Author name code: labrosse ADS astronomy entries on 2022-09-14 author:"Labrosse, Nicolas" ------------------------------------------------------------------------ Title: Solar prominence diagnostics from non-LTE modelling of Mgii h&k line profiles Authors: Peat, Aaron; Labrosse, Nicolas; Barczynski, Krzysztof; Schmieder, Brigitte Bibcode: 2022cosp...44.2542P Altcode: We investigate a new method to obtain the plasma parameters of solar prominences observed in the Mg II h&k spectral lines by comparing line profiles from the IRIS satellite to a bank of profiles computed with a one-dimensional non-LTE radiative transfer code. The prominence observations were carried out by the IRIS satellite on 19th April 2018. Using a grid of 22933 one-dimensional non-LTE radiative transfer models, some including a prominence-corona transition region (PCTR), we are able to recover satisfactory matches in areas of the prominence where single-line profiles are observed. Large values of ionization degree are found by the procedure in areas where the line of sight crosses mostly plasma from the PCTR, correlating with high mean temperatures and correspondingly no H$\alpha$α emission. The models were unable to recover satisfactory fits in the regions where we see H$\alpha$ emission. This is due to the complex line shapes manifesting from many unresolved independently moving threads. This new method naturally returns information on how closely the observed and computed profiles match, allowing the user to identify areas where no satisfactory match between models and observations can be obtained. The inclusion of the PCTR was found to be important, as regions where satisfactory fits were found were more likely to contain a model encompassing a PCTR. Title: Photospheric Flow Fields in a Coronal Bright Point Authors: Peat, Aaron; Labrosse, Nicolas; Muglach, Karin Bibcode: 2022cosp...44.2565P Altcode: The relationship between the flows in the photosphere and the migration of magnetic polarity patches leading to a coronal bright point is investigated. As seen in SDO/AIA images the formation of this coronal bright point began end of day on 2017-09-24, with the event peaking at approximately 10.00 on 2017-09-25, and ending 2017-09-27. In all, the evolution of the bright point was followed over about 3 days. We employ Fourier Local Correlation Tracking (FLCT) to recover the photospheric flow fields in HMI Intensity images around the area in which the bright point forms. Then, using the flow vectors produced by FLCT, we investigate the relationship between these photospheric flow fields and the flux emergence, and the effect they have on the formation and evolution of the coronal bright point. Title: First high resolution interferometric observation of a solar prominence with ALMA Authors: Labrosse, Nicolas; Rodger, Andrew S.; Radziszewski, Krzysztof; Rudawy, Paweł; Antolin, Patrick; Fletcher, Lyndsay; Levens, Peter J.; Peat, Aaron W.; Schmieder, Brigitte; Simões, Paulo J. A. Bibcode: 2022MNRAS.513L..30L Altcode: 2022arXiv220212434L; 2022MNRAS.tmpL..22L We present the first observation of a solar prominence at 84 - 116 GHz using the high resolution interferometric imaging of ALMA. Simultaneous observations in Hα from Białkaw Observatory and with SDO/AIA reveal similar prominence morphology to the ALMA observation. The contribution functions of 3 mm and Hα emission are shown to have significant overlap across a range of gas pressures. We estimate the maximum millimetre-continuum optical thickness to be τ3mm ≍ 2, and the brightness temperature from the observed Hα intensity. The brightness temperature measured by ALMA is ~6000 - 7000 K in the prominence spine, which correlates well with the estimated brightness temperature for a kinetic temperature of 8000 K. 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: HiRISE - High-Resolution Imaging and Spectroscopy Explorer - Ultrahigh resolution, interferometric and external occulting coronagraphic science Authors: Erdélyi, Robertus; Damé, Luc; Fludra, Andrzej; Mathioudakis, Mihalis; Amari, T.; Belucz, B.; Berrilli, F.; Bogachev, S.; Bolsée, D.; Bothmer, V.; Brun, S.; Dewitte, S.; de Wit, T. Dudok; Faurobert, M.; Gizon, L.; Gyenge, N.; Korsós, M. B.; Labrosse, N.; Matthews, S.; Meftah, M.; Morgan, H.; Pallé, P.; Rochus, P.; Rozanov, E.; Schmieder, B.; Tsinganos, K.; Verwichte, E.; Zharkov, S.; Zuccarello, F.; Wimmer-Schweingruber, R. Bibcode: 2022ExA...tmp...21E Altcode: Recent solar physics missions have shown the definite role of waves and magnetic fields deep in the inner corona, at the chromosphere-corona interface, where dramatic and physically dominant changes occur. HiRISE (High Resolution Imaging and Spectroscopy Explorer), the ambitious new generation ultra-high resolution, interferometric, and coronagraphic, solar physics mission, proposed in response to the ESA Voyage 2050 Call, would address these issues and provide the best-ever and most complete solar observatory, capable of ultra-high spatial, spectral, and temporal resolution observations of the solar atmosphere, from the photosphere to the corona, and of new insights of the solar interior from the core to the photosphere. HiRISE, at the L1 Lagrangian point, would provide meter class FUV imaging and spectro-imaging, EUV and XUV imaging and spectroscopy, magnetic fields measurements, and ambitious and comprehensive coronagraphy by a remote external occulter (two satellites formation flying 375 m apart, with a coronagraph on a chaser satellite). This major and state-of-the-art payload would allow us to characterize temperatures, densities, and velocities in the solar upper chromosphere, transition zone, and inner corona with, in particular, 2D very high resolution multi-spectral imaging-spectroscopy, and, direct coronal magnetic field measurement, thus providing a unique set of tools to understand the structure and onset of coronal heating. HiRISE's objectives are natural complements to the Parker Solar Probe and Solar Orbiter-type missions. We present the science case for HiRISE which will address: i) the fine structure of the chromosphere-corona interface by 2D spectroscopy in FUV at very high resolution; ii) coronal heating roots in the inner corona by ambitious externally-occulted coronagraphy; iii) resolved and global helioseismology thanks to continuity and stability of observing at the L1 Lagrange point; and iv) solar variability and space climate with, in addition, a global comprehensive view of UV variability. Title: Spectro-imagery of an active tornado-like prominence: Formation and evolution Authors: Barczynski, Krzysztof; Schmieder, Brigitte; Peat, Aaron W.; Labrosse, Nicolas; Mein, Pierre; Mein, Nicole Bibcode: 2021A&A...653A..94B Altcode: 2021arXiv210604259B Context. The dynamical nature of fine structures in prominences remains an open issue, including rotating flows in tornado prominences. While the Atmospheric Imaging Assembly imager aboard the Solar Dynamics Observatory allowed us to follow the global structure of a tornado-like prominence for five hours, the Interface Region Imaging Spectrograph, and the Multichannel Subtractive Double Pass spectrograph permitted to obtain plasma diagnostics of its fine structures.
Aims: We aim to address two questions. Firstly, is the observed plasma rotation conceptually acceptable in a flux rope magnetic support configuration with dips? Secondly, how is the plasma density distributed in the tornado-like prominence?
Methods: We calculated line-of-sight velocities and non-thermal line widths using Gaussian fitting for Mg II lines and the bisector method for Hα line. We determined the electron density from Mg II line integrated intensities and profile fitting methods using 1D non-LTE radiative transfer theory models.
Results: The global structure of the prominence observed in Hα, and Mg II h, and k line fits with a magnetic field structure configuration with dips. Coherent Doppler shifts in redshifted and blueshifted areas observed in both lines were detected along rapidly-changing vertical and horizontal structures. However, the tornado at the top of the prominence consists of multiple fine threads with opposite flows, suggesting counter-streaming flows rather than rotation. Surprisingly we found that the electron density at the top of the prominence could be larger (1011 cm−3) than in the inner part of the prominence.
Conclusions: We suggest that the tornado is in a formation state with cooling of hot plasma in a first phase, and following that, a phase of leakage of the formed blobs with large transverse flows of material along long loops extended away from the UV prominence top. The existence of such long magnetic field lines on both sides of the prominence would stop the tornado-like prominence from really turning around its axis.

Movies are available at https://www.aanda.org Title: Solar prominence diagnostics from non-LTE modelling of Mg II h&k line profiles Authors: Peat, A. W.; Labrosse, N.; Schmieder, B.; Barczynski, K. Bibcode: 2021A&A...653A...5P Altcode: 2021arXiv210610351P
Aims: We investigate a new method to for obtaining the plasma parameters of solar prominences observed in the Mg II h&k spectral lines by comparing line profiles from the IRIS satellite to a bank of profiles computed with a one-dimensional non-local thermodynamic equilibrium (non-LTE) radiative transfer code.
Methods: Using a grid of 1007 one-dimensional non-LTE radiative transfer models, some including a prominence-corona transition region (PCTR), we carry out this new method to match computed spectra to observed line profiles while accounting for line core shifts not present in the models. The prominence observations were carried out by the IRIS satellite on 19 April 2018.
Results: The prominence is very dynamic with many flows, including a large arm extending from the main body seen near the end of the observation. This flow is found to be redshifted, as is the prominence overall. The models are able to recover satisfactory matches in areas of the prominence where single line profiles are observed. We recover: mean temperatures of 6000-50 000 K; mean pressures of 0.01-0.5 dyne cm−2; column masses of 3.7 × 10−8-5 × 10−4 g cm−2; a mean electron density of 7.3 × 108-1.8 × 1011 cm−3; and an ionisation degree nHII/nHI = 0.03 − 4500. The highest values for the ionisation degree are found in areas where the line of sight crosses mostly plasma from the PCTR, correlating with high mean temperatures and correspondingly no Hα emission.
Conclusions: This new method naturally returns information on how closely the observed and computed profiles match, allowing the user to identify areas where no satisfactory match between models and observations can be obtained. The inclusion of the PCTR was found to be important when fitting models to data as regions where satisfactory fits were found were more likely to contain a model encompassing a PCTR. The line core shift can also be recovered from this new method, and it shows a good qualitative match with that of the line core shift found by the quantile method. This demonstrates the effectiveness of the approach to line core shifts in the new method.

