes and the emission source regions. Possibilities include heating in the chromosphere causing optically thin or thick emission from free-bound transitions of Hydrogen, and heating of the photosphere causing enhanced H- continuum brightness. To investigate these possibilities, we combine observations from Interface Region Imaging Spectrograph (IRIS), SDO/Helioseismic and Magnetic Imager, and the ground-based Facility Infrared Spectrometer instrument, covering wavelengths in the far-UV, near-UV (NUV), visible, and infrared during the X1 flare SOL20140329T17:48. Fits of blackbody spectra to infrared and visible wavelengths are reasonable, yielding radiation temperatures ∼6000-6300 K. The NUV emission, formed in the upper photosphere under undisturbed conditions, exceeds these simple fits during the flare, requiring extra emission from the Balmer continuum in the chromosphere. Thus, the continuum originates from enhanced radiation from photosphere (visible-IR) and chromosphere (NUV). From the standard thick-target flare model, we calculate the energy of the nonthermal electrons observed by Reuven Ramaty High Energy Solar Spectroscope Imager (RHESSI) and compare it to the energy radiated by the continuum emission. We find that the energy contained in most electrons >40 keV, or alternatively, of ∼10%-20% of electrons >20 keV is sufficient to explain the extra continuum emission of ∼(4-8) × 1010 erg s-1 cm-2. Also, from the timing of the RHESSI HXR and the IRIS observations, we conclude that the NUV continuum is emitted nearly instantaneously when HXR emission is observed with a time difference of no more than 15 s. Title: Lines of MgI Detected in Solar Prominences Authors: Heinzel, P.; Kupryakov, Yu.; Schwartz, P. Bibcode: 2016CEAB...40...87H Altcode: Using the flare spectrograph at Ondřejov observatory, we have observed several prominences with the aim to detect the MgI lines. These lines play an important diagnostic role, complementary to MgII resonance lines now routinely observed by the IRIS satellite. Our preliminary analysis shows that a rather weak MgI emission, e.g. in the 5172.7 Å line, is detectable and this correlates well with the presence of extended bright regions on the solar disk visible in SDO/AIA 1600 Å band. Physical reasons for such a correlation are discussed. Title: Observed IRIS Profiles of the h and k Doublet of Mg II and Comparison with Profiles from Quiescent Prominence NLTE Models Authors: Vial, Jean-Claude; Pelouze, Gabriel; Heinzel, Petr; Kleint, Lucia; Anzer, Ulrich Bibcode: 2016SoPh..291...67V Altcode: 2015SoPh..tmp..173V With the launch of the Interface Region Imaging Spectrograph (IRIS) mission, it is now possible to obtain high-resolution solar prominence spectra and to begin to distinguish the contributions of the many (apparent or not) threads that structure prominences. We aim at comparing unique observations obtained in the Mg II h and k lines of a polar crown prominence with the radiative outputs from one-dimensional models built with non-local-thermodynamic equilibrium codes (Heinzel et al.Astron. Astrophys.564, A132, 2014). We characterize the profiles obtained through thorough calibration procedures, with attention paid to the absolute values, full-width at half-maximum, and the ratio of k to h intensities. We also show that at the top of some structures, line-of-sight velocities of about 9 kms−1 can be detected. We find a range of static, low-pressure, low-thickness, low-temperature models that could fit k or h observed values, but that cannot satisfy the low observed k/h ratio. We investigate whether these low values might be explained by the inclusion of horizontal flows in small-scale threads. These flows are also necessary in another class of models, where the pressure is kept low but thickness and temperature are increased up to the observed thickness and up to 15 000 K. Title: Solar and Stellar Flares and their Effects on Planets Authors: Kosovichev, A. G.; Hawley, S. L.; Heinzel, P. Bibcode: 2016IAUS..320.....K Altcode: No abstract at ADS 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: Preface Authors: Fletcher, L.; Heinzel, P.; van Driel-Gesztelyi, L.; Mandrini, C. H.; Fárník, F. Bibcode: 2015SoPh..290.3379F Altcode: 2015SoPh..tmp..168F No abstract at ADS Title: Mg II Lines Observed During the X-class Flare on 29 March 2014 by the Interface Region Imaging Spectrograph Authors: Liu, W.; Heinzel, P.; Kleint, L.; Kašparová, J. Bibcode: 2015SoPh..290.3525L Altcode: 2015SoPh..tmp..166L; 2015arXiv151100480L Mg II lines represent one of the strongest emissions from the chromospheric plasma during solar flares. In this article, we studied the Mg II lines observed during the X1 flare on 29 March 2014 (SOL2014-03-29T17:48) by the Interface Region Imaging Spectrograph (IRIS). IRIS detected large intensity enhancements of the Mg II h and k lines, subordinate triplet lines, and several other metallic lines at the flare footpoints during this flare. We have used the advantage of the slit-scanning mode (rastering) of IRIS and performed, for the first time, a detailed analysis of spatial and temporal variations of the spectra. Moreover, we were also able to identify positions of strongest hard X-ray (HXR) emissions using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations and to correlate them with the spatial and temporal evolution of IRIS Mg II spectra. The light curves of the Mg II lines increase and peak contemporarily with the HXR emissions but decay more gradually. There are large red asymmetries in the Mg IIh and k lines after the flare peak. We see two spatially well-separated groups of Mg II line profiles, non-reversed and reversed. In some cases, the Mg II footpoints with reversed profiles are correlated with HXR sources. We show the spatial and temporal behavior of several other line parameters (line metrics) and briefly discuss them. Finally, we have synthesized the Mg IIk line using our non-LTE code with the Multilevel Accelerated Lambda Iteration (MALI) technique. Two kinds of models are considered, the flare model F2 of Machado et al. (Astrophys. J.242, 336, 1980) and the models of Ricchiazzi and Canfield (Astrophys. J.272, 739, 1983, RC models). Model F2 reproduces the peak intensity of the non-reversed Mg IIk profile at flare maximum, but does not account for high wing intensities. On the other hand, the RC models show the sensitivity of Mg II line intensities to various electron-beam parameters. Our simulations also show that the microturbulence produces a broader line core, while the intense line wings are caused by an enhanced line source function. Title: White-light continuum emission from solar flare and plages: observations and modeling Authors: Berlicki, Arkadiusz; Awasthi, Arun Kumar; Heinzel, Petr Bibcode: 2015IAUGA..2256469B Altcode: Observations of flares in optical continuum emission are very rare. Therefore, the analysis of such observations is very useful and may contribute to our understanding of the flaring chromosphere. We study the white-light continuum emission observed during the X6.9 flare observed on August 09, 2011. This emission comes not only from the flare ribbons but also form the nearby plage area observed within the active region. The main aim of this work is to disentangle the flare and plage emission and to understand the physical mechanisms responsible for the production of white-light continuum.There are two main mechanisms which can be responsible for the optical continuum emission of the solar atmosphere: enhanced photospheric H- continuum due to the temperature increase below the temperature minimum region, or hydrogen recombination continua (Balmer, Paschen) formed in solar chromosphere. In our work we analyse the physical conditions in solar active atmosphere in order to obtain the contribution from these two mechanisms to the whole continuum emission of the flare and plage.We analyzed the spatial, spectral and temporal evolution study of the flare and plage parameters by analyzing multi-wavelength observations obtained from ground and space based solar observatories. We study the morphological correlation of the white-light continuum emission observed with different instruments. Moreover, we also explore the non-thermal electron beam properties by forward fitting the observed X-ray spectra.The unique opportunity of an intense X6.9 flare occurrence close to the limb enabled us to explore the origin of white-light continuum with better visibility. The analysis of multi-wavelength data revealed the origin of this emission from the foot-points of the loops. Spatial association of HXR foot-points synthesized from RHESSI observations confirmed this finding. In addition, we found a good temporal correlation of hard (>30 keV) X-ray with the white-light emission. However, some active region areas which produce the continuum emission correspond rather to plages than to the flare kernels. Title: Multi-wavelength diagnostics and modelling of the emission during a B6.4 flare of August 20, 2005 Authors: Awasthi, Arun Kumar; Berlicki, Arkadiusz; Rudawy, Powel; Heinzel, Petr Bibcode: 2015IAUGA..2256580A Altcode: We study the temporal, spatial and spectral evolution of multi-wavelength emission observed during a B6.4 flare occurred on August 20, 2005 with the motivation to outline the thermal and non-thermal processes during the precursor and gradual phase of the flare. Precursor phase is designated as the gradual enhancement of soft X-ray emission prior to onset of the impulsive phase. Observations from several space and ground based observatories viz. RHESSI, TRACE, GONG, SoHO/EIT and NoRP are included in this study. Temporal evolution of X-ray emission does not show the presence of hard X-rays (>12 keV) emission during the precursor phase of the flare. We synthesized X-ray images in 6-12 keV from RHESSI observations, which show several discrete sources during the precursor phase. Following to this, one of these sources pronounced during the main phase of the flare. We carry out in-depth analysis of chromospheric response in various phases of the flare employing high temporal cadence images of the Sun in Hα line centre as well as wings obtained from the Multi-channel Subtractive Double Pass Spectrograph (MSDP) at the Bialkow Observatory of the University of Wroclaw, Poland. Our analysis of Hα images during the main phase of the flare suggests localized emission in the form of kernels. On the contrary, we note extended and diffused source morphology of emitting region during the precursor phase of the flare. We also study various kinematic properties of different structures visible in the Hα images in the line centre as well as wings. In addition, the correlation of the relative timing of X-ray and Hα emission profile is performed to estimate the delay in the chromospheric response during different phases of flare. Further, we employ thermal plasma parameters estimated during the precursor and gradual phase to model the associated Hα emission. For the modeling we employ NLTE numerical codes modified for flare conditions. The modeled and observed flare emission parameters are then compared. Finally, we propose a unified schematic scenario for the trigger and energy release during this low-intensity class flare. Title: Observations and modeling of the ultraviolet emission of solar flares Authors: Berlicki, Arkadiusz; Heinzel, Petr; Mikula, Katarzyna Bibcode: 2015IAUGA..2257337B Altcode: It is well known that during solar flares the heated chromospheric plasma emits the ultraviolet (UV) radiation in spectral lines and continua. UV space telescopes (e.g. TRACE, Solar Dynamic Observatory/Atmospheric Imaging Assembly - SDO/AIA) provide images of solar flares where the complicated fine structure of the flaring atmosphere is well visible. However, these broadband images contain the mixture of line and continuum UV emission and it is not possible to disentangle between these two contributions. E.g. solar flare brightening observed in SDO/AIA 160 nm channel can be visible both due to the strong line emission in C IV 154.8 nm or due to the continuum increase. Spectral lines and continua are formed in plasma of different temperature and location. Therefore, in order to obtain the parameters of plasma we should know quantitatively the contribution from lines and continua.Such analysis would be possible using the UV spectrograph, where we can see the intensity of lines and continua separately. For example Interface Region Imaging Spectrograph (IRIS) provides such spectra of flares, where the enhanced lines and continuum is visible both in NUV (near UV) and FUV (far UV) channels.In our work we used IRIS flare observations in FUV channel to determine the intensity of spectral lines, including Si IV 139.4 nm line. Then, using CHIANTI procedures and the observed intensities of some FUV lines we computed the synthetic UV spectrum for given flare model. IRIS spectrum does not include C IV line, which contaminates the SDO/AIA images, but this line can be calculated in the theoretical CHIANTI spectrum. In this way, we can subtract the C IV (and other lines) emission from SDO/AIA images and obtain the pure UV continuum intensity. Finally, the obtained continuum emission can used to study the physics of heated chromosphere of flares. 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: On the Visibility of Prominence Fine Structures at Radio Millimeter Wavelengths Authors: Heinzel, P.; Berlicki, A.; Bárta, M.; Karlický, M.; Rudawy, P. Bibcode: 2015SoPh..290.1981H Altcode: 2015SoPh..tmp...87H Prominence temperatures have so far mainly been determined by analyzing spectral line shapes, which is difficult when the spectral lines are optically thick. The radio spectra in the millimeter range offer a unique possibility to measure the kinetic temperature. However, studies in the past used data with insufficient spatial resolution to resolve the prominence fine structures. The aim of this article is to predict the visibility of prominence fine structures in the submillimeter/millimeter (SMM) domain, to estimate their brightness temperatures at various wavelengths, and to demonstrate the feasibility and usefulness of future high-resolution radio observations of solar prominences with ALMA (Atacama Large Millimeter-submillimeter Array). Our novel approach is the conversion of Hα coronagraphic images into microwave spectral images. We show that the spatial variations of the prominence brightness both in the Hα line and in the SMM domain predominantly depend on the line-of-sight emission measure of the cool plasma, which we derive from the integrated intensities of the observed Hα line. This relation also offers a new possibility to determine the SMM optical thickness from simultaneous Hα observations with high resolution. We also describe how we determine the prominence kinetic temperature from SMM spectral images. Finally, we apply the ALMA image-processing software Common Astronomy Software Applications (CASA) to our simulated images to assess what ALMA would detect at a resolution level that is similar to the coronagraphic Hα images used in this study. Our results can thus help in preparations of first ALMA prominence observations in the frame of science and technical verification tests. 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: Prominence Visibility in Hinode/XRT Images Authors: Schwartz, P.; Jejčič, S.; Heinzel, P.; Anzer, U.; Jibben, P. R. Bibcode: 2015ApJ...807...97S Altcode: 2015arXiv150606078S In this paper we study the soft X-ray (SXR) signatures of one particular prominence. The X-ray observations used here were made by the Hinode/X-Ray Telescope instrument using two different filters. Both of them have a pronounced peak of the response function around 10 Å. One of them has a secondary smaller peak around 170 Å, which leads to a contamination of SXR images. The observed darkening in both of these filters has a very large vertical extension. The position and shape of the darkening correspond nicely with the prominence structure seen in SDO/AIA images. First, we have investigated the possibility that the darkening is caused by X-ray absorption. However, detailed calculations of the optical thickness in this spectral range show clearly that this effect is completely negligible. Therefore, the alternative is the presence of an extended region with a large emissivity deficit, which can be caused by the presence of cool prominence plasmas within an otherwise hot corona. To reproduce the observed darkening, one needs a very large extension along the line of sight of the region amounting to around 105 km. We interpret this region as the prominence spine, which is also consistent with SDO/AIA observations in EUV. 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: Total mass of six quiescent prominences estimated from their multi-spectral observations Authors: Schwartz, P.; Heinzel, P.; Kotrč, P.; Fárník, F.; Kupryakov, Yu. A.; DeLuca, E. E.; Golub, L. Bibcode: 2015A&A...574A..62S Altcode: Context. Total masses of six solar prominences were estimated using prominence multi-spectral observations (in EUV, X-rays, Hα, and Ca ii H). The observations were made during the observing campaign from April through June 2011.
Aims: The aim of the work was to apply a complex method for the prominence mass estimations that can be used later for other prominences observed during the observing campaign.
Methods: Our method is based on the fact that intensity of the EUV solar corona at wavelengths below 912 Å is reduced by the absorption in resonance continua of hydrogen and helium (photoionisation) and at the same time also by a deficit of the coronal emissivity in volume occupied by the cool prominence plasma. Both mechanisms contribute to intensity decrease simultaneously. The observations in X-rays allow us to separate these mechanisms from each other. Coronal emission behind a prominence is not estimated by any temporal or spatial interpolation, but by using a new method based on comparing the ratio of the optical thickness at 193 Å and 211 Å determined from the observations with the theoretical ratio.
Results: Values of the total mass estimated for six prominences are between 2.9 × 1011 and 1.7 × 1012 kg. The column density of hydrogen is of the order of 1018-1019 cm-2. Our results agree with results of other authors.
Conclusions: The method is now ready to be used for all 30 prominences observed during the campaign. Then in the near future it will be possible to obtain a statistics of the total mass of quiescent solar prominences. Title: Radiative Transfer in Solar Prominences Authors: Heinzel, Petr Bibcode: 2015ASSL..415..103H Altcode: Critical information about prominence physical conditions can be obtained only by analyzing prominence spectra or high-resolution monochromatic images. Solar prominences are low-density structures and, therefore, the non-equilibrium (NLTE) spectroscopy tools have to be used. We describe the basics of the NLTE radiative-transfer theory applied to typical prominence conditions and demonstrate why the NLTE approach is necessary. Starting from the simplest 1D slab models, we gradually move to more complex problems which include 2D transfer, importance of partial redistribution in the formation of resonance lines and details of multilevel problems including the most up-to-date numerical methods for constructing NLTE models. We also mention some recent achievements in prominence modeling (e.g. magnetic dips, radiative equilibrium models, oscillations), although detailed description of such results is the subject of other chapters. Title: On the Origin of Linear Polarization in Solar Flares Authors: Štěpán, J.; Heinzel, P. Bibcode: 2014ASPC..489..133S Altcode: A significant degree of linear polarization (up to few percent) of some spectral lines is occasionally reported from the observations of solar flares. This polarization is often found at the edges of the flare ribbons and it is usually radial or tangential. The mechanism usually considered as being responsible for this effect is the impact polarization by electron and/or proton beams bombarding the chromosphere. We point out that resonant scattering polarization in a multi-dimensional geometry of the chromosphere has to be considered as an important ingredient of the problem. The significant horizontal inhomogeneities at the boundaries of the flare ribbons causes a considerable change in the radiation field anisotropy which may lead to emission of strongly linearly polarized spectral lines. For more details see Štěpán, & Heinzel (2013) Title: Hydrogen Balmer Continuum in Solar Flares Detected by the Interface Region Imaging Spectrograph (IRIS) Authors: Heinzel, P.; Kleint, L. Bibcode: 2014ApJ...794L..23H Altcode: 2014arXiv1409.5680H We present a novel observation of the white light flare (WLF) continuum, which was significantly enhanced during the X1 flare on 2014 March 29 (SOL2014-03-29T17:48). Data from the Interface Region Imaging Spectrograph (IRIS) in its near-UV channel show that at the peak of the continuum enhancement, the contrast at the quasi-continuum window above 2813 Å reached 100%-200% and can be even larger closer to Mg II lines. This is fully consistent with the hydrogen recombination Balmer-continuum emission, which follows an impulsive thermal and non-thermal ionization caused by the precipitation of electron beams through the chromosphere. However, a less probable photospheric continuum enhancement cannot be excluded. The light curves of the Balmer continuum have an impulsive character with a gradual fading, similar to those detected recently in the optical region on the Solar Optical Telescope on board Hinode. This observation represents a first Balmer-continuum detection from space far beyond the Balmer limit (3646 Å), eliminating seeing effects known to complicate the WLF detection. Moreover, we use a spectral window so far unexplored for flare studies, which provides the potential to study the Balmer continuum, as well as many metallic lines appearing in emission during flares. Combined with future ground-based observations of the continuum near the Balmer limit, we will be able to disentangle various scenarios of the WLF origin. IRIS observations also provide a critical quantitative measure of the energy radiated in the Balmer continuum, which constrains various models of the energy transport and deposit during flares. 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: Observations and NLTE modeling of Ellerman bombs Authors: Berlicki, A.; Heinzel, P. Bibcode: 2014A&A...567A.110B Altcode: 2014arXiv1406.5702B Context. Ellerman bombs (EBs) are short-lived, compact, and spatially well localized emission structures that are observed well in the wings of the hydrogen Hα line. EBs are also observed in the chromospheric CaII lines and in UV continua as bright points located within active regions. Hα line profiles of EBs show a deep absorption at the line center and enhanced emission in the line wings with maxima around ±1 Å from the line center. Similar shapes of the line profiles are observed for the CaII IR line at 8542 Å. In CaII H and K lines the emission peaks are much stronger, and EBs emission is also enhanced in the line center.
Aims: It is generally accepted that EBs may be considered as compact microflares located in lower solar atmosphere that contribute to the heating of these low-lying regions, close to the temperature minimum of the atmosphere. However, it is still not clear where exactly the emission of EBs is formed in the solar atmosphere. High-resolution spectrophotometric observations of EBs were used for determining of their physical parameters and construction of semi-empirical models. Obtained models allow us to determine the position of EBs in the solar atmosphere, as well as the vertical structure of the activated EB atmosphere
Methods: In our analysis we used observations of EBs obtained in the Hα and CaII H lines with the Dutch Open Telescope (DOT). These one-hour long simultaneous sequences obtained with high temporal and spatial resolution were used to determine the line emissions. To analyze them, we used NLTE numerical codes for the construction of grids of 243 semi-empirical models simulating EBs structures. In this way, the observed emission could be compared with the synthetic line spectra calculated for all such models.
Results: For a specific model we found reasonable agreement between the observed and theoretical emission and thus we consider such model as a good approximation to EBs atmospheres. This model is characterized by an enhanced temperature in the lower chromosphere and can be considered as a compact structure (hot spot), which is responsible for the emission observed in the wings of chromospheric lines, in particular in the Hα and CaII H lines.
Conclusions: For the first time the set of two lines Hα and CaII H was used to construct semi-empirical models of EBs. Our analysis shows that EBs can be described by a "hot spot" model, with the temperature and/or density increase through a few hundred km atmospheric structure. We confirmed that EBs are located close to the temperature minimum or in the lower chromosphere. Two spectral features (lines in our case), observed simultaneously, significantly strengthen the constraints on a realistic model. 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: F-CHROMA.Flare Chromospheres: Observations, Models and Archives Authors: Cauzzi, Gianna; Fletcher, Lyndsay; Mathioudakis, Mihalis; Carlsson, Mats; Heinzel, Petr; Berlicki, Arek; Zuccarello, Francesca Bibcode: 2014AAS...22412339C Altcode: F-CHROMA is a collaborative project newly funded under the EU-Framework Programme 7 "FP7-SPACE-2013-1", involving seven different European research Institutes and Universities. The goal of F-CHROMA is to substantially advance our understanding of the physics of energy dissipation and radiation in the flaring solar atmosphere, with a particular focus on the flares' chromosphere. A major outcome of the F-CHROMA project will be the creation of an archive of chromospheric flare observations and models to be made available to the community for further research.In this poster we describe the structure and milestones of the project, the different activities planned, as well as early results. Emphasis will be given to the dissemination efforts of the project to make results of these activities available to and usable by the community. Title: On the formation of Mg ii h and k lines in solar prominences Authors: Heinzel, P.; Vial, J. -C.; Anzer, U. Bibcode: 2014A&A...564A.132H Altcode:
Aims: With the recent launch of the IRIS mission, it has become urgent to develop the spectral diagnostics using the Mg ii resonance h and k lines. In this paper, we aim to demonstrate the behavior of these lines under various prominence conditions. Our results serve as a basis for analysis of new IRIS data and for more sophisticated prominence modeling.
Methods: For this exploratory work, we use a canonical 1D prominence-slab model, which is isobaric and may have three different temperature structures: isothermal, PCTR-like (prominence-corona transition region), and consistent with the radiative equilibrium. The slabs are illuminated by a realistic incident solar radiation obtained from the UV observations. A five-level plus continuum Mg ii model atom is used to solve the full NLTE problem of the radiative transfer. We use the numerical code based on the ALI techniques and apply the partial frequency redistribution for both Mg ii resonance lines. We also use the velocity-dependent boundary conditions to study the effect of Doppler dimming in the case of moving prominences. Finally, the relaxation technique is used to compute a grid of models in radiative equilibrium.
Results: We computed the Mg ii h and k line profiles that are emergent from prominence-slab models and show their dependence on kinetic temperature, gas pressure, geometrical extension, and microturbulent velocity. By increasing the line opacity, significant departures from the complete frequency redistribution take place in the line wings. Models with a PCTR temperature structure show that Mg ii becomes ionized to Mg iii in the temperature range between roughly 15 000 and 30 000 K. Doppler dimming is significant for Mg ii resonance lines. At the velocity 300 km s-1, the line intensity decreases to about 20% of the value for static prominences. Finally, we demonstrate the role of Mg ii h and k radiation losses on the prominence energy balance. Their dominant role is at lower pressures, while the losses due to hydrogen and Ca ii dominate at higher pressures. Title: Synthetic hydrogen spectra of prominence oscillations Authors: Heinzel, P.; Zapiór, M.; Oliver, R.; Ballester, J. L. Bibcode: 2014A&A...562A.103H Altcode: 2014arXiv1401.2131H Context. Prominence oscillations have been mostly detected using Doppler velocity, although there are also claimed detections by means of periodic variations in half-width or line intensity. However, scarce observational evidence exists about simultaneous detection of oscillations in several spectral indicators.
Aims: Our main aim here is to explore the relationship between spectral indicators, such as Doppler shift, line intensity, and line half-width, and the linear perturbations excited in a simple prominence model.
Methods: Our equilibrium background model consists of a bounded, homogeneous slab, which is permeated by a transverse magnetic field, having prominence-like physical properties. Assuming linear perturbations, the dispersion relation for fast and slow modes has been derived, as well as the perturbations for the different physical quantities. These perturbations have been used as the input variables in a one-dimensional radiative transfer code, which calculates the full spectral profile of the hydrogen Hα and Hβ lines.
Results: We have found that different oscillatory modes produce spectral indicator variations in different magnitudes. Detectable variations in the Doppler velocity were found for the fundamental slow mode only. Substantial variations in the Hβ line intensity were found for specific modes. Other modes lead to lower and even undetectable parameter variations.