Movies associated to Figs. 10 and A.1 are available at https://www.aanda.org Title: Active tornado in a prominence observed in H-alpha with MSDP and Mg II with IRIS Authors: Barczynski, Krzysztof; Schmieder, Brigitte; Mein, Pierre; Labrosse, Nicolas; Mein, Nicole; Peat, Aaron Bibcode: 2021cosp...43E.973B Altcode: Large prominences with highly dynamic plasma features expand outwards in the solar atmosphere, often in loop or arch-shape or as a tornado. The origin of the rotating flow in prominence tornadoes is not fully understood yet. We aim to find an answer to two long-standing questions: what is the nature of the plasma flow and rotation in the prominence, and the role of the magnetic field configuration in the prominence dynamics? To this aim, we use observations from the Atmospheric Imaging Assembly (AIA) imager aboard the Solar Dynamics Observatory (SDO) to follow the plasma dynamics related to magnetic field. Simultaneous observations from the Interface Region Imaging Spectrograph (IRIS) and the Multi subtractive Double pass spectrograph (MSDP) allow us to study the plasma properties (intensity, Doppler velocity, non-thermal line broadening) of a tornado-like structure. We calculate line-of-sight velocities and non-thermal line width using Gaussian fitting for Mg II lines (IRIS) and a bisector method for H$\alpha$ line (MSDP). We determine the electron density and temperature from Mg II line integrated intensities using radiative transfer theory. We find that the red and blue Doppler-shifted areas present a coherent position in H$\alpha$ and Mg II h\&k lines along the fast-evolving prominence features. The EUV observations suggest long magnetic field lines on the sides of the prominence. The tornado-like at the top of the prominence consists of multiplefine threads with opposite flows, all of them being supported in dips of long magnetic field lines. From time to time, condensed blobs escape along these field lines. We conjecture that micro or macro turbulence exists at the top of the prominence and could form the small threads giving the impression of rotation. Title: The Solar Orbiter Science Activity Plan. Translating solar and heliospheric physics questions into action Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.; Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra, A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.; Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.; Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.; Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.; Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.; Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio, L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun, A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso, F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.; Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.; Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.; van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi, L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine, D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot, S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham, G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier, K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins, J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis, I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.; Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis, G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.; Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.; Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis, K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien, H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.; Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.; Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines, J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.; Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.; Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.; Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.; Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.; Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula, G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio, A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.; Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann, T.; Young, P. R.; Zhukov, A. N. Bibcode: 2020A&A...642A...3Z Altcode: 2020arXiv200910772Z Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) What drives the solar wind and where does the coronal magnetic field originate?; (2) How do solar transients drive heliospheric variability?; (3) How do solar eruptions produce energetic particle radiation that fills the heliosphere?; (4) How does the solar dynamo work and drive connections between the Sun and the heliosphere? Maximising the mission's science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to Earth (affecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, since each orbit's science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. It is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. First, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called Science Activity Plan (SAP) is developed to achieve this. The SAP groups objectives that require similar observations into Solar Orbiter Observing Plans, resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime. This allows for all four mission goals to be addressed. In this paper, we introduce Solar Orbiter's SAP through a series of examples and the strategy being followed. 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: John Campbell Brown OBE (1947-2019) Authors: Fletcher, Lyndsay; Labrosse, Nicolas; Mackinnon, Alexander Bibcode: 2020A&G....61b2.14F Altcode: Astronomer Royal for Scotland and inspirational solar physicist, by Lyndsay Fletcher, Nicolas Labrosse and Alec MacKinnon. Title: Rapid time variability of the UV spectral line profiles in a small flare - evidence of chromospheric turbulence and heating Authors: Fletcher, L.; Jeffrey, N. L. S.; Labrosse, N.; Simoes, P. J. D. A. Bibcode: 2019AGUFMSH13D3424F Altcode: We present observations of rapid variations in the spectral line profiles in the B-class flare SOL2016-12-06T10:36:58 detected by the Interface Region Imaging Spectograph (IRIS). The flare was observed at a cadence of 1.7s, a time resolution that allows us to detect variations during the flare rise and its rapid subsequent evolution, as follows: (i) For Si IV 1402.77Å, the line broadens significantly above its expected thermal width around 10 seconds prior to the flare's strong radiative signatures. Modelling shows that in this event the Si IV line is optically thin, so the evolving line broadening suggests the development of transition region turbulence, leading to flare heating; (ii) In the optically thick Mg II k line, formed deeper in the chromosphere, marked differences appear in the time profiles of the core and wing intensities, and there are also rapidly varying line asymmetries and a filling in of the pre-flare central reversal of this line. An increase in the line core width is also seen. We will discuss possible interpretations of the evolution these two lines in the context of evolving turbulence and chromospheric pressure, and opacity effects. Title: Modelling of Mg II lines in solar prominences Authors: Levens, P. J.; Labrosse, N. Bibcode: 2019A&A...625A..30L Altcode: 2019arXiv190200086L Context. Observations of the Mg II h and k lines in solar prominences with IRIS reveal a wide range of line shapes from simple non-reversed profiles to typical double-peaked reversed profiles, and with many other possible complex line shapes. The physical conditions responsible for this variety are not well understood.
Aims: Our aim is to understand how physical conditions inside a prominence slab influence shapes and properties of emergent Mg II line profiles.
Methods: We compute the spectrum of Mg II lines using a one-dimensional non-LTE radiative transfer code for two large grids of model atmospheres (isothermal isobaric, and with a transition region).
Results: The influence of the plasma parameters on the emergent spectrum is discussed in detail. Our results agree with previous studies. We present several dependencies between observables and prominence parameters which will help with the interpretation of observations. A comparison with known limits of observed line parameters suggests that most observed prominences emitting in Mg II h and k lines are cold, low-pressure, and optically thick structures. Our results indicate that there are good correlations between the Mg II k line intensities and the intensities of hydrogen lines, and the emission measure.
Conclusions: One-dimensional non-LTE radiative transfer codes allow us to understand the main characteristics of the Mg II h and k line profiles in solar prominences, but more advanced codes will be necessary for detailed comparisons. Title: First Spectral Analysis of a Solar Plasma Eruption Using ALMA Authors: Rodger, Andrew S.; Labrosse, Nicolas; Wedemeyer, Sven; Szydlarski, Mikolaj; Simões, Paulo J. A.; Fletcher, Lyndsay Bibcode: 2019ApJ...875..163R Altcode: 2019arXiv190201319R The aim of this study is to demonstrate how the logarithmic millimeter continuum gradient observed using the Atacama Large Millimeter/submillimeter Array (ALMA) may be used to estimate optical thickness in the solar atmosphere. We discuss how using multiwavelength millimeter measurements can refine plasma analysis through knowledge of the absorption mechanisms. Here we use subband observations from the publicly available science verification (SV) data, while our methodology will also be applicable to regular ALMA data. The spectral resolving capacity of ALMA SV data is tested using the enhancement coincident with an X-ray bright point and from a plasmoid ejection event near active region NOAA12470 observed in Band 3 (84-116 GHz) on 2015 December 17. We compute the interferometric brightness temperature light curve for both features at each of the four constituent subbands to find the logarithmic millimeter spectrum. We compared the observed logarithmic spectral gradient with the derived relationship with optical thickness for an isothermal plasma to estimate the structures’ optical thicknesses. We conclude, within 90% confidence, that the stationary enhancement has an optical thickness between 0.02 ≤ τ ≤ 2.78, and that the moving enhancement has 0.11 ≤ τ ≤ 2.78, thus both lie near to the transition between optically thin and thick plasma at 100 GHz. From these estimates, isothermal plasmas with typical Band 3 background brightness temperatures would be expected to have electron temperatures of ∼7370-15300 K for the stationary enhancement and between ∼7440 and 9560 K for the moving enhancement, thus demonstrating the benefit of subband ALMA spectral analysis. Title: Spectral gradient of the thermal millimetre continuum as a diagnostic for optical thickness in the solar atmosphere (Corrigendum) Authors: Rodger, A. S.; Labrosse, N. Bibcode: 2019A&A...623C...3R Altcode: No abstract at ADS Title: Exploration of long-period oscillations in an Hα prominence Authors: Zapiór, M.; Schmieder, B.; Mein, P.; Mein, N.; Labrosse, N.; Luna, M. Bibcode: 2019A&A...623A.144Z Altcode: 2019arXiv190300230Z Context. In previous work, we studied a prominence which appeared like a tornado in a movie made from 193 Å filtergrams obtained with the Atmospheric Imaging Assembly (AIA) imager aboard the Solar Dynamics Observatory (SDO). The observations in Hα obtained simultaneously during two consecutive sequences of one hour with the Multi-channel Subtractive Double Pass Spectrograph (MSDP) operating at the solar tower in Meudon showed that the cool plasma inside the tornado was not rotating around its vertical axis. Furthermore, the evolution of the Dopplershift pattern suggested the existence of oscillations of periods close to the time-span of each sequence.
Aims: The aim of the present work is to assemble the two sequences of Hα observations as a full data set lasting two hours to confirm the existence of oscillations, and determine their nature.
Methods: After having coaligned the Doppler maps of the two sequences, we use a Scargle periodogram analysis and cosine fitting to compute the periods and the phase of the oscillations in the full data set.
Results: Our analysis confirms the existence of oscillations with periods between 40 and 80 min. In the Dopplershift maps, we identify large areas with strong spectral power. In two of them, the oscillations of individual pixels are in phase. However, in the top area of the prominence, the phase is varying slowly, suggesting wave propagation.
Conclusions: We conclude that the prominence does not oscillate as a whole structure but exhibits different areas with their own oscillation periods and characteristics: standing or propagating waves. We discuss the nature of the standing oscillations and the propagating waves. These can be interpreted in terms of gravito-acoustic modes and magnetosonic waves, respectively.

Movie attached to Fig. 2 is available at https://www.aanda.org Title: The development of lower-atmosphere turbulence early in a solar flare Authors: Jeffrey, N. L. S.; Fletcher, L.; Labrosse, N.; Simões, P. J. A. Bibcode: 2018SciA....4.2794J Altcode: 2018arXiv181209906J We present the first observational study of the onset and evolution of solar flare turbulence in the lower solar atmosphere on an unprecedented time scale of 1.7 s using the Interface Region Imaging Spectrograph observing plasma at a temperature of 80,000 K. At this time resolution, nonthermal spectral line broadening, indicating turbulent velocity fluctuations, precedes the flare onset at this temperature and is coincident with net blue-shifts. The broadening decreases as the flare brightens and then oscillates with a period of 10 s. These observations are consistent with turbulence in the lower solar atmosphere at the flare onset, heating that region as it dissipates. This challenges the current view of energy release and transport in the standard solar flare model, suggesting that turbulence partly heats the lower atmosphere. Title: On the Dynamic Nature of a Quiescent Prominence Observed by IRIS and MSDP Spectrographs Authors: Ruan, Guiping; Schmieder, Brigitte; Mein, Pierre; Mein, Nicole; Labrosse, Nicolas; Gunár, Stanislav; Chen, Yao Bibcode: 2018ApJ...865..123R Altcode: Quiescent solar prominences are generally considered to have a stable large-scale structure. However, they consist of multiple small-scale structures that are often significantly dynamic. To understand the nature of prominence plasma dynamics we use the high spatial, temporal, and spectral resolution observations obtained by Interface Region Imaging Spectrograph (IRIS) during a coordinated campaign with the Multichannel Subtractive Double Pass spectrograph at the Meudon Solar Tower. Detailed analysis of the IRIS observations of Mg II lines, including the analysis of Dopplershift and line width obtained with two different methods (quantile method and Gaussian-fit method) are discussed in the frame of the dynamic nature of the structures. Large-scale coherent blueshift and redshift features are observed in Mg II lines and Hα exhibiting a slow evolution during 1:40 hr of observations. We explain the presence of several significantly asymmetric peaks in the observed Mg II line profiles by the presence of several prominence fine structures moving with different velocities located along the line of sight (LOS). In such a case, the decrease of the intensity of individual components of the observed spectra with the distance from the central wavelength can be explained by the Doppler dimming effect. We show that C II line profiles may be used to confirm the existence of multi-components along the LOS. Title: Spectral gradient of the thermal millimetre continuum as a diagnostic for optical thickness in the solar atmosphere Authors: Rodger, A. S.; Labrosse, N. Bibcode: 2018A&A...617L...6R Altcode: 2018arXiv180807797R
Aims: In this Letter we aim to show how the gradient of the thermal millimetre continuum spectrum, as emitted from the quiet solar atmosphere, may be used as a diagnostic for the optical thickness regime at the centre of the observing frequency band.
Methods: We show the theoretical derivation of the gradient of the millimetre continuum for both logarithmic- and linear-scale spectra. We compare this expression with the empirical relationship between the slope of the millimetre continuum spectrum and the plasma optical thickness computed from both isothermal and multi-thermal two-dimensional cylindrical radiative transfer models.
Results: It is found that the logarithmic-scale spectral gradient provides a clear diagnostic for the optical thickness regime for both isothermal and multi-thermal plasmas, provided that a suitable correction is made for a non-constant gaunt factor over the frequency band. For the use of observers we present values for this correction at all ALMA bands and at a wide range of electron temperatures.