Conclusions: To perform prominence seismology, analysis of the Hα and Hβ spectral line parameters could be a good tool to detect and identify oscillatory modes. Title: A comparison between observed IRIS profiles of the h & k doublet of Mg II and profiles from quiescent prominence NLTE models Authors: Vial, Jean-Claude; Anzer, Ulrich; Heinzel, Petr; Kleint, Lucia Bibcode: 2014cosp...40E3515V Altcode: With the advent of IRIS, it is now possible to investigate the cool core of prominences through the detailed profiles of the Mg II resonance lines with an unprecedented spatial resolution of 0.33 arcsecond. The slit-jaw camera also allows to record the temporal evolution of the prominence fine structure. We present IRIS observations of quiescent prominence profiles that we analyse in terms of reversal (if any), width, k/h line ratio, prominence/ quiet Sun line ratio. Comparing these parameters with the results of NLTE modelling (see Heinzel et al. 2014), we can derive thermodynamic parameters of the cool prominence plasma, along with the (line-of-sight) velocities and mass flows. Title: Possible measurements of the magnetic field in eruptive prominences using the PROBA-3 coronagraph Authors: Serge, Koutchmy; Zhukov, Andrei; Dolla, Laurent; Heinzel, Petr; Lamy, Philippe; Bazin, Cyrille; Bommier, Veronique; Faurobert, Marianne Bibcode: 2014cosp...40E2971S Altcode: The PROBA-3 mission will fly a spacecraft put in the shadow of a precisely occulting sister satellite orbiting “in formation” at a distance of 150 m in front of it to make artificial total eclipses. The region right above the solar limb will be studied for the first time over a coronal background not polluted by any spurious light. Although the priority will be the high-resolution fast imaging of the dynamic white-light corona, the use of a narrow filter centered on a low excitation D3 line of He I, is planned for imaging prominences. Adding the linear polarization analysis would permit the measurements of the magnetic field using the Hanle effect. We evaluate the possibility offered during the eruptive phase of a CME with prominence material inserted inside, for studying the associated magnetic field changes related to both the heating process and the ejection of material. The background highly polarized K-corona is taken into account. Sequences of quasi- simultaneous white-light processed images at high resolution are an additional feature of great interest for interpreting the overall magnetic structure. Title: A study of H I Lyman-alpha emission from prominences erupting in the intermediate corona and possible future applications for Solar Orbiter/METIS data Authors: Bemporad, Alessandro; Heinzel, Petr; Jejcic, Sonja; Susino, Roberto Bibcode: 2014cosp...40E.273B Altcode: Over almost the last 20 years hundreds of Coronal Mass Ejections (CME) have been observed by the UV Coronagraph Spectrometer (UVCS) onboard SOHO. For many of these events a significant emission in the HI Lyman-alpha lambda 1216 Å line was sampled during the transit across the slit of the erupting prominences embedded in the core of CMEs. The origin of this emission is completely different from what is typically observed by UVCS: because of the higher density and lower temperatures of such plasmas, the number of neutral H atoms is much larger than under typical coronal conditions, and the plasma is generally not optically thin at these wavelengths, as it is usually true for other coronal structures. Hence, the observed H I Lyman-alpha emission can be explained only if a radiative transport treatment across a moving plasma structure is considered. Once the proper boundary conditions are derived from the UV data, in combination with white light (WL) coronagraphic observations (from LASCO), we will show how the temperature and density of the erupting prominence could be derived even at large altitudes (typically larger than 0.6 solar radii above the limb), thus providing information on heating/cooling and ionization of the CME core during the eruption. These results are very important in the light of coronagraphic observations that will be provided by the METIS instrument onboard the Solar Orbiter: because METIS will contemporary observe the solar corona in WL and in UV (HI Lyman-alpha), it will be possible to derive, with a technique similar to what is shown here, very important information on prominence plasmas embedded in the core of CMEs and crossing the METIS instrument field of view. Title: Chromospheric heating during a flare Authors: Heinzel, Petr Bibcode: 2014cosp...40E1183H Altcode: Flares are now believed to be complex processes initiated in the corona and largely influencing the lower atmospheric layers. The energy is transported from the corona down to the chromosphere and even photosphere in various modes and this leads to significant heating of the chromospheric plasma. We will review individual processes among which the most important is the particle-beam propagation and dissipation, but others as conduction, XUV heating, wave heating etc. are also to be considered. We will summarize recent results of the radiation-hydrodynamical simulations of the chromospheric heating during flares and the progress in our understanding of the basic heating mechanisms and flows. We will also point to new space and ground observations which provide the critical constraints to modeling. 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: An Estimate of Chromospheric Heating by Acoustic Waves Authors: Sobotka, M.; Švanda, M.; Jurčak, J.; Heinzel, P.; Del Moro, D.; Berrilli, F. Bibcode: 2014CEAB...38...53S Altcode: Several mechanisms may heat the solar chromosphere: acoustic waves, magnetoacoustic waves (slow, fast, and Alfvén waves), and small-scale magnetic reconnections. Based on observations in the Ca II 854.2 nm line, the contribution of acoustic waves to the heating of quiet and plage regions in the chromosphere is discussed. The energy released by radiative losses is compared with the energy deposited by acoustic waves. Radiative losses are computed using a grid of six semi-empirical models VAL A--F. The deposited acoustic flux is calculated using power spectra of Doppler oscillations measured in the Ca~II line core. The comparison shows that the spatial correlation of maps of radiative losses and acoustic flux is 70 %. The deposited acoustic flux provides at least 25--30~% of the energy radiated in the quiet chromosphere and 50~% in plage regions. Title: Non-LTE Modeling and Observations of Oscillating Prominences Authors: Zapiór, M.; Heinzel, P.; Oliver, R.; Ballester, J. L.; Kotrč, P. Bibcode: 2014IAUS..300...52Z Altcode: Prominence oscillations have been mostly detected using Doppler velocity, although there are also claimed detections by means of the periodic variations of half-width or line intensity. Our main aim here is to explore the relationship between spectral indicators such as Doppler shift, line intensity and line half-width and the linear perturbations excited in a simple prominence model. Title: Kappa-distributions and Temperature Structure of the Prominence-Corona Transition Region Authors: Dzifčáková, Elena; Mackovjak, Šimon; Heinzel, Petr Bibcode: 2014IAUS..300..408D Altcode: The influence of the electron κ - distributions on the differential emission measure (DEM) of the prominence-corona transition region (PCTR) derived from observed line intensities has been investigated. An important consequence of the κ - distribution is formation of the emission lines in much wider temperature ranges. The implications for the formation temperature of the observed SDO/AIA band emissions are shown. Title: MgII lines in solar flares: IRIS observations and NLTE modeling Authors: Heinzel, Petr; Kasparova, Jana; Kleint, Lucia; Dzifcakova, Elena Bibcode: 2014cosp...40E1182H Altcode: Chromospheric flares have been recently observed in MgII resonance lines by the IRIS instrument. Apart from the resonance lines h and k, also subordinate line emissions due to transitions between the MgII levels 3P and 3D have been now detected by IRIS during flares. We apply the NLTE radiative-transfer code to synthesize all these MgII lines under typical flare conditions. In particular, we focus on the role of the non-thermal excitations and ionizations, which are due to the presence of the electron beams and corresponding return currents. The results of this modeling are compared with new IRIS data. Title: Dynamics of the solar atmosphere above a pore with a light bridge Authors: Sobotka, M.; Švanda, M.; Jurčák, J.; Heinzel, P.; Del Moro, D.; Berrilli, F. Bibcode: 2013A&A...560A..84S Altcode: 2013arXiv1309.7790S Context. Solar pores are small sunspots lacking a penumbra that have a prevailing vertical magnetic-field component. They can include light bridges at places with locally reduced magnetic field. Like sunspots, they exhibit a wide range of oscillatory phenomena.
Aims: A large isolated pore with a light bridge (NOAA 11005) is studied to obtain characteristics of a chromospheric filamentary structure around the pore, to analyse oscillations and waves in and around the pore, and to understand the structure and brightness of the light bridge.
Methods: Spectral imaging observations in the line Ca II 854.2 nm and complementary spectropolarimetry in Fe I lines, obtained with the DST/IBIS spectrometer and HINODE/SOT spectropolarimeter, were used to measure photospheric and chromospheric velocity fields, oscillations, waves, the magnetic field in the photosphere, and acoustic energy flux and radiative losses in the chromosphere.
Results: The chromospheric filamentary structure around the pore has all important characteristics of a superpenumbra: it shows an inverse Evershed effect and running waves, and has a similar morphology and oscillation character. The granular structure of the light bridge in the upper photosphere can be explained by radiative heating. Acoustic waves leaking up from the photosphere along the inclined magnetic field in the light bridge transfer enough energy flux to balance the entire radiative losses of the light-bridge chromosphere.
Conclusions: A penumbra is not a necessary condition for the formation of a superpenumbra. The light bridge is heated by radiation in the photosphere and by acoustic waves in the chromosphere. Title: Scattering Polarization in Solar Flares Authors: Štěpán, Jiří; Heinzel, Petr Bibcode: 2013ApJ...778L...6S Altcode: 2013arXiv1310.3284S There is ongoing debate about the origin and even the very existence of a high degree of linear polarization of some chromospheric spectral lines observed in solar flares. The standard explanation of these measurements is in terms of the impact polarization caused by non-thermal proton and/or electron beams. In this work, we study the possible role of resonance line polarization due to radiation anisotropy in the inhomogeneous medium of the flare ribbons. We consider a simple two-dimensional model of the flaring chromosphere and we self-consistently solve the non-LTE problem taking into account the role of resonant scattering polarization and of the Hanle effect. Our calculations show that the horizontal plasma inhomogeneities at the boundary of the flare ribbons can lead to a significant radiation anisotropy in the line formation region and, consequently, to a fractional linear polarization of the emergent radiation of the order of several percent. Neglecting the effects of impact polarization, our model can provide a clue for resolving some of the common observational findings, namely: (1) why a high degree of polarization appears mainly at the edges of the flare ribbons; (2) why polarization can also be observed during the gradual phase of a flare; and (3) why polarization is mostly radial or tangential. We conclude that radiation transfer in realistic multi-dimensional models of solar flares needs to be considered as an essential ingredient for understanding the observed spectral line polarization. Title: Atmosphere above a large solar pore Authors: Sobotka, M.; Švanda, M.; Jurčák, J.; Heinzel, P.; Del Moro, D. Bibcode: 2013JPhCS.440a2049S Altcode: 2013arXiv1302.4893S A large solar pore with a granular light bridge was observed on October 15, 2008 with the IBIS spectrometer at the Dunn Solar Telescope and a 69-min long time series of spectral scans in the lines Ca II 854.2 nm and Fe I 617.3 nm was obtained. The intensity and Doppler signals in the Ca II line were separated. This line samples the middle chromosphere in the core and the middle photosphere in the wings. Although no indication of a penumbra is seen in the photosphere, an extended filamentary structure, both in intensity and Doppler signals, is observed in the Ca II line core. An analysis of morphological and dynamical properties of the structure shows a close similarity to a superpenumbra of a sunspot with developed penumbra. A special attention is paid to the light bridge, which is the brightest feature in the pore seen in the Ca II line centre and shows an enhanced power of chromospheric oscillations at 3-5 mHz. Although the acoustic power flux in the light bridge is five times higher than in the "quiet" chromosphere, it cannot explain the observed brightness. 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: Observations and Modeling of Stellar Flares Authors: Heinzel, P. Bibcode: 2013POBeo..92...87H Altcode: We briefly review the current status of observations of stellar flares with meter-class telescopes and their relation to observations of flares on the Sun-as-a-star. Both stellar photometry and spectroscopy will be discussed. Solar and stellar flares are modeled using the methods of radiation hydrodynamics and we will make a summary of recent results. 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: SDO/AIA Prominence physical conditions Authors: Schmieder, B.; Parenti, S.; Dudik, J.; Aulanier, G.; Heinzel, P.; Zapior, M.; Golub, L. Bibcode: 2013enss.confE..27S Altcode: SDO/AIA has carried out continuous observations of prominences in multiple wavelengths, with high spatial and temporal resolution. These data provide us an opportunity to understand the physical conditions and dynamics of prominences. The surprising brightness of prominences in some coronal lines has been well explained by the presence of transition region lines in the bandpass of the filters (171 A, 131 A), a result that leads us to revise our model of the transition region of prominences and to consider a relatively dense transition region in some prominence evolutionary phases or in some viewing orientation. An additional aspect of prominence dynamics will be presented with a new quasi-static MHD model proposed for bubbles and plumes. We propose an alternative to the interpretation that thermal instabilities are responsible for the formation of bubbles. The bubbles are found to correspond to magnetic separatrices formed by emerging magnetic field close to prominence footpoints. Title: Magnetic Topology of Bubbles in Quiescent Prominences Authors: Dudík, J.; Aulanier, G.; Schmieder, B.; Zapiór, M.; Heinzel, P. Bibcode: 2012ApJ...761....9D Altcode: We study a polar-crown prominence with a bubble and its plume observed in several coronal filters by the SDO/AIA and in Hα by the MSDP spectrograph in Białków (Poland) to address the following questions: what is the brightness of prominence bubbles in EUV with respect to the corona outside of the prominence and the prominence coronal cavity? What is the geometry and topology of the magnetic field in the bubble? What is the nature of the vertical threads seen within prominences? We find that the brightness of the bubble and plume is lower than the brightness of the corona outside of the prominence, and is similar to that of the coronal cavity. We constructed linear force-free models of prominences with bubbles, where the flux rope is perturbed by inclusion of parasitic bipoles. The arcade field lines of the bipole create the bubble, which is thus devoid of magnetic dips. Shearing the bipole or adding a second one can lead to cusp-shaped prominences with bubbles similar to the observed ones. The bubbles have complex magnetic topology, with a pair of coronal magnetic null points linked by a separator outlining the boundary between the bubble and the prominence body. We conjecture that plume formation involves magnetic reconnection at the separator. Depending on the viewing angle, the prominence can appear either anvil-shaped with predominantly horizontal structures, or cusp-shaped with predominantly vertical structuring. The latter is an artifact of the alignment of magnetic dips with respect to the prominence axis and the line of sight. Title: Magnetism of Solar Flares and Prominences Authors: Heinzel, P.; Hudson, H. S. Bibcode: 2012ASPC..463..121H Altcode: We give an overview of magnetic fields in solar flares and prominences. Magnetic fields related to flares play a crucial role in the process of energy release and transport to the lower atmosphere, and thus magnetometry under the coronal and chromospheric conditions is extremely challenging. Magnetic fields in prominences are supposed to keep the prominence plasma at coronal heights against the gravity. Their measurements have been numerous, but high-resolution mapping is still missing. We discuss various flare and prominence models in connection to current and future high-resolution observations. Title: Study of an Extended EUV Filament Using SoHO/SUMER Observations of the Hydrogen Lyman Lines. II. Lyman α Line Observed During a Multi-wavelength Campaign Authors: Schwartz, P.; Schmieder, B.; Heinzel, P.; Kotrč, P. Bibcode: 2012SoPh..281..707S Altcode: 2012SoPh..tmp..201S A filament and its channel close to the solar disk were observed in the complete hydrogen Lyman spectrum, and in several EUV lines by the SUMER (Solar Ultraviolet Measurement of Emitted Radiation) and CDS (Coronal Diagnostic Spectrometer) spectrographs on the SoHO satellite, and in Hα by ground-based telescopes during a multi-instrument campaign in May 2005. It was a good opportunity to get an overview of the volume and the density of the cold plasma in the filament channel; these are essential parameters for coronal mass ejections. We found that the width of the filament depends on the wavelength in which the filament is observed (around 15 arcsec in Hα, 30 arcsec in Lα, and 60 arcsec in EUV). In Lα the filament is wider than in Hα because cool plasma, not visible in Hα, is optically thick at the Lα line center, and its presence blocks the coronal emission. We have derived physical plasma properties of this filament fitting the Lyman spectra and Hα profiles by using a 1D isobaric NLTE model. The vertical temperature profile of the filament slab is flat (T≈7000 K) with an increase to ≈ 20 000 K at the top and the bottom of the slab. From an analysis of the Lα and Hα source functions we have concluded that these lines are formed over the whole filament slab. We have estimated the geometrical filling factor in the filament channel. Its low value indicates the presence of multi-threads. Title: Formation of Balmer Lines in Impulsively Heated Flare Atmosphere by Neutral Beams Authors: Varady, M.; Kašparová, J.; Moravec, Z.; Karlický, M.; Heinzel, P. Bibcode: 2012ASPC..454..341V Altcode: In the context of interpreting non-thermal hard X-ray emission and γ lines emanating from the footpoints of flare loops, most contemporary flare models assign a fundamental role during the flare energy release, transport and deposition to the high energy non-thermal particle beams. In this contribution we concentrate on modelling of the spectroscopic properties of chromospheric flare emission in optical hydrogen lines generated due to the bombardment of the chromosphere and photosphere by neutral beams with power-law spectra. In order to obtain an estimate of the neutral beam flare heating in the solar atmosphere we produced a simple model describing the propagation and thermalisation of neutral beams. We compare the neutral beam flare heating with the flare heating produced by corresponding pure electron and proton beams. Further we compare the contribution functions for Hα line obtained for neutral and electron beam heating. Title: Velocity Vector, Ionization Degree, and Temperature of Prominence Fine Structures Observed by Hinode/SOT Authors: Schmieder, B.; Mein, P.; Chandra, R.; Molodij, G.; Heinzel, P.; Berlicki, A.; Schwartz, P.; Fárník, F.; Labrosse, N.; Anzer, U.; Watanabe, T. Bibcode: 2012ASPC..454..107S Altcode: Prominences have been successfully observed by Hinode in April 2007 exhibiting a strong dynamics of their fine structures. The dynamics of a prominence is a challenge to understand the formation of cool prominence plasma embedded in the hot corona. Combining simultaneous observations obtained in Hα with Hinode/SOT and the MSDP spectrograph operating at the Meudon solar tower, velocity vectors have been derived. The Doppler-shifts of bright threads are of the same order as the velocities measured perpendicular to the line of sight. This suggests that the vertical structures of the prominence could be a pile up of dips in magnetic field lines viewed in 3D. Using Hα, Hinode/XRT and TRACE data, the hydrogen ionization degree has been determined to be 0.5-0.8, and the optical thickness in Hα between 0.2 and 1.3. The Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode produced images of the prominence in 11 selected lines with formation temperatures between log(T) = 4.7 and log(T) = 6.1. We comment on the absorption, emissivity blocking and emission involved for interpreting the different structures of the prominence in terms of the temperature and density. Title: Mass of Solar Prominences Estimated from Multi-Wavelength Data Authors: Schwartz, P.; Fárník, F.; Heinzel, P.; Kotrč, P.; Anzer, U. Bibcode: 2012ASPC..454..117S Altcode: The mass of selected prominences was estimated using their multi-wavelength observations: in Hα by the HSFA2 spectrograph of the Ondřejov observatory, in EUV by SoHO/EIT and in the soft X-rays by Hinode XRT. The results are compared with values estimated by other authors. Title: Prominences observations with SDO/AIA Authors: Parenti, Susanna; Schmieder, Brigitte; Golub, Leon; Heinzel, Petr Bibcode: 2012cosp...39.1447P Altcode: 2012cosp.meet.1447P The Prominence-Corona-Transition-Region (PCTR) plays a key role in the thermal and pressure equilibrium of prominences. However, several open issues limit our knowledge of this important interface. Among them we find the thermal structure and the maximum temperature of its emitting plasma. This work is a new step toward resolving these issues. By noting that prominences may be observed in emission in the 171 and 131 SDO/AIA images, while they are seen in absorption in others (e.g. 193) we investigate the temperature content of these channels. Using the CHIANTI atomic database and previously derived prominence DEMs, we built synthetic spectra in these AIA channels to establish the main contributors. We find that the Fe IX line always dominates the 171 band, even in absence of a coronal plasma, while the 131 channel is dominated by Fe VIII. Our conclusion is that the PCTR reaches, at least, 4x 10^5 K. Title: On the Nature of Prominence Emission Observed by SDO/AIA Authors: Parenti, S.; Schmieder, B.; Heinzel, P.; Golub, L. Bibcode: 2012ApJ...754...66P Altcode: 2012arXiv1205.5460P The prominence-corona transition region (PCTR) plays a key role in the thermal and pressure equilibrium of solar prominences. Our knowledge of this interface is limited and several major issues remain open, including the thermal structure and, in particular, the maximum temperature of the detectable plasma. The high signal-to-noise ratio of images obtained by the Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory clearly shows that prominences are often seen in emission in the 171 and 131 bands. We investigate the temperature sensitivity of these AIA bands for prominence observations, in order to infer the temperature content in an effort to explain the emission. Using the CHIANTI atomic database and previously determined prominence differential emission measure distributions, we build synthetic spectra to establish the main emission-line contributors in the AIA bands. We find that the Fe IX line always dominates the 171 band, even in the absence of plasma at >106 K temperatures, while the 131 band is dominated by Fe VIII. We conclude that the PCTR has sufficient plasma emitting at >4 × 105 K to be detected by AIA. Title: Dynamics of quiescent prominences Authors: Heinzel, Petr Bibcode: 2012cosp...39..742H Altcode: 2012cosp.meet..742H We review the state-of-the-art of the observations and modeling of prominence fine structures, with special emphasis on the dynamics. Fine structures of quiescent prominences have been recently observed by Hinode/SOT and these observations revealed a rather complex dynamics of bright threads and blobs and of dark plumes originating from large prominence bubbles. SOHO/SUMER spectra of hydrogen Lyman lines, together with H-alpha observations from MSDP, provide us with constraints on the dynamics of cool fine structures. 2D non-LTE modeling is used for analysis of the line profiles and their asymmetries. On the contrary, the SDO/AIA images, together with RHD modeling of dipped magnetic loops, lead to a better understanding of the dynamics and energetics of hotter prominence plasmas. Finally, some more global dynamics is revealed by the spectroscopic detection of quiescent prominence oscillations. We show recent results of such observations and new radiative-transfer modeling. Title: Can bubbles in quiescent prominences be purely magnetic phenomena? Authors: Dudik, Jaroslav; Schmieder, Brigitte; Aulanier, Guillaume; Zapior, Maciej; Heinzel, Petr Bibcode: 2012cosp...39..486D Altcode: 2012cosp.meet..486D We present a model of the magnetic field constituting quiescent prominences. The model assumes a linear force-free field with a weakly twisted flux-tube in an OX/OF topology perturbed by presence of parasitic polarities within the filament channel. The parasitic polarities locally create the cusp-shaped prominences with bubbles exactly as those observed by the SDO/AIA and Bialkow Observatory. We find that the observations are best reproduced if the parasitic bipoles are sheared with respect to the main inversion line. We show that the bubbles are in fact constituted by the arcade-like field lines, as opposed to that of the prominence, which is created by magnetic dips. A pair of null points is always associated with the parasitic bipole. These null points are connected by a separator passing through the prominence bubble. We show how the presence of an additional parasitic bipole moves the separator to the boundary between the bubble and the rest of the prominence, producing a topology favorable for reconnection and possibly for the formation of plumes. 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: SDO/EVE spectra of solar flares Authors: Heinzel, Petr; Avrett, Eugene; Dzifcakova, Elena; Hudson, Hugh S. Bibcode: 2012cosp...39..743H Altcode: 2012cosp.meet..743H For selected flare events we present the SDO/EVE spectra of hydrogen and helium resonance continua and compare them with the results of non-LTE transfer computations based on various flare models. We discuss the formation of these continua and their diagnostic potential for determination of the temperature structure of the flaring atmosphere. Under the optically-thin conditions, we synthesize these resonance continua using the CHIANTI database where we added the relevant non-thermal atomic rates. This shows how the electron or proton beams may affect the continua during an impulsive phase of solar flares. As a benchmark we present our comparison of the quiet-Sun EVE spectra with the flux synthesized from the model C6 of Avrett and Loeser (2008). Our study has a more general relevance to the physics of stellar flares. 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: On the Visibility of Solar Prominences in SDO/AIA Channels Authors: Heinzel, P.; Schmieder, B.; Parenti, S.; Golub, L. Bibcode: 2012ASPC..456...75H Altcode: Prominences in EUV lines are observed as dark structures over the limb due absorption and emission blocking mechanisms. However, at 171 Å is observed emission in prominences with TRACE and SDO/AIA, and it is believed to be due to the prominence-corona transition region (PCTR) emitting in cool lines. To check this, we use the Differential Emission Measure (DEM) recently obtained for quiescent prominences using SOHO/SUMER spectra (Parenti and Vial 2007) and compute the synthetic spectra in selected AIA channels. We then compare 171 Å and 195 Å channels and derive conclusions concerning the PCTR emissivity, as well well as the absorption and blocking. The emission seen in the 171 Å channel can be used to better constrain prominence DEM curves. Title: On the Nature of Prominence Bubbles and Plumes Authors: Schmieder, B.; Zapior, M.; Heinzel, P.; Aulanier, G. Bibcode: 2012ASPC..456...77S Altcode: An example of bubble and related plume, using time series in selected SDO/AIA channels and co-temporal MSDP observations in the Hα line obtained at Wroclaw-Bialkow observatory on April 20, 2011 is presented. The formation of bubbles may be due to emerging arcades in the filament channel, below the prominence. After discussing on MHD modeling, we conclude that bubbles and plumes are parts of the corona observed through gaps/windows in the prominence. Title: Optical-to-Radio Continua in Solar Flares Authors: Heinzel, P.; Avrett, E. H. Bibcode: 2012SoPh..277...31H Altcode: Spectral continua observed during solar flares may contain information about both thermal and non-thermal heating mechanisms. Using two semi-empirical flare models F2 and FLA, we synthesize the thermal continua from optical to mm-radio domains and compare their intensities with quiet-Sun values computed from a recent model C7. In this way, the far-infrared and sub-mm/mm continua are studied for the first time, and we present our results as a benchmark for further modeling and for planning new observations, especially with the ALMA instrument. Finally, we demonstrate how these continua are formed and show a close correspondence between their brightness temperature and the kinetic-temperature structure of the flaring atmosphere. Title: Radiative equilibrium in solar prominences reconsidered Authors: Heinzel, P.; Anzer, U. Bibcode: 2012A&A...539A..49H Altcode:
Aims: We reconsider the question which kinetic temperatures can lead to prominence configurations that are in radiative equilibrium. We compare these temperatures to those from other calculations.
Methods: For this purpose we solved the full non-LTE radiative-transfer problem for a gas consisting of hydrogen, helium and calcium. We used simple isobaric 1D slabs and began with isothermal models. Then we solved the radiative-relaxation problem and determined the radiative-equilibrium conditions within the whole slab.
Results: By adding the calcium radiative losses, we found that these equilibrium temperatures are considerably lower than those obtained for a pure hydrogen gas. This is because the newly calculated CaII line losses appear to play a significant role in the energy balance, similar to chromospheric conditions. The equilibrium temperatures obtained span the range between 4400-9500 K, depending on the gas pressure and slab thickness. Title: The nature of hydrogen and helium continua in SDO/EVE spectra of solar flares Authors: Heinzel, P.; Avrett, E. H. Bibcode: 2012decs.confE.109H Altcode: For selected flare events we present the SDO/EVE spectra of hydrogen and helium resonance continua and compare them with the results of the non-LTE transfer computations based on semi-empirical flare models. We discuss the formation of these continua and their diagnostic potential for determination of the temperature structure of the flaring atmosphere. Non-thermal processes are also considered. As a benchmark we present our comparison of the quiet-Sun EVE spectra with the flux synthesized from the model C6 of Avrett and Loeser (2008). Title: Formation of MgII lines in solar prominences Authors: Heinzel, Petr Bibcode: 2012decs.confE.108H Altcode: Solar prominences have been observed in MgII h and k lines, both from space (OSO-8) or from stratospheric balloons. Non-LTE modeling of these resonance lines was then performed and the results have been compared to available observations. We briefly review this past effort and present new transfer computations which take into account all details of the MgII line formation under realistic prominence conditions. We estimate the role of MgII lines in radiation cooling of prominence plasmas and show how they affect the radiative relaxation in these structures. Finally, we also demonstrate the diagnostic capabilities of these lines useful for thermodynamic and velocity measurements. Title: Splinter Session "Solar and Stellar Flares" Authors: Fletcher, L.; Hudson, H.; Cauzzi, G.; Getman, K. V.; Giampapa, M.; Hawley, S. L.; Heinzel, P.; Johnstone, C.; Kowalski, A. F.; Osten, R. A.; Pye, J. Bibcode: 2011ASPC..448..441F Altcode: 2011csss...16..441F; 2012arXiv1206.3997F This summary reports on papers presented at the Cool Stars-16 meeting in the splinter session "Solar and Stellar flares." Although many topics were discussed, the main themes were the commonality of interests, and of physics, between the solar and stellar flare communities, and the opportunities for important new observations in the near future. 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: EUV lines observed with EIS/Hinode in a solar prominence Authors: Labrosse, N.; Schmieder, B.; Heinzel, P.; Watanabe, T. Bibcode: 2011A&A...531A..69L Altcode: 2011arXiv1105.1400L Context. During a multi-wavelength observation campaign with Hinode and ground-based instruments, a solar prominence was observed for three consecutive days as it crossed the western limb of the Sun in April 2007.
Aims: We report on observations obtained on 26 April 2007 using EIS (Extreme ultraviolet Imaging Spectrometer) on Hinode. They are analysed to provide a qualitative diagnostic of the plasma in different parts of the prominence.
Methods: After correcting for instrumental effects, the rasters at different wavelengths are presented. Several regions within the same prominence are identified for further analysis. Selected profiles for lines with formation temperatures between log (T) = 4.7 and log (T) = 6.3, as well as their integrated intensities, are given. The profiles of coronal, transition region, and He ii lines are discussed. We pay special attention to the He ii line, which is blended with coronal lines.
Results: Some quantitative results are obtained by analysing the line profiles. They confirm that depression in EUV lines can be interpreted in terms of two mechanisms: absorption of coronal radiation by the hydrogen and neutral helium resonance continua, and emissivity blocking. We present estimates of the He ii line integrated intensity in different parts of the prominence according to different scenarios for the relative contribution of absorption and emissivity blocking to the coronal lines blended with the He ii line. We estimate the contribution of the He ii 256.32 Å line to the He ii raster image to vary between ~44% and 70% of the raster's total intensity in the prominence according to the different models used to take into account the blending coronal lines. The inferred integrated intensities of the He ii 256 Å line are consistent with the theoretical intensities obtained with previous 1D non-LTE radiative transfer calculations, yielding a preliminary estimate of the central temperature of 8700 K, a central pressure of 0.33 dyn cm-2, and a column mass of 2.5 × 10-4 g cm-2. The corresponding theoretical hydrogen column density (1020 cm-2) is about two orders of magnitude higher than those inferred from the opacity estimates at 195 Å. The non-LTE calculations indicate that the He ii 256.32 Å line is essentially formed in the prominence-to-corona transition region by resonant scattering of the incident radiation.