Conclusions: We find that the spectral gradient can be used to find (a) whether the source is fully optically thin, (b) the optical thickness of the source if it lies within the transitional regime between optically thin and thick plasma (τ ≈ 10-1-101), or (c) whether the source is fully optically thick for an isothermal plasma. A multi-thermal plasma will act the same as an isothermal plasma for case (a), however, the transitional regime will only extend from τ ≈ 10-1 to τ ≈ 100. Above τ = 1 the slope of the continuum will depend increasingly on the temperature gradient, as well as the optical thickness, reducing the reliability of the diagnostic. Title: Modeling of the Hydrogen Lyman Lines in Solar Flares Authors: Brown, Stephen A.; Fletcher, Lyndsay; Kerr, Graham S.; Labrosse, Nicolas; Kowalski, Adam F.; De La Cruz Rodríguez, Jaime Bibcode: 2018ApJ...862...59B Altcode: 2018arXiv180703373B The hydrogen Lyman lines (91.2 nm < λ < 121.6 nm) are significant contributors to the radiative losses of the solar chromosphere, and they are enhanced during flares. We have shown previously that the Lyman lines observed by the Extreme Ultraviolet Variability instrument onboard the Solar Dynamics Observatory exhibit Doppler motions equivalent to speeds on the order of 30 km s-1. However, contrary to expectations, both redshifts and blueshifts were present and no dominant flow direction was observed. To understand the formation of the Lyman lines, particularly their Doppler motions, we have used the radiative hydrodynamic code, RADYN, along with the radiative transfer code, RH, to simulate the evolution of the flaring chromosphere and the response of the Lyman lines during solar flares. We find that upflows in the simulated atmospheres lead to blueshifts in the line cores, which exhibit central reversals. We then model the effects of the instrument on the profiles, using the Extreme Ultraviolet Variability Experiment (EVE) instrument's properties. What may be interpreted as downflows (redshifted emission) in the lines, after they have been convolved with the instrumental line profile, may not necessarily correspond to actual downflows. Dynamic features in the atmosphere can introduce complex features in the line profiles that will not be detected by instruments with the spectral resolution of EVE, but which leave more of a signature at the resolution of the Spectral Investigation of the Coronal Environment instrument onboard the Solar Orbiter. Title: Observing turbulence early in a solar flare with the high time resolution of IRIS Authors: Jeffrey, Natasha; Simões, Paulo; Fletcher, Lyndsay; Labrosse, Nicolas Bibcode: 2018cosp...42E1609J Altcode: Wave and turbulent dissipation play a key role in the transfer of energy in magnetized plasmas. Here we report the first high time-resolution, <2 s, spectroscopic study of flare turbulence in the lower solar atmosphere, using the Interface Region Imaging Spectrograph (IRIS). We observe the line Si IV 1402.77 Å, formed at a transition region temperature of 80000 K, at the eastern flare footpoint, over a region of <0.3'' during the flare duration. The non-thermal broadening indicates turbulent motions with velocities of 60-70 km/s. The line broadening rises sharply, and precedes the flare onset as indicated by its impulsive radiation signatures in Si IV intensity, extreme ultraviolet (EUV) and X-rays. The <2 s cadence shows that the line broadening oscillates with a period of ∼10 s before its decay, coinciding with motions in the Si IV line centroid position. The results are consistent with the dissipation of turbulent energy in the lower atmosphere, early in the solar flare, and before the flare brightening. Title: Prominence/Tornado plasma parameters Authors: Schmieder, Brigitte; Mein, Pierre; Zapior, Maciej; Labrosse, Nicolas; Lopez Ariste, Arturo Bibcode: 2018cosp...42E3025S Altcode: We present a comparison of the plasma physical parameters in prominences and tornadoes using IRIS data and ground based polarimetry measurements obtained with THEMIS. Mg II lines give a good diagnostics of the temperature and optical thickness of the structures. The Stokes parameters from the He D3 line allow to distinguish the behaviour of the magnetic field in typical prominences and atypical prominences (e.g. bubbles, eruptive prominence). We concentrate on the Dopplershifts in a tornado observed in transition region lines and in Halpha. Our results support the existence of oscillations in tornadoes but not rotation.A reconstruction of the 3D geometry of a helical prominence obtained by following the trajectory of kernels yields surprising results. The loops are shown to be quasi-horizontal structures with no curvature.We conclude that it is important to take into account the 3D structure of the prominence to study the dynamics of the prominence plasma. 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: The Influence of the Solar Coronal Radiation on Coronal Plasma Structures, I: Determination of the Incident Coronal Radiation Authors: Brown, Gerrard M.; Labrosse, Nicolas Bibcode: 2018SoPh..293...35B Altcode: Coronal structures receive radiation not only from the solar disc, but also from the corona. This height-dependent incident radiation plays a crucial role in the excitation and the ionisation of the illuminated plasma. The aim of this article is to present a method for computing the detailed incident radiation coming from the solar corona, which is perceived at a point located at an arbitrary height. The coronal radiation is calculated by integrating the radiation received at a point in the corona over all of the corona visible from this point. The emission from the corona at all wavelengths of interest is computed using atomic data provided by CHIANTI. We obtain the spectrum illuminating points located at varying heights in the corona at wavelengths between 100 and 912 Å when photons can ionise H or He atoms and ions in their ground states. As expected, individual spectral lines will contribute most at the height within the corona where the local temperature is closest to their formation temperature. As there are many spectral lines produced by many ions, the coronal intensity cannot be assumed to vary in the same way at all wavelengths and so must be calculated for each separate height that is to be considered. This code can be used to compute the spectrum from the corona illuminating a point at any given height above the solar surface. This brings a necessary improvement to models where an accurate determination of the excitation and ionisation states of coronal plasma structures is crucial. Title: Reconstruction of a helical prominence in 3D from IRIS spectra and images Authors: Schmieder, B.; Zapiór, M.; López Ariste, A.; Levens, P.; Labrosse, N.; Gravet, R. Bibcode: 2017A&A...606A..30S Altcode: 2017arXiv170608078S Context. Movies of prominences obtained by space instruments e.g. the Solar Optical Telescope (SOT) aboard the Hinode satellite and the Interface Region Imaging Spectrograph (IRIS) with high temporal and spatial resolution revealed the tremendous dynamical nature of prominences. Knots of plasma belonging to prominences appear to travel along both vertical and horizontal thread-like loops, with highly dynamical nature.
Aims: The aim of the paper is to reconstruct the 3D shape of a helical prominence observed over two and a half hours by IRIS.
Methods: From the IRIS Mg II k spectra we compute Doppler shifts of the plasma inside the prominence and from the slit-jaw images (SJI) we derive the transverse field in the plane of the sky. Finally we obtain the velocity vector field of the knots in 3D. Results.We reconstruct the real trajectories of nine knots travelling along ellipses.
Conclusions: The spiral-like structure of the prominence observed in the plane of the sky is mainly due to the projection effect of long arches of threads (up to 8 × 104 km). Knots run along more or less horizontal threads with velocities reaching 65 km s-1. The dominant driving force is the gas pressure.

Movies associated to Figs. 1, 9, 10, and 13 are available at http://www.aanda.org Title: Comparing UV/EUV line parameters and magnetic field in a quiescent prominence with tornadoes Authors: Levens, P. J.; Labrosse, N.; Schmieder, B.; López Ariste, A.; Fletcher, L. Bibcode: 2017A&A...607A..16L Altcode: 2017arXiv170804606L Context. Understanding the relationship between plasma and the magnetic field is important for describing and explaining the observed dynamics of solar prominences.
Aims: We determine if a close relationship can be found between plasma and magnetic field parameters, measured at high resolution in a well-observed prominence.
Methods: A prominence observed on 15 July 2014 by the Interface Region Imaging Spectrograph (IRIS), Hinode, the Solar Dynamics Observatory (SDO), and the Télescope Héliographique pour l'Étude du Magnétisme et des Instabilités Solaires (THEMIS) is selected. We perform a robust co-alignment of data sets using a 2D cross-correlation technique. Magnetic field parameters are derived from spectropolarimetric measurements of the He I D3 line from THEMIS. Line ratios and line-of-sight velocities from the Mg II h and k lines observed by IRIS are compared with magnetic field strength, inclination, and azimuth. Electron densities are calculated using Fe xii line ratios from the Hinode Extreme-ultraviolet Imaging Spectrometer, which are compared to THEMIS and IRIS data.
Results: We find Mg II k/h ratios of around 1.4 everywhere, similar to values found previously in prominences. Also, the magnetic field is strongest ( 30 G) and predominantly horizontal in the tornado-like legs of the prominence. The k3 Doppler shift is found to be between ±10 km s-1 everywhere. Electron densities at a temperature of 1.5 × 106 K are found to be around 109 cm-3. No significant correlations are found between the magnetic field parameters and any of the other plasma parameters inferred from spectroscopy, which may be explained by the large differences in the temperatures of the lines used in this study.