The movie associated to Fig. 2 is available in electronic form at http://www.aanda.org 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: Solar Research with ALMA Authors: Karlický, M.; Bárta, M.; Da̧browski, B. P.; Heinzel, P. Bibcode: 2011SoPh..268..165K Altcode: 2010SoPh..tmp..231K; 2010SoPh..tmp..207K The Atacama Large Millimeter/sub-millimeter Array (ALMA) is a large interferometer that will consist up to 64 high-precision antennas operating in the 31.3 - 950 GHz frequency range. In this frequency range, which is largely unexplored, unique observations with a broad range of scientific objectives (cosmology, cold universe, galaxies, stars and their formation, planets and so on) are expected. Among these tasks there is a unique possibility to observe the Sun and to address several outstanding issues of solar physics. First, the ALMA is briefly described and then the new ESO-ALMA European node (ARC), built at Ondřejov Observatory, is presented. In Europe, this ARC is the only one oriented to solar physics. Consequently, the requirements and limitations for ALMA solar observations, as well as some examples of possible solar-oriented ALMA projects, are shown. A procedure of the preparation and submission of proposals for ALMA observations is mentioned. Title: Solar Flares and the Chromosphere Authors: Fletcher, L.; Turkmani, R.; Hudson, H. S.; Hawley, S. L.; Kowalski, A.; Berlicki, A.; Heinzel, P. Bibcode: 2010arXiv1011.4650F Altcode: A white paper prepared for the Space Studies Board, National Academy of Sciences (USA), for its Decadal Survey of Solar and Space Physics (Heliophysics), reviewing and encouraging studies of flare physics in the chromosphere. Title: Solar Flares and the Chromosphere: A white paper for the Decadal Survey Authors: Hudson, H. S.; Fletcher, L.; Turkmani, R.; Hawley, S. L.; Kowalski, A. F.; Berlicki, A.; Heinzel, P. Bibcode: 2010helio2010....1H Altcode: No abstract at ADS Title: Modeling of Solar Flare Plasma and Its Radiation Authors: Varady, Michal; Kasparova, Jana; Moravec, Zdeněk; Heinzel, Petr; Karlicky, Marian Bibcode: 2010ITPS...38.2249V Altcode: No abstract at ADS Title: Towards a New Formation Flying Solar Coronagraph Authors: Lamy, P.; Vives, S.; Curdt, W.; Dame, L.; Davila, J.; Defise, J. M.; Fineschi, S.; Heinzel, P.; Kuzin, S.; Schmutz, W.; Tsinganos, K.; Turck-Chieze, S.; Zhukov, A. Bibcode: 2010ASPC..424...15L Altcode: We briefly describe an investigation aiming at the development of a giant solar coronagraph instrument onboard of two satellites, separated by about 150 m in formation flight for the detailed observation of the solar coronal plasma. The European Space Agency (ESA) has selected this instrument as the only payload onboard the Proba 3 satellites which will be launched in 2013. The Greek team is developing the command control board of the coronagraph. 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: ASPIICS / PROBA-3: a formation flying externally-occulted giant coronagraph mission Authors: Lamy, Philippe; Damé, Luc; Curdt, W.; Davila, J.; Defise, J. M.; Fineschi, S.; Heinzel, P.; Howard, R.; Kuzin, S.; Schmutz, W.; Tsinganos, K.; Turck-Chièze, S.; Zhukov, A. Bibcode: 2010cosp...38.2858L Altcode: 2010cosp.meet.2858L Classical externally-occulted coronagraphs are presently limited in their performances by the distance between the external occulter and the front objective. The diffraction fringe from the occulter and the vignetted pupil which degrades the spatial resolution prevent useful observa-tions of the white light corona inside typically 2-2.5 Rsun. Formation flying offers an elegant solution to these limitations and allows conceiving giant, externally-occulted coronagraphs us-ing a two-component space system with the external occulter on one spacecraft and the optical instrument on the other spacecraft at distances of hundred meters. Such an instrument has just been selected by ESA to fly (by the end of 2013) on its PROBA-3 mission, presently in phase B, to demonstrate formation flying. It will perform both high spatial resolution imaging of the solar corona as well as 2-dimensional spectroscopy of several emission lines (in partic-ular the forbidden line of FeXIV at 530.285 nm) from the coronal base out to 3 Rsun using a Fabry-Perot interferometer. The classical design of an externally-occulted coronagraph is adapted to the formation flying configuration allowing the detection of the very inner corona as close as 0.05 Rsun from the solar limb. By tuning the position of the occulter spacecraft, it may even be possible to try reaching the chromosphere and the upper part of the spicules. ASPIICS/PROBA-3 mission, payload and scientific objectives are detailed. 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: Multi-spacecraft observation of a magnetic cloud Authors: de Lucas, Aline; Dal Lago, Alisson; Schwenn, Rainer; Clúa de Gonzalez, Alicia L.; Marsch, Eckart; Lamy, Philippe; Damé, Luc; Curdt, W.; Davila, J.; Defise, J. M.; Fineschi, S.; Heinzel, P.; Howard, R.; Kuzin, S.; Schmutz, W.; Tsinganos, K.; Turck-Chièze, S.; Zhukov, A. Bibcode: 2010cosp...38.1921D Altcode: 2010cosp.meet.1921D Classical externally-occulted coronagraphs are presently limited in their performances by the distance between the external occulter and the front objective. The diffraction fringe from the occulter and the vignetted pupil which degrades the spatial resolution prevent useful observa-tions of the white light corona inside typically 2-2.5 Rsun. Formation flying offers an elegant solution to these limitations and allows conceiving giant, externally-occulted coronagraphs us-ing a two-component space system with the external occulter on one spacecraft and the optical instrument on the other spacecraft at distances of hundred meters. Such an instrument has just been selected by ESA to fly (by the end of 2013) on its PROBA-3 mission, presently in phase B, to demonstrate formation flying. It will perform both high spatial resolution imaging of the solar corona as well as 2-dimensional spectroscopy of several emission lines (in partic-ular the forbidden line of FeXIV at 530.285 nm) from the coronal base out to 3 Rsun using a Fabry-Perot interferometer. The classical design of an externally-occulted coronagraph is adapted to the formation flying configuration allowing the detection of the very inner corona as close as 0.05 Rsun from the solar limb. By tuning the position of the occulter spacecraft, it may even be possible to try reaching the chromosphere and the upper part of the spicules. ASPIICS/PROBA-3 mission, payload and scientific objectives are presented. 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: Photometric analysis of Ellerman bombs . Authors: Berlicki, A.; Heinzel, P.; Avrett, E. H. Bibcode: 2010MmSAI..81..646B Altcode: Observations of Ellerman bombs (EBs) show them as short-lived, compact, and spatially localized emissions that are well observable in the wings of the Halpha hydrogen line. The Halpha line profiles of EBs are characterized by deep absorption at the line center and enhanced emission in the wings with maximum around ± 1 Å from the line center, fading beyond ± 5 Å. EBs may also be observed in the chromospheric Ca II lines and in the UV as bright points often located within active regions. Previous work suggests that EBs may be considered as micro-flares and may contribute significantly to the heating of the lower chromosphere in newly emerging magnetic flux regions. However, it is still not clear at what height in the solar atmosphere the emission of EBs originates. In our analysis we used observations of EBs obtained in the Halpha line with the Dutch Open Telescope (DOT) and in the UV range with the TRACE 1600 Å channel. These one-hour long simultaneous sequences obtained with high temporal and spatial resolution were used to analyze the relation between the emission in the Halpha line and at 1600 Å. The observations show fast variations of EB emission in both channels. Comparison between the observed emission in Halpha and at 1600 Å and theoretical calculations allowed us to draw conclusions about the vertical structure of EBs. 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: RMHS Modeling of Solar Prominences Authors: Heinzel, P. Bibcode: 2009AIPC.1171..331H Altcode: In 1976 J. Heasley and D. Mihalas published a seminal paper devoted to the modeling of solar prominences. They applied their stellar atmospheric code based on the novel complete linearization method to model the radiation-magnetohydrostatic (RMHS) coupling in prominences, to solve the multilevel transfer problem for a mixture of hydrogen and helium and to investigate the prominence energy balance. Their results served as a benchmark for future developments in this field and today, 33 years after that, we would like to show how significantly they influenced the current research. With the link to this pioneering work, we will discuss recent progress in the RMHS modeling of solar prominences, focused on multidimensional/multithread radiative transfer, coupling of non-LTE transfer to MHS, the importance of partial redistribution for interpreting strong UV lines etc. New light was shed recently on the issues of energy balance, again having a direct link to the 1976 paper. Title: Response of optical hydrogen lines to beam heating. I. Electron beams Authors: Kašparová, J.; Varady, M.; Heinzel, P.; Karlický, M.; Moravec, Z. Bibcode: 2009A&A...499..923K Altcode: 2009arXiv0904.2084K Context: Observations of hydrogen Balmer lines in solar flares remain an important source of information on flare processes in the chromosphere during the impulsive phase of flares. The intensity profiles of optically thick hydrogen lines are determined by the temperature, density, and ionisation structure of the flaring atmosphere, by the plasma velocities and by the velocity distribution of particles in the line formation regions.
Aims: We investigate the role of non-thermal electrons in the formation regions of Hα, Hβ, and Hγ lines in order to unfold their influence on the formation of these lines. We concentrate on pulse-beam heating varying on a subsecond timescale. Furthermore, we theoretically explore possibility that a new diagnostic tool exists indicating the presence of non-thermal electrons in the flaring chromosphere based on observations of optical hydrogen lines.
Methods: To model the evolution of the flaring atmosphere and the time-dependent hydrogen excitation and ionisation, we used a 1-D radiative hydrodynamic code combined with a test-particle code that simulates the propagation, scattering, and thermalisation of a power-law electron beam in order to obtain the flare heating and the non-thermal collisional rates due to the interaction of the beam with the hydrogen atoms. To not bias the results by other effects, we calculate only short time evolutions of the flaring atmosphere and neglect the plasma velocities in the radiative transfer.
Results: All calculated models have shown a time-correlated response of the modelled Balmer line intensities on a subsecond timescale, with a subsecond timelag behind the beam flux. Depending on the beam parameters, both line centres and wings can show pronounced intensity variations. The non-thermal collisional rates generally result in an increased emission from a secondary region formed in the chromosphere.
Conclusions: Despite the clear influence of the non-thermal electron beams on the Balmer line intensity profiles, we were not able on the basis of our simulations to produce any unambiguous diagnostic of non-thermal electrons in the line-emitting region, which would be based on comparison of individual Balmer line intensity profiles. However, fast line intensity variations, well-correlated with the beam flux variations, represent an indirect indication of pulsating beams. Title: Examples of Science Cases and Requirements for EST Authors: Sobotka, M.; Heinzel, P.; Kašparová, J. Bibcode: 2009ASPC..405..455S Altcode: We present various suggestions for the study of flares (fast emission variations, heating mechanisms), prominences (fine structure, magnetic field, energy balance), and sunspots (umbral structure, heating mechanisms, depth and structure of the penumbra, Evershed flow). From these cases we derive the requirements for the future European Solar Telescope: spectropolarimetric capabilities, high signal-to-noise ratio, multi-line spectroscopy, high spatial and temporal resolution. Title: Oscillatory phenomena in a solar network region Authors: Tsiropoula, Georgia; Tziotziou, Kostas; Schwartz, Pavol; Heinzel, Petr Bibcode: 2009IAUS..257..181T Altcode: We examine oscillatory phenomena in a solar network region from multi-wavelength, observations obtained by the ground-based Dutch Open Telescope (DOT), and by instruments on the spacecraft Solar and Heliospheric Observatory (SoHO). The observations were obtained during a coordinated observing campaign on October 14, 2005. The temporal variations of the intensities and velocities in two distinct regions of the quiet Sun were investigated: one containing several dark mottles and the other several bright points defining the network boundaries (NB). The aim is to find similarities and/or differences in the oscillatory phenomena observed in these two regions and in different spectral lines formed from the chromosphere to the transition region, as well as propagation characteristics of waves. Title: Multiwavelength analysis of a solar quiet region Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Heinzel, P. Bibcode: 2009A&A...493..217T Altcode: Context: We examine oscillatory phenomena in a solar network region from multi-wavelength observations obtained by the ground-based Dutch Open Telescope (DOT) and by the Coronal Diagnostic Spectrometer (CDS) on the spacecraft Solar and Heliospheric Observatory (SoHO). The observations were obtained during a coordinated observing campaign in October 2005.
Aims: We investigate the temporal variations of the intensities and the velocities in two distinct regions of the quiet Sun, one containing several dark mottles and the other several bright points defining the network boundaries (NB). The aim is to find similarities and/or differences in the oscillatory phenomena observed in these two regions and in different spectral lines formed from the chromosphere to the transition region, as well as the propagation characteristics of waves.
Methods: Intensity and velocity variations are studied with wavelet and phase difference analyses.
Results: Both regions (i.e. mottles and NB) show a periodicity of ~5 min in all considered lines. The V-V phase differences in the NB region point to an upward propagation of waves; in the region of mottles, for periods of 250-400 s, the phase difference is mainly negative, which suggests a downward propagation, in turn indicating a refraction of waves from the inclined magnetic field of mottles along the line-of-sight.
Conclusions: The phase differences at the NB arise from a predominance of upward propagating waves. In the mottles' region, the negative phase differences we found suggest that propagating waves encounter a boundary and are refracted and reflected. Of course, several limitations exist in the exact interpretation of the phase differences, e.g. the complex topology of the magnetic field, the formation conditions and heights of the examined spectral lines, and the low spatial resolution. Title: Far-IR and Radio Thermal Continua in Solar Flares Authors: Kašparová, J.; Heinzel, P.; Karlický, M.; Moravec, Z.; Varady, M. Bibcode: 2009CEAB...33..309K Altcode: 2009arXiv0901.3465K With the invention of new far-infrared (FIR) and radio mm and sub-mm instruments (DESIR on SMESE satellite, ESO-ALMA), there is a growing interest in observations and analysis of solar flares in this so far unexplored wavelength region. Two principal radiation mechanisms play a role: the synchrotron emission due to accelerated particle beams moving in the magnetic field and the thermal emission due to the energy deposit in the lower atmospheric layers. In this contribution we explore the time-dependent effects of beams on thermal FIR and radio continua. We show how and where these continua are formed in the presence of time dependent beam heating and non-thermal excitation/ionisation of the chromospheric hydrogen plasma. Title: Electron Densities in Quiescent Prominences Derived from Eclipse Observations Authors: Jejčič, S.; Heinzel, P. Bibcode: 2009SoPh..254...89J Altcode: We develop a diagnostic tool for determination of the electron densities in solar prominences using eclipse data. The method is based on analysis of the hydrogen Balmer-line intensities (namely Hα and Hβ) and the white-light emission due to Thomson scattering on the prominence electrons. Our approach represents a generalization of the ratio method already used by Koutchmy, Lebecq, and Stellmacher (Astron. Astrophys.119, 261, 1983). In this paper we use an extended grid of non-LTE prominence models of Gouttebroze, Heinzel, and Vial (Astron. Astrophys. Suppl. Ser.99, 513, 1993) and derive various useful relations between prominence radiation properties and electron densities. Simultaneously, an effective geometrical thickness of the prominence can also be obtained. As an example we apply our general technique to original eclipse data of Koutchmy, Lebecq, and Stellmacher (Astron. Astrophys.119, 261, 1983). Finally, we use our results to determine the color of prominences as it should be seen during total eclipses. 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: NLTE modelling of the flaring atmosphere above sunspot Authors: Berlicki, A.; Heinzel, P.; Schmieder, B.; Li, H. Bibcode: 2008A&A...490..315B Altcode: Aims: We performed an analysis of the solar flaring atmosphere above sunspots. During the flare on October 20, 2003 many flaring structures were observed projected onto the sunspots. We analysed the Hα and Ca II line profiles emitted by the ribbons partially overlapping the sunspots. In the penumbra, the line intensity in the far wings is lower than in a typical quiet Sun profile but the core emission of Hα and Ca II lines is typical for flares. We tried to find the structure of the flare observed above the sunspot penumbra using the observations of these chromospheric line profiles.
Methods: NLTE radiative transfer techniques allowed us to model the atmosphere of flaring structures and fit both the synthetic Hα and Ca II line profiles to the observed ones. We have derived semiempirical models of the flaring structure observed above sunspots.
Results: Our analysis shows that the flare emission observed within the sunspot penumbra comes from geometrically thin loop-like structures (cool flare loops) located above the fibrils of the penumbra. The structure of the penumbra located below the flare is almost not affected by the flare i.e. the flare emission in Hα and Ca II comes not from the upper chromosphere but from the structures that are higher in the corona. Therefore, a two-component modelling is necessary to reproduce the flare emission above the sunspot penumbra detected in our observations. Title: Hinode, TRACE, SOHO, and Ground-based Observations of a Quiescent Prominence Authors: Heinzel, P.; Schmieder, B.; Fárník, F.; Schwartz, P.; Labrosse, N.; Kotrč, P.; Anzer, U.; Molodij, G.; Berlicki, A.; DeLuca, E. E.; Golub, L.; Watanabe, T.; Berger, T. Bibcode: 2008ApJ...686.1383H Altcode: A quiescent prominence was observed by several instruments on 2007 April 25. The temporal evolution was recorded in Hα by the Hinode SOT, in X-rays by the Hinode XRT, and in the 195 Å channel by TRACE. Moreover, ground-based observatories (GBOs) provided calibrated Hα intensities. Simultaneous extreme-UV (EUV) data were also taken by the Hinode EIS and SOHO SUMER and CDS instruments. Here we have selected the SOT Hα image taken at 13:19 UT, which nicely shows the prominence fine structure. We compare this image with cotemporaneous ones taken by the XRT and TRACE and show the intensity variations along several cuts parallel to the solar limb. EIS spectra were obtained about half an hour later. Dark prominence structure clearly seen in the TRACE and EIS 195 Å images is due to the prominence absorption in H I, He I, and He II resonance continua plus the coronal emissivity blocking due to the prominence void (cavity). The void clearly visible in the XRT images is entirely due to X-ray emissivity blocking. We use TRACE, EIS, and XRT data to estimate the amount of absorption and blocking. The Hα integrated intensities independently provide us with an estimate of the Hα opacity, which is related to the opacity of resonance continua as follows from the non-LTE radiative-transfer modeling. However, spatial averaging of the Hα and EUV data have quite different natures, which must be taken into account when evaluating the true opacities. We demonstrate this important effect here for the first time. Finally, based on this multiwavelength analysis, we discuss the determination of the column densities and the ionization degree of hydrogen in the prominence. Title: Modelling of the Flare Observed Above Sunspot Penumbra Authors: Berlicki, A.; Heinzel, P.; Schmieder, B.; Li, H. Bibcode: 2008ESPM...12.3.19B Altcode: The solar flaring atmosphere above sunspot observed during the event on October 20, 2003 was analysed. Many flaring structures were visible in projection onto the sunspot penumbra. We analysed the H? and Ca II line profiles emitted by the ribbons partially overlapping the sunspots. These observations were performed with the Multi-channel Infrared Solar Spectrograph (MISS) at Purple Mountain Observatory (PMO, China).

In the sunspot penumbra, the line intensity in far wings is lower than in a typical quiet-Sun profile but in the line centre the intensity of H? and Ca II lines is typical for flares. Using 1D approximation we tried to find the vertical structure of the flare observed above sunspot penumbra using the observations of these chromospheric line profiles.

NLTE radiative transfer techniques allowed us to model the atmosphere of flaring structures and fit both the synthetic H? and Ca II line profiles to the observed ones. We have determined semiempirical models of the flaring structure observed above sunspots.

In our analysis we showed that the flare emission observed within sunspot penumbra comes from geometrically thin loop-like structures located above the fibrils of the penumbra. The structure of the penumbra located below the flare is almost not affected by the flare. The flare emission in chromospheric lines comes not from the upper chromosphere but from the structures located higher in the corona. Therefore, we performed two-component modelling which well reproduce the flare emission above sunspot penumbra. In our model of the flaring layer we included the transition region which is necessary to obtain agreement between the observed and calculated line profiles. Title: Hydrogen Balmer Lines in the Solar Atmosphere Heated by Electron Beams Authors: Kasparova, J.; Varady, M.; Moravec, Z.; Heinzel, P.; Karlicky, M. Bibcode: 2008ESPM...12.3.16K Altcode: Accelerated particle beam are one of the mechanisms of the flare energy transport from the corona to the transition region and the chromosphere. Such beams heat ambient plasma and may affect atomic population via collisions. Using 1D NLTE radiative hydrodynamics we model influence of electron beams on hydrogen Balmer lines. In the contribution we focus on the effect of so-called non-thermal collisional rates on Halpha and Hbeta lines. Based on our results we discuss diagnostic methods for determination of beam presence in the formation regions of Halpha and Hbeta lines. Title: Understanding the Solar Chromosphere Authors: Heinzel, P. Bibcode: 2008AIPC.1043..238H Altcode: We discuss the latest high-resolution ground and space-based observations of the solar chromosphere and their relevance to problems of chromospheric modeling. In particular, we briefly review recent as well as previous attempts to understand the solar chromosphere as the atmospheric layer with an apparently increasing temperature. Various heating mechanisms are also mentioned. 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: Far-IR and Radio Continua in Solar Flares Authors: Heinzel, P.; Kasparova, J.; Varady, M.; Karlicky, M.; Moravec, Z. Bibcode: 2008ESPM...12.3.20H Altcode: With the invention of new far-infrared (FIR) and radio mm and sub-mm instruments (DESIR on SMESE satellite, ESO ALMA), there is a growing interest in observations and analysis of solar flares in this so far unexplored wavelength region. Two principal radition mechanisms play a role: the synchrotron emission due to accelerated particle beams moving in the magnetic field and the thermal emission due to energy deposit in the lower atmospheric layers. The latter one was recently explored for the case of semiempirical flare models, without considering the temporal evolution. However, as the radiation-hydrodynamical simulations do show, the lower atmosphere heated by beams exhibits fast temporal changes which are typically reflected in variations of spectral-line intensities. In this contribution we explore the time-dependent effects of beams on FIR and radio continua. We show how and where these continua are formed in the presence of time dependent beam heating and non-thermal excitation/ionization of the chromospheric hydrogen plasma. Our results should contribute to planning of new observations in FIR and radio domain. Title: Influence of Seeing on Cloud Model Parameters Obtained from Hα Observations Authors: Tziotziou, K.; Tsiropoula, G.; Heinzel, P. Bibcode: 2008ASPC..397...63T Altcode: We study the influence of atmospheric seeing due to terrestrial atmospheric turbulence on cloud model parameters obtained from Hα observations with Beckers' cloud model. The analysis indicates that atmospheric seeing does not affect the velocity determination, but does influence significantly the determination of the Doppler width when velocity gradients are present, and hence, the determination of the temperature, while the optical thickness and source function are also quantitatively affected, especially for high values of atmospheric seeing. 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: Eclipse Observations of Quiescent Prominences Authors: Jejcic, S.; Heinzel, P.; Kotrc, P.; Druckmuller, M. Bibcode: 2008ESPM...12.2.66J Altcode: In this study we demonstrate how to analyze the solar eclipse data taken by a digital camera. We use the observations of a quiescent prominence obtained during the total solar eclipse on March 29, 2006 (Side, Turkey). Using the RGB signal of the white light emission and co-temporal H? spectra taken at Ondrejov Observatory, we derive the electron density, temperature and geometrical thickness of the studied prominence. 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: Contrast of Fine-scale Structures in a Quiet Sun Network Region Authors: Schwartz, P.; Tziotziou, K.; Heinzel, P.; Tsiropoula, G. Bibcode: 2008ESPM...12.2.35S Altcode: We study the contrast of fine structures (mottles), found in a quiet-Sun network region and close to a filament, observed by the SOHO/SUMER spectrograph. The observations were made during August 29 -- 30, 1996, in several chromospheric, transition-region and coronal EUV lines. The contrasts of the fine-scale structures were obtained in the different spectral lines and compared to find whether they have any dependence on the inclination of the magnetic field lines and the line formation height. Also contributions of the absorption and emissivity blocking to the depression of brightness in these fine-scale structures are studied by comparing the observations in transition-region lines with wavelengths above and below 912 A (the head of the hydrogen Lyman continuum). Title: Oscillatory Phenomena in a Solar Network Region Authors: Tziotziou, K.; Tsiropoula, G.; Schwartz, P.; Heinzel, P. Bibcode: 2008ESPM...12.2.41T Altcode: Multi-wavelength, multi-instrument observations, obtained during a coordinated observing campaign on October 2005 by the ground-based Dutch Open Telescope (DOT), and by instruments on the spacecraft Solar and Heliospheric Observatory (SoHO) and Transition Region and Coronal Explorer (TRACE), are used to study oscillatory phenomena in a solar network region. Temporal variations of the intensities and velocities in a region of the quiet Sun containing several dark mottles and in a region with several bright points defining the network boundaries (NB) are investigated with the aim of finding similarities and/or differences in the oscillatory phenomena observed in these two regions and in different spectral lines formed from the chromosphere to the transition region, as well as propagation characteristics of waves. A wavelet, phase difference and coherence analyses were performed indicating a periodicity around 5 min in all considered lines for both regions. V-V phase differences in the NB region point to an upward propagation of, most probably, acoustic waves, while in the region of mottles they indicate a non vertical propagation of waves, due to the presence of several inclined mottles along the line-of-sight. In mottles, for periods of 250-400 s the phase difference is mainly negative suggesting that propagating waves encounter a boundary and are refracted and reflected. However, limitations arising from the complex topology of the magnetic field, the formation conditions and heights of the examined spectral lines and the low spatial resolution of the space instruments influence the exact interpretation of the phase differences. Title: Prominence modelling: from observed emission measures to temperature profiles Authors: Anzer, U.; Heinzel, P. Bibcode: 2008A&A...480..537A Altcode: Aims:We outline the construction of prominence - corona transition region models based upon the observations of one particular prominence.
Methods: The differential emission measure curves from observations were approximated by simple analytical functions. On this basis we constructed the temperature curve and calculated the radiative losses, the gains by thermal conduction, and some estimates for the wave heating.
Results: The temperature curve was calculated in the range between 23 000 K and 450 000 K. The resulting transition region can be divided into an inner region where the temperature is low and the radiative losses are very large, a part with a very steep temperature rise from 40 000 K to around 250 000 K over a width of only 500 km, and an extended high temperature region. Both the conductive heating and our estimates for a possible wave cooling/heating peak very sharply in the region with the very large temperature gradient. The consequences for the energy balance are discussed. Title: Modelling of Optical Emission in Solar Flares Authors: Varady, M.; Kašparová, J.; Heinzel, P.; Karlický, M.; Moravec, Z. Bibcode: 2008CEAB...32..101V Altcode: We present recent progress achieved by our group in the field of flare optical emission modelling. We concentrate on two problems. Firstly, on the possibility of modelling of the time evolution of several Balmer line profiles calculated for real electron fluxes obtained from the hard X--ray observations of a particular flare with the prospect to compare the theoretical results with the observed data for the corresponding flare. Secondly, we discuss the influence of the non--thermal electrons in the line emitting region on the formation and time evolution of Balmer hydrogen line profiles. Title: Multi-wavelength Analysis of a Solar Network Region Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Heinzel, P. Bibcode: 2008CEAB...32..109T Altcode: We analyse co-temporal observations of a network region found near the solar disc centre, obtained by the Dutch Open Telescope (DOT) and the Coronal Diagnostic Spectrometer (CDS) on-board SOHO during a coordinated observing campaign in October 2005. DOT obtained images in 5 wavelengths along the ha\ profile, while CDS obtained sit-and-stare observations in several EUV spectral lines that span the upper solar atmosphere. After fitting the CDS spectral line profiles we obtained 2-D space-time maps of intensities, Doppler velocities and Doppler widths. We study the appearance of the network region in the different spectral lines and the temporal variations of the obtained physical parameters. We employ a wavelet analysis to examine the existence of oscillations at the network in the different solar layers. Title: Limb Prominences Seen in UV, EUV and SXR Authors: Heinzel, P.; Fárník, F.; Anzer, U.; Dammasch, I. Bibcode: 2007ASPC..369..279H Altcode: We use SOHO/SUMER, EIT and Yohkoh/SXT prominence observations to study the absorption and/or volume blocking of UV, EUV and SXR coronal radiation by cool prominence plasma. An example of such a complex behaviour is the limb prominence observed on 5 September 1996. The SUMER spectrograph has detected two coronal lines, MgX at 625 Å, which is absorbed by the hydrogen Lyman continuum and blocked within a volume occupied by cool prominence plasma, and FeXII at 1242 Å, where the prominence appears dark due to blocking (no absorption at this wavelength). A similar behaviour show also the EUV images taken by EIT. We find that a darkening similar to that detected in the FeXII line is quite well visible also in the SXR images obtained by Yohkoh/SXT. To explain this feature, we exclude the absorption by the HeI and HeII resonance continua (hydrogen absorption is quite negligible) and suggest that it is entirely due to the volume blocking. Based on a quantitative analysis of these data, we discuss the physical conditions in cool prominences and their coronal environment. Finally, we propose new high-resolution EUV and SXR observations of prominences by Solar-B, using the EUV imaging spectrometer (EIS) and the X-ray telescope (XRT), respectively. Title: Hydrogen Balmer line formation in solar flares affected by return currents Authors: Štepán, J. Å.; Kašparová, J.; Karlický, M.; Heinzel, P. Bibcode: 2007A&A...472L..55S Altcode: 2007arXiv0708.0265S Aims:We investigate the effect of the electric return currents in solar flares on the profiles of hydrogen Balmer lines. We consider the monoenergetic approximation for the primary beam and runaway model of the neutralizing return current.