Conclusions: This is the first time that a detailed statistical study of plasma and magnetic field parameters has been performed at high spatial resolution in a prominence. Our results provide important constraints on future models of the plasma and magnetic field in these structures. Title: Solar Prominence Modelling and Plasma Diagnostics at ALMA Wavelengths Authors: Rodger, Andrew; Labrosse, Nicolas Bibcode: 2017SoPh..292..130R Altcode: 2017arXiv170405385R Our aim is to test potential solar prominence plasma diagnostics as obtained with the new solar capability of the Atacama Large Millimeter/submillimeter Array (ALMA). We investigate the thermal and plasma diagnostic potential of ALMA for solar prominences through the computation of brightness temperatures at ALMA wavelengths. The brightness temperature, for a chosen line of sight, is calculated using the densities of electrons, hydrogen, and helium obtained from a radiative transfer code under non-local thermodynamic equilibrium (non-LTE) conditions, as well as the input internal parameters of the prominence model in consideration. Two distinct sets of prominence models were used: isothermal-isobaric fine-structure threads, and large-scale structures with radially increasing temperature distributions representing the prominence-to-corona transition region. We compute brightness temperatures over the range of wavelengths in which ALMA is capable of observing (0.32 - 9.6 mm), however, we particularly focus on the bands available to solar observers in ALMA cycles 4 and 5, namely 2.6 - 3.6 mm (Band 3) and 1.1 - 1.4 mm (Band 6). We show how the computed brightness temperatures and optical thicknesses in our models vary with the plasma parameters (temperature and pressure) and the wavelength of observation. We then study how ALMA observables such as the ratio of brightness temperatures at two frequencies can be used to estimate the optical thickness and the emission measure for isothermal and non-isothermal prominences. From this study we conclude that for both sets of models, ALMA presents a strong thermal diagnostic capability, provided that the interpretation of observations is supported by the use of non-LTE simulation results. Title: Prominence and tornado dynamics observed with IRIS and THEMIS Authors: Schmieder, Brigitte; Levens, Peter; Labrosse, Nicolas; Mein, Pierre; Lopez Ariste, Arturo; Zapior, Maciek Bibcode: 2017SPD....4820104S Altcode: Several prominences were observed during campaigns in September 2013 and July 2014 with the IRIS spectrometer and the vector magnetograph THEMIS (Tenerife). SDO/AIA and IRIS provided images and spectra of prominences and tornadoes corresponding to different physical conditions of the transition region between the cool plasma and the corona. The vector magnetic field was derived from THEMIS observations by using the He D3 depolarisation due to the magnetic field. The inversion code (PCA) takes into account the Hanle and Zeeman effects and allows us to compute the strength and the inclination of the magnetic field which is shown to be mostly horizontal in prominences as well as in tornadoes. Movies from SDO/AIA in 304 A and Hinode/SOT in Ca II show the highly dynamic nature of the fine structures. From spectra in Mg II and Si IV lines provided by IRIS and H-alpha observed by the Multi-channel Subtractive Double Pass (MSDP) spectrograph in the Meudon Solar Tower we derived the Doppler shifts of the fine structures and reconstructed the 3D structure of tornadoes. We conclude that the apparent rotation of AIA tornadoes is due to large-scale quasi-periodic oscillations of the plasma along more or less horizontal magnetic structures. Title: Modelling of the hydrogen Lyman lines during solar flares Authors: Brown, Stephen Alistair; Fletcher, Lyndsay; Labrosse, Nicolas Bibcode: 2017SPD....4810303B Altcode: The hydrogen Lyman series and continuum are both observed with high cadence and spectral resolution by the EVE instrument on NASA’s solar dynamics observatory. The Lyman lines, some of which will also be observed by the SPICE spectrometer on Solar Orbiter, can provide useful information about the dynamics of the solar chromosphere during a flare, where most of the event’s energy is deposited. In Brown et al (2016), we measured line shifts in the Lyman lines using the EVE instrument and calculated corresponding plasma flow speeds of around 30 kilometres per second. However, the observed signs of these shifts varied. We have also modelled Lyman line profiles output from the radiative hydrodynamic code RADYN (Carlsson & Stein 1997, Allred et al 2015) and the radiative transfer code RH (Uitenbroek 2001) and present our initial findings. We show that the dynamics of the plasma are reflected in complex features in the true line profile, but that the detection of a line shift in a particular direction from EVE observations may not be indicative of the true plasma flow, particularly when these model profiles are passed through the EVE instrumental response. We present several cases of atmospheric responses for differing amounts of energy input, and outline interesting features in the Lyman line profiles which are thought to be linked to the response of the dynamic atmosphere. Title: Non-Gaussian Velocity Distributions in Solar Flares from Extreme Ultraviolet Lines: A Possible Diagnostic of Ion Acceleration Authors: Jeffrey, Natasha L. S.; Fletcher, Lyndsay; Labrosse, Nicolas Bibcode: 2017ApJ...836...35J Altcode: 2017arXiv170102196J In a solar flare, a large fraction of the magnetic energy released is converted rapidly to the kinetic energy of non-thermal particles and bulk plasma motion. This will likely result in non-equilibrium particle distributions and turbulent plasma conditions. We investigate this by analyzing the profiles of high temperature extreme ultraviolet emission lines from a major flare (SOL2014-03-29T17:44) observed by the EUV Imaging Spectrometer (EIS) on Hinode. We find that in many locations the line profiles are non-Gaussian, consistent with a kappa distribution of emitting ions with properties that vary in space and time. At the flare footpoints, close to sites of hard X-ray emission from non-thermal electrons, the κ index for the Fe xvi 262.976 Å line at 3 MK takes values of 3-5. In the corona, close to a low-energy HXR source, the Fe xxiii 263.760 Å line at 15 MK shows κ values of typically 4-7. The observed trends in the κ parameter show that we are most likely detecting the properties of the ion population rather than any instrumental effects. We calculate that a non-thermal ion population could exist if locally accelerated on timescales ≤0.1 s. However, observations of net redshifts in the lines also imply the presence of plasma downflows, which could lead to bulk turbulence, with increased non-Gaussianity in cooler regions. Both interpretations have important implications for theories of solar flare particle acceleration. Title: Hα Doppler shifts in a tornado in the solar corona Authors: Schmieder, B.; Mein, P.; Mein, N.; Levens, P. J.; Labrosse, N.; Ofman, L. Bibcode: 2017A&A...597A.109S Altcode: 2016arXiv161202232S Context. High resolution movies in 193 Å from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamic Observatory (SDO) show apparent rotation in the leg of a prominence observed during a coordinated campaign. Such structures are commonly referred to as tornadoes. Time-distance intensity diagrams of the AIA data show the existence of oscillations suggesting that the structure is rotating.
Aims: The aim of this paper is to understand if the cool plasma at chromospheric temperatures inside the tornado is rotating around its central axis.
Methods: The tornado was also observed in Hα with a cadence of 30 s by the MSDP spectrograph, operating at the Solar Tower in Meudon. The MSDP provides sequences of simultaneous spectra in a 2D field of view from which a cube of Doppler velocity maps is retrieved.
Results: The Hα Doppler maps show a pattern with alternatively blueshifted and redshifted areas of 5 to 10'' wide. Over time the blueshifted areas become redshifted and vice versa, with a quasi-periodicity of 40 to 60 min. Weaker amplitude oscillations with periods of 4 to 6 min are superimposed onto these large period oscillations.
Conclusions: The Doppler pattern observed in Hα cannot be interpreted as rotation of the cool plasma inside the tornado. The Hα velocity observations give strong constraints on the possible interpretations of the AIA tornado. Title: Evidence for kappa distributions of ions in the flaring solar atmosphere from extreme ultraviolet spectroscopy Authors: Fletcher, L.; Jeffrey, N. L. S.; Labrosse, N. Bibcode: 2016AGUFMSH13D..02F Altcode: We present new evidence for ion kappa distributions in the lower solar atmosphere, and in the solar corona, during the impulsive energy release phase of solar flares. The existence of non-Maxwellian electron distributions during flares is well established from X-ray spectroscopy, but ion populations are harder to diagnose. By careful fitting of the spectral line profiles from highly ionised states of iron observed during flares by the Extreme Ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft, and taking into account the spectrometer's known instrumental characteristics, we establish that the physical line profile is consistent with that emitted by a kappa distribution of ions. Kappa distributions provide a far better fit than Maxwellian distributions in many cases, and are detected both at the chromospheric footpoints and in the corona during flares, but with different parameters. We discuss the possible origins of these ion distributions, and their implications for solar flare ion acceleration. Title: Doppler speeds of the hydrogen Lyman lines in solar flares from EVE Authors: Brown, Stephen A.; Fletcher, Lyndsay; Labrosse, Nicolas Bibcode: 2016A&A...596A..51B Altcode: 2016arXiv161004007B
Aims: The hydrogen Lyman lines provide important diagnostic information about the dynamics of the chromosphere, but there have been few systematic studies of their variability during flares. We investigate Doppler shifts in these lines in several flares, and use these to calculate plasma speeds.
Methods: We use spectral data from the Multiple EUV Grating Spectrograph B (MEGS-B) detector of the Extreme-Ultraviolet Variability Experiment (EVE) instrument on the Solar Dynamics Observatory. MEGS-B obtains full-disk spectra of the Sun at a resolution of 0.1 nm in the range 37-105 nm, which we analyse using three independent methods. The first method performs Gaussian fits to the lines, and compares the quiet-Sun centroids with the flaring ones to obtain the Doppler shifts. The second method uses cross-correlation to detect wavelength shifts between the quiet-Sun and flaring line profiles. The final method calculates the "center-of-mass" of the line profile, and compares the quiet-Sun and flaring centroids to obtain the shift.
Results: In a study of 6 flares we find strong signatures of both upflow and downflow in the Lyman lines, with speeds measured in Sun-as-a-Star data of around 10 km s-1, and speeds in the flare excess signal of around 30 km s-1.
Conclusions: All events showing upflows in Lyman lines are associated with some kind of eruption or coronal flow in imaging data, which may be responsible for the net blueshifts. Events showing downflows in the Lyman lines may be associated with loop contraction or faint downflows, but it is likely that chromospheric condensation flows are also contributing. Title: Doppler speeds of the hydrogen Lyman lines in solar flares from EVE Authors: Brown, Stephen; Fletcher, Lyndsay; Labrosse, Nicolas Bibcode: 2016usc..confE...7B Altcode: The hydrogen Lyman lines provide important diagnostic information about the dynamics of the chromosphere, but until recently there have been few systematic studies of their variability during flares. We investigate Doppler shifts in these lines in several flares, and use these to calculate plasma speeds. We use spectral data from the Multiple EUV Grating Spectrograph B (MEGS-B) detector on board the Extreme-Ultraviolet Variability Experiment (EVE) instrument on the Solar Dynamics Observatory. MEGS-B obtains full-disk spectra of the Sun at a resolution of 0.1nm in the range 37-105nm, which we analyse using three independent methods. The first method performs Gaussian fits to the lines, and compares the quiet-Sun centroids with the flaring ones to obtain the Doppler shifts. The second method uses cross-correlation to detect wavelength shifts between the quiet-Sun and flaring line profiles. The final method calculates the "center-of-mass" of the line profile, and compares the quiet-Sun and flaring centroids to obtain the shift. In a study of 6 flares we find signatures of both upflow and downflow in the Lyman lines, with speeds of around 10 km s^-1 in the line profiles that have not undergone pre-flare subtraction, and speeds in the flare-excess profiles of around 30 km s^-1 . We include analysis of AIA images of these events in order to understand potential contributions from material ejections, and find that not all upflows can be explained by ejecta. We discuss current and future attempts at modelling these line profiles. Title: Magnetic Field in Atypical Prominence Structures: Bubble, Tornado, and Eruption Authors: Levens, P. J.; Schmieder, B.; López Ariste, A.; Labrosse, N.; Dalmasse, K.; Gelly, B. Bibcode: 2016ApJ...826..164L Altcode: 2016arXiv160505964L Spectropolarimetric observations of prominences have been obtained with the THEMIS telescope during four years of coordinated campaigns. Our aim is now to understand the conditions of the cool plasma and magnetism in “atypical” prominences, namely when the measured inclination of the magnetic field departs, to some extent, from the predominantly horizontal field found in “typical” prominences. What is the role of the magnetic field in these prominence types? Are plasma dynamics more important in these cases than the magnetic support? We focus our study on three types of “atypical” prominences (tornadoes, bubbles, and jet-like prominence eruptions) that have all been observed by THEMIS in the He I D3 line, from which the Stokes parameters can be derived. The magnetic field strength, inclination, and azimuth in each pixel are obtained by using the inversion method of principal component analysis on a model of single scattering in the presence of the Hanle effect. The magnetic field in tornadoes is found to be more or less horizontal, whereas for the eruptive prominence it is mostly vertical. We estimate a tendency toward higher values of magnetic field strength inside the bubbles than outside in the surrounding prominence. In all of the models in our database, only one magnetic field orientation is considered for each pixel. While sufficient for most of the main prominence body, this assumption appears to be oversimplified in atypical prominence structures. We should consider these observations as the result of superposition of multiple magnetic fields, possibly even with a turbulent field component. Title: Prominence plasma and magnetic field structure - A coordinated observation with IRIS, Hinode and THEMIS Authors: Schmieder, Brigitte; Labrosse, Nicolas; Levens, Peter; Lopez Ariste, Arturo Bibcode: 2016cosp...41E1749S Altcode: During an international campaign in 2014, utilising both space-based (IRIS and Hinode) and ground-based (THEMIS) instruments, we focused on observing prominences. We compare IRIS observations with those of Hinode (EIS and SOT) in order to build a more complete picture of the prominence structure for a quiescent prominence observed on 15 July 2014, identified to have tornado-like structure. THEMIS provides valuable information on the orientation and strength of the internal magnetic field. Here we find there is almost ubiquitously horizontal field with respect to the local limb, with possibly a turbulent component. The Mg II lines form the majority of our IRIS analysis, with a mixture of reversed and non-reversed profiles present in the prominence spectra. Comparing the differences between the Mg II data from IRIS and the Ca II images from Hinode/SOT provides an intriguing insight into the prominence legs in these channels. We present plasma diagnostics from IRIS, with line of sight velocities of around 10 km/s in either direction along the magnetic loops of material in the front of the prominence, and line widths comparable to those found for prominences by previous authors (e.g. Schmieder et al. 2014). We also take a look into the lines formed at higher, coronal plasma temperatures, as seen by Hinode/EIS, to compare plasma structures at a full range of temperatures. Title: First evidence of non-Gaussian solar flare EUV spectral line profiles and accelerated non-thermal ion motion Authors: Jeffrey, Natasha L. S.; Fletcher, Lyndsay; Labrosse, Nicolas Bibcode: 2016A&A...590A..99J Altcode: 2016arXiv160107308J Context. The properties of solar flare plasma can be determined from the observation of optically thin lines. The emitting ion distribution determines the shape of the spectral line profile, with an isothermal Maxwellian ion distribution producing a Gaussian profile. Non-Gaussian line profiles may indicate more complex ion distributions.
Aims: We investigate the possibility of determining flare-accelerated non-thermal ion and/or plasma velocity distributions.
Methods: We study EUV spectral lines produced during a flare SOL2013-05-15T01:45 using the Hinode EUV Imaging Spectrometer (EIS). The flare is located close to the eastern solar limb with an extended loop structure, allowing the different flare features: ribbons, hard X-ray (HXR) footpoints and the loop-top source to be clearly observed in UV, EUV and X-rays. EUV line spectroscopy is performed in seven different regions covering the flare. We study the line profiles of the isolated and unblended Fe XVI lines (λ262.9760 Å ) mainly formed at temperatures of ~2 to 4 MK. Suitable Fe XVI line profiles at one time close to the peak soft X-ray emission and free of directed mass motions are examined using: 1. a higher moments analysis, 2. Gaussian fitting, and 3. by fitting a kappa distribution line profile convolved with a Gaussian to account for the EIS instrumental profile.
Results: Fe XVI line profiles in the flaring loop-top, HXR footpoint and ribbon regions can be confidently fitted with a kappa line profile with an extra variable κ, giving low, non-thermal κ values between 2 and 3.3. An independent higher moments analysis also finds that many of the spectral line kurtosis values are higher than the Gaussian value of 3, even with the presence of a broad Gaussian instrumental profile.
Conclusions: A flare-accelerated non-thermal ion population could account for both the observed non-Gaussian line profiles, and for the Fe XVI "excess" broadening found from Gaussian fitting, if the emitting ions are interacting with a thermalised ~4 MK electron population, and the instrumental profile is well-approximated by a Gaussian profile. 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: 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: Observations and Modelling of Helium Lines in Solar Flares Authors: Simões, P. J. A.; Fletcher, L.; Labrosse, N.; Kerr, G. S. Bibcode: 2016ASPC..504..197S Altcode: 2015arXiv151203477S We explore the response of the He <small>II</small> 304 Å and He <small>I</small> 584 Å line intensities to electron beam heating in solar flares using radiative hydrodynamic simulations. Comparing different electron beams parameters, we found that the intensities of both He lines are very sensitive to the energy flux deposited in the chromosphere, or more specifically to the heating rate, with He <font size=2>II 304 Å being more sensitive to the heating than He <small>I</small> 584 Å. Therefore, the He line ratio increases for larger heating rates in the chromosphere. A similar trend is found in observations, using SDO/EVE He irradiance ratios and estimates of the electron beam energy rate obtained from hard X-ray data. From the simulations, we also found that spectral index of the electrons can affect the He ratio but a similar effect was not found in the observations. Title: Radiative transfer in cylindrical threads with incident radiation. VII. Multi-thread models Authors: Labrosse, N.; Rodger, A. S. Bibcode: 2016A&A...587A.113L Altcode: 2016arXiv160102392L
Aims: Our aim is to improve on previous radiative transfer calculations in illuminated cylindrical threads to better understand the physical conditions in cool solar chromospheric and coronal structures commonly observed in hydrogen and helium lines.
Methods: We solved the radiative transfer and statistical equilibrium equations in a two-dimensional cross-section of a cylindrical structure oriented horizontally and lying above the solar surface. The cylinder is filled with a mixture of hydrogen and helium and is illuminated at a given altitude from the solar disc. We constructed simple models made from a single thread or from an ensemble of several threads along the line of sight. This first use of two-dimensional, multi-thread fine structure modelling combining hydrogen and helium radiative transfer allowed us to compute synthetic emergent spectra from cylindrical structures and to study the effect of line-of-sight integration of an ensemble of threads under a range of physical conditions. We analysed the effects of variations in temperature distribution and in gas pressure. We considered the effect of multi-thread structures within a given field of view and the effect of peculiar velocities between the structures in a multi-thread model. We compared these new models to the single thread model and tested them with varying parameters.
Results: The presence of a temperature gradient, with temperature increasing towards the edge of the cylindrical thread, reduces the relative importance of the incident radiation coming from the solar disc on the emergent intensities of most hydrogen and helium lines. We also find that when assuming randomly displaced threads in a given field of view, the integrated intensities of optically thick and thin transitions behave considerably differently. In optically thin lines, the emergent intensity increases proportionally with the number of threads, and the spatial variation of the intensity becomes increasingly homogeneous. Optically thick lines, however, saturate after only a few threads. As a consequence, the spatial variation of the intensity retains much similarity with that of the first few threads. The multi-thread model produces complex line profiles with significant asymmetries if randomly generated line-of-sight velocities are added for each thread.
Conclusions: These new computations show, for the first time, the effect of integrating the radiation emitted in H and He lines by several cylindrical threads that are static or moving along the line of sight. They can be used to interpret high-spatial and spectral resolutions of cylindrical structures found in the solar atmosphere, such as cool coronal loops or prominence threads. Title: Structure of Prominence Legs: Plasma and Magnetic Field Authors: Levens, P. J.; Schmieder, B.; Labrosse, N.; López Ariste, A. Bibcode: 2016ApJ...818...31L Altcode: 2015arXiv151204727L We investigate the properties of a “solar tornado” observed on 2014 July 15, and aim to link the behavior of the plasma to the internal magnetic field structure of the associated prominence. We made multi-wavelength observations with high spatial resolution and high cadence using SDO/AIA, the Interface Region Imaging Spectrograph (IRIS) spectrograph, and the Hinode/Solar Optical Telescope (SOT) instrument. Along with spectropolarimetry provided by the Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Solaires telescope we have coverage of both optically thick emission lines and magnetic field information. AIA reveals that the two legs of the prominence are strongly absorbing structures which look like they are rotating, or oscillating in the plane of the sky. The two prominence legs, which are both very bright in Ca II (SOT), are not visible in the IRIS Mg II slit-jaw images. This is explained by the large optical thickness of the structures in Mg II, which leads to reversed profiles, and hence to lower integrated intensities at these locations than in the surroundings. Using lines formed at temperatures lower than 1 MK, we measure relatively low Doppler shifts on the order of ±10 km s-1 in the tornado-like structure. Between the two legs we see loops in Mg II, with material flowing from one leg to the other, as well as counterstreaming. It is difficult to interpret our data as showing two rotating, vertical structures that are unrelated to the loops. This kind of “tornado” scenario does not fit with our observations. The magnetic field in the two legs of the prominence is found to be preferentially horizontal. Title: ALMA Observations of the Sun in Cycle 4 and Beyond Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.; Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.; Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson, M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.; Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov, V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões, P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig, A.; White, S.; Yagoubov, P.; Zaqarashvili, T. Bibcode: 2016arXiv160100587W Altcode: This document was created by the Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) in preparation of the first regular observations of the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA), which are anticipated to start in ALMA Cycle 4 in October 2016. The science cases presented here demonstrate that a large number of scientifically highly interesting observations could be made already with the still limited solar observing modes foreseen for Cycle 4 and that ALMA has the potential to make important contributions to answering long-standing scientific questions in solar physics. With the proposal deadline for ALMA Cycle 4 in April 2016 and the Commissioning and Science Verification campaign in December 2015 in sight, several of the SSALMON Expert Teams composed strategic documents in which they outlined potential solar observations that could be feasible given the anticipated technical capabilities in Cycle 4. These documents have been combined and supplemented with an analysis, resulting in recommendations for solar observing with ALMA in Cycle 4. In addition, the detailed science cases also demonstrate the scientific priorities of the solar physics community and which capabilities are wanted for the next observing cycles. The work on this White Paper effort was coordinated in close cooperation with the two international solar ALMA development studies led by T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be further updated until the beginning of Cycle 4 in October 2016. In particular, we plan to adjust the technical capabilities of the solar observing modes once finally decided and to further demonstrate the feasibility and scientific potential of the included science cases by means of numerical simulations of the solar atmosphere and corresponding simulated ALMA observations. Title: SSALMON - The Solar Simulations for the Atacama Large Millimeter Observatory Network Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu, B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.; Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.; Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier, A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M. Bibcode: 2015AdSpR..56.2679W Altcode: 2015arXiv150205601W The Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) was initiated in 2014 in connection with two ALMA development studies. The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful new tool, which can also observe the Sun at high spatial, temporal, and spectral resolution. The international SSALMONetwork aims at co-ordinating the further development of solar observing modes for ALMA and at promoting scientific opportunities for solar physics with particular focus on numerical simulations, which can provide important constraints for the observing modes and can aid the interpretation of future observations. The radiation detected by ALMA originates mostly in the solar chromosphere - a complex and dynamic layer between the photosphere and corona, which plays an important role in the transport of energy and matter and the heating of the outer layers of the solar atmosphere. Potential targets include active regions, prominences, quiet Sun regions, flares. Here, we give a brief overview over the network and potential science cases for future solar observations with ALMA. Title: Determining energy balance in the flaring chromosphere from oxygen V line ratios Authors: Graham, D. R.; Fletcher, L.; Labrosse, N. Bibcode: 2015A&A...584A...6G Altcode: 2014arXiv1411.4603G Context. The impulsive phase of solar flares is a time of rapid energy deposition and heating in the lower solar atmosphere, leading to changes in the temperature and density structure of the region.
Aims: We use an O v density diagnostic formed from the λ192 /λ248 line ratio, provided by the Hinode/EIS instrument, to determine the density of flare footpoint plasma at O v formation temperatures of ~2.5 × 105 K, giving a constraint on the properties of the heated transition region.
Methods: Hinode/EIS rasters from 2 small flare events in December 2007 were used. Raster images were co-aligned to identify and establish the footpoint pixels, multiple-component Gaussian line fitting of the spectra was carried out to isolate the density diagnostic pair, and the density was calculated for several footpoint areas. The assumptions of equilibrium ionisation and optically-thin radiation for the O v lines used were assessed and found to be acceptable. For one of the events, properties of the electron distribution were deduced from earlier RHESSI hard X-ray observations. These were used to calculate the plasma heating rate delivered by an electron beam for 2 semi-empirical atmospheres under collisional thick-target assumptions. The radiative loss rate for this plasma was also calculated for comparison with possible energy input mechanisms.
Results: Electron number densities of up to 1011.9 cm-3 were measured during the flare impulsive phase using the O v λ192 /λ248 diagnostic ratio. The heating rate delivered by an electron beam was found to exceed the radiative losses at this density, corresponding to a height of 450 km, and when assuming a completely ionised target atmosphere far exceed the losses but at a height of 1450-1600 km. A chromospheric thickness of 70-700 km was found to be required to balance a conductive input to the O v-emitting region with radiative losses.
Conclusions: Electron densities have been observed in footpoint sources at transition region temperatures, comparable to previous results but with improved spatial information. The observed densities can be explained by heating of the chromosphere by collisional electrons, with O v formed at heights of 450-1600 km above the photosphere, depending on the atmospheric ionisation fraction. Title: A solar tornado observed by EIS. Plasma diagnostics Authors: Levens, P. J.; Labrosse, N.; Fletcher, L.; Schmieder, B. Bibcode: 2015A&A...582A..27L Altcode: 2015arXiv150801377L Context. The term "solar tornadoes" has been used to describe apparently rotating magnetic structures above the solar limb, as seen in high resolution images and movies from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO). These often form part of the larger magnetic structure of a prominence, however the links between them remain unclear. Here we present plasma diagnostics on a tornado-like structure and its surroundings, seen above the limb by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard the Hinode satellite.