Methods: Propagation of the 10 keV electron beam from a coronal reconnection site is considered for the semiempirical chromosphere model F1. We estimate the local number density of return current using two approximations for beam energy fluxes between 4 × 1011 and 1 × 1012 erg cm-2 s-1. Inelastic collisions of beam and return-current electrons with hydrogen are included according to their energy distributions, and the hydrogen Balmer line intensities are computed using an NLTE radiative transfer approach.
Results: In comparison to traditional NLTE models of solar flares that neglect the return-current effects, we found a significant increase emission in the Balmer line cores due to nonthermal excitation by return current. Contrary to the model without return current, the line shapes are sensitive to a beam flux. It is the result of variation in the return-current energy that is close to the hydrogen excitation thresholds and the density of return-current electrons. Title: Influence of seeing effects on cloud model inversions Authors: Tziotziou, K.; Heinzel, P.; Tsiropoula, G. Bibcode: 2007A&A...472..287T Altcode: Context: Atmospheric seeing due to terrestrial atmospheric turbulence is a process that distorts solar ground-based observations.
Aims: We study the influence of atmospheric seeing on Hα cloud model inversions.
Methods: We use Beckers' cloud model which assumes a constant source function to obtain physical parameters from observed quiet-Sun Hα profiles, and profiles convolved with a Gaussian point spread function that simulates the effect of atmospheric seeing on solar observations.
Results: Our analysis indicates that atmospheric seeing does not affect the velocity determination, but does influence significantly the determination of the Doppler width when velocity gradients are present, and hence, the determination of the temperature, while the optical thickness and source function are also quantitatively affected, especially for high values of atmospheric seeing.
Conclusions: The effects of atmospheric seeing on cloud model inversions also depend on the actual size of the structures under study. For the presented observations, the derived cloud model parameter distributions do not change significantly for atmospheric seeing up to ∼0.5''. 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: Is the magnetic field in quiescent prominences force-free? Authors: Anzer, U.; Heinzel, P. Bibcode: 2007A&A...467.1285A Altcode: Aims:We describe under which conditions the magnetic fields of quiescent prominences are force-free and under which gravity plays the dominant role.
Methods: The existing observational determinations of the magnetic field are summarised and the calculation of the plasma β is outlined. We derive the dependence of β on the prominence weight and the field strength.
Results: We show that in many cases of well-developed quiescent prominences the field can deviate substantially from the force-free situation and gravity fully determines the structure of the magnetic dips. Title: Hα with Heating by Particle Beams Authors: Kašparová, J.; Varady, M.; Karlický, M.; Heinzel, P.; Moravec, Z. Bibcode: 2007ASPC..368..441K Altcode: 2007astro.ph..3800K Using 1D NLTE radiative hydrodynamics we model the influence of the particle beams on the Hα line profile treating the beam propagation and the atmosphere evolution self-consistently. We focus on the influence of the non-thermal collisional rates and the return current. Based on our results, we propose a diagnostic method for determination of the particle beam presence in the formation regions of the Hα line. 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: Multiwavelength Observations of Solar Prominences Authors: Heinzel, P. Bibcode: 2007ASPC..370...46H Altcode: We briefly review the multiwavelength observations of solar prominences and filaments ranging from the infrared up to soft X-rays. We give several examples of current observations and mention those specific to the total solar eclipses. Our particular focus is on the ultraviolet (UV) and extreme-UV images taken in various lines of different species. Title: The Physics of Chromospheric Plasmas Authors: Heinzel, P.; Dorotovič, I.; Rutten, R. J. Bibcode: 2007ASPC..368.....H Altcode: No abstract at ADS Title: Prominences on the Limb: Diagnostics with UV EUV Lines and the Soft X-Ray Continuum Authors: Anzer, U.; Heinzel, P.; Fárnik, F. Bibcode: 2007SoPh..242...43A Altcode: In this paper we discuss the two mechanisms by which solar prominences on the limb can manifest themselves when observed in coronal UV - EUV lines and in the soft X-ray continuum. These mechanisms are the absorption in the resonance continua of hydrogen and helium on one hand and the reduction of the emissivity in a part of the coronal volume occupied by a prominence on the other one. We briefly describe earlier observations made with SOHO/SUMER, EIT and Yohkoh/SXT. We then discuss how the instruments on the new Japanese satellite Hinode can be used for more detailed studies of prominences. We also propose some combined observations between the Hinode satellite and the SOHO/SUMER instrument. Title: Non-LTE Analysis of Lyman-Line Observations of a Filament with SUMER Authors: Schwartz, P.; Schmieder, B.; Heinzel, P. Bibcode: 2007ASPC..368..359S Altcode: 2007arXiv0704.3539S We present non-LTE diagnostics of the filament observed by SOHO/SUMER on May 27, 2005 in the whole Lyman series. The filament was situated close to the disk center. The Lα observations were carried out with normal voltage of detector A. The slit was placed at the central part of the detector -- outside the Lα attenuator. Therefore, the observed profiles of this line could be calibrated reliably. Title: Multi-wavelength Analysis of a Quiet Solar Region Authors: Tsiropoula, G.; Tziotziou, K.; Giannikakis, J.; Young, P.; Schühle, U.; Heinzel, P. Bibcode: 2007ASPC..368..171T Altcode: 2007arXiv0704.1592T We present observations of a solar quiet region obtained by the ground-based Dutch Open Telescope (DOT), and by instruments on the spacecraft SOHO and TRACE. The observations were obtained during a coordinated observing campaign on October 2005. The aim of this work is to present the rich diversity of fine-scale structures that are found at the network boundaries and their appearance in different instruments and different spectral lines that span the photosphere to the corona. Detailed studies of these structures are crucial to understanding their dynamics in different solar layers, as well as the role such structures play in the mass balance and heating of the solar atmosphere. Title: Optical and UV Emission of Solar Flares: Multiwavelength Observations and Modelling Authors: Kasparova, J.; Heinzel, P. Bibcode: 2007AGUSMSH22A..07K Altcode: Solar flares reveal themselves in various ranges of electromagnetic emission and exhibit temporal variations down to sub-second scale, namely during the so-called impulsive phase. This contribution will focus on spatial and temporal variations of the optical and UV emissions which are thought to be driven by flare energy transport in the form of accelerated particles. We will review our current understanding of the formation of optical and UV emissions during the impulsive phase. Namely, we will discuss recent radiative-hydrodynamic models and various physical processes playing an important role in radiation transfer and formation of optical and UV spectra. We will also report on recent interpretations of observations in various lines and continua and discuss their importance for the diagnostics of the flare atmosphere structure and the presence of accelerated particles in the emission formation regions. Title: White-Light Emission of Solar Prominences Authors: Jejčič, S.; Heinzel, P. Bibcode: 2007ASPC..368..325J Altcode: Using an extended grid of prominence models we compute the prominence white-light (WL) emission due to Thomson scattering and compare it with that in Hα. The ratio of the WL emission and the total emission can explain the color of prominences as observed during the total eclipses and can tell us whether the pink color of prominences is due to their intrinsic white-light emission or due to coronal contribution at the prominence location. We also show how this ratio depends on the prominence electron density, temperature and thickness. Title: The Fine Structure of Solar Prominences Authors: Heinzel, P. Bibcode: 2007ASPC..368..271H Altcode: 2007arXiv0705.1464H Solar prominences and filaments (prominences projected against the solar disk) exhibit a large variety of fine structures which are well observed down to the resolution limit of ground-based telescopes. We describe the morphological aspects of these fine structures which basically depend on the type of a prominence (quiescent or active-region). Then we review current theoretical scenarios which are aimed at explaining the nature of these structures. In particular we discuss in detail the relative roles of magnetic pressure and gas pressure (i.e., the value of the plasma-β), as well as the dynamical aspects of the fine structures. Special attention is paid to recent numerical simulations which include a complex magnetic topology, energy balance (heating and cooling processes), as well as the multidimensional radiative transfer. Finally, we also show how new ground-based and space observations can reveal various physical aspects of the fine structures including their prominence-corona transition regions in relation to the orientation of the magnetic field. Title: Hydrogen Hα line polarization in solar flares. Theoretical investigation of atomic polarization by proton beams considering self-consistent NLTE polarized radiative transfer Authors: Štěpán, J.; Heinzel, P.; Sahal-Bréchot, S. Bibcode: 2007A&A...465..621S Altcode: 2007astro.ph..1617S Context: We present a theoretical review of the effect of impact polarization of a hydrogen Hα line due to an expected proton beam bombardment in solar flares.
Aims: Several observations indicate the presence of the linear polarization of the hydrogen Hα line observed near the solar limb above 5% and preferentially in the radial direction. We theoretically review the problem of deceleration of the beam originating in the coronal reconnection site due to its interaction with the chromospheric plasma, and describe the formalism of the density matrix used in our description of the atomic processes and the treatment of collisional rates.
Methods: We solve the self-consistent NLTE radiation transfer problem for the particular semiempirical chromosphere models for both intensity and linear polarization components of the radiation field.
Results: In contrast to recent calculations, our results show that the energy distribution of the proton beam at Hα formation levels and depolarizing collisions by background electrons and protons cause a significant reduction of the effect below 0.1%. The radiation transfer solution shows that tangential resonance-scattering polarization dominates over the impact polarization effect in all considered models.
Conclusions: . In the models studied, proton beams are unlikely to be a satisfying explanation for the observed linear polarization of the Hα line. 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: Study of an extended EUV filament using SoHO/SUMER observations of the hydrogen Lyman lines Authors: Schwartz, P.; Heinzel, P.; Schmieder, B.; Anzer, U. Bibcode: 2006A&A...459..651S Altcode: Context: .In previous work we determined the 3D structure of an EUV extension of the filament observed by SoHO/CDS on 15 October 1999. The determination of the 3D structure depends on the optical thickness τ912 at the hydrogen Lyman-continuum edge at 912 Å. The τ912 value was unknown, therefore it was taken as a free parameter for the 3D-structure determinations.
Aims: .The plasma properties (including τ912) of this EUV filament are estimated using non-LTE modelling of profiles of the hydrogen Lyman lines.
Methods: .The lines Lβ, Lδ, L ɛ, L6 and L7 were observed by SoHO/SUMER with the slit positioned across the EUV filament. In our modelling the EUV filament was approximated by a horizontal 1D slab with constant pressure and the temperature decreasing vertically from the edges to interior of the slab. The values of the geometrical thickness of the slab in the EUV extension were taken from its 3D structure determined for the τ912 values estimated iteratively. The synthetic profiles were fitted to observed ones using the χ2 minimization.
Results: .For the Hα-filament part we obtained the expected results: a small geometrical thickness between several thousand and 15 000 km, temperatures around 5000 K in the interior and around 20 000 K in PCTRs, and pressure ~0.1~dyn~cm-2. That leads to an optical thickness in the Hα line center larger than 1. In the EUV extension, temperatures of 10 000-40 000 K in the interior and 35 000-50 000 K in the vertically extended PCTRs and a pressure of ~0.01~dyn~cm-2 were determined. Such large variations of the temperature lead to large variations of τ912.
Conclusions: .The EUV extension is inhomogeneous - areas both optically thick and thin at 912 Å are present close to each other. Parts optically thick at 912 Å are visible also in Hα as faint and tiny dark structures around the very dark and well pronounced Hα filament. The volume blocking mechanism is an important mechanism throughout the whole EUV extension even in its optically thick parts. The absorption dominates only in the Hα-filament part of the EUV filament. Title: Polarization Diagnostics of Proton Beams in Solar Flares Authors: Stepan, J.; Heinzel, P.; Kasparova, J.; Sahal-Brechot, S. Bibcode: 2006IAUJD...1E..55S Altcode: We review the problem of proton beam bombardment of solar chromosphere considering the self-consistent NLTE polarized radiation transfer in hydrogen lines. Several observations indicate a linear polarization of H-alpha line of the order of 5% or higher and preferentially in radial direction. This polarization is often explained as anisotropic collisional excitation of the n= 3 level by vertical proton beams. Our calculations indicate that deceleration of the proton beam with initial power-law energy distribution together with increased electron and proton densities in H-alpha forming layers lead to negligible line polarization. Thus the proton beams seem not to be a good candidate for explanation of the observed polarization degree. Title: Study of a Small-Scale Eruptive Event Observed by SOHO/SUMER Authors: Tomasz, F.; Régnier, S.; Schwarz, P.; Rybák, J.; Kucera, A.; Heinzel, P.; Curdt, W.; Wöhl Bibcode: 2006ESASP.617E..79T Altcode: 2006soho...17E..79T No abstract at ADS Title: What We Have Learned about Prominences and Filaments from SOHO/SUMER and CDS Spectral Observations Authors: Heinzel, P.; Schmieder, B.; Vial, J. -C. Bibcode: 2006ESASP.617E..65H Altcode: 2006soho...17E..65H No abstract at ADS Title: Hα Chromospheric Mottles and their UV/EUV Counterparts Seen by SOHO/Sumer Authors: Tziotziou, K.; Heinzel, P.; Tsiropoula, G.; Schühle, U. Bibcode: 2006ESASP.617E.112T Altcode: 2006soho...17E.112T No abstract at ADS Title: Darkening of Coronal Lines by Limb Prominences Observed by SOHO/SUMER Authors: Dammasch, I. E.; Heinzel, P.; Anzer, U. Bibcode: 2006ESASP.617E..66D Altcode: 2006soho...17E..66D No abstract at ADS Title: Importance of Absorption and Volume Blocking for Line Intensity Depression in EUV Filaments Authors: Schwartz, P.; Schmieder, B.; Heinzel, P. Bibcode: 2006ESASP.617E..75S Altcode: 2006soho...17E..75S No abstract at ADS 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: The Dynamics and Structure of the Solar Atmosphere As Obtained from Combined SUMER/SOHO and TIP2/VTT Observations Authors: Tomasz, F.; Régnier, S.; Schwartz, P.; Rybák, J.; Kucera, A.; Heinzel, P.; Curdt, W.; Wöhl Bibcode: 2006ESASP.617E..78T Altcode: 2006soho...17E..78T No abstract at ADS Title: New perspectives on prominences as observed by SOHO/SUMER Authors: Schmieder, B.; Vial, J. -C.; Heinzel, P. Bibcode: 2006sf2a.conf..563S Altcode: We summarize the results of our prominence and filament studies based on extensive spectral observations with SOHO/SUMER and CDS instruments. During the past decade we have gathered several sets of UV and EUV spectral data, containing various emission lines of different species. Our main objective was to better understand the formation of hydrogen Lyman lines and continuum (using the results of complex non-LTE transfer simulations). However we have also analysed also UV and EUV lines formed under transition-region and coronal conditions. Some highlights of our studies are: reproduction of Lyman-line profiles with partial redistribution, understanding the role of prominence-corona interface in the formation of Lyman-line cores, establishing the effect of the magnetic-field orientation on the shape of Lyman lines, discovery of EUV filament extensions (invisible in the Hα line) and their explanation, reconstruction of a 3D topology of the filament using EUV coronal lines, temperature diagnostics based on measurements of the hydrogen Lyman continuum, proper explanation of a prominence darkening detected in coronal lines. Title: On the Fine Structure of Solar Filaments Authors: Heinzel, P.; Anzer, U. Bibcode: 2006ApJ...643L..65H Altcode: High-resolution Hα images of solar filaments show a variety of dark fine-structure fibrils, most of them aligned with the magnetic field that is sheared with respect to the filament long axis. Here we demonstrate how such fibrils can be explained in terms of the magnetic field dips produced by realistic mass loading due to plasma condensation along the top of a magnetic prominence arcade. Our interpretation is supported by (2+1)-dimensional radiation-magnetohydrostatic simulations that predict quantitatively the properties of such condensations that are suspended in the dipped magnetic field. Title: A periodic arcade model for extended EUV filaments Authors: Anzer, U.; Heinzel, P. Bibcode: 2006A&A...446..301A Altcode: The extensions of Hα filaments that are observed in EUV spectral lines require the presence of cool material in a large volume surrounding these filaments. This material can only be supported by magnetic fields with dips. Such dips can be generated by a sufficiently strong twisting of magnetic flux tubes. In the present paper we have extended earlier work to more realistic magnetic field configurations that are periodic in the x-direction. We derived approximate equilibria for twisted slender flux tubes and determined the region that contains dips. In addition we investigated the effects on our models of the mass loading due to a heavy prominence. Finally we compared our theoretical models with the EUV - observations. We conclude that these types of models are capable of explaining the basic features of the observations. 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: Multi-Wavelength Analysis of Plasma Flows during Solar Flares Authors: Berlicki, A.; Schmieder, B.; Heinzel, P.; Li, H.; Del Zanna, G.; Rudawy, P. Bibcode: 2005ESASP.600E..58B Altcode: 2005dysu.confE..58B; 2005ESPM...11...58B No abstract at ADS Title: Physical Parameters of Dark Mottles Derived from High Resolution Optical Spectra Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Kotrč, P.; Heinzel, P. Bibcode: 2005ESASP.600E..72T Altcode: 2005ESPM...11...72T; 2005dysu.confE..72T No abstract at ADS Title: Non-Lte Modelling of the EUV Filament Based on Soho/sumer Observations of the Hydrogen Lyman Lines Authors: Schwartz, P.; Heinzel, P.; Schmieder, B. Bibcode: 2005ESASP.600E..97S Altcode: 2005dysu.confE..97S; 2005ESPM...11...97S No abstract at ADS Title: Hα Line in Solar Atmosphere Heated by Particle Beams Authors: Kašparová, J.; Varady, M.; Karlický, M.; Moravec, Z.; Heinzel, P. Bibcode: 2005ESASP.600E.127K Altcode: 2005dysu.confE.127K; 2005ESPM...11..127K 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). Title: On the Nature of Dark Extreme Ultraviolet Structures Seen by SOHO/EIT and TRACE Authors: Anzer, U.; Heinzel, P. Bibcode: 2005ApJ...622..714A Altcode: Spectral lines in the extreme ultraviolet (EUV) observed on the Sun can originate either from the hot corona or the cooler chromosphere to corona transition region. In the present paper we concentrate on coronal lines and in particular on iron lines at 171, 195, and 284 Å, which have been frequently observed by the Solar and Heliospheric Observatory (SOHO)/Extreme Ultraviolet Imaging Telescope (EIT) and the Transition Region and Coronal Explorer (TRACE). The intensity of these lines emitted by the corona can be reduced by the presence of a cool gas, e.g., by prominence-like material, located in the corona. There are two mechanisms that can lead to a reduction of the line intensity: absorption and volume blocking. That part of the coronal radiation that comes from behind the cool gas can be partially absorbed. The main absorbers for the iron lines studied here are neutral hydrogen and neutral plus singly ionized helium. In this paper we calculate the optical thickness of their resonance continua at the wavelength positions of iron lines and compare it with that in the Hα line center. The comparison of the derived values shows that they are quite similar. The second effect is due to the fact that cool structures in the corona do not emit any radiation in the EUV lines, which gives rise to an additional reduction of the observed intensity as compared with the surrounding corona-we have termed this ``volume blocking.'' We further describe in this paper how these two effects can be used in a new way of performing prominence diagnostics. Our results are also applicable to other coronal lines detected by, e.g., the SOHO CDS or SUMER instruments. Title: Non-LTE diagnostics of velocity fields during the gradual phase of a solar flare Authors: Berlicki, A.; Heinzel, P.; Schmieder, B.; Mein, P.; Mein, N. Bibcode: 2005A&A...430..679B Altcode: We perform an analysis of the velocity field within the Hα ribbons during the gradual phase of an M 1.0 solar flare observed on October 22, 2002. We use spectroscopic observations performed with the German VTT (Vacuum Tower Telescope) working in the MSDP (Multichannel Subtractive Double Pass spectrograph) observing mode. From these observations the Hα line profiles in chosen areas of the flare ribbons were reconstructed and these observational profiles were compared with a grid of synthetic Hα line profiles calculated by the non-LTE radiative-transfer code. This code allows us to calculate different models of the chromosphere with a prescribed velocity field. By optimising the best fit between the observed and synthetic profiles we find the most appropriate models of the chromosphere and vertical structure of the velocity field in the analysed areas of the flare ribbons. By means of the non-LTE radiative-transfer calculations we show that in most analysed areas of the Hα flare ribbons the chromospheric plasma exhibited upward motion with a mean velocity of a few km;s-1. These results are consistent with previous estimates and support the scenario of a gentle evaporation during the gradual phase. Title: Physics of Solar Prominences Authors: Heinzel, P.; Anzed, U. Bibcode: 2005ASSL..320..115H Altcode: 2005smp..conf..115H No abstract at ADS Title: Diagnostics of Dark Chromospheric Mottles Based on High Resolution Spectra I - Observational Data Authors: Kotrč, P.; Schwartz, P.; Heinzel, P.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2005HvaOB..29..289K Altcode: High resolution optical spectra of dark mottles in H and Ca lines were observed with the Echelle spectrograph of the VTT at Sacramento Peak Observatory. Until now, only Hα spectra and slit-jaw images were processed. Used methods of identification of the dark mottles in the slit-jaw images and in the spectra, as well as a calibration and correction on the scattered light are described. Individual steps of the procedure, as well as crucial problems are discussed. The finally processed line profiles

are comparable to the profiles of dark mottles obtained by other instruments including MSDP. Title: Influence of Electron Beam Pulses on Hα Line Formation Authors: Varady, M.; Kašparova, J.; Karlický, M.; Heinzel, P.; Moravec, Z. Bibcode: 2005HvaOB..29..167V Altcode: In this contribution we present results of our simulations focused on determination of spectroscopic signs of the presence of non--thermal electrons in the formation region of Hα using three mutually communicating codes. The originally autonomous and highly specialised codes model three simultaneously acting processes in flares: the precipitation and energy dissipation of the non-thermal power--law electron beams in the solar atmosphere, the hydrodynamic response of the atmosphere to the energy deposited by the beams, and the radiative transfer in chromosphere and photosphere which determines the hydrogen line profiles and their time evolution. The results show possible existence of a new diagnostic method on presence of electron beams in the formation region of the Hα line. Title: Determination of the 3D structure of an EUV-filament observed by SoHO/CDS, SoHO/SUMER and VTT/MSDP Authors: Schwartz, P.; Heinzel, P.; Anzer, U.; Schmieder, B. Bibcode: 2004A&A...421..323S Altcode: Heinzel et al. (\cite{hein1}) found that filaments seem to be much more extended in EUV spectral lines than in Hα. In this paper we reconstruct the 3D structure of the extensions of the EUV-filament observed on 15 October 1999 by SoHO/CDS and SoHO/SUMER. Small Hα structures were observed by VTT/MSDP. We computed the bottom and top heights of the EUV-filament extensions for several values of the hydrogen Lyman-continuum optical thickness τ912 using the spectroscopic model of Heinzel et al. (\cite{hein2}). For this we used CDS observations of the two coronal lines Mg X 624.94 Å and Si XII 520.60 Å. Further, we develop a new method for estimating τ912 using the O V line measured by CDS and the O VI measured by SUMER onboard SoHO. The latter line is used as a proxy to deduce the intensity variations of O V underneath the filament. This method also takes into account the presence of prominence-corona transition regions.

Resulting heights of the EUV-filament extensions are around 15 000 km for the bottom and around 40 000 km for the top boundaries. However, there are significant variations around these representative values and we show that in about half of observed pixels the Lyman-continuum absorption dominates in the coronal-line depression, while in the other half it is the volume blocking effect. The latter situation corresponds to a large (larger than 30 000 km) geometrical thickness of the EUV-filament extension. From the heights of the boundaries of the EUV-filament the geometrical thickness can be computed and used to estimate the total mass loading which was found to be comparable to that of typical CMEs. Title: Soft X-ray heating of the solar chromosphere during the gradual phase of two solar flares Authors: Berlicki, A.; Heinzel, P. Bibcode: 2004A&A...420..319B Altcode: In this paper we perform an analysis of the energetics of the solar flaring chromosphere irradiated by soft X-rays (SXR) emitted from overlying hot flare loops. To study an expected SXR heating we used the observations of two solar flares obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph attached to the Large Coronagraph of the Wrocław University. SXR observations of these flares come from the Yohkoh SXR telescope (SXT). From MSDP spectral images we derived mean Hα line profiles which were then used to construct semi-empirical non-LTE models of the chromosphere in the analyzed areas of flares. On the basis of SXR observations we calculated the mean emission measure EM and the temperature in flaring coronal structures located above the Hα kernels under study and these two quantities were used to compute the SXR irradiation of the chromosphere between 1-300 Å. For each flare model we then evaluated the energy deposit due to such irradiation and compared it with the net radiative cooling rates at all depths in the chromosphere. By means of such modelling we were able to demonstrate that the enhanced emission of selected Hα kernels observed during the gradual phase of these two solar flares cannot be explained in terms of the SXR heating of the chromosphere. We found that radiative losses in all layers of the chromosphere exceeded the amount of the energy deposited by the SXR radiation. However, for stronger flares with much enhanced EM a certain contribution of SXR to the heating cannot be ruled out. Title: Multi-wavelength study of a high-latitude EUV filament Authors: Schmieder, Brigitte; Lin, Yong; Heinzel, Petr; Schwartz, Pavol Bibcode: 2004SoPh..221..297S Altcode: A large filament was observed during a multi-wavelength coordinated campaign on June 19, 1998 in the Hα line with the Swedish Vacuum Solar Telescope (SVST) at La Palma, in the coronal lines Fe ix/x 171 Å and Fe xi 195 Å with the Transition Region and Coronal Explorer (TRACE) and in EUV lines with the SOHO/CDS spectrometer and the hydrogen Lyman series with the SOHO/SUMER spectrometer. Because of its high-latitude location, it is possible to disentangle the physical properties of the Hα filament and the filament channel seen in EUV lines. TRACE images point out a dark region fitting the Hα fine-structure threads and a dark corridor (filament channel), well extended south of the magnetic inversion line. A similar pattern is observed in the CDS EUV-line images. The opacity of the hydrogen and helium resonance continua at 171 Å is almost two orders of magnitude lower than that at the Hi head (912 Å) and thus similar to the opacity of the Hα line. Since we do not see the filament channel in Hα, this would imply that it should also be invisible in TRACE lines. Thus, the diffuse dark corridor is interpreted as due to the coronal `volume blocking' by a cool plasma which extends to large altitudes. Such extensions were also confirmed by computing the heights from the projection geometry and by simulations of the CDS and TRACE line intensities using the spectroscopic model of EUV filaments (Heinzel, Anzer, and Schmieder, 2003). Finally, our NLTE analysis of selected hydrogen Lyman lines observed by SUMER also leads to a conclusion that the dark filament channel is due to a presence of relatively cool plasma having low densities and being distributed at altitudes reaching the Hα filament. Title: Collisional excitation and ionization of hydrogen by return current in solar flares Authors: Karlický, M.; Kašparová, J.; Heinzel, P. Bibcode: 2004A&A...416L..13K Altcode: First a problem of the transport of electron beams with high energy fluxes into the cold chromosphere during the flare is presented. Then it is shown that the problem might be solved by the return current formed by superthermal (runaway) electrons. In such a case the return current electrons could influence hydrogen excitations and ionizations. Therefore, we computed collisional rates of such a return current and compared them with those of the thermal plasma and of a monoenergetic (10 keV) electron beam with the energy flux FE = 1012 erg cm-2 s-1 penetrating into the flare atmosphere described by the F1 model (Machado et al. \cite{Machado1980}). We show that in this situation the return current collisional rates can be dominant for some transitions. Title: Collisional Excitation and Ionization of Hydrogen by Return Current in Solar Flares Authors: Kašparová, J.; Heinzel, P.; Karlický, M. Bibcode: 2004IAUS..219..760K Altcode: No abstract at ADS Title: Parameters of dark mottles based on high resolution optical spectra Authors: Kotrc, P.; Heinzel, P.; Tziotziou, K.; Tsiropoula, G. Bibcode: 2004IAUS..223..275K Altcode: 2005IAUS..223..275K High resolution optical spectra of hydrogen and calcium lines observed with the Echelle spectrograph of the VTT at Sacramento Peak Observatory were analyzed. The observed line profiles in some parts of dark chromospheric mottles are to be matched with theoretical ones using the cloud model and several parameters (e.g. the temperature, gas pressure, flow velocity) are to be derived. Individual steps of the procedure, as well as crucial problems are discussed. Title: Multi-Wavelength Observations of an M1.0 Flare on 22 October 2002 Authors: Berlicki, A.; Schmieder, B.; Vilmer, N.; Mein, P.; Mein, N.; Heinzel, P.; Staiger, J.; Deluca, E. E. Bibcode: 2004IAUS..219..669B Altcode: No abstract at ADS Title: Multiwavelength determination of the density and total mass of the EUV filament observed by SoHO/CDS, SoHO/SUMER and MSDP/VTT Authors: Schwartz, P.; Schmieder, B.; Heinzel, P.; Anzer, U. Bibcode: 2004IAUS..223..219S Altcode: 2005IAUS..223..219S It was found that filaments observed in EUV could be much more extended than in Halpha. These extended dark structures visible in EUV are named EUV filaments. Their parts seen only in EUV (not observable in Halpha because of low opacity at the Halpha wavelength) are called EUV-filament extensions (or simply EUV extensions). For the EUV filament observed by SoHO on 15 October 1999 as northern polar crown filament, only a few small dark structures were seen in Halpha. This suggests that the mass of the EUV extension is larger than, or at least comparable with, the mass of the parts of the filament observed in Halpha. In our previous work we determined the 3D structure of the EUV extension of this EUV filament. In this paper we present the determinations of mass and average density of this EUV extension. For better density estimates we interpret the hydrogen Lyman lines observed by SUMER using non-LTE radiative transfer code. From the best fitting of Lyman lines we obtained a reasonable model of the EUV extension with low gas pressure, temperatures from 2times10^4 K to 10^5 K and with extended prominence-corona transition regions. Title: A Spectroscopic Model of euv Filaments Authors: Heinzel, P.; Anzer, U.; Schmieder, B. Bibcode: 2003SoPh..216..159H Altcode: We propose a new spectroscopic model for extended dark structures around Hα filaments observed in EUV lines. As in previous papers, we call these structures EUV filaments. Our model uses at least three observed EUV lines (located shortward the hydrogen Lyman-continuum limit) to compute iteratively the altitudes at which the EUV filament extensions are located. A transition-region line (O v in the present case) can be used to derive the opacity of the Lyman continuum and the other two coronal lines (e.g., Mg x and Si xii) then give two heights: the bottom and top of the EUV filament. The method takes into account self-consistently the absorption of EUV-line radiation by the Lyman continuum, as well as the volume-blocking effect potentially important for coronal lines. As an example we compute the heights of the EUV filament at one particular position, using CDS data for the 5 May 2000 filament. At this position, the EUV filament extension lies between altitudes 28 700 and 39 000 km, so that the geometrical thickness of the structure is 10300 km (we discuss also the sensitivity of our models to variations of the line intensities). These heights are consistent with the concept of twisted magnetic flux tubes, but there could be also some influence on our results due to additional low lying cool structures from parasitic polarities. Title: Determination of the 3D-topology of an EUV-filament observed by SoHO/CDS SoHO/SUMER and VTT/MSDP Authors: Schwartz, P.; Heinzel, P.; Schmieder, B.; Anzer, U. Bibcode: 2003ESASP.535..495S Altcode: 2003iscs.symp..495S We have constructed a spatial model of an extended EUV-filament observed on 15 October 1999 (polar crown N 38 deg) by SoHO/CDS. The narrow Hα counterparts were observed by VTT/MSDP. As found in 2001, EUV-filaments are much more extended than those parts visible in Hα. We have computed the bottom and top heights of this EUV-filament for the whole CDS raster for different values of the Lyman-continuum optical thickness using CDS measurements of two coronal lines (Mg X 624.94 Å and Si XII 520.60 Å) and the model of Heinzel et al., 2003. For the scale height of the MgX line we used the value from Fludra et al. 1999, assuming that this line is not solar cycle and activity dependent. We created a new method for τ912 determination from O VI and O V line intensities. Because of the inhomogeneity in the O V 629.37 Å line intensity distribution in the vicinitiy of the EUV-filament it was not possible to estimate this intensity under the filament. So we used observations made by SoHO/SUMER of the O VI 1031.91 Å line not absorbed by EUV-filament cold plasma. The knowledge of the heights of the bottom and top boundaries of an EUV-filament gives us the EUV-filament geometrical thickness. From this the mass of the EUV-filament was computed. Title: EUV-filaments and their mass loading Authors: Heinzel, P.; Anzer, U.; Schmieder, B.; Schwartz, P. Bibcode: 2003ESASP.535..447H Altcode: 2003iscs.symp..447H It was found recently (Heinzel et al., 2001; Schmieder et al., 2003) that solar filaments observed in EUV lines by SOHO/CDS are much more extended than their Hα counterparts. This was explained by a large difference between the hydrogen Lyman-continuum and Hα opacities. Two different MHD models were suggested to explain the EUV-filament extensions: the model based on parasitic polarities (Aulanier & Schmieder, 2002) and the model with twisted flux tubes (Anzer & Heinzel, 2003). The latter model can explain our recent findings that at least some parts of the EUV-filament extensions are located relatively high in the corona. These heights can be computed using a new spectroscopic model of EUV-filaments. The mass which is loaded into the EUV-filament extensions is then estimated on the basis of non-LTE transfer calculation. The total filament mass is larger than that derived for the Hα filament itself and this may have consequences for the structure and mass loading of CMEs whenever they form from such filaments - this may answer the question how the extended CME structures can form from rather narrow Hα filaments. We summarize the basic properties of EUV-filaments, present their spectroscopic analysis and give some estimates for mass loading. We then discuss possible relations between EUV-filaments and CMEs, in particular the problems of their masses. Title: On the nature of extended EUV filaments Authors: Anzer, U.; Heinzel, P. Bibcode: 2003A&A...404.1139A Altcode: This paper describes the properties of extended EUV filaments and the theoretical modelling of them. We summarise the general aspects of the depression of EUV-line emission and give an interpretation of recent filament observations in transition-region and coronal lines. The EUV filament was found to be located relatively high in the corona (at least 20 000 km above the solar surface) and this requires an MHD scenario alternative to the parasitic-polarity model of Aulanier & Schmieder (\cite{Aulanier02}). Here we present a new idea for the support of cool gas in the magnetic arcade of a prominence which is capable of explaining both wide and vertically extended EUV filaments. Our mechanism is based upon the twisting of individual flux tubes, similar to the one which was suggested by Priest et al. (\cite{Priest89}). Finally, the consequences of this new model are discussed. Title: Spectroscopic diagnostics of an Hα and EUV filament observed with THEMIS and SOHO Authors: Schmieder, B.; Tziotziou, K.; Heinzel, P. Bibcode: 2003A&A...401..361S Altcode: A long filament has been observed with THEMIS/MSDP and SOHO/CDS - SUMER, during a coordinated campaign (JOPs 131/95) on May 5, 2000. The data were (a) 2-D Hα spectra, observed using THEMIS, (b) Lyman series spectra and Lyman continuum, observed using SOHO/SUMER, and (c) EUV spectra (in O V 629 Å, Mg X 624 Å, Si Xii 520 Å, Ca X 557 Å and He I 584 Å) observed using SOHO/CDS. A large depression of the line emissions in CDS images represents the EUV filament. A computed model shows that the EUV filament consists of an extended in height cloud of low gas pressure at an altitude lower than the top of the Hα filament, volume-blocking and absorbing coronal emission and absorbing transition region line emission. The optical thickness of the Lyman continuum is estimated by using the ratio of O V intensity inside and outside the EUV filament, while the optical thickness of Hα is computed from the Hα line profile by using an inversion technique. Using simultaneous Hα , Lyman lines and Lyman continuum spectroscopic data, we performed detailed, non-LTE radiative transfer diagnostics of the filament plasma conditions. The optical thickness of the Lyman continuum is larger than that of the Hα line by one to two orders of magnitude. This could be of a great importance for filament formation modeling, if we consider that more cool material exists in filament channels but is optically too thin to be visible in Hα images. Title: 2D Radiative Transfer in Magnetically Confined Structures Authors: Heinzel, P.; Anzer, U. Bibcode: 2003ASPC..288..441H Altcode: 2003sam..conf..441H Magnetically confined structures in the solar atmosphere exhibit a large complexity in their shapes and physical conditions. As an example, we show the case of so-called magnetic dips in prominences which are in magnetohydrostatic equilibria. For such models we solve 2D non-LTE multilevel problem for hydrogen with PRD in Lyman resonance lines. The iterative technique used is based on the MALI approach with simple diagonal ALO and SC formal solver.

To compute the hydrogen ionization balance, the preconditioned MALI equations are linearized with respect to atomic level populations and electron density and solved iteratively using the Newton-Raphson scheme. Two additional problems are addressed: (i) an adequate iteration method for cases when the column-mass scale is used in one of the two dimensions but varies along the other dimension (which has a geometrical scaling); and (ii) a possibility of using AMR (Adaptive Mesh Refinement) algorithms to account for steep 2D gradients of selected variables (temperature, density, etc.). Title: Transport of Energy from the Corona to the Chromosphere During Flares Authors: Heinzel, P.; Karlický, M. Bibcode: 2003LNP...612..161H Altcode: 2003ecpa.conf..161H Hard X-ray (HXR) observations frequently exhibit fast temporal variations during the impulsive phase of solar flares and this is usually ascribed to the propagation of beams of accelerated particles and to the dissipation of their energy in lower layers of the solar atmosphere. As a result of fast heating and non-thermal processes, several chromospheric lines show significant impulsive brightenings. We first review observational attempts of detecting such fast (sub-second) variations of the line intensities, namely in the Halpha line, and discuss the problems associated with such observations. Second, we describe new radiation-hydrodynamical (RHD) simulations of the pulse-beam heating and show how they predict both HXR and optical-line intensity variations on very short time scales. We also discuss the effect of the return current on the energy deposit in the atmosphere. Using new spatially-resolved HXR observations (RHESSI) made simultaneously with a high-cadence detection of selected optical lines, one should be able to diagnose the properties of particle beams, provided that the response of the lower atmospheric layers to beam pulses is strong enough. Title: Understanding solar flares from optical observations: How do particle beams affect the lower atmosphere? Authors: Heinzel, P. Bibcode: 2003AdSpR..32.2393H Altcode: During the impulsive phase of solar flares, both hard X-ray (HXR) and optical emissions exhibit fast temporal fluctuations detectable down to sub-second scales. This is usually ascribed to the propagation of beams of accelerated particles and to the dissipation of their energy in lower layers of the solar atmosphere. Although it is rather difficult to prove a temporal correlation between HXR and optical intensity variations, we discuss here some previous results and recent attempts. Namely in coordination with RHESSI observations, several ground-based observatories started to detect fast optical variations in the H α line. In addition to this, we also mention a possibility of using some other diagnostically important lines. The proper interpretation of coordinated HXR and optical observations further requires robust tools for radiation-hydrodynamical (RHD) forward modeling. We briefly describe a new 'hybrid' code which consists of RHD part and particle-simulation part. Short-duration heating due to beam pulses is modeled which allows us to predict temporal fluctuations of HXR and selected optical and UV lines formed in chromospheric layers and in the transition region. Particularly the line asymmetries originating in a highly dynamical lower atmosphere of the flare can be used to diagnose the response of these layers to particle beams. Title: Soft X-ray Heating of Stellar Chromospheres Authors: Heinzel, P.; Berlicki, A. Bibcode: 2003IAUS..210P.B15H Altcode: No abstract at ADS Title: Time-dependent Flare Models with MALI Authors: Kašparová, J.; Heinzel, P.; Varady, M.; Karlický, M. Bibcode: 2003ASPC..288..544K Altcode: 2003sam..conf..544K Temporal variations of Hα line profile intensities related to electron beams are presented. We show first results of time dependent simulations of a chromospheric response to a 1 sec monoenergetic electron beam. 1-D hydrodynamic code together with particle representation of the beam have been used to calculate atmospheric evolution. Time dependent radiative transfer problem has been solved for the resulting atmosphere in the MALI approach, using the Crank-Nicholson implicit scheme. Non-thermal collisional rates were included in linearised equations of statistical equilibrium. Title: Time dependent flare model with non-LTE radiative transfer Authors: Varady, M.; Karlický, M.; Kašparová, J.; Heinzel, P. Bibcode: 2002ESASP.506..521V Altcode: 2002svco.conf..521V; 2002ESPM...10..521V The first results of a time dependent simulation of chromospheric response to a high energy electron beam are presented. The hybrid code, i.e. a combination of a 1-D hydrodynamic code and a test particle code, has been used to calculate the energy losses of a high energy electron beam propagating through the solar atmosphere and the consequent response of the ambient solar plasma to the energy deposition. The resulting time evolution of the solar plasma temperature, density, velocity and energy deposit on hydrogen has then been used as an input for a time dependent radiative transfer code in the MALI approach to determine the time variation of the Hα line profile. Non-thermal collisional rates have been included in the linearised ESE. Title: A prominence with transition region: horizontal two-dimensional filament model Authors: Gorshkov, A. B.; Anzer, U.; Heinzel, P. Bibcode: 2002ESASP.506..405G Altcode: 2002ESPM...10..405G; 2002svco.conf..405G SOHO/SUMER observations of solar filaments in Lyman lines of hydrogen have revealed, in general, a two-peak form of the emission line profiles with peak to center ratio less than an order of magnitude. This fact strongly contradicts the results of numerical radiative transfer simulations, where profiles with strong dips and large (1.5-2 orders of magnitude) peak to center ratio are usually obtained due to the absence of incident radiation from above the filament and, as a consequence, very low atomic populations on the upper energy levels at the top of the filament. Recently it was shown (Schmieder et al. 1998) that this discrepancy can be removed by introducing a prominence-corona transition region (PCTR) to the radiative transfer models. This paper continues a set of publications (Anzer & Heinzel, 1999 and Heinzel & Anzer, 2001) devoted to the modelling of prominences as structures in MHS equilibrium. Here the prominence is represented by a horizontal 2D slab supported by a magnetic field. In our model we use a constant gas pressure and assume that the kinetic temperature profile and the PCTR extension are different in the vertical and horizontal directions due to magnetic field. In the PCTR the temperature sharply increases outwards from 8000K to 50000K on the scale of 100-600 km. To solve the radiative transfer problem we apply a 2D code based on the MALI iteration scheme and the modified long characteristics method. Title: Soft X-ray heating of the solar chromosphere: gradual phase of a solar flare Authors: Berlicki, A.; Heinzel, P.; Jakimiec, J. Bibcode: 2002ESASP.506..549B Altcode: 2002svco.conf..549B; 2002ESPM...10..549B In this paper we present the analysis of energetics of solar flaring chromosphere heated by soft X-ray radiation coming from overlying hot flare loops. During the solar flare, a large amount of its energy is emitted from hot coronal part in soft X-ray spectral range. This radiation can penetrate into the chromosphere and transmit the energy. This additional heating modifies vertical structure of the chromosphere and it can cause the enhanced emission from some parts of the flare. Therefore, such a mechanism can be responsible for emission of chromospheric flaring structures commonly observed in Hα and other spectral lines during the gradual phases when non-thermal processes are unimportant. To analyze the effect of X-ray heating we used the observations of the solar flare of 25 September 1997. This flare was observed with the Wroclaw Multichannel Subtractive Double Pass spectrograph (MSDP) coupled with the Large Coronagraph. We also use X-ray observations of the flare taken with the SXT telescope. Within the approximation of the quasi steady-state we have calculated the deposit of X-ray energy in the chromosphere. By means of the non-LTE radiative transfer calculations we show that enhanced emission of some H-alpha structures observed during the gradual phase of this solar flare can be partially explained in terms of the soft X-ray heating of the chromosphere by hot 'post-flare' loops seen on the SXT images. We also analyzed the energy budget of X-ray heated flaring chromosphere and found that radiative losses from the chromosphere can be balanced by soft X-ray heating only in some layers of the solar chromosphere. Title: Line profiles and intensity ratios in prominence models with a prominence to corona interface Authors: Labrosse, N.; Gouttebroze, P.; Heinzel, P.; Vial, J. -C. Bibcode: 2002ESASP.506..451L Altcode: 2002svco.conf..451L; 2002ESPM...10..451L In this work we study the hydrogen, helium and calcium spectra emitted by a one-dimensional prominence model in magneto-hydrostatic equilibrium. The prominence slab consists of two parts: a cool core where the plasma is optically thick for some lines, and a prominence-to-corona transition region (PCTR) with a strong temperature gradient. The models are defined by 5 parameters: temperature, pressure, slab thickness, microturbulent velocity and altitude. We solve the NLTE radiative transfer equations for all optically thick transitions. We present line ratios between infrared, optical and EUV lines, as well as line profiles. We show that the presence of a PCTR, where both collisional and radiative excitations are important, affects H, He, and Ca populations and emergent lines in different manners. Title: Spectral diagnostics of the magnetic field orientation in a round-shaped filament Authors: Schmieder, B.; Mein, N.; Heinzel, P.; Anzer, U. Bibcode: 2002ESASP.506..469S Altcode: 2002ESPM...10..469S; 2002svco.conf..469S 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 Lyman lines, the non-LTE radiative-transfer computations have shown the importance of the prominence-corona transition region (PCTR) and its relation to the magnetic field orientation for the explanation of the observed line profiles (Schmieder et al. 1998, Heinzel et al. 2001). Moreover, Heinzel and Anzer (2001) developed new 2D models which demonstrate how the shapes of Lyman lines vary depending on the orientation of the magnetic field with respect to the line of sight. To confirm 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 and we interpret these differences by the change of orientation of the prominence axis (and therefore the magnetic field direction) with respect to the line-of-sight. Title: Prediction of line intensity ratios in solar prominences Authors: Gouttebroze, P.; Labrosse, N.; Heinzel, P.; Vial, J. -C. Bibcode: 2002ESASP.505..421G Altcode: 2002solm.conf..421G; 2002IAUCo.188..421G Solar prominences are made of relatively cool and dense plasma embedded in the solar corona, supported and structured by the magnetic field. Since this plasma is definitely out of LTE, the diagnosis of physical conditions in prominences needs the use of specific radiative transfer (RT) codes to predict the spectrum emitted by models and compare it to observations. For optically thin lines, the solution of RT equations in the transition itself is not required, but the emitted intensities depend, via the statistical equilibrium equations, on RT in other transitions which are optically thick. We use two different sets of models. The first one contains monolithic models defined by 5 parameters: temperature, pressure, thickness, microturbulent velocity and altitude above the solar surface. For each parameter, we assume a range of variation. For each model, the values of the 5 parameters are randomly chosen within the corresponding range of variation. The second set contains composite models made of multiple layers, in order to simulate the penetration of radiation into inhomogeneous prominences. We use NLTE radiative transfer codes to compute the intensities of the lines of hydrogen, helium and calcium emitted by each model. So, for any couple of lines, we may obtained their intensity ratio as a function of the 5 parameters. We discuss the behaviour of some of these intensity ratios as a function of the principal parameters and construct distribution diagrams, which are compared to different published observations. Title: Calcium to hydrogen line ratios in solar prominences Authors: Gouttebroze, P.; Heinzel, P. Bibcode: 2002A&A...385..273G Altcode: The ratio of Ca II 8542 Å to Hβ line intensities has been used for a long time to diagnose the gas pressure in solar prominences. In this paper we reconsider the theoretical dependence of E(8542)/E(Hβ ) on the gas pressure, as originally computed by Heasley & Milkey (1978), and extend this theoretical correlation to higher pressures. Firstly, we revise the formation of calcium lines in prominences, using in parallel two independently developed NLTE radiative transfer codes. Computations consist of two subsequent steps: (i) the formation of hydrogen spectrum (treated in a similar way as in Gouttebroze et al. 1993), and (ii) the formation of calcium lines, using the electron-density structure obtained in step (i). The influence of hydrogen Lyman lines on Ca II to Ca III ionization is found to be very important for the determination of calcium-to-hydrogen line ratios. In particular, the intensities obtained for calcium lines at low pressures are significantly lower than those obtained by Heasley & Milkey (1978), which is the result of a greater Ca III/Ca II ratio. Our numerical results have been further checked against an approximate analytical model. Secondly, we have performed an extended computation using a large grid of models covering different temperatures, gas pressures, geometrical thicknesses, microturbulent velocities and prominence altitudes. For temperatures lower than 10 000 K and pressures lower than 0.1 dyn cm-2, the line ratio E(8542)/E(Hβ ) undergoes only small variations, remaining between 0.2 and 0.3. At higher pressures (0.1 to 1 dyn cm-2), the behaviour of this ratio appears to be strongly dependent on temperature: rapidly increasing below 6000 K, moderately increasing between 6000 and 8000 K, and generally decreasing at higher temperatures. A comparison of the present models with recent observations of Stellmacher & Wiehr (2000) suggests the existence of cool prominence structures with temperatures around 6000 K and gas pressures higher than 0.1 dyn cm-2. Title: Theoretical hydrogen population relations for horizontal cloud-like solar structures Authors: Tziotziou, K.; Mein, N.; Mein, P.; Heinzel, P. Bibcode: 2002ESASP.477..183T Altcode: 2002scsw.conf..183T A large set of parameterized NLTE models has been computed for a 1D horizontal cloud-like structure standing above the solar surface. The used input model parameters are temperature, velocity, microturbulence, electronic density and geometrical thickness of the structure. From the output of our computations which is the hydrogen level populations as a function of the line center optical depth, we calculate several relations between the hydrogen population levels and the considered electron density. These relations are important for the study of prominence-like structures from observations. Title: Diagnostics of electron bombardment in solar flares from hydrogen Balmer lines Authors: Kašparová, J.; Heinzel, P. Bibcode: 2002A&A...382..688K Altcode: Influence of non-thermal collisional rates, related to an electron beam, on hydrogen Balmer line profiles is investigated. Semi-empirical temperature structure of the flare model F1 has been used for computing non-LTE profiles of Hα , Hβ , and Hγ . Contribution functions and their change due to different values of beam parameters are shown. Unlike the line core intensity, the intensity of line wings considerably depends on beam parameters and it is significantly enhanced for typical values of the beam energy flux. The ratio of line intensities at a selected wavelength is proposed to be used for diagnostics of electron beams during solar flares, particularly at impulsive phases. Obtained Hα line profiles are compared to those of Fang et al. (\cite{fhg93}). Title: Understanding solar flares from optical observations Authors: Heinzel, P. Bibcode: 2002cosp...34E1097H Altcode: 2002cosp.meetE1097H During the impulsive phase of solar flares, both hard X-ray (HXR) and optical emissions exhibit fast temporal fluctuations detectable down to sub-second scales. This is usually ascribed to the propagation of beams of accelerated particles and to the dissipation of their energy in lower layers of the solar atmosphere. Although it is rather difficult to prove a temporal correlation between HXR and optical intensity variations, we discuss here some previous results and recent attempts. Namely in coordination with RHESSI observations, several GBO's started to detect fast optical variations in the H-alpha line. In addition to this, we also explore a possibility of using some other diagnostically relevant lines. The