Aims: We aim to extend our view of the velocity patterns seen in tornado-like structures with EIS to a wider range of temperatures and to use density diagnostics, non-thermal line widths, and differential emission measures to provide insight into the physical characteristics of the plasma.
Methods: Using Gaussian fitting to fit and de-blend the spectral lines seen by EIS, we calculated line-of-sight velocities and non-thermal line widths. Along with information from the CHIANTI database, we used line intensity ratios to calculate electron densities at each pixel. Using a regularised inversion code we also calculated the differential emission measure (DEM) at different locations in the prominence.
Results: The split Doppler-shift pattern is found to be visible down to a temperature of around log T = 6.0. At temperatures lower than this, the pattern is unclear in this data set. We obtain an electron density of log ne = 8.5 when looking towards the centre of the tornado structure at a plasma temperature of log T = 6.2, as compared to the surroundings of the tornado structure where we find log ne to be nearer 9. Non-thermal line widths show broader profiles at the tornado location when compared to the surrounding corona. We discuss the differential emission measure in both the tornado and the prominence body, which suggests that there is more contribution in the tornado at temperatures below log T = 6.0 than in the prominence.

A movie is available in electronic form at http://www.aanda.org Title: Polarimetric measurements in prominences and "tornadoe" observed by THEMIS Authors: Schmieder, Brigitte; López Ariste, Arturo; Levens, Peter; Labrosse, Nicolas; Dalmasse, Kévin Bibcode: 2015IAUS..305..275S Altcode: Since 2013, coordinated campaigns with the THEMIS spectropolarimeter in Tenerife and other instruments (space based: Hinode/SOT, IRIS or ground based: Sac Peak, Meudon) are organized to observe prominences. THEMIS records spectropolarimetry at the He I D3 and we use the PCA inversion technique to derive their field strength, inclination and azimuth. Title: Derivation of the Major Properties of Prominences Using NLTE Modelling Authors: Labrosse, Nicolas Bibcode: 2015ASSL..415..131L Altcode: I introduce techniques to derive the major properties of prominences based on NLTE modelling. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. Modelling the radiative transfer processes out of local thermodynamic equilibrium allows one to retrieve the prominence plasma parameters (temperature, density, pressure, ionisation degree) as well as the prominence's mass. Title: Plasma properties in eruptive prominences Authors: Labrosse, Nicolas Bibcode: 2014IAUS..300...79L Altcode: Prominence eruptions are one of the most spectacular manifestations of our Sun's activity. Yet there is still some mystery surrounding their relevant physical conditions. What are their plasma parameters? How different are they from those of quiescent prominences? How do they relate to those within coronal mass ejections? We briefly review some recent results in non-LTE radiative transfer modelling which contribute to our knowledge of the plasma properties in eruptive prominences. We discuss in particular how these results, combined with observational data analysis, can help us in determining the plasma parameters in eruptive prominences. Title: Prominences in SDO/EVE spectra: contributions from large solar structures Authors: Labrosse, Nicolas; Hudson, Hugh; Kazachenko, Maria Bibcode: 2014IAUS..300..439L Altcode: The EVE instrument on SDO is making accurate measurements of the solar spectral irradiance in the EUV between 30 and 1069 Å, with 1 Å spectral resolution and 10 s sampling rate. These data define solar variability in the ``Sun-as-a-star'' mode and reveal many interesting kinds of variation. Its high sensitivity also makes it suitable for spectroscopic diagnostics of solar features such as flares. Here we present EVE's potential contribution to the diagnostics of large-scale, slowly evolving features such as prominences and active regions, and what we can learn from this. Title: A new approach to model particle acceleration and energy transfer in solar flares Authors: Rubio Da Costa, Fatima; Zuccarello, F.; Fletcher, L.; Labrosse, N.; Kasparova, J.; Prosecký, T.; Carlsson, M.; Petrosian, V.; Liu, W. Bibcode: 2013SPD....4440401R Altcode: Motivated by available observations of two different flares in Lyα and Hα, we model the conditions of the solar atmosphere using a radiation hydrodynamics code (RADYN, Carlsson & Stein, 1992) and analyze the energy transport carried by a beam of non-thermal electrons injected at the top of a 1D coronal loop. The numerical Lyα and Hα intensities match with the observations. The electron energy distribution is assumed to follow a power law of the form (E/Ec )-δ for energies greater than a cutoff value of Ec. Abbett & Hawley (1999) and Allred et al. (2005) assumed that the non-thermal electrons flux injected at the top of a flaring loop, the cut-off energy and the power law index are constant over time. An improvement was achieved by Allred & Hawley (2006), who modified the RADYN code in such a way that the input parameters were time dependent. Their inputs were based on observations of a flare obtained with RHESSI. By combining RADYN with the “flare” code from Stanford University which models the acceleration and transport of particles and radiation of solar flares in non-LTE regime, we can calculate the non-thermal electrons flux, the cut-off energy and the power law index at every simulated time step. The atmospheric parameters calculated by RADYN could in turn be used as updated inputs for "flare", providing several advantages over the results from Liu et al. (2009), who combined the particle acceleration code with a 1-D hydrodynamic code, improving the atmospheric conditions. Title: PROM4: 1D isothermal and isobaric modeler for solar prominences Authors: Gouttebroze, P.; Labrosse, N. Bibcode: 2013ascl.soft06004G Altcode: PROM4 computes simple models of solar prominences which consist of plane-parallel slabs standing vertically above the solar surface. Each model is defined by 5 parameters: temperature, density, geometrical thickness, microturbulent velocity and height above the solar surface. PROM4 solves the equations of radiative transfer, statistical equilibrium, ionization and pressure equilibria, and computes electron and hydrogen level populations and hydrogen line profiles. Written in Fortran 90 and with two versions available (one with text in English, one with text in French), the code needs 64-bit arithmetic for real numbers.

PROM7 (ascl:1805.023) is a more recent version of this code. 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: The role of filament activation in a solar eruption Authors: Rubio da Costa, F.; Zuccarello, F.; Fletcher, L.; Romano, P.; Labrosse, N. Bibcode: 2012A&A...539A..27R Altcode: 2014arXiv1412.1858R Context. Observations show that the mutual relationship between filament eruptions and solar flares cannot be described in terms of an unique scenario. In some cases, the eruption of a filament appears to trigger a flare, while in others the observations are more consistent with magnetic reconnection that produces both the flare observational signatures (e.g., ribbons, plasma jets, post-flare loops, etc.) and later the destabilization and eruption of a filament.
Aims: Contributing to a better comprehension of the role played by filament eruptions in solar flares, we study an event which occurred in NOAA 8471, where a flare and the activation of (at least) two filaments were observed on 28 February 1999.
Methods: By using imaging data acquired in the 1216, 1600, 171 and 195 Å TRACE channels and by BBSO in the continnum and in the Hα line, a morphological study of the event is carried out. Moreover, using TRACE 1216 and 1600 Å data, an estimate of the "pure" Lyα power is obtained. The extrapolation of the magnetic field lines is done using the SOHO/MDI magnetograms and assuming a potential field.
Results: Initially an area hosting a filament located over a δ spot becomes brighter than the surroundings, both in the chromosphere and in the corona. This area increases in brightness and extension, eventually assuming a two-ribbon morphology, until it reaches the eastern part of the active region. Here a second filament becomes activated and the brightening propagates to the south, passing over a large supergranular cell. The potential magnetic field extrapolation indicates that the field line connectivity changes after the flare.
Conclusions: The event is triggered by the destabilization of a filament located between the two polarities of a δ spot. This destabilization involves the magnetic arcades of the active region and causes the eruption of a second filament, that gives rise to a CME and to plasma motions over a supergranular cell. We conclude that in this event the two filaments play an active and decisive role, albeit in different stages of the phenomenon, in fact the destabilization of one filament causes brightenings, reconnection and ribbons, while the second one, whose eruption is caused by the field reconfiguration resulting from the previous reconnection, undergoes the greatest changes and causes the CME. Title: Plasma diagnostic in eruptive prominences from SDO/AIA observations at 304 Å Authors: Labrosse, N.; McGlinchey, K. Bibcode: 2012A&A...537A.100L Altcode: 2011arXiv1111.4847L Context. Theoretical calculations have shown that when solar prominences move away from the surface of the Sun, their radiative output is affected via the Doppler dimming or brightening effects.
Aims: In this paper we ask whether observational signatures of the changes in the radiative output of eruptive prominences can be found in EUV (extreme ultraviolet) observations of the first resonance line of ionised helium at 304 Å. We also investigate whether these observations can be used to perform a diagnostic of the plasma of the eruptive prominence.
Methods: We first look for suitable events in the SDO/AIA database. The variation of intensity of arbitrarily selected features in the 304 channel is studied as a function of velocity in the plane of the sky. These results are then compared with new non-LTE radiative transfer calculations of the intensity of the He ii 304 resonance line.
Results: We find that observations of intensities in various parts of the four eruptive prominences studied here are sometimes consistent with the Doppler dimming effect on the He ii 304 Å line. However, in some cases, one observes an increase in intensity in the 304 channel with velocity, in contradiction to what is expected from the Doppler dimming effect alone. The use of the non-LTE models allows us to explain the different behaviour of the intensity by changes in the plasma parameters inside the prominence, in particular the column mass of the plasma and its temperature.