proper interpretation of coordinated HXR and optical observations further requires robust tools for radiation-hydrodynamical (RHD) forward modeling. We briefly describe a new 'hybrid' code which consists of RHD part and particle-simulation part. Short-duration beam heating (pulses) is modeled and we predict temporal fluctuations of HXR and selected optical and UV lines formed in chromospheric layers and in the transition region. Particularly the line asymmetries originating in a highly dynamical lower atmosphere of the flare can be used to diagnose the response of these layers to particle beams. Title: Why Are Solar Filaments More Extended in Extreme-Ultraviolet Lines than in Hα? Authors: Heinzel, P.; Schmieder, B.; Tziotziou, K. Bibcode: 2001ApJ...561L.223H Altcode: A long solar filament was observed simultaneously in the Hα line by THEMIS/MSDP and in selected EUV lines by the Coronal Diagnostic Spectrometer on SOHO. Co-alignment of optical and EUV images reveals that the dark EUV filament is much more extended than the Hα filament. Assuming that the EUV filament represents Lyman continuum absorption of the background EUV-line radiation, a straightforward explanation of this effect is suggested. Based on non-LTE filament models, we demonstrate that the ratio of the Lyman continuum to Hα opacity can reach a factor of 50-100, and thus the EUV filament is still well visible while the Hα line contrast diminishes below the detection limit. This kind of interpretation leads to an important conclusion that the cool filament material in which the Lyman continuum absorption takes place is more abundant than one would expect from Hα disk observations. This then may have significant consequences on the filament structure and on formation models, as well as on mass considerations related to coronal mass ejections. Title: Prominence fine structures in a magnetic equilibrium: Two-dimensional models with multilevel radiative transfer Authors: Heinzel, P.; Anzer, U. Bibcode: 2001A&A...375.1082H Altcode: In this paper we construct theoretical models for vertical prominence threads which are in magnetohydrostatic (MHS) equilibrium. These models are fully two-dimensional (2D) and take the form of vertically infinite threads hanging in a horizontal magnetic field. A typical example of such a 2D magnetic-dip structure is shown for the case when the central cool parts are surrounded by the prominence-corona transition region (PCTR). We display 2D variations of the pressure, density and temperature. While the pressure variations follow from the MHS equilibrium, the kinetic temperature was specified empirically. As a next step, we have solved the 2D multilevel non-LTE transfer problem in such thread-like structures, in order to predict the spatial variations of the emergent hydrogen spectrum. It is demonstrated that the hydrogen Lyman lines (treated with partial redistribution) show significant spatial variations of the intensity and that an important difference exists between the line profiles emergent along and across the magnetic field lines. We also discuss how these intensity variations compare to recent SOHO/SUMER prominence observations, namely we show the effects of line-profile averaging over the fine-structure threads which are below the instrumental resolution. Finally we make some suggestions for future modelling and observations. Title: A Study of Hydrogen Density in Emerging Flux Loops from a Coordinated Transition Region and Coronal Explorer and Canary Islands Observation Campaign Authors: Mein, N.; Schmieder, B.; DeLuca, E. E.; Heinzel, P.; Mein, P.; Malherbe, J. M.; Staiger, J. Bibcode: 2001ApJ...556..438M Altcode: During an international ground-based campaign in the Canary Islands coordinated with space instruments (i.e., Transition Region and Coronal Explorer [TRACE]), we observed an active region on 1998 September 10 with high spatial and temporal resolution. New emerging flux in the central part of the active region was observed in magnetograms of the Swedish Vacuum Solar Telescope, La Palma. Emerging loops (arch-filament systems [AFSs]) are well developed in Hα and Ca II according to the observations made at the Vacuum Tower Telescope (VTT) and THEMIS telescope in Tenerife with the Multichannel Subtractive Double Pass (MSDP) spectrographs. The TRACE images obtained at 171 and 195 Å show low-emission regions that are easily identified as the individual AFS. They are due to absorption by hydrogen and helium continua in the cool filament plasma. We compare two techniques of measuring the hydrogen density in the cool dense fibrils of AFSs. The first method based on TRACE observations derived the neutral hydrogen column density of the plasma absorbing coronal lines. The second one using Hα line profiles provided by the MSDP spectrographs is based on the cloud model. The results are consistent. We derive also electron density values using Hα lines that are in good agreement with those derived from the 8542 Å Ca II line observed with THEMIS (Mein et al.). The three types of observations (TRACE, VTT, THEMIS) are well complementary: absorption of coronal lines giving a good approximation for the maximum value of the neutral hydrogen column density, the Hα line giving a good determination of ne, and the 8542 Å Ca II line a good determination of the electronic temperature. Title: SOHO/SUMER observations and analysis of the hydrogen Lyman spectrum in solar prominences Authors: Heinzel, P.; Schmieder, B.; Vial, J. -C.; Kotrč, P. Bibcode: 2001A&A...370..281H Altcode: The complete hydrogen Lyman spectrum in several prominences has been observed with the UV spectrometer SUMER on-board the SOHO, during the Joint Observing Programme 107, together with other space and ground-based observatories. Based on these observations, we are able to demonstrate, for the first time, that there exists a large variety of intensities and shapes of Lyman lines in different prominences and in various parts thereof. Therefore, no ``canonical'' Lyman spectrum can be considered for modelling purposes. However, we have identified at least two representative properties of the observed spectra: in one case (May 28, 1999 prominence) we detected high integrated intensities and no reversals in lines higher than Lalpha . Another prominence (June 2, 1999) exhibited quite similar integrated intensities, but all lines have rather strongly reversed profiles. This behaviour cannot be explained in terms of standard isothermal-isobaric models and we thus consider more general models which are in pressure equilibrium with the magnetic field and which have significant prominence-corona transition region (PCTR) temperature gradients. This type of model, recently suggested by Anzer & Heinzel (\cite{anhe99}), is capable of explaining strong emission profiles without reversal. Based on extended non-LTE computations, we suggest that quite different Lyman spectra mentioned above may correspond to two types of PCTRs, one seen along the magnetic-field lines (unreversed profiles) and the other one seen across the field lines (reversed profiles). Finally, we again confirm the importance of partial-redistribution (PRD) scattering processes for Lyman lines in prominences. However, our analysis of new SUMER data also points to a critical role of the PCTR in radiative transport in these lines. Title: Non-LTE inversion of chromospheric {\Ca Ii} cloud-like features Authors: Tziotziou, K.; Heinzel, P.; Mein, P.; Mein, N. Bibcode: 2001A&A...366..686T Altcode: A chromospheric cloud-like feature observed in the 8542 Å {{Ca Ii} line is studied by a two step inversion procedure which provides estimates of its temperature, electronic density, microturbulence, geometrical thickness and bulk velocity. The first step involves the computation of a large grid of models by a multi-level non-LTE transfer code which gives the {{Ca Ii} line depth-dependent mean intensity inside an isolated, isothermal cloud lying above the chromosphere. The second step involves the inversion of the observed profiles with the grid of computed synthetic {{Ca Ii} profiles. A searching and matching chi 2 algorithm is implemented followed by an interpolation algorithm which permits a more accurate determination of the parameters on which the profiles depend. The five grid parameters are reduced to four by defining the emission measure from the geometrical thickness and electronic density. We show that this inversion procedure gives accurate results for some of our inversion parameters when dealing with solar filaments and is complementary to a previous study of the same object in the {{Hα }} line. The main advantages, problems and future extension of the inversion approach are also discussed. Title: Simultaneous SOHO and Ground-Based Observations of a Large Eruptive Prominence and Coronal Mass Ejection Authors: Plunkett, S. P.; Vourlidas, A.; Šimberová, S.; Karlický, M.; Kotrč, P.; Heinzel, P.; Kupryakov, Yu. A.; Guo, W. P.; Wu, S. T. Bibcode: 2000SoPh..194..371P Altcode: Coronal mass ejections (CMEs) are frequently associated with erupting prominences near the solar surface. A spectacular eruption of the southern polar crown prominence was observed on 2 June 1998, accompanied by a CME that was well-observed by the LASCO coronagraphs on SOHO. The prominence was observed in its quiescent state and was followed throughout its eruption by the SOHO EIT and later by LASCO as the bright, twisted core of the CME. Ground-based Hα observations of the prominence were obtained at the Ondřejov Observatory in the Czech Republic. A great deal of fine structure was observed within the prominence as it erupted. The prominence motion was found to rotate about its axis as it moved outward. The CME contained a helical structure that is consistent with the ejection of a magnetic flux rope from the Sun. Similar structures have been observed by LASCO in many other CMEs. The relationship of the flux rope to other structures in the CME is often not clear. In this event, the prominence clearly lies near the trailing edge of the structure identified as a flux rope. This structure can be observed from the onset of the CME in the low corona all the way out to the edge of the LASCO field of view. The initiation and evolution of the CME are modeled using a fully self-consistent, 3D axisymmetric, MHD code. Title: Energy considerations for solar prominences with mass inflow Authors: Anzer, U.; Heinzel, P. Bibcode: 2000A&A...358L..75A Altcode: In this Letter we study the inflow of enthalpy and ionisation energy into solar prominences. We use 1D stationary slab models for the prominence to calculate this inflow. We compare the resulting energy gain with the integrated radiative losses obtained for such slab models. We find that for reasonable inflow velocities many of our models can be in energy equilibrium; only the very massive prominences will either require some additional heating or they have to cool down to low central temperatures. We also discuss the possibility or heating the prominence by vertical downflows. Title: Decaying post-flare loops system observed by SOHO/CDS and Yohkoh/SXT Authors: Varady, M.; Fludra, A.; Heinzel, P. Bibcode: 2000A&A...355..769V Altcode: The results of an analysis of joint SOHO/CDS and Yohkoh/SXT observations of a decaying post-flare loops system with a rapid time evolution are presented. The loop system was a remnant of a small single loop flare (GOES class C2.9). Using the CDS raster taken in several EUV lines with different formation temperatures and a temperature sensitive line pair Fe XVI 360.8/Si XII 520.7 we confirmed the existence of the vertical stratification in the loop system according to the line formation temperature. The analysis of the SXT data showed a strong decay of the system with time. While the temperature of the hot part of the system (T =~ 2.5 MK) decreased only slightly, the total emission measure dropped by more than a factor of four in approximately 103 s. This could be explained by a plasma outflow from the loops with velocity approximately 10 km/s. On the other hand, signs of rapid, probably radiative cooling can be identified in the images obtained from the CDS raster taken in cool lines of O V and O III. Using the density sensitive line pair of Fe XIV 334.2/353.8 and the integrated intensity of Fe XIV 334.2 line we determined the electron densities and emission measures across the top of the loop system. From the results of these measurements, taking all known uncertainties into account, we obtained that the geometrical filling factor at the top of the system in the regions with maximum electron density in the Fe XIV line lies in the interval from =~ 0.01 to =~ 0.2. A simple theoretical approximation of the energy balance in the post-flare plasma gives a total cooling time =~ 750 s. Title: Solar arch filaments observed with THEMIS Authors: Mein, P.; Briand, C.; Heinzel, P.; Mein, N. Bibcode: 2000A&A...355.1146M Altcode: Arch Filaments (AF) have been observed in the Ca Ii 8542 Å line with the THEMIS telescope in September 1998. We present a preliminary analysis of MSDP spectro-imaging data. A cloud-model fit provides line-of-sight velocities and a set of plausible values for the model parameters. The high sensitivity of the filament opacity to temperature, coupled with the rough linearity versus electronic density, shows that this Ca Ii line should be very efficient to complement usual Hα data for a more rigorous diagnostics. Based on observations made with the THEMIS telescope operated on the island of Tenerife by CNRS-CNR in the spanish Observatorio del Teide of the Instituto de Astrofisica de Canarias Title: Study of Chromospheric Ca II Cloud-like Structures Authors: Tziotziou, K.; Heinzel, P.; Mein, P.; Mein, N. Bibcode: 2000ESASP.463..443T Altcode: 2000sctc.proc..443T No abstract at ADS Title: Commission 12: Solar Radiation and Structure (Radiation et Structure Solaires) Authors: Foukal, Peter; Solanki, Sami; Mariska, J.; Baliunas, S.; Dravins, D.; Duvall, T.; Fang, C.; Gaizauskas, V.; Heinzel, P.; Kononovich, E.; Koutchmy, S.; Melrose, D.; Stix, M.; Suematsu, Y.; Deubner, F. Bibcode: 2000IAUTA..24...73F Altcode: No abstract at ADS Title: Models of the solar atmosphere Authors: Heinzel, P. Bibcode: 2000ASIC..558..201H Altcode: 2000asre.conf..201H Contents: Basic equations of radiation hydrodynamics. Solution of NLTE problems. Semiempirical models of the solar atmosphere. Dynamical models. Title: Phase Relations between Chromospheric and Transition Region Oscillations Authors: Krijger, J. M.; Curdt, W.; Heinzel, P.; Schmidt, W. Bibcode: 2000ESASP.463..353K Altcode: 2000sctc.proc..353K No abstract at ADS Title: Solar Prominences Observed by Soho (SUMER, CDS, EIT) and Ground-Based Observatories (GBO) Authors: Heinzel, P.; Schmieder, B.; Vial, J. C.; Rudawy, P. Bibcode: 2000AdSpR..25.1777H Altcode: We present two sets of prominence observations in higher lines of the hydrogen Lyman series (from Lδ to L-9), together with some other UV lines. These data have been obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) onboard the SOHO satellite in June 1997. Coordinated observations were also taken by other SOHO instruments: Coronal Diagnostic Spectrometer (CDS) and Extreme-Ultraviolet Imaging Telescope(EIT) and with the coronagraph of the Wroclaw University Observatory at Bialkóv, the spectrograph of the Ondřejov Observatory. We demonstrate the basic characteristics of the calibrated line profiles and compare them with the theoretical profiles computed from isothermal-isobaric models Title: Chromospheric Response to a Short-Duration Beam Heating: Observing Programme and Numerical Simulations Authors: Heinzel, P.; Karlický, M.; Kotrč, P.; Kupryakov, Yu. A. Bibcode: 2000ASPC..206..289H Altcode: 2000hesp.conf..289H No abstract at ADS Title: Diagnostics Constraints on Prominence Parameters from SOHO and Ground-based Observations Authors: Schmieder, B.; Kotrč, P.; Heinzel, P.; Kucera, T.; Andretta, V. Bibcode: 1999ESASP.448..439S Altcode: 1999ESPM....9..439S; 1999mfsp.conf..439S No abstract at ADS Title: Simultaneous Observations of Chromospheric and Transition Region Oscillations in HI Lyman Transitions and in Optical Lines Authors: Curdt, W.; Heinzel, P.; Schmidt, W.; Tarbell, T.; von Uexküll, M.; Wilken, V. Bibcode: 1999ESASP.448..177C Altcode: 1999mfsp.conf..177C; 1999ESPM....9..177C No abstract at ADS Title: Decaying Post-Flare Loops System Observed By SOHO/CDS And Yohkoh/SXT Authors: Varady, M.; Fludra, A.; Heinzel, P. Bibcode: 1999ESASP.446..669V Altcode: 1999soho....8..669V The results of an analysis of joint CDS of SOHO and SXT of Yohkoh observations of a decaying post-flare loop system are presented. The SXT images were used to explain some peculiar structural features visible in the examined CDS raster, resulting from the rapid evolution of the observed system and from the way the CDS rasters are built. The SXT data was also used to determine the time evolution of the temperature and the emission measure of the hot part of the system during its decay. The CDS data, with a very good temperature coverage, contains a density sensitive line pair of Fe XIV which was used for electron density analysis and a temperature sensitive line pair of Fe XVI and Si XII which was used to study the temperature structure of the loop system. From the integrated intensities of selected lines the emission measures were calculated. From these measurements we estimated the filling factor of the loop system in Fe XIV line. Title: Hydrogen Lyman Lines and Continuum Emission in a Polar-Crown Prominence Observed with SUMER/SOHO Authors: Schmieder, B.; Kucera, T.; Heinzel, P.; Vial, J. -C. Bibcode: 1999ESASP.446..605S Altcode: 1999soho....8..605S We present, for the first time, a quasi-simultaneous spectroscopic observation of the whole Lyman series of HI and continuum in a quiescent prominence. Namely we have extended our previous study of higher Lyman lines to lower members of the series, particularly L-alpha and L-beta. For the latter two lines, we compare our calibrated profiles (free of geocoronal absorption) with previous data from OSO-8 LPSP spectrometer and (for L-alpha) from UVSP/SMM. We demonstrate the importance of Lyman lines for studies of the base of the prominence-corona transition region. Title: SOHO/SUMER observations and analysis of hydrogen Lyman lines in a quiescent prominence Authors: Schmieder, B.; Heinzel, P.; Vial, J. C.; Rudawy, P. Bibcode: 1999SoPh..189..109S Altcode: A quiescent prominence was observed in June 1997 by instruments onboard the SOHO spacecraft: the Solar Ultraviolet Measurements of Emitted Radiation (SUMER), Coronal Diagnostic Spectrometer (CDS) and Extreme-Ultraviolet Imaging Telescope (EIT), along with the coronagraph of the Wrocław University Observatory at Bialków and the spectrograph of the Ondřejov Observatory. We present prominence observations in higher lines of the hydrogen Lyman series (from Lδ to L-9), together with some other UV lines obtained by SUMER. We extract the basic characteristics of the calibrated line profiles of these Lyman lines and compare them with the theoretical profiles computed from three kinds of NLTE models which also include prominence filamentation. Our principal result is that the current NLTE models are in principle capable of explaining the SUMER calibrated intensities in the observed Lyman lines. We also find that in order to fit all these lines, one has to consider a prominence-corona transition region (PCTR) with a temperature gradient. At low pressures, higher Lyman lines are still rather sensitive to the incident radiation which must be carefully taken into account in the modeling. From PCTR models, which also take into account the effect of ambipolar diffusion on the heating, we have derived the formation depths for the Lyman series lines. High Lyman lines seem to be formed just at the base of the PCTR. Title: Coordinated Prominence Observations by SOHO and Ground-Based Observatories Authors: Schmieder, B.; Heinzel, P.; Vial, J. -C.; Malherbe, J. M.; Mein, P.; Rudawy, P.; Ceppatelli, G. Bibcode: 1999ASPC..184..296S Altcode: Coordinated observations obtained during the JOP12 (Joint Observing Programme between SOHO and ground-based instruments) allow us to analyse the physical conditions in a prominence of 5 June 1997 and its environment in the solar corona. The arch-shaped prominence shows either vertical or horizontal structures according to the observed lines (Hα with the coronagraph of the Wroclaw University Observatory at Bialków and lines in a broad temperature range by the Coronal Diagnostic Spectrometer CDS). The less dynamic behaviour of this prominence was shown by the persistence of bubbles in the prominence and confirmed by the Dopplershifts measured in CDS lines and in Hα by the Italian Panoramic Monochromator (IPM) filter on the THEMIS telescope in Tenerife. We explain the complex morphology of this prominence by recent 3D MHD models. Finally, we present prominence spectra in higher lines of the hydrogen Lyman series (from Lδ to L-9), together with some other UV lines. These data have been obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER). We demonstrate the basic characteristics of the calibrated line profiles of Lyman lines and compare them with the theoretical profiles computed from isothermal-isobaric models. This leads to some constraints on the environment of the prominence. Title: Chromospheric Oscillations Observed by SUMER/SOHO Authors: Heinzel, P.; Curdt, W. Bibcode: 1999ASPC..184..201H Altcode: We discuss first observations of the temporal behaviour of the hydrogen Lyman lines made by the SUMER/SOHO spectrometer. Using the Ly 5 line, we show here the global oscillatory pattern of the whole line profile for three representative quiet-Sun structures: cell interior, network boundary, and bright network. Mean power spectra for these structures show several maxima, some of which are quite well correlated with the maxima derived from Ca II K_2V observations. In the cell interior, the power peak is centred between 4.5-5 mHz. No clear evidence of a 3 minute chromospheric mode was found. In the network, we observe a broad range of frequencies, with a maximum between 2-3 mHz. Lyman lines exhibit certain Doppler shifts and asymmetries, but the oscillatory behaviour is mainly due to the intensity variations which are small compared to the line intensity itself (they reach 10-20 % of the mean line intensity). Title: The energy balance in solar prominences Authors: Anzer, U.; Heinzel, P. Bibcode: 1999A&A...349..974A Altcode: In this paper we study the energy balance in quiescent solar prominences. For this investigation we use a simple 1D slab model in magneto-hydrostatic equilibrium. We divide the studied region into two parts: The inner region consisting of the prominence itself and the cool part of the transition region (up to 30000 K). In this region the plasma is optically thick in several atomic transitions and therefore we have to solve the non-LTE radiative transfer problem in this part. This allows us to derive self-consistently the gas density, the ionization degree of hydrogen and the hydrogenic radiation losses. The energy transport by thermal conduction can be neglected in this region. In the outer part of the transition region, the thermal conduction becomes very important but the treatment of radiation is simplified by the fact that the plasma is optically thin. We find that energy balance in prominences can only be obtained for special forms of the heating function. This requirement is very stringent for the inner parts, while in the outer region thermal conduction can transport large amounts of the heat energy and therefore a wider class of heating functions will be allowed. Title: Proton and hydrogen temperatures at the base of the solar polar corona Authors: Marsch, E.; Tu, C. -Y.; Heinzel, P.; Wilhelm, K.; Curdt, W. Bibcode: 1999A&A...347..676M Altcode: The SUMER (Solar Ultraviolet Measurements of Emitted Radiation) Spectrometer on SOHO (Solar and Heliospheric Observatory) has been used to observe the lines of the Lyman series (up to quantum numbers larger than 20) of hydrogen emitted in the solar atmosphere. The line shapes and intensities versus height are obtained near the limb from about -10\arcsec to 70\arcsec. The lines are broad and show the typical self-absorption reversal near the limb, where the emission comes from optically thick material, and change systematically with increasing height. The H i Ly6, Ly7 and Ly9 lines attain a Gaussian shape at heights above the visible limb between about 19\arcsec and 22\arcsec, where the emission comes from an optically thin plasma. The line shapes and intensities can be fitted well by model profiles obtained from multilevel NLTE (Non Local-Thermodynamic-Equilibrium) radiative transfer calculations which allow us, assuming excitation and ionization equilibrium, to derive consistently the temperatures and densities of the hydrogen atoms and, with additional assumptions, of the protons. Temperature values range between 1 10(5) K to 2 10(5) K. We present the systematics of the line shapes as observed in different emission regions and discuss briefly the relevance of these results for the solar wind acceleration and coronal heating. Title: Cloud model with variable source function for solar Hα structures. II. Dynamical models Authors: Heinzel, P.; Mein, N.; Mein, P. Bibcode: 1999A&A...346..322H Altcode: It was demonstrated in the previous paper (Paper I)that the cloud model technique can be largely improved if one considers realistic boundary conditions in evaluating the true form of the line source function. For structures seen against the solar disk, the Hα line source function is decreasing from bottom towards the top. In the present paper we investigate the effect of Doppler brightening on Hα source function. In frame of 1D non-LTE models it is demonstrated how the Hα line source function is increased depending on the velocity of the moving cloud and direction of the motion. For the same set of cloud models as used in Paper I, we have reevaluated the variations of the source function with optical depth including the effect of cloud motion. The resulting curves have been approximated by a second-degree polynomial and the respective coefficients have been subsequently used in a modified iterative method in order to derive the cloud model parameters. As expected, dynamical models lead to more precise specification of these parameters, namely the optical thickness, as compared to the static case investigated in Paper I. We have applied this new method to MSDP observations of a dark chromospheric feature (loop) with considerable flows. Title: A non-LTE inversion procedure for chromospheric cloud-like features Authors: Molowny-Horas, R.; Heinzel, P.; Mein, P.; Mein, N. Bibcode: 1999A&A...345..618M Altcode: A fast inversion procedure which provides estimates of the temperature, electronic density, microturbulence, geometrical thickness and bulk velocity of chromospheric features, so-called ``clouds'', has been implemented. The procedure has been divided into two steps: 1) the construction of a large grid of models by means of a multi-level non-LTE transfer code, which solves in a fast and reliable way the radiative transfer problem of the formation of the Hα line inside an isolated, isothermal cloud laying above the photosphere, and 2) the implementation of searching, matching and interpolating algorithms which yield an inversion of the observed line profile in terms of the grid's computed profiles. The aforementioned 5 parameters, on which the profiles depend, can be reduced to 4 if one defines the so-called emission measure from the geometrical thickness and electronic density parameters. We show that this strategy yields excellent results when dealing with solar filaments. The main advantages of this approach are also discussed. Title: Magnetic Dips in Prominences Authors: Heinzel, P.; Anzer, U. Bibcode: 1999SoPh..184..103H Altcode: Magnetic dips are generally assumed to be basic equilibrium configurations in quiescent solar prominences. Here we discuss two types of the magnetic dips which were considered in the literature: (1) dips resulting from a force-free magnetic equilibrium in the corona, and (2) magnetic dips which are formed in situations where the Lorentz force balances the weight of the prominence plasma. An important parameter which decides between these two cases is the plasma β. For β⋘1, the effect of the prominence material on the equilibrium structure is quite negligible and the case (1) holds. If, however, β is larger, say between 0.1 and 1 or even higher, magnetic dips of the second kind are formed and they can be characterized by the angle ψ1 between the vertical and the direction of the field lines at the surface of the prominence structure. A simple and illustratory formula is derived to relate this angle to the plasma β at the prominence center, namely βc≃cot2ψ1. βc=1 thus corresponds to ψ1=45°. Finally, we discuss the range of values of both βc and ψ1 as deduced from various observations and conclude that the dips of the second kind are important for the prominence equilibria. We also suggest a new method for determination of the field-line inclination. Title: Eruptive filament of May 31, 1997, observed by SOHO. Authors: Schmieder, B.; Heinzel, P.; Vial, J. -C.; Delaboudinière, J. -P.; Delannée, C. Bibcode: 1999joso.proc..147S Altcode: In the frame of the SUMER/CDS Joint Programme (JOP 17) the authors have detected the four Lyman lines in an erupting filament. The strong self-absorption in these lines, already reported for quiescent filaments, is still present in this highly dynamical event, but the authors observe a significant red asymmetry in the intensities of the two peaks. They ascribe it to an upward bulk motion of the filament, which they can actually see on a series of EIT images taken in the Fe XII line. Both sets of observations can lead to a determination of the velocity vector. The Doppler velocities are also derived from other lines detected by SUMER/CDS and can be correlated with the observations of the Pic-du-Midi MSDP obtained for this event. The filament eruption was also well observed by other GBO instruments in the Hα line (Meudon and Ondřejov). Title: Chromospheric Oscillations Observed by SOHO/SUMER and VTT/GCT on Tenerife Authors: Curdt, W.; Heinzel, P.; Schmidt, W.; von Uexküll, M.; Wilken, V. Bibcode: 1999AGAb...15R..11C Altcode: 1999AGM....15..A12C Previous studies have revealed various oscillations in higher Lyman lines of hydrogen, as observed with SUMER on SOHO (Curdt & Heinzel 1998). The assumption that these periodic phenomena might be related to similar effects observed in optical lines like Ca II K led to the idea of simultaneous observations with the SOHO/SUMER instrument and the VTT/GCT telescopes on Tenerife. First results are presented here for the Lyman series and Lyman continuum. Power spectra in network and internetwork regions have been derived and a preliminary interpretation based on the wave propagation concept is given. In SUMER spectra we found a well-pronounced asymmetry of all Lyman lines, which is related to atmospheric dynamics. The time variation of co-spatial UV and optical data is presented and basic characteristics are discussed. Title: Non-LTE inversions of solar filament in Hα profiles. Authors: Molowny-Horas, R.; Mein, P.; Mein, N.; Heinzel, P. Bibcode: 1999joso.proc..209M Altcode: Results are shown of a new grid-based, non-LTE inversion procedure which can carry out fast and accurate spectral inversions of Hα line profiles. The code has been applied to a set of observed MSDP Hα line profiles of a solar filament. The results of this inversion are shown as 2-D maps of temperature, microturbulence and emission measure. Title: Dynamic Behavior of the Upper Solar Atmosphere: Sumer/ Solar and Heliospheric Observatory Observations of Hydrogen Lyman Lines Authors: Curdt, Werner; Heinzel, Petr Bibcode: 1998ApJ...503L..95C Altcode: We present first observations of the temporal evolution of hydrogen Lyman lines, made by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory. A time series of about 33 minutes was obtained on 1997 June 5. The entrance slit has crossed a quiet-Sun region of 115.3" with two internetwork structures (cells) and the bright network regions. A data set of 59 spectra with30 s exposure time was obtained, using the SUMER tracking system to compensate for the solar rotation. For our analysis, we have selected a Lyman continuum window around 907 Å and the three Lyman