Conclusions: The non-LTE models used here are more realistic than what was used in previous calculations. They are able to reproduce qualitatively the range of observations from SDO/AIA analysed in this study. With the help of non-LTE modelling, we can infer the plasma parameters in eruptive prominences from SDO/AIA observations at 304 Å. Title: Relationship between an M6.6 solar flare and subsequent filament activations. Authors: Rubio da Costa, F.; Zuccarello, F.; Romano, P.; Fletcher, L.; Labrosse, N. Bibcode: 2012MSAIS..19..113R Altcode: We study an event which occurred in NOAA 8471, where an M6.6 flare and the activation of two filaments were observed on 28 February 1999. A multi-wavelength study allows us to investigate the behavior of the several features observed at different atmospheric levels, that might be used to answer to the question whether and in what conditions the eruption of filaments can play an active or a passive role in the flare occurrence. Imaging data were acquired by BBSO in the Halpha line and by TRACE in the 1216, 1600, 171 and 195 Å channels, allowing us to deduce the morphology and temporal evolution of the event and to estimate the Ly-alpha power. Moreover, in order to study the magnetic topology, the extrapolation of the photospheric magnetic field lines was done assuming potential field and using SOHO/MDI magnetograms. Title: Solar flares in Halpha and Ly-alpha : observations vs simulations. Authors: Rubio da Costa, F.; Zuccarello, F.; Fletcher, L.; Labrosse, N.; Prosecký, T.; Kašparová, J. Bibcode: 2012MSAIS..19..117R Altcode: In order to study the properties of faint, moderate and bright flares, we simulate the conditions of the solar atmosphere using a radiative hydrodynamic model \citep{2005ApJ...630..573A}. A constant beam of non-thermal electrons is injected at the apex of a 1D coronal loop and heating from thermal soft X-ray and UV emission is included. We study the contribution of different processes to the total intensity of different lines at different atmospheric layers. We obtain the total integrated intensity of different lines and we compare those of the Ly-alpha and Halpha lines with the observational values for Ly-alpha (using TRACE 1216 and 1600 Å data and estimating the ``pure'' Ly-alpha emission) and Halpha (using data from the Ondřejov Observatory). We inferred from the analysis of the values obtained by simulation that the X-ray energy of the different kind of flares does not strongly affect the Ly-alpha results; the Halpha results are comparable to the observed ones, concluding that the simulated solar atmosphere fits better at lower layers of the chromosphere than at upper layers. Title: The EVE Doppler Sensitivity and Flare Observations Authors: Hudson, H. S.; Woods, T. N.; Chamberlin, P. C.; Fletcher, L.; Del Zanna, G.; Didkovsky, L.; Labrosse, N.; Graham, D. Bibcode: 2011SoPh..273...69H Altcode: 2011SoPh..tmp..362H The Extreme-ultraviolet Variability Experiment (EVE; see Woods et al., 2009) obtains continuous EUV spectra of the Sun viewed as a star. Its primary objective is the characterization of solar spectral irradiance, but its sensitivity and stability make it extremely interesting for observations of variability on time scales down to the limit imposed by its basic 10 s sample interval. In this paper we characterize the Doppler sensitivity of the EVE data. We find that the 30.4 nm line of He II has a random Doppler error below 0.001 nm (1 pm, better than 10 km s−1 as a redshift), with ample stability to detect the orbital motion of its satellite, the Solar Dynamics Observatory (SDO). Solar flares also displace the spectrum, both because of Doppler shifts and because of EVE's optical layout, which (as with a slitless spectrograph) confuses position and wavelength. As a flare develops, the centroid of the line displays variations that reflect Doppler shifts and therefore flare dynamics. For the impulsive phase of the flare SOL2010-06-12, we find the line centroid to have a redshift of 16.8 ± 5.9 km s−1 relative to that of the flare gradual phase (statistical errors only). We find also that high-temperature lines, such as Fe XXIV 19.2 nm, have well-determined Doppler components for major flares, with decreasing apparent blueshifts as expected from chromospheric evaporation flows. 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: Solar flares: observations vs simulations Authors: Rubio da Costa, Fatima; Zuccarello, Francesca; Labrosse, Nicolas; Fletcher, Lyndsay; Prosecký, Tomáš; Kašparová, Jana Bibcode: 2011IAUS..274..182R Altcode: In order to study the properties of faint, moderate and bright flares, we simulate the conditions of the solar atmosphere using a radiative hydrodynamic model (Abbett & Hawley, 1999). A constant beam of non-thermal electrons is injected at the apex of a 1D coronal loop and heating from thermal soft X-ray emission is included. We compare the results with some observational data in Ly-α (using TRACE 1216 and 1600 Å data and estimating the ``pure'' Ly-α emission) and in Hα (data taken with a Multichannel Flare Spectrograph, at the Ondrejov Observatory). Title: Automatic Detection of Limb Prominences in 304 Å EUV Images Authors: Labrosse, N.; Dalla, S.; Marshall, S. Bibcode: 2010SoPh..262..449L Altcode: 2009arXiv0912.1099L; 2010SoPh..tmp....6L A new algorithm for automatic detection of prominences on the solar limb in 304 Å EUV images is presented, and results of its application to SOHO/EIT data discussed. The detection is based on the method of moments combined with a classifier analysis aimed at discriminating between limb prominences, active regions, and the quiet corona. This classifier analysis is based on a Support Vector Machine (SVM). Using a set of 12 moments of the radial intensity profiles, the algorithm performs well in discriminating between the above three categories of limb structures, with a misclassification rate of 7%. Pixels detected as belonging to a prominence are then used as the starting point to reconstruct the whole prominence by morphological image-processing techniques. It is planned that a catalogue of limb prominences identified in SOHO and STEREO data using this method will be made publicly available to the scientific community. 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: Integrated Ly-alpha intensity emission in ribbon flares Authors: Rubio da Costa, F.; Fletcher, L.; Labrosse, N.; Zuccarello, F. Bibcode: 2010MSAIS..14..193R Altcode: We have analyzed two flares observed by TRACE in Ly alpha (on 8th September 1999 and 28th February 1999) in order to deduce their morphology, temporal evolution, radiative outputs and compare these results with data obtained in the X-range (SXT and HXT on Yohkoh) and with magnetograms (MDI/SOHO). These observational data and the results obtained by a theoretical study of the intensity of the radiation emitted by hydrogen lines, contribute to construct semi-empirical and theoretical models of the chromospheric emission during flares. Future observations by the planned Extreme Ultraviolet Imager selected for the Solar Orbiter mission -which will have a Lyman alpha channel- and this work, can help in designing observational flare studies. Title: Observations of a solar flare and filament eruption in Lyman α and X-rays Authors: Rubio da Costa, F.; Fletcher, L.; Labrosse, N.; Zuccarello, F. Bibcode: 2009A&A...507.1005R Altcode: 2009arXiv0909.4705R Context: Lα is a strong chromospheric emission line, which has been relatively rarely observed in flares. The Transition Region and Coronal Explorer (TRACE) has a broad “Lyman α” channel centered at 1216 Å used primarily at the beginning of the mission. A small number of flares were observed in this channel.
Aims: We aim to characterise the appearance and behaviour of a flare and filament ejection which occurred on 8th September 1999 and was observed by TRACE in Lα, as well as by the Yohkoh Soft and Hard X-ray telescopes. We explore the flare energetics and its spatial and temporal evolution. We have in mind the fact that the Lα line is a target for the Extreme Ultraviolet Imaging telescope (EUI) which has been selected for the Solar Orbiter mission, as well as the LYOT telescope on the proposed SMESE mission.
Methods: We use imaging data from the TRACE 1216 Å, 1600 Å and 171 Å channels, and the Yohkoh hard and soft X-ray telescopes. A correction is applied to the TRACE data to obtain a better estimate of the pure Lα signature. The Lα power is obtained from a knowledge of the TRACE response function, and the flare electron energy budget is estimated by interpreting Yohkoh/HXT emission in the context of the collisional thick target model.
Results: We find that the Lα flare is characterised by strong, compact footpoints (smaller than the UV ribbons) which correlate well with HXR footpoints. The Lα power radiated by the flare footpoints can be estimated, and is found to be on the order of 1026 erg s-1 at the peak. This is less than 10% of the power inferred for the electrons which generate the co-spatial HXR emission, and can thus readily be provided by them. The early stages of the filament eruption that accompany the flare are also visible, and show a diffuse, roughly circular spreading sheet-like morphology, with embedded denser blobs.
Conclusions: On the basis of this observation, we conclude that flare and filament observations in the Lα line with the planned EUI and LYOT telescopes will provide valuable insight into solar flare evolution and energetics, especially when accompanied by HXR imaging and spectroscopy. Title: Radiative transfer in cylindrical threads with incident radiation. VI. A hydrogen plus helium system Authors: Gouttebroze, P.; Labrosse, N. Bibcode: 2009A&A...503..663G Altcode: 2009arXiv0905.3466G Context: Spectral lines of helium are commonly observed on the Sun. These observations contain important information about physical conditions and He/H abundance variations within solar outer structures.
Aims: The modeling of chromospheric and coronal loop-like structures visible in hydrogen and helium lines requires the use of appropriate diagnostic tools based on NLTE radiative tranfer in cylindrical geometry.
Methods: We use iterative numerical methods to solve the equations of NLTE radiative transfer and statistical equilibrium of atomic level populations. These equations are solved alternatively for hydrogen and helium atoms, using cylindrical coordinates and prescribed solar incident radiation. Electron density is determined by the ionization equilibria of both atoms. Two-dimensional effects are included.
Results: The mechanisms of formation of the principal helium lines are analyzed and the sources of emission inside the cylinder are located. The variations of spectral line intensities with temperature, pressure, and helium abundance, are studied.
Conclusions: The simultaneous computation of hydrogen and helium lines, performed by the new numerical code, allows the construction of loop models including an extended range of temperatures. Title: Formation of Helium Lines in Solar Prominences Authors: Labrosse, Nicolas; Gouttebroze, Pierre Bibcode: 2009AIPC.1171..361L Altcode: We summarize the results on the formation of the helium spectrum in solar prominences obtained over recent years. The radiative transfer problem under non-LTE conditions is solved to compute the profiles of the lines of He I and He II. The structure of the prominence-to-corona transition region (PCTR) has a major influence on the resulting spectrum of the resonance lines since they are formed mostly in this part of the prominence. However, subordinate lines are also affected by the structure of the PCTR. We pay particular attention to the formation of the He II 304 A˚ resonance line which is routinely observed from space, but yet not fully understood. Future steps in the modelling will be addressed. 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: Diagnostics of active and eruptive prominences through hydrogen and helium lines modelling Authors: Labrosse, N.; Vial, J. -C.; Gouttebroze, P. Bibcode: 2008AnGeo..26.2961L Altcode: 2008arXiv0804.4625L In this study we show how hydrogen and helium lines modelling can be used to make a diagnostic of active and eruptive prominences. One motivation for this work is to identify the physical conditions during prominence activation and eruption. Hydrogen and helium lines are key in probing different parts of the prominence structure and inferring the plasma parameters. However, the interpretation of observations, being either spectroscopic or obtained with imaging, is not straightforward. Their resonance lines are optically thick, and the prominence plasma is out of local thermodynamic equilibrium due to the strong incident radiation coming from the solar disk. In view of the shift of the incident radiation occuring when the prominence plasma flows radially, it is essential to take into account velocity fields in the prominence diagnostic. Therefore we need to investigate the effects of the radial motion of the prominence plasma on hydrogen and helium lines. The method that we use is the resolution of the radiative transfer problem in the hydrogen and helium lines out of local thermodynamic equilibrium. We study the variation of the computed integrated intensities in H and He lines with the radial velocity of the prominence plasma. We can confirm that there exist suitable lines which can be used to make a diagnostic of the plasma in active and eruptive prominences in the presence of velocity fields. Title: Investigation of Lyman <alpha> Emission in a Solar Flare Authors: Rubio da Costa, F.; Fletcher, L.; Labrosse, N.; Zuccarello, F. Bibcode: 2008ESPM...12.2.64R Altcode: The TRACE satellite observed a small number of solar flares in the Lyman alpha channel, which have until now not been analysed. We look at a well-observed flare on 8th September 1999 to investigate different topics. We carry out a study of the spatial and temporal evolution of the flare and associated filament eruption in Lyman alpha, hard X-rays and soft X-rays, and examine the flare energetics using the hard X-rays (in the collisional thick target approximation) to estimate the energy flux carried by electrons, and TRACE Lyman alpha/1600 Å channels to estimate the temperature and radiative power in UV. We will use these observations to anticipate what can be observed in the future by the proposed SMESE satellite mission, and to compare with predictions of semi-empirical and theoretical models of the flare chromosphere. Title: The Lyman-alpha Line in Active and Eruptive Solar Prominences Authors: Labrosse, N.; Vial, J. -C. Bibcode: 2008ESPM...12.3.17L Altcode: We investigate the effects of radial motions on the Ly-alpha emission in moving prominences under various temperature and pressure conditions and for various prominence masses. The ability to compute the Ly-alpha line intensity in active and erupting prominences with our non-LTE radiative transfer code is especially relevant to VAULT and to the LYOT instrument on SMESE. In the case of erupting prominences, high-cadence imaging as anticipated from LYOT/SMESE, will allow us to observe the dimming of the line as the prominence expands in the radial direction. In conjunction with our non-LTE radiative transfer code, the diagnostic of the thermodynamical plasma parameters and the velocity field can be done. This should provide new constraints for models of filament and prominence eruptions. 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: On VI and H2 Lines in Sunspots Authors: Labrosse, N.; Morgan, H.; Habbal, S. R.; Brown, D. Bibcode: 2007ASPC..368..247L Altcode: 2006astro.ph.11490L Sunspots are locations on the Sun where unique atmospheric conditions prevail. In particular, the very low temperatures found above sunspots allow the emission of H2 lines. In this study we are interested in the radiation emitted by sunspots in the O VI lines at 1031.96 Å and 1037.60 Å. We use SOHO/SUMER observations of a sunspot performed in March 1999 and investigate the interaction between the O VI lines and a H2 line at 1031.87 Å found in the Werner band. The unique features of sunspots atmospheres may very well have important implications regarding the illumination of coronal O+5 ions in the low corona, affecting our interpretation of Doppler dimming diagnostics. Title: Spectral Diagnostics of Active Prominences Authors: Labrosse, N.; Gouttebroze, P.; Vial, J. -C. Bibcode: 2007ASPC..368..337L Altcode: 2006astro.ph.11488L Active prominences exhibit plasma motions, resulting in difficulties with the interpretation of spectroscopic observations. These solar features being strongly influenced by the radiation coming from the solar disk, Doppler dimming or brightening effects may arise, depending on which lines are observed and on the velocity of the plasma. Interlocking between the different atomic energy levels and non local thermodynamic equilibrium lead to non-trivial spectral line profiles, and this calls for complex numerical modeling of the radiative transfer in order to understand the observations. We present such a tool, which solves the radiative transfer and statistical equilibrium for H, He I, He II, and Ca II in moving prominences where radial plasma motions are taking place. It is found that for isothermal, isobaric prominence models, the He II resonance lines are very sensitive to the Doppler effect and thus show a strong Doppler dimming. The Ca II lines Doppler effect for the prominence models considered here. We illustrate how the code makes it possible to retrieve the plasma thermodynamic parameters by comparing computed and observed line profiles of hydrogen and helium resonance lines in a quiescent prominence. This new non-LTE radiative transfer code including velocities allows us to better understand the formation of several lines of importance in prominences, and in conjunction with observations, infer the prominence plasma thermodynamic properties and full velocity vector. Title: Effect of motions in prominences on the helium resonance lines in the extreme ultraviolet Authors: Labrosse, N.; Gouttebroze, P.; Vial, J. -C. Bibcode: 2007A&A...463.1171L Altcode: 2006astro.ph..8221L Context: Extreme ultraviolet resonance lines of neutral and ionised helium observed in prominences are difficult to interpret as the prominence plasma is optically thick at these wavelengths. If mass motions are taking place, as is the case in active and eruptive prominences, the diagnostic is even more complex.