lines Ly5, Ly9, and Ly15, which are formed at different depths in the upper chromosphere. In the cell interiors, we have detected significant periodic intensity variations with a Fourier transform power peak at 3.3-3.5 minutes, which is consistent with 3 minute internetwork oscillations. They seem to be associated with spatially unresolved ``clusters'' of grains. In the bright network regions, we detect slower oscillations of 6.9-7.6 minutes. These waves seem to propagate upward as we deduce from a phase shift between the three Lyman lines studied. The phase velocity was estimated to be roughly 3 km s-1 in the network. Finally, we discuss the potential usefulness of the hydrogen Lyman lines for diagnostics of the temperature structure of the upper solar atmosphere. Our observations, in particular the fact that we see all Lyman lines in emission all of the time, put certain constraints on the temperature gradients above the region in which numerical simulations do predict a decrease of the mean kinetic temperature. Title: Filament Observations with SOHO Sumer/cds: The Behaviour of Hydrogen Lyman Lines Authors: Schmieder, B.; Heinzel, P.; Kucera, T.; Vial, J. -C. Bibcode: 1998SoPh..181..309S Altcode: On 21 September 1996, a filament close to an area of enhanced network was observed with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer and Coronal Diagnostic Spectrometer (CDS). CDS provided intensity, Doppler shift and linewidth maps of the region in six lines whose temperature range covers 104 to 106 K. SUMER observations consisted of maps of the region in four hydrogen Lyman lines (Lδ, L∈, L-6, L-7) and a Svi line (944 Å). In all the Lyman lines we detect a central absorption and an asymmetry in the intensity of the two peaks. First NLTE computations indicate that such reversed Lyman profiles and their absolute intensities can be reproduced with the existing filament models provided that we take into account a prominence-corona transition region (PCTR). We discuss the Lyman lines' asymmetry in terms of macroscopic flows by comparison with the Hei line Doppler shifts observed with CDS. Title: Prominence Parameters Derived from Magnetic-Field Measurements and NLTE Diagnostics Authors: Anzer, U.; Heinzel, P. Bibcode: 1998SoPh..179...75A Altcode: In this paper we present a detailed analysis of a number of quiescent prominences for which the components of the magnetic field as well as the electron density and emission measure were previously obtained from quasi-simultaneous measurements in hydrogen Hα and helium D3 lines. From magnetic equilibrium models of the Kippenhahn-Schlüter type one can calculate the gas pressure, density, column mass and geometrical width. The same set of physical parameters can also be derived from a NLTE hydrogen-line analysis. We have studied the mutual correlations between these two sets of parameters. Very large differences, reaching an order of magnitude, were found between these two sets, both for individual prominences and for the mean values over all prominences used in this investigation. Finally, we discuss some implications of our results. Title: Lyman Lines in Prominences and Filaments: NLTE ModellingStrategies Authors: Heinzel, P. Bibcode: 1998ASPC..150..188H Altcode: 1998IAUCo.167..188H; 1998npsp.conf..188H No abstract at ADS Title: SUMER/SOHO Filament Observations in Selected Lyman Lines Authors: Schmieder, B.; Kucera, T.; Heinzel, P.; Vial, J. -C. Bibcode: 1998ASPC..150..205S Altcode: 1998IAUCo.167..205S; 1998npsp.conf..205S No abstract at ADS Title: 2-D Radiative Transfer Simulations with Angle-Dependent Partial Frequency Redistribution Authors: Gorshkov, A. B.; Heinzel, P. Bibcode: 1998ASPC..150..209G Altcode: 1998IAUCo.167..209G; 1998npsp.conf..209G No abstract at ADS Title: XIVth consultation on solar physics : conference proceedings Authors: Rompolt, B.; Jakimiec, J.; Heinzel, P. Bibcode: 1998PAICz..88.....R Altcode: No abstract at ADS Title: Modelling of Non-Uniform Prominence Slabs Authors: Heinzel, P.; Anzer, U. Bibcode: 1998ASPC..150..213H Altcode: 1998IAUCo.167..213H; 1998npsp.conf..213H No abstract at ADS Title: New Evidence of Chromospheric Evaporation Authors: Kasparova, J.; Kotrc, P.; Heinzel, P.; Nikulin, I. F.; Rudawy, P. Bibcode: 1998ASPC..150..397K Altcode: 1998IAUCo.167..397K; 1998npsp.conf..397K No abstract at ADS Title: Height variations of prominence plasma parameters Authors: Kotrč , P.; Heinzel, P.; Vial, J. -C.; Rompolt, B. Bibcode: 1998PAICz..88..208K Altcode: No abstract at ADS Title: Problems in prominence NLTE modeling Authors: Heinzel, P. Bibcode: 1998PAICz..88..195H Altcode: No abstract at ADS Title: Filament observations with SOHO SUMER/CDS. Authors: Schmieder, B.; Kučera, T.; Heinzel, P.; Vial, J. -C. Bibcode: 1998joso.proc..136S Altcode: During a coordinated campaign between SOHO and ground-based instruments a filament located close to the central meridian has been the target of SUMER and CDS spectrometers on September 21, 1996. Title: A chromospheric response to pulse beam heating (abstract) Authors: Heinzel, P. Bibcode: 1998PAICz..88..137H Altcode: No abstract at ADS Title: Flare Multi-Line 2D-SPECTROSCOPY Authors: Mein, P.; Mein, N.; Malherbe, J. -M.; Heinzel, P.; Kneer, F.; von Uexkull, M.; Staiger, J. Bibcode: 1997SoPh..172..161M Altcode: 1997ESPM....8..161M A small flare was observed at the Teide Observatory on October 5, 1994. Simultaneous data were obtained at the German Vacuum Tower Telescope (VTT) with the MSDP spectrograph providing high-resolution imaging spectroscopy in two chromospheric lines, and the Gregory Coudé Telescope (GCT) providing information about the magnetic field. Basic flare characteristics are: Title: Formation of CA II Lines in Solar Prominences Authors: Gouttebroze, P.; Vial, J. -C.; Heinzel, P. Bibcode: 1997SoPh..172..125G Altcode: 1997ESPM....8..125G We compute the profiles of the resonance lines and infrared triplet of ionized calcium emitted by some representative models of prominences. These models consist of plane-parallel slabs of different temperatures, pressures and thicknesses, standing vertically above the solar surface. These slabs are assumed to be observed at the limb, and to be perpendicular to the line of sight. They are irradiated by the Sun on both sides, and the incoming intensities, at every relevant wavelength, are taken from observations. The model atom includes 3 stages of ionization (Cai, Caii and Caiii) with 5 discrete levels for Caii. We study the relations between emitted intensities and physical properties of the slabs, and compare the intensities emitted in Caii and hydrogen lines for the same set of models. As a result of ionization, the intensity decreases more rapidly with temperature in Caii lines than in Hi lines, so that the ratio of Caii to Hi line intensities may be used as a temperature indicator. The intensity ratio between resonance and infrared lines of Caii depends principally on the optical thickness of the structure. At high pressure and low temperature, the ratio Caii 8542Å/Hβ is found to increase with pressure. This behaviour, which is due to the saturation of Hβ, is opposite to that found by Heasley and Milkey (1978) for low pressures (optically thin structures). Title: Optical and Radio Spectral Analysis of a Recurrent Surge Authors: Kotrč, Pavel; Schmieder, Brigitte; Karlický, Marian; Heinzel, Petr Bibcode: 1997SoPh..172..199K Altcode: 1997ESPM....8..199K Coordinated observations obtained at Meudon (MSDP) and at Ondřejov provide surge spectra in optical range (Hα, Hβ, Hγ, Hµ, Ca H and K lines) and in radio range. The MSDP data allowed us to follow the time evolution of the surge. The spectra of Balmer lines were used to derive the electron density of the expelled cool material. The radio bursts indicate that the acceleration of electrons took place in the low and dense atmosphere, giving a good argument for a reconnection near the transition region. Title: Solar and heliospheric plasma physics. Proceedings. 8th European Solar Physics Meeting, Halkidiki (Greece), 13 - 18 May 1996. Authors: Heinzel, P.; Simnett, G. Bibcode: 1997SoPh..172....1H Altcode: 1997ESPM....8....1H The main topic was the interaction of the Sun with the heliosphere, focused on first results from SOHO and new results from Ulysses. The following topics were dealt with: solar dynamos, solar shape, convection zone, solar pulsations, solar activity, solar atmosphere, solar corona, solar spectra, solar prominences, solar flares, UV spectra, solar wind, radiowave emissions, solar instruments. Title: NLTE Analysis of SUMER Filament Observations on SOHO Authors: Heinzel, P.; Schmieder, B.; Vial, J. -C. Bibcode: 1997ESASP.404..427H Altcode: 1997cswn.conf..427H No abstract at ADS Title: A Comparison of Two Approximations for the Cooling of Hot Post-Flare Loops Authors: Varady, M.; Heinzel, P. Bibcode: 1997ESASP.404..705V Altcode: 1997cswn.conf..705V No abstract at ADS Title: Dynamics and evolution of the post-flare loops of June 1992 Authors: Wiik, J. E.; van Driel-Gesztely, L.; Schmieder, B.; Heinzel, P. Bibcode: 1997AdSpR..20.2345W Altcode: Observations in X-rays (Yohkoh/SXT) and in Hα of a system of post-flare loops which developed after a flare on 25 June 1992 provide a unique set of data for a study of the relationship between the hot and cool post-flare loops as they evolve. Through a study of the magnetic configuration in which the flare occurred, we are able to reconstruct the true, 3D geometry of the loops. We derive the bulk-flow velocities along the loop as a function of height using Doppler velocities and the results from the loop reconstruction. We also provide a set of relative altitude data. These results are used to check the validity of the reconnection model in the frame of the cooling time needed to cool X-ray loops to Hα temperature. Title: Structure and Dynamics of Post-Flare Loops Authors: Varady, M.; Heinzel, P. Bibcode: 1997HvaOB..21...33V Altcode: We briefly review basic properties of the post-flare loops and their structural and dynamical characteristics. Several new results have been recently published using the Yohkoh SXT images, simultaneously obtained with high-resolution H-alpha data. We pay a particular attention to the problem of cooling times of hot loops. Title: Post-Flare Loops of 26 June 1992, III Authors: Wiik, J. E.; Schmieder, B.; Heinzel, P.; Roudier, T. Bibcode: 1996SoPh..166...89W Altcode: Post-flare loops were observed on June 26, 1992 in the Hα line with the Multichannel Subtractive Double-Pass spectrograph (MSDP) on Pic-du-Midi and with the Swedish telescope on La Palma. The highly dynamic loops are inhomogeneous (blobs). The cool loops were observed 10-12 hours after the X 3.9 class flare which had a maximum on June 25 at 20∶11 UT. From 2D images obtained with the MSDP on June 26 we derive Hα intensities and Doppler velocities of the loop plasma. Using a geometrical reconstruction technique we show that these loops are mainly perpendicular to the solar surface and have the shape of a dipole magnetic configuration. We derive the bulk-flow velocities along the loop as a function of height using the Doppler velocities and the results from the loop reconstruction. Where the Doppler velocities are too small, we derive the bulk-flow velocities from the displacements of the falling blobs. We discuss existing deviations from free-fall velocity in the lower parts of the loops. Title: Post-Flare Loops of 26 June 1992, II Authors: Schmieder, B.; Heinzel, P.; Van Driel-Gesztelyi, L.; Lemen, J. R. Bibcode: 1996SoPh..165..303S Altcode: We observed the large post-flare loop system, which developed after the X 3.9 flare of 25 June 1992 at 20∶11 UT, in Hα with the Multichannel Subtractive Double Pass Spectrograph at Pic-du-Midi and in X-rays with the it Yohkoh/SXT instrument. Following the long-term development of cool and hot plasmas, we have determined the emission measure of the cool plasma and, for the first time, the temporal evolution of the hot-loop emission measure and temperature during the entire gradual phase. Thus, it was possible to infer the temporal variation of electron densities, leading to estimates of cooling times. A gradual decrease of the hot-loop emission measure was observed, from 4 × 1030 cm−5 at 23∶00 UT on 25 June 1992 to 3 × 1028 cm−5 at 13∶10 UT on 26 June 1992. During the same period, the temperature decreased only slowly from 7.2 to 6.0 × 106 K. Using recent results of NLTE modeling of prominence-like plasmas, we also derive the emission measure of cool Hα loops and discuss their temperature and ionisation degree. During two hours of Hα observations (11-13 hours after the flare) the averaged emission measure does not show any significant change, though the amount of visible cool material decreases and the volume of the loops increases. The emission measure in Hα, after correction for the Doppler-brightening effect, is slightly lower than in soft X-rays. Since the hot plasma seems to be more spatially extended, we arrive at electron densities in the range ninfesupho≤ ninfesupcool∼ 2 × 1010 cm−3 at the time of the Hα observations. Title: Cloud model with variable source function for solar Hα structures. Authors: Mein, N.; Mein, P.; Heinzel, P.; Vial, J. -C.; Malherbe, J. M.; Staiger, J. Bibcode: 1996A&A...309..275M Altcode: The "cloud model" used to derive the physical parameters of solar chromospheric features is extended to the cases of non-constant source function and of velocity gradients. This model assumes a given relationship between the source function and the opacity of the cloud which is derived from non-LTE modelling. An algorithm using 4 points of the Halpha_ profile is proposed to derive the optical thickness, the line-of-sight velocity and the dopplerwidth. The results are compared with a 5-points inversion which does not use the given relationship between source function and opacity. Effects of the uncertainty about the radiation coming from the underlying chromosphere, as well as effects of data noise, are discussed. The inversion method is illustrated by some examples of observed profiles obtained with the MSDP spectrograph of the VTT telescope (Teide Observatory). Title: A Complex Diagnostic of Solar Prominences Authors: Heinzel, P.; Bommier, V.; Vial, J. C. Bibcode: 1996SoPh..164..211H Altcode: We use the polarimetric and intensity measurements of Hα and HeI D3 lines in solar prominences to derive the true geometrical thickness for several quiescent prominences. The electron densities, derived from the collisional depolarization in Hα by Bommier et al. (1994), are used to evaluate the thickness from the emission measure. The emission measure was obtained from the theoretical correlation with the Hα integrated intensity, according to Gouttebroze, Heinzel, and Vial (1993). Theoretical electron densities obtained by latter authors are also compared with those of Bommier et al. (1994) and we find a very good agreement between them. The prominence geometrical thickness exhibits a relatively large range of values from about 100 km up to a few 104 km. The plasma densities vary by almost two orders of magnitude in the observed structures, but the total column mass in the direction perpendicular to the prominence sheet seems to be fairly constant for the set of prominences studied. Title: Structure and evolution of post-flare loops: analysis of YOHKOH and MSDP observations Authors: Schmieder, B.; Heinzel, P.; Wiik, J. E.; Lemen, J.; Hiei, E. Bibcode: 1996AdSpR..17d.111S Altcode: 1996AdSpR..17..111S Using coordinated observations of the June 26 1992 post-flare loops (Yohkoh-SXT and MSDP at Pic-du-Midi), we have analyzed the physical conditions in both hot and cool loops and studied their spatial structure and temporal evolution. Coalignment of high-resolution images from SXT and MSDP indicates that the cool Hα loops are located just below the hot ones and that the whole loop system grows in time with a velocity 1.4 km s^-1. The temperature of hot loops as derived from SXT data amounts to 5 x 10^6 K, while the cool loops have temperatures around 10^4 K. The electron density of hot loops was estimated from SXT emission-measure analysis to 7 x 10^9 cm^-3, while Hα integrated intensity gives an electron density in cool loops of 2.2 x 10^10 cm^-3. With these plasma parameters we have solved the energy equation in order to estimate the cooling time. The basic result of this work is that the cooling time is comparable to the characteristic growing time of the loop system (~ 1500 - 2000 sec), which is in agreement with the scenario of the post-flare loop system development. Title: NLTE modelling based on SOHO/SUMER and GBO coordinated observations. Authors: Heinzel, P. Bibcode: 1996joso.proc...92H Altcode: No abstract at ADS Title: Observations and Analysis of Surges in Chromosphere and Lower Corona Authors: Kotrc, P.; Schmieder, B.; Karlický, M.; Heinzel, P. Bibcode: 1996RoAJ....6...69K Altcode: No abstract at ADS Title: Hot and Cool Post-Flare Loops: Formation and Dynamics Authors: Schmieder, B.; Heinzel, P.; van Driel-Gesztelyi, L.; Wiik, J. E.; Lemen, J. Bibcode: 1996mpsa.conf..211S Altcode: 1996IAUCo.153..211S No abstract at ADS Title: Dynamics of solar magnetic arches in the photosphere and the chromosphere. Authors: Mein, P.; Demoulin, P.; Mein, N.; Engvold, O.; Molowny-Horas, R.; Heinzel, P.; Gontikakis, C. Bibcode: 1996A&A...305..343M Altcode: Mass motions in chromospheric arch filaments have been observed with imaging spectroscopy (MSDP) at the VTT telescope of the Teide Observatory. Coordinated observations of time sequences of continuum images were carried out at the SVST telescope of the Observatorio del Roque de los Muchachos, which provided transverse velocities of photospheric tracers, by "local correlation tracking." Hα profiles along 3 arch filaments are analysed in terms of "differential cloud MODel", to discuss the Doppler velocities of chromospheric material. Models of ascending arches with downflows in both legs are investigated. The gas pressure is neglected, but the free-fall equations are integrated versus time (non-stationary case). We first assume circular lines of force with constant radius. We can account for chromospheric velocities, but we cannot fit the slow motion of footpoints derived from photospheric tracers. A better agreement is obtained by assuming lines of force with fixed footpoints and variable radius. Typical values are: half distance between footpoints of 10 to 15Mm, upward velocity at the top of loops of 4km/s after an integration time of 800s. The obtained values are consistent with the sizes and the lifetime of arch filaments. Title: Relative Altitude of Hot and Cool Post-Flare Loops Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Wiik, J. E.; Tarbell, T.; Heinzel, P.; Kitai, R.; Funakoshi, Y.; Anwar, B. Bibcode: 1996ASPC..111..359V Altcode: 1997ASPC..111..359V The authors collected a unique set of data obtained simultaneously at 4 different ground based observatories and with the Yohkoh satellite to study the relationship between hot X-ray and cool Hα post-flare loops as they evolved during the long gradual phase of the X3.9 flare which occurred on 25 June 1992. They found reasonably good agreement between the computed 'theoretical' cooling times and the 'observed' cooling times derived from the relative altitudes of hot and cool loops. Taking into account evolutionary effects, the authors also found similar shape and configuration of hot and cool loops during the entire observing period and confirmed that at any time hot loops are at higher altitude than cool loops, suggesting that cool loops indeed descend from hot loops. The results provide support for the reconnection model. Title: High resolution flare observations with multi-line imaging spectroscopy. Authors: Mein, P.; Heinzel, P.; Malherbe, J. -M.; Staiger, J. Bibcode: 1996joso.proc...68M Altcode: No abstract at ADS Title: On the nature of bright rims of filaments Authors: Heinzel, Petr; Kotrč, Pavel; Mouradian, Zadig; Buyukliev, Georgi T. Bibcode: 1995SoPh..160...19H Altcode: A filament with a very bright rim was observed in the Hα line on May 11, 1989, using the Meudon spectroheliograph. Absolute calibration of the spectroheliogram allows us to express the intensities in particular sites of the filament, in its bright rim and inside the surrounding chromosphere. From a large number of photometric scans, we obtained a histogram of the intensity excess of the bright rim relative to the quiet chromosphere. The mean value of this excess amounts to about 4%. We present a theoretical explanation of bright rims, based on the nature of Hα radiative diffusion in the filaments. Computed NLTE model of the filament leads to a rim intensity excess which is in good agreement with our observations. Title: Multilevel NLTE radiative transfer in isolated atmospheric structures: implementation of the MALI-technique. Authors: Heinzel, P. Bibcode: 1995A&A...299..563H Altcode: We have developed and extensively tested a new multilevel NLTE transfer code for isolated solar atmospheric structures (loops, prominences, spicules etc.). The code is based on the MALI approach of Rybicki & Hummer (1991, 1992) to multilevel accelerated lambda iterations. It is demonstrated that this method is fully capable of treating a difficult problem of NLTE hydrogen excitation and ionization equilibrium, provided that we linearize the preconditioned statistical equilibrium equations with respect to atomic level populations and the electron density. With this generalization of the original MALI approach, the numerical code is robust and stable. As compared to the standard linearization method of Auer & Mihalas (1969), the new MALI code designed for 1D slabs is more than one order of magnitude faster and its accuracy is quite satisfactory. We discuss several details of our implementation of the MALI technique to isolated, externally irradiated, 1D structures and finally draw some future prospects. Title: Relation between Cool and Hot Post-Flare Loops of 26 June 1992 Derived from Optical and X-Ray (SXT-YOHKOH) Observations Authors: Schmieder, B.; Heinzel, P.; Wiik, J. E.; Lemen, J.; Anwar, B.; Kotrc, P.; Hiei, E. Bibcode: 1995SoPh..156..337S Altcode: We have analyzed the physical conditions of the plasma in post-flare loops with special emphasis on dynamics and energy transport using SXT-data (hot plasma) and optical ground-based data from Pic du Midi, Wrocław, and Ondřejov (cool plasma). By combining the Hα observations with the SXT images we can understand the relationship between cool and hot plasmas, the process of cooling post-flare loops and the mechanism which maintains the long duration of these loops. Using recent results of NLTE modeling of prominence-like plasmas, we derive the emission measure of cool Hα loops and this gives us a realistic estimate of the electron density (2.2 × 1010 cm−3). Then, by comparing this emission measure with that of hot loops derived from SXT data, we are able to estimate the ratio between electron densities in hot and cool loops taking into account the effect of geometrical filling factors. This leads to the electron density in hot loops 7 × 109 cm−3. We also derive the temperature of hot X-ray loops (≃ 5.5 × 106 K), which, together with the electron density, provides the initial values for solving the time-dependent energy balance equation. We obtain the cooling times which are compared to a typical growth-time of the whole loop system (∼ 2000 s). In the legs of cool Hα loops, we observe an excess of the emission measure which we attribute to the effect of Doppler brightening (due to large downflow velocities). Title: Dynamic loops in the corona Authors: Heinzel, P. Bibcode: 1994ESASP.373..133H Altcode: 1994soho....3..133H No abstract at ADS Title: Theoretical correlations between prominence plasma parameters and the emitted radiation. Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. -C. Bibcode: 1994A&A...292..656H Altcode: Recently a set of 140 prominence NLTE models has been computed using the best available numerical techniques (Gouttebroze et al. 1993, hereafter GHV). Models are represented by one-dimensional (1D) slabs vertically standing on the solar surface and irradiated by photospheric and chromospheric radiation. They are parametrized by the gas pressure and temperature (uniform), the geometrical thickness of the 1D slab, the microturbulent velocity and the height above the solar surface. As outputs we obtained several physical quantities and optical parameters like the electron density, the total hydrogen density, the optical thickness in hydrogen lines and continua, spectral line intensities etc. (see GHV). In order to establish mutual correlations between various plasma parameters and the basic characteristics of the synthesized hydrogen spectrum, we construct some basic correlation curves. A very important relation already mentioned in GHV concerns the plasma emission measure found to be closely related to the integrated intensity of the Balmer Hα line. We present several other correlations which can be divided into four categories: (i) relations between radiation properties themselves; (ii) radiation properties versus plasma parameters; (iii) the Hα source function behaviour; and (iv) correlations between plasma parameters. Together with the 24 presented figures, we discuss the physical interpretation of these correlations and we give some hints for their application to the observed data. When appropriate, we also compare our results with existing observations. Title: Dynamics of post-flare loops observed on June 26, 1992 Authors: Wiik, J. E.; Schmieder, B.; Heinzel, P.; Roudier, T. Bibcode: 1994ESASP.373..207W Altcode: 1994soho....3..207W No abstract at ADS Title: Chromospheric and transition-region heating phenomena: coordinated GBO and SOHO observations Authors: Heinzel, P.; Kotrc, P.; Karlicky, M.; Nejezchleba, T.; Knizek, M. Bibcode: 1994ESASP.373..369H Altcode: 1994soho....3..369H No abstract at ADS Title: Coordinated optical and YOHKOH observations of 26 June 1992 flare loops Authors: Heinzel, P.; Kotrč, P.; Schmieder, B.; Hiei, E.; Anwar, B. Bibcode: 1994SSRv...70..181H Altcode: Optical spectra of large flare loops were detected by the Ondřejov Multichannel Flare Spectrograph (MFS) during coordinated observations with MSDP at Pic du Midi (Hα) and the soft X-ray telescope (SXT) on Yohkoh. The CCD video images taken by the MFS slit-jaw camera document the time-development of the flare loops as seen through the Hα filter. Preliminary analysis of the MSDP images shows the intensity structure of the cool flare loops and their velocity fields. From the spectra we can clearly see the intensity variations along the cool loops. SXT images show the structure of hot X-ray loops similar to that of cool loops. Special attention is devoted to the bright tops, simultaneously observed in X-rays, Hα and other optical lines. Based on a preliminary analysis of the optical spectra, we speculate about possible mechanisms leading to an observed bright emission at the tops of cool loops. We suggest that direct soft X-ray irradiation of cool loops at their tops could be, at least partly, responsible for such a strong brightening. Title: Energy Transport and Dynamics Authors: Schmieder, B.; Peres, G.; Enome, S.; Falciani, R.; Heinzel, P.; Hénoux, J. C.; Mariska, J.; Reale, F.; Rilee, M. L.; Rompolt, B.; Shibasaki, K.; Stepanov, A. V.; Wülser, J. P.; Zarro, D.; Zharkova, V. Bibcode: 1994SoPh..153...55S Altcode: We report findings concerning energy transport and dynamics in flares during the impulsive and gradual phases based on new ground-based and space observations (notably fromYohkoh). A preheating sometimes occurs during the impulsive phase. CaXIX line shifts are confirmed to be good tracers of bulk plasma motions, although strong blue shifts are not as frequent as previously claimed. They often appear correlated with hard X-rays but, forsome events, the concept that electron beams provide the whole energy input to the thermal component seems not to apply. Theory now yields: new diagnostics of low-energy proton and electron beams; accurate hydrodynamical modeling of pulse beam heating of the atmosphere; possible diagnostics of microflares (based on X-ray line ratio or on loop variability); and simulated images of chromospheric evaporation fronts. For the gradual phase, the continual reorganization of magnetic field lines over active regions determines where and when magnetic reconnection, the mechanism favoured for energy release, will occur. Spatial and temporal fragmentation of the energy release, observed at different wavelengths, is considered to be a factor as well in energy transport and plasma dynamics. Title: On the Occurrence of Blue Asymmetry in Chromospheric Flare Spectra Authors: Heinzel, Petr; Karlicky, Marian; Kotrc, Pavel; Svestka, Zdenek Bibcode: 1994SoPh..152..393H Altcode: We present observations of optical spectra of a flare in which blue line asymmetry was seen for more than 4 min close to the flare onset. The maximum blue asymmetry coincided with the maximum of a hard X-ray and microwave burst. We discuss possible interpretations of the blue asymmetry and conclude that the most plausible one is electron-beam heating with return current. Although this process predicts downflows in the lower transition region and upper chromosphere, its ultimate effect on the line profiles can be blue asymmetry: the upper layers moving away from us absorb the radiation of the red peak thus lowering its intensity in comparison to the blue one. Title: Chromospheric fine structure: Black & white mottles Authors: Heinzel, P.; Schmieder, B. Bibcode: 1994A&A...282..939H Altcode: H-alpha observations of the chromosphere have been obtained on June 17, 1986 with a high spatial resolution using the MSDP (Multichannel Subtractive Double Pass) spectrograph operating at Pic du Midi observatory. Various fine structures are observed in the chromosphere: bushes of fibrils around supergranules and fibrils (mottles) in the rosettes. They are relatively stable, but line-of-sight velocities +/- 5-10 km/s are observed at the boundaries of supergranules (rosettes). Velocity images exhibit finer structures than intensity ones, with no cospatial relationship between both of them. Typical H-alpha line profiles of dark and bright (black & white) mottles, constructed from 11 MSDP channels, are used to derive the physical conditions in these structures. Non-local thermodynamic equilibrium (NLTE) models of dark and bright mottles are represented by a grid of prominence-like models of Goutebroze et al. (1993). It is demonstrated that higher-pressure models(pg approximately = 0.5-1 dyn/sq cm) with temperature around 104 K naturally explain the profiles of both dark and bright structures. By introducing a generalized two-cloud model with non-uniform source function, we account schematically for a shear-type velocity field. However, the velocities are found to be of a secondary importance when the broad U-shaped profiles formation is considered. We conclude that dark and bright mottles have a similar nature and that their brightness difference is predominantly due to pressure variations of the plasma injected into the rosette flux tubes. Finally, we discuss the ambiguity of H-alpha contrast profiles and comment on applicability of the classical cloud model. Title: Fine structures of the solar chromosphere Authors: Schmieder, B.; Heinzel, P.; Tsiropoula, G.; Alessandrakis, C. E. Bibcode: 1994ASIC..433..151S Altcode: No abstract at ADS Title: Spectral Analysis of a Quiescent Filament Authors: Kotrc, P.; Heinzel, P.; Gorshkov, A. V.; Kononovich, E. V.; Kupryakov, Yu. A.; Smirnova, O. B. Bibcode: 1994scs..conf..361K Altcode: 1994IAUCo.144..361K The authors have determined principal plasma parameters in a filament by applying the appropriate cloud model to several observed spectral lines. Then they compared them to prominence models from the recent numerical NLTE modelling of Gouttebroze et al. (1993). Some preliminary results of such an attempt are described and related problems are briefly discussed. Title: Theoretical Correlations Between Various Prominence Parameters Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. -C. Bibcode: 1994scs..conf..439H Altcode: 1994IAUCo.144..439H The authors present some examples of important correlations between the prominence plasma parameters and radiation properties. For example, the plasma emission measure was found to be closely related to the integrated Hα line intensity which provides a new diagnostic tool for determination of plasma densities. Title: Evolution of an Eruptive Prominence and its Magnetic System on 2 September 1991 Authors: Rudawy, P.; Rompolt, B.; Kotrič, P.; Heinzel, P.; Knižek, M.; Garczyńska, I.; Cader-Sroka, B. Bibcode: 1994emsp.conf...95R Altcode: No abstract at ADS Title: Contrast of Filament Bright Rims Authors: Kononovich, E. V.; Smirnova, O. B.; Heinzel, P.; Kotrc, P. Bibcode: 1994scs..conf..365K Altcode: 1994IAUCo.144..365K Hα filtergrams were measured in order to specify the bright rims contrast at different points along the line profile. The mean contrast value in the line center is about 25 percent. The bright rims interpretation as the bases of magnetic structures supporting the filaments is suggested. Title: Dragging out of the near-surface magnetic fields during the prominence eruptions Authors: Rudawy, P.; Rompolt, B.; Kotrč, P.; Heinzel, P.; Knižek, M. Bibcode: 1994smf..conf..372R Altcode: No abstract at ADS Title: Solar coronal structures Authors: Rusin, Vojtech; Heinzel, Petr; Vial, Jean-Claude Bibcode: 1994scs..conf.....R Altcode: 1994IAUCo.144.....R No abstract at ADS Title: Electron Densities in Solar Prominences Authors: Wiik, J. E.; Heinzel, P.; Schmieder, B. Bibcode: 1994scs..conf..381W Altcode: 1994IAUCo.144..381W The authors concentrate on the determination of electron densities, using the MSDP spectrograph at Pic du Midi. They discuss a new approach for diagnosing the electron densities by comparing the observed Hα intensities with theoretically predicted variations of the line-center intensity versus Ne. Title: Black and White Mottles Authors: Heinzel, P.; Schmieder, B. Bibcode: 1994emsp.conf...81H Altcode: No abstract at ADS Title: The hydrogen spectrum of model prominences. Authors: Gouttebroze, P.; Heinzel, P.; Vial, J. C. Bibcode: 1993A&AS...99..513G Altcode: The emission of hydrogen lines and continua from solar prominences is investigated using a set of 140 simple models, covering the range of physical conditions usually assumed for these objects. These models are plane-parallel, isobaric and isothermal. The computations have been carried out using a 20 level plus continuum hydrogen atom, and taking into account the effects of partial frequency redistribution in the Lyman-alpha and beta lines. The aim of these computations is twofold: firstly, to describe the variations of hydrogen lines and continua emitted by prominences when physical conditions vary. Secondly, to provide observers with some diagnostic tool to interpret data such as intensity ratios, line widths, etc... The results of computations are given as mixed table-figure panels, each of them corresponding to a given model and summarizing the associated physical parameters and the principal features of the emitted hydrogen spectrum. Finally, for some specific parameters (or couple of parameters), we present figures illustrating the variations of these quantities across the whole set of models. Title: Book Review: Solar interior and atmosphere / U Arizona Press, 1991 Authors: Heinzel, P.; Priest, E. R.; Heinzel, P. Bibcode: 1993SoPh..144..203H Altcode: 1993SoPh..144..203C No abstract at ADS Title: Book Review: Applying Fractals in Astronomy Authors: Martens, P. C.; Kleczek, Josip; Heinzel, P. Bibcode: 1993SoPh..143..401M Altcode: No abstract at ADS Title: Book Review: Eruptive solar flares / Springer-Verlag, 1992 Authors: Heinzel, P. Bibcode: 1993SoPh..143..402H Altcode: No abstract at ADS Title: Pulse-beam heating in flare loops. Authors: Heinzel, Petr; Karlicky, M. Bibcode: 1992ESASP.348..237H Altcode: 1992cscl.work..237H Using a 1D hydbrid code, the authors evaluate a response of the flare loop atmosphere to a series of very short electron beam pulses with subsecond duration. Loop dynamics and energy balance are treated by solving the standard set of hydrodynamic equations, while the beam deceleration in denser atmospheric layers is evaluated by using a particle simulation technique. Ionization of hydrogen below T ≍ 104K is obtained by solving simultaneously the time-dependent non-LTE problem for a three-level hydrogen atom with continuum. The resulting electron densities are then used to compute radiation losses at each time step. The authors discuss the behaviour of time-dependent heating, the ionization structure of the chromosphere, and the role of relaxation processes. A series of short-duration electron beam pulses represents schematically the non-stationary heating in the flare loops. However, the time-dependent radiation-hydrodynamical approach used in this paper can also be applied to study other processes taking place in coronal loops. Title: Book Review: Exploring the sun; solar science since Galileo / Johns Hopkins, 1991 Authors: Heinzel, P. Bibcode: 1992SoPh..141..411H Altcode: No abstract at ADS Title: Book reviews Authors: Trams, N. R.; Heinzel, P. Bibcode: 1992SoPh..141..411T Altcode: No abstract at ADS Title: Determination of plasma parameters in a quiescent prominence Authors: Wiik, J. E.; Heinzel, P.; Schmieder, B. Bibcode: 1992A&A...260..419W Altcode: We present H-alpha observations and analysis of a quiescent, polar crown prominence observed on June 11, 1988 with the MSDP spectrograph at the Pic du Midi Observatory. Two-dimensional maps of H-alpha intensities and line-of-sight velocities have been obtained. The large-scale velocity pattern consisting of cells and elongated structures is stable on a time scale of about 1 min, but evolves continuously and undergoes large changes in shape and amplitude during one hour. This behavior of the velocity field suggests the presence of twists in flux ropes or shear motions. Further, comparing the absolute observed intensities with values from non-LTE radiative computations we estimate the range of electron densities, source functions and optical thicknesses in different parts of the prominence. For upper parts of the prominence we obtain electron densities in the range 1 - 5 x l0 exp 10/cu cm. Title: The fine structure of prominences. Authors: Heinzel, P.; Vial, J. -C. Bibcode: 1992ESASP.344...57H Altcode: 1992spai.rept...57H Ground-based observations evidence in prominences a fine structure both in density and velocity fields at a subarcsec scale. The modeling of such structures is necessary in order to account for heating and cooling processes which depend critically on the geometry and the structure of the magnetic field. For a rigorous treatment of the radiative losses, one needs to solve the full NLTE problem especially in UV lines, which are critical for the energy balance. Although some attempts have already been made to model individual fine-structure elements, quiescent prominences are still mostly considered as one-dimensional structures. We discuss current improvements such as two-dimensional geometry and bundle of threads. Title: Structure and Dynamics of Cool Flare Loops Authors: Heinzel, P.; Schmieder, B.; Mein, P. Bibcode: 1992SoPh..139...81H Altcode: MSDP observations of the 16 May, 1981 two-ribbon flare are used to study the physical structure and the dynamical behaviour of cool flare loops. The loops have been detected in the Hα line just after the flare maximum and they appeared in absorption against the disk. Using the first-order differential cloud model (DCM1) technique, we derive empirically some basic plasma parameters at 15 points along one loop leg. The flow velocities and the true heights have been reconstructed with respect to a geometrical projection. Subsequently, detailed non-LTE models of cool loops have been constructed in order to fit Hα source function values previously derived from DCM1 analysis. It is demonstrated that this source function is rather sensitive to the radial component of the flow velocity (the so-called Doppler brightening) and to enhanced irradiation of the loops from the underlying flare ribbons. In this way, we have been able to estimate quantitatively all plasma parameters which determine the physical structure of cool loops (i.e., the temperature, pressure, density), as well as the momentum-balance condition within the loops. For these dark loops we have arrived at relatively low gas pressures of the order of 0.1-0.5 dyne cm-2 with corresponding electron densities around 1011 cm-3. Pressure-gradient forces have been found to be of small importance in the momentum-balance equation, and thus they cannot explain departures from a free-fall motion found in our MSDP data analysis. We propose three possible solutions to this problem. Title: Hydrogen Photoionization Rates for Chromospheric and Prominence Plasmas Authors: Rudawy, P.; Heinzel, P. Bibcode: 1992SoPh..138..123R Altcode: New values of hydrogen photoionization rates for subordinate continua arising from bound levels with the principal quantum number i = 2-5 have been evaluated numerically, using an extensive compilation of the observed photospheric radiation fields. These rates can be directly incorporated into the equations of statistical equilibrium as so-called fixed rates. We tabulate the photoionization rates and equivalent radiation temperatures for various heights above the photosphere, which is particularly useful for chromospheric and prominence non-LTE modeling. Finally, we compare our results with those previously obtained by other authors. Title: Subsecond Variations of HXR and Hα Flare Emission Authors: Heinzel, P.; Karlicky, M. Bibcode: 1992LNP...399..359H Altcode: 1992esf..coll..359H; 1992IAUCo.133..359H For a series of electron beam pulses, we have computed the time-dependent chromospheric heating and the corresponding hard X-ray (HXR) flux. Moreover, by solving the time-dependent NLTE problem for hydrogen, we theoretically predict the Ha-line intensity variations on sub-second time scales. Both HXR-fluxes and Ha wing intensities do exhibit a spiky behaviour, consistent with short pulse-beam heating. However, the spikes in Ha are unexpectedly inverse, i.e. the line intensity decreases during the beam heating. They correlate rather well with HXR emission peaks computed for 24 keV channel. We compare our theoretical results with recent observations of Kiplinger et al. (1991). Title: Fine structure analysis of a prominence in H-alpha and coronal lines Authors: Wiik, J. E.; Schmieder, B.; Noens, J. C.; Heinzel, P. Bibcode: 1992sws..coll..131W Altcode: Prominence observations made simultaneously with the MSDP spectrograph and with the coronagraph at Pic du Midi are presented. The existence of a coronal cavity is discussed. 2D maps of H-alpha intensities and the line-of-sight velocities have been obtained. The behavior of the velocity field suggests the presence of twists along flux ropes or shear motions. Further, using a probabilistic approach to the H-alpha-line formation, we estimate the range of temperatures, electron densities and optical thicknesses in different parts of the prominence by fitting the observed H-alpha intensity profiles. Title: Plasma Parameters Derived from MSDP Observations of Cool Flare Loops Authors: Heinzel, P.; Schmieder, B.; Mein, P. Bibcode: 1992LNP...399..134H Altcode: 1992IAUCo.133..134H; 1992esf..coll..134H MSDP observations of 16 May 1981 two-ribbon flare are used to study the physical structure and dynamical behaviour of cool flare loops. The loops have been detected in the H line just after the flare maximum and they appeared in absorption against the disk. Using the first-order differential cloud model (DCM1) technique, we derive empirically some basic plasma parameters at 15 points along one loop leg. The flow velocities and true heights have been reconstructed with respect to a geometrical projection. Subsequently, detailed non-LTE models of cool loops have been constructed in order to fit H source-function values previously derived from DCM1 analysis. It is demonstrated that this source function is rather sensitive to the radial component of the flow velocity (the so-called Doppler brightening) and to the enhanced irradiation of the loops from the underlying flare ribbons. In this way, we have been able to estimate quantitatively all plasma parameters which determine the physical structure of cool loops (i. e. the temperature, pressure, density, etc.), as well as the momentum-balance condition within the loops. For these dark loops we have arrived at relatively low gas pressures of the order of 0.1 - 0.5 dyn cm-2 , with corresponding electron densities around 1011 cm-3. Pressure-gradient forces have been found to be of small importance in the momentum-balance equation. However, the classical momentum equation is not capable of explaining significant departures from a free-fall motion under the gravity force, found from our MSDP data. We propose three possible explanations to this problem. Title: A Chromospheric Response to Pulse Beam Heating Authors: Heinzel, Petr Bibcode: 1991SoPh..135...65H Altcode: Starting from the new flare models of Karlický (1990) and Karlický and Hénoux (1991), we present here the first time-dependent numerical simulations of hydrogen plasma excitation and ionization on time scales of less than one second. These time scales are consistent with the spiky behaviour of the kinetic temperature produced by non-thermal collisional processes. Such temperature spikes represent a chromospheric response to a series of short-duration electron beam pulses which are supposed to heat the flare atmosphere. Self-consistent numerical solution of a simplified, time-dependent, non-LTE problem for a three-level hydrogen atom model with continuum allows us to predict theoretically a qualitative behaviour of the Hα line intensity variations on very short time intervals. Our Hα temporal profiles, evaluated at the line center and for Δλ = 1 Å, can be qualitatively compared with some recent flare observations obtained with high temporal resolution. Title: Chromospheric Inhomogeneities in Cool Stars - Possible Effect on Hydrogen Line Profiles Authors: Heinzel, P. Bibcode: 1991ASIC..341..297H Altcode: 1991sabc.conf..297H No abstract at ADS Title: Formation of hydrogen lines under the influence of turbulent electric fields in solar flares. Authors: Heinzel, Petr Bibcode: 1990JQSRT..44..185H Altcode: A new method of detecting low-frequency ion-sound turbulence in solar chromospheric flares is proposed. The method is based on analysis of the hydrogen Paschen γ line profiles, which exhibit - under the appropriate conditions - diagnostically important humps in the line wings around Δλ ≅ 1 Å. The author discusses the problem of Paschen γ line formation under the influence of low-frequency turbulent electric fields and compares his theoretical results with recent spectral observations. From comparison with the observed profile, the author derives a turbulent electric field mean intensity of F0 ≅ 3 CGS. Title: Spectral line formation in plasmas under extreme or unusual conditions. Proceedings. Workshop on Spectral Line Formation in Plasmas Under Extreme or Unusual Conditions, Nice (France), 31 Aug - 4 Sep 1987. Authors: Peyraud, N.; Heinzel, P.; Hooper, C. F., Jr. Bibcode: 1990JQSRT..44.....P Altcode: Contents: 1. Plasma electric fields. 2. Diagnostics of laboratory plasmas. 3. Spectral line formation and broadening. 4. Astrophysical plasmas. Title: On the Presence of High-frequency Turbulent Electric Fields in the August 7, 1960 Flare Authors: Firstova, N. M.; Heinzel, P.; Kotrc, P. Bibcode: 1990BAICz..41...88F Altcode: According to Oks (1978), the wings of some hydrogen Balmer lines observed in the spectrum of the moustache-like flare of August 7, 1960 do exhibit theoretically predicted dips, which should indicate the presence of Langmuir turbulence. However, these features are rather subtle and thus several difficulties arise if one tries to identify them in the noisy spectra with typically many blends. Moreover, the Balmer profiles used for Oks' analysis were already 'filtered' in a special manner, which strongly affects the results. In view of these problems, consideration is given to whether these dips in this particular flare were real, starting with newly obtained microphotometric records. Using the same lines as Oks (i.e., H7, H8, H11-13), together with H14, none of the expected dips in the line wings were identified. All observational aspects of this analysis are discussed in detail, and new special observations are proposed. The role of electron density variations within the flare volume is also briefly discussed. Title: Hα diagnostics of 16 May 1981 flare loops. Authors: Heinzel, P.; Mein, P.; Schmieder, B. Bibcode: 1990PDHO....7..272H Altcode: MSDP observations (Meudon) of 16 May 1981 post-flare loops are used to derive the hydrogen plasma parameters in flare loops. The authors compare two recently developed methods: a differential cloud model and a probabilistic transfer technique. Title: Hydrogen Line Formation in Filamentary Prominences Authors: Heinzel, Petr Bibcode: 1990LNP...363..279H Altcode: 1990doqp.coll..279H; 1990IAUCo.117..279H No abstract at ADS Title: Chromospheric Structure under an H-alpha Filament Authors: Heinzel, P.; Kononovich, E. V.; Smirnova, O. B. Bibcode: 1990PDHO....7..172H Altcode: 1990dysu.conf..172H; 1990ESPM....6..172H The authors discuss the morphology and intensity structure of the chromosphere underlying the Hα filament located close to the solar limb. Title: Analysis of HeI 10830 a line in a quiescent prominence Authors: Kotrč, P.; Heinzel, P. Bibcode: 1990LNP...363..285K Altcode: 1990doqp.coll..285K; 1990IAUCo.117..285K No abstract at ADS Title: Hydrogen Lines Formation in Filamentary Prominences Authors: Heinzel, P. Bibcode: 1989HvaOB..13..317H Altcode: No abstract at ADS Title: Analysis of HeI 10830 Line in a Quiescent Prominence Authors: Kotrc, P.; Heinzel, P. Bibcode: 1989HvaOB..13..371K Altcode: No abstract at ADS Title: Non LTE modelling of prominences. Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. -C. Bibcode: 1988dssp.conf...71H Altcode: The authors present the results on non-LTE computations performed in the major lines and continua of the hydrogen atom. The prominence is represented by a slab illuminated by the neighbouring chromosphere and corona. Classical models are recomputed and it appears that the low pressure model represent well the observed Lα profiles. However the Lβ-computed value is much lower than the observed one. Preliminary computations where a transition region to the corona is included that the Lβ line may be improved. Title: Hα diagnostics of (post)-flare loops based on narrow-band filtergram observations Authors: Heinzel, P.; Karlicky, M. Bibcode: 1987SoPh..110..343H Altcode: Using narrow-band Hα filtergrams, we develop a quantitative non-LTE approach to determine the physical conditions prevailing at the tops of (post)-flare loops observed against the solar disc. At temperatures 10000-15000 K, the tops of flare loops turn to emission at Hα line center when the gas pressure Pg reaches 1 dyn cm−2 and should be clearly visible for Pg≳ 3 dyn cm−2, independently of the loop diameter. This situation corresponds to the electron density of the order 1012 cm−3. The contrast of flare-loops (in projection on the disc) at Hα line center is mainly the function of Pg, while in the line wings (Hα ± 1 Å) the loop can be visible in absorption or emission only when rather strong microturbulence is present or for unrealistically high gas pressures. Finally, we briefly discuss our diagnostical results in frame of the latest (post)-flare loop model. Title: Formation of the hydrogen spectrum in quiescent prominences - One-dimensional models with standard partial redistribution Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. -C. Bibcode: 1987A&A...183..351H Altcode: One-dimensional isothermal-isobaric static slab models are used to study departures from complete frequency redistribution (CRD) in hydrogen lines for quiescent solar prominences. Partial redistribution (PRD) effects on the hydrogen L-alpha line are shown to be significant in the near wings in addition to the far wings of L-alpha. It is suggested that strong symmetrical peaks found in the theoretical PRD L-alpha profiles are due to partially coherent penetration of the incidence double-peaked solar L-alpha. The present results are found to be consistent with OSO-8/LPSP observations and with UVSP/SMM data. The possible interplay between the effects of lateral transport or radiation, level-interlocking, and PRD is considered. Title: Book review Authors: Heinzel, Petr Bibcode: 1987SoPh..110..411H Altcode: No abstract at ADS Title: Hydrogen Emission from Moving Solar Prominences Authors: Heinzel, P.; Rompolt, B. Bibcode: 1987SoPh..110..171H Altcode: Brightness variations of the lines arising from a five-level hydrogen model atom, depending upon prominence velocities, have been investigated using a combination of two non-LTE techniques. The importance of the Doppler brightening and/or Doppler dimming effects is demonstrated for the lines of the Lyman and Balmer series. Title: Optical and infrared spectrophotometry of quiescent prominences. Authors: Novocky, D.; Heinzel, P. Bibcode: 1987PAICz..66..257N Altcode: 1987eram....1..257N High-dispersion Ca II H and K, Ca II IR λ8542 Å, Hα, Hβ, and D3 emission line profiles of quiescent prominences have been recorded in Stará Lesná Observatory. After data reduction, a full set of calibrated profiles is used to discuss semiempirical non-LTE prominence models. Title: Non-Lte Modelling of Prominences Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. C. Bibcode: 1987dssp.work...71H Altcode: 1987ASSL..150...71H No abstract at ADS Title: Physical conditions in cool flare loops. Authors: Heinzel, P. Bibcode: 1987PAICz..66..199H Altcode: 1987eram....1..199H Large two-ribbon flares are frequently accompanied by a system of (post)-flare loops, cooler structures being visible in several optical and UV lines. The author investigates the non-LTE formation of hydrogen lines in stationary loop structures, taking into account the influence of macroscopic velocity flows along the loop. Title: Non-LTE hydrogen-line formation in moving prominences. Authors: Heinzel, P.; Rompolt, B. Bibcode: 1986NASCP2442..163H Altcode: 1986copp.nasa..163H The behavior of hydrogen-line brightness variations, depending on the prominence-velocity changes were investigated. By solving the NON-Local thermodynamic equilibrium (LTE) problem for hydrogen researchers determine quantitatively the effect of Doppler brightening and/or Doppler dimming (DBE, DDE) in the lines of Lyman and Balmer series. It is demonstrated that in low-density prominence plasmas, DBE in H alpha and H beta lines can reach a factor of three for velocities around 160 km/sec, while the L alpha line exhibits typical DDE. L beta brightness variations follow from a combined DBE in the H alpha and DDE in L alpha and L beta itself, providing that all relevant multilevel interlocking processes are taken into account. Title: Partial redistribution effects in the formation of hydrogen lines in quiescent prominences. Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. C. Bibcode: 1986NASCP2442..155H Altcode: 1986copp.nasa..155H Departures from complete frequency redistribution (CRD) in hydrogen lines are investigated for solar prominences. Partial redistribution effects (PRD) are found both in the wings (their already known lowering) and in the central part of the L alpha line; a new feature is evidenced here: the partially coherent scattering in the near wings of the line leads to a double-peaked profile mirroring the incident solar radiation. With a low density model, we obtain a good agreement with OSO 8 observed profiles. On the contrary, the PRD computed L beta profile (lower density, no reversal) departs from the observed one, a result which calls for more progress in terms of non-LTE transfer and modelling. Title: Comments on "The angle-dependent redistribution functions RIII and RIV" by S. J. McKenna. Authors: Hubeny, I.; Heinzel, P. Bibcode: 1986Ap&SS.119..409H Altcode: It is shown that the complicated form of the line absorption probability function for scattering in subordinate lines, derived by McKenna (1984), is an artifact of adopting a mathematically inconvenient expression for the corresponding redistribution function. It is demonstrated that the absorption probability must be given by the Voigt function. Title: Non-LTE models of solar prominences Authors: Heinzel, P.; Vial, J. C.; Gouttebroze, P.; Rompolt, B. Bibcode: 1986CoSka..15..183H Altcode: The authors briefly review some representative non-LTE models of solar prominences, developed during the past decade. Particular attention is devoted to recent interpretation of hydrogen Lyman α line profiles in quiescent prominences and to the solution of the non-LTE problem for moving active prominences. Finally, the authors outline some of the most important prospects of prominence plasma diagnostics. Title: Infrared observations of quiescent prominences Authors: Heinzel, P.; Kotrč, P.; Sobotka, M.; Zloch, F.; Scherbakova, Z. A. Bibcode: 1986CoSka..15..171H Altcode: The authors have developed a sophisticated numerical technique to reduce infrared photographic spectra of quiescent prominences, taking into account the influence of instrumental profiles, scattered light and the noise. The reduced profiles were subsequently compared with theoretical ones. Title: Partial redistribution interlocking in the solar chromosphere. Authors: Heinzel, P.; Hubeny, I. Bibcode: 1985ASIC..152..137H Altcode: 1985pssl.proc..137H Starting with the model of a quiet solar chromosphere, the authors have calculated the relative probabilities of radiative and natural population of the second and third hydrogen levels, pertinent to various population processes. The analysis indicates that, while the Lα line is formed by resonance scattering between the first two levels, the third hydrogen level, from which Lβ and Hα are generated, is populated partly by direct photoexcitation 1→3 (about 55%), and partly by two-photon absorption 1→2→3 (about 45%). Title: Redistribution functions: a review of computational methods. Authors: Heinzel, P. Bibcode: 1985ASIC..152..115H Altcode: 1985pssl.proc..115H This paper reviews and compares the existing computational methods developed to evaluate various types of redistribution functions applicable in astrophysics. It discusses in detail several numerical aspects (codes) of calculating both the angle-dependent and angle-averaged laboratory-frame functions. Title: Non-coherent scattering in subordinate lines - V. Solutions of the transfer problem. Authors: Hubeny, I.; Heinzel, P. Bibcode: 1984JQSRT..32..159H Altcode: Redistribution functions are defined for resonance scattering and shown to be of use in astrophysics problems. An isotropic approximation is included in a definition of a two-level atom line source function and the redistribution function is angle-averaged for scattered photons, which are treated as negative absorption. Various redistribution functions, either partial or complete, are then applied to slab, isothermal, finite, and semi-infinite atmospheres for a given absorption profile and the line source function to examine the resulting transfer functions. The ratios of the upper/lower level damping are found to have a significant impact on the type of redistribution expected. An approximate form of the redistribution function is determined as adequate for calculating line profiles, especially in the wings. Title: Non-coherent scattering in subordinate lines: IV. Angle-averaged redistribution functions. Authors: Heinzel, P.; Hubený, I. Bibcode: 1983JQSRT..30...77H Altcode: It is demonstrated that a simple Gaussian quadrature over the scattering angles provides a sufficiently accurate and stable method for evaluating all the angle-averaged redistribution functions Ri(xarcmin,x) (i = I-V). The authors display graphically the functions RII,III,V and discuss in detail the behaviour of the newly calculated redistribution RV(xarcmin,x). Title: OSO-8 observations of a quiescent prominence - A comparison of Lyman-alpha with theoretical intensities Authors: Heinzel, P.; Vial, J. -C. Bibcode: 1983A&A...121..155H Altcode: Using simultaneous observations of hydrogen Lyman-α and Ca II K lines obtained with the OSO 8 LPSP instrument, the authors compare Lα emission from a quiescent prominence with those predicted from the existing theoretical models. They use the observed relation between Hα and Ca II K integrated intensities to obtain an estimate of E(Hα)/E(Lα) vs. E(Hα). This ratio differs significantly from those predicted theoretically under the assumption of complete frequency redistribution during the scattering of Lα photons. On the other hand, using the partial-redistribution treatment in the Lα wings, as suggested by Milkey et al., the authors arrived at a reasonable agreement with the corresponding theoretical curve. The possible influence of macroscopic velocities on line ratios is briefly discussed. Title: Resonance Scattering of Radiation in Solar Prominences. I. Partial Redistribution in Optically Thin Subordinate Lines Authors: Heinzel, P. Bibcode: 1983BAICz..34....1H Altcode: In the present paper the author studies the resonance scattering of photospheric and chromospheric radiation by a prominence located at any given height above the solar surface. Applying the newly developed partial redistribution treatment (PRD), he evaluates numerically the scattering integral in order to assess possible PRD effects on subordinate-line emission profiles and/or integrated intensities emerging from an optically thin prominence plasma. Title: Book-Review - Laser Spectroscopy - Basic Concepts and Instrumentation Authors: Demtroder, W.; Heinzel, P. Bibcode: 1982BAICz..33..192D Altcode: No abstract at ADS Title: Nekoherentní rozptyl záření v subordinátních čarách Title: Nekoherentní rozptyl záření v subordinátních čarách Authors: Heinzel, Petr Bibcode: 1982PhDT.......141H Altcode: No abstract at ADS Title: Erratum: "Non-coherent scattering in subordinate lines: a unified approach to redistributions" [J. Quant. Spectrosc. Radiat. Transfer, Vol. 25, p. 483 - 499 (1981)]. Authors: Heinzel, P. Bibcode: 1982JQSRT..27..109H Altcode: No abstract at ADS Title: Non-coherent scattering in subordinate lines: II. Collisional redistribution. Authors: Heinzel, P.; Hubený, I. Bibcode: 1982JQSRT..27....1H Altcode: No abstract at ADS Title: Partial frequency redistribution in subordinate lines. Authors: Heinzel, P. Bibcode: 1981PAICz..57....5H Altcode: No abstract at ADS Title: Non-coherent scattering in subordinate lines: a unified approach to redistribution functions. Authors: Heinzel, P. Bibcode: 1981JQSRT..25..483H Altcode: No abstract at ADS Title: Book-Review - Nonradial and Nonlinear Stellar Pulsation - Workshop - Tucson - 1979MAR12-16 Authors: Hill, H. A.; Dziembowski, W. A.; Heinzel, P. Bibcode: 1981BAICz..32..254H Altcode: No abstract at ADS Title: Conference on stellar atmospheres, June 1981, Brno. Authors: Heinzel, P. Bibcode: 1981Rise...62..203H Altcode: No abstract at ADS Title: Partial frequency redistribution in subordinate lines Authors: Heinzel, P. Bibcode: 1981sspi.book....5H Altcode: An appropriate laboratory-frame redistribution function (LFR) subordinate lines formed in stellar atmospheres and solar prominences is presented under the assumption of a Maxwellian velocity distribution for the lower state atoms. Starting from quantum mechanical results. A LFR is obtained for the case of radiative broadening of both levels. One general routine that can be used to evaluate all is R sub IS. Title: Derivatives of the Voigt Functions Authors: Heinzel, P. Bibcode: 1978BAICz..29..159H Altcode: A procedure for computing the partial derivatives of the Voigt functions H(a, u) and K(a, u) is set forth, based on introducing the complex function D(w) = H(a, u) + iK(a, u). Recurrence relations for the partial derivatives up to the n-th order with respect to the variables a and u are derived. The direct formulas for these derivatives up to third order are also given. As an example of an astrophysical application, the expression for a hydrogen line profile as a linear combination of the partial derivatives of a Voigt function is given. Title: Astronomy at the Jagellonian University. Authors: Heinzel, P. Bibcode: 1976Rise...57...81H Altcode: No abstract at ADS Title: Precise Measurements of Radial Velocity Using a Lirepho Microphotometer Authors: Heinzel, P.; Hadrava, P. Bibcode: 1975BAICz..26...90H Altcode: No abstract at ADS Title: European seminary of the students of astronomy in Poland, 1973. Authors: Heinzel, P.; Solc, M. Bibcode: 1974Rise...55...29H Altcode: No abstract at ADS