Aims: We aim at studying the effect of radial motions on the spectrum emitted by moving prominences in the helium resonance lines and at facilitating the interpretation of observations, in order to improve our understanding of these dynamic structures.
Methods: We develop our non-local thermodynamic equilibrium radiative transfer code formerly used for the study of quiescent prominences. The new numerical code is now able to solve the statistical equilibrium and radiative transfer equations in the non-static case by using velocity-dependent boundary conditions for the solution of the radiative transfer problem. This first study investigates the effects of different physical conditions (temperature, pressure, geometrical thickness) on the emergent helium radiation.
Results: The motion of the prominence plasma induces a Doppler dimming effect on the resonance lines of He I and He II. The velocity effects are particularly important for the He II λ 304 Å line as it is mostly formed by resonant diffusion of incident radiation under prominence conditions. The He I resonance lines at 584 and 537 Å also show some sensitivity to the motion of the plasma, all the more when thermal emission is not too important in these lines. We also show that it is necessary to consider partial redistribution in frequency for the scattering of the incident radiation.
Conclusions: .This set of helium lines offers strong diagnostic possibilities that can be exploited with the SOHO spectrometers and with the EIS spectrometer on board the Hinode satellite. The addition of other helium lines and of lines from other elements (in particular hydrogen) in the diagnostics will further enhance the strength of the method.

Figures [see full text], [see full text] and [see full text] are only available in electronic form at http://www.aanda.org Title: On the Lyman α and β lines in solar coronal streamers Authors: Labrosse, N.; Li, X.; Li, B. Bibcode: 2006A&A...455..719L Altcode: 2006astro.ph..6099L Aims.We investigate the formation of the H I Lyman α and Lyman β lines in an equatorial coronal streamer. Particular attention is paid to frequency redistribution for the scattering of the incident radiation. The properties of the spectral lines are studied.
Methods.The coronal model is given by a global 2.5D three fluid solar wind model with α particles. The emergent intensities and line profiles are calculated from the solution of the statistical equilibrium and radiative transfer equations for an hydrogen atom with 11 energy levels under non local thermodynamic equilibrium. The formation of the lines results from radiative excitation, collisional excitation, and takes into account the coupling with all other transitions between the hydrogen energy levels.
Results.We present new estimates of the radiative and collisional contributions of the Lyman line intensities within the streamer. It is also shown that within the streamer, the full width at half-maximum (FWHM) of the Lyman β line is a better indicator of the plasma temperature than that of Lyman α. These results show that care should be taken when inferring the proton temperature from the Lyman α line profile as observed in coronal streamers, e.g. by the Ultraviolet Coronagraph Spectrometer or the Solar Ultraviolet Measurements of Emitted Radiation experiments on board the Solar and Heliospheric Observatory.
Title: A global 2.5-dimensional three fluid solar wind model with alpha particles Authors: Li, Bo; Li, Xing; Labrosse, Nicolas Bibcode: 2006JGRA..111.8106L Altcode: 2006JGRA..11108106L A global 2.5-dimensional three fluid solar wind model is presented. Two ion species, namely protons and alpha particles, are heated by an empirical energy flux while electrons are heated by the classical heat flux and Coulomb coupling with ions. It is found that for a reasonable relative speed between alpha particles and protons at 1 AU to be achieved, the alphas need to be preferentially heated in the inner corona. No external heating is applied in the streamer base, the closed magnetic field region. A hot coronal boundary, the electron heat flux, and Coulomb coupling keep plasma species in equilibrium inside the streamer, and a nonisothermal streamer is found. The abundance of alpha particles varies within the streamer base. It is small in the streamer core compared with streamer legs, and alphas continuously drain out of the streamer core along magnetic field due to gravitational settling. The settling operates over a timescale of several days. Alpha particles in the slow wind have a smaller abundance than in the fast wind at 1 AU, in agreement with observations. This is mainly determined in the near-Sun region. For the coronal alpha abundances in the range 0.015-0.15, it is found that alpha particles play a negligible role in determining the magnetic field. In this sense, treating alphas as test particles is justified. However, alphas have an important impact on solar wind parameters. Coulomb collisions and heating drag alphas into the solar wind. The Coulomb friction with protons by itself is, however, unable to drive into the slow solar wind a flux of alphas flowing at roughly the same speed of protons as observed by in situ measurements at 1 AU. Title: The Helium Spectrum in Erupting Solar Prominences Authors: Labrosse, N.; Vial, J. C.; Gouttebroze, P. Bibcode: 2006IAUJD...3E..47L Altcode: 2006astro.ph..9511L Even quiescent solar prominences may become active and sometimes erupt. These events are occasionally linked to coronal mass ejections. However we know very little about the plasma properties during the activation and eruption processes. We present the first computations of the helium line profiles emitted by an eruptive prominence. We follow the approach of Gontikakis et al. (1997) who computed the hydrogen spectrum in moving prominences. The prominence is modelled as a plane-parallel slab standing vertically above the solar surface and moving upward as a solid body. The helium spectrum is computed with a non local thermodynamic equilibrium radiative transfer code. The effect of Doppler dimming / brightening is investigated in the resonance lines of He I and He II formed in the EUV, as well as on the He I 10830 Å and He I 5876 Å lines. We focus on the line profile properties and the resulting integrated intensities. We also study the effect of frequency redistribution in the formation mechanisms of the resonance lines. It is shown that the helium lines are very sensitive to Doppler dimming effects. Together with the hydrogen lines they offer the possibility of a powerful diagnostic of the active and eruptive prominence plasma. We discuss the results in view of observations provided by SOHO, and by the upcoming EUS spectrometer on SOLAR-B. Title: The Helium Spectrum in Moving Solar Prominences Authors: Labrosse, N.; Gouttebroze, P.; Vial, J. -C. Bibcode: 2006ESASP.617E.134L Altcode: 2006soho...17E.134L No abstract at ADS Title: The Lyman α and Lyman β Lines in Solar Coronal Streamers Authors: Labrosse, N.; Li, X.; Li, B. Bibcode: 2006ESASP.617E..93L Altcode: 2006soho...17E..93L No abstract at ADS Title: Plasma diagnostic of a solar prominence from hydrogen and helium resonance lines Authors: Labrosse, N.; Vial, J. -C.; Gouttebroze, P. Bibcode: 2006sf2a.conf..549L Altcode: 2006astro.ph..9643L We present the first comparison of profiles of H et He resonance lines observed by SUMER with theoretical profiles computed with our non-LTE radiative transfer code. We use the HI Lyman β, HI Lyman ɛ, and He I λ 584 Å lines. Our code allows us to obtain the plasma parameters in prominences in conjunction with a multi-line, multi-element set of observations. The plasma temperature in the prominence core is ∼ 8600 K and the pressure is 0.03 dyn cm-2. The Lyβ line is formed in a higher temperature region (more than 11,000 K). Title: Non-LTE Radiative Transfer in Model Prominences. I. Integrated Intensities of He I Triplet Lines Authors: Labrosse, N.; Gouttebroze, P. Bibcode: 2004ApJ...617..614L Altcode: In this work we use new results of radiative transfer calculations out of local thermodynamical equilibrium to study the triplet lines emitted by neutral helium in solar quiescent prominences. We compare two types of prominence atmospheres: isothermal and isobaric models versus nonisothermal and nonisobaric ones. We can thus investigate the effect of the presence of a prominence-to-corona transition region (PCTR) on the emergent intensities in detail. It is found that the presence of the PCTR affects the emitted intensities of the triplet lines, even though they are formed in the central parts of the prominence. We show that the inclusion of a transition region reduces the impact of collisional excitation at high temperatures in comparison with the isothermal and isobaric case. A simple study of helium energy level populations shows how statistical equilibrium is changed when a transition region is present. This points to the necessity of including an interface between the prominence body and the corona to predict all emergent intensities, whatever the region of formation of the radiation. We have found a correlation between most of the He I triplet line ratios and the altitude of the model prominence. Comparisons of our predicted intensity ratios with observations yield generally good agreement. Remaining discrepancies may be resolved by extrapolating our predicted results to higher altitudes. 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: Radiative transfer effects on hydrogen (and helium) in the solar atmosphere Authors: Labrosse, N.; Li, X.; Habbal, S. R.; Gouttebroze, P.; Mountford, C. J. Bibcode: 2002ESASP.506...13L Altcode: 2002svco.conf...13L; 2002ESPM...10...13L In this work we present Non-Local Thermodynamic Equilibrium (non-LTE) computations for hydrogen for a VAL-C model of the Sun's atmosphere. The solar atmosphere is represented by a one-dimensional plane-parallel horizontal slab. The purpose of this study is to investigate the effects of the transfer of radiation in the chromosphere and the transition region. In particular, we aim at understanding how the radiative losses in the energy balance for electrons are affected by the non-LTE radiative transfer, which has to be considered in the regions where the temperature is less than 25000K. The numerical code used here allows us to study the properties of, and the spectrum emitted by, the hydrogen particles. The non-LTE radiative transfer equations (RT) are solved for all optically thick resonance lines. The solutions of the RT in the optically thick lines affect all population densities of atoms and ions through the statistical equilibrium equations (SE). For the VAL-C atmosphere model there is a peak around 6×103K in the net radiative cooling rates due to several lines and continua from hydrogen. To our knowledge this peak has never been considered when evaluating the radiative losses in the chromosphere in the frame of solar wind modelling. We mention some consequences for solar wind models in the description of the chromosphere and the transition region which is often made under the assumption of full ionization and optically thin plasma. 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: Formation of helium spectrum in solar quiescent prominences Authors: Labrosse, N.; Gouttebroze, P. Bibcode: 2001A&A...380..323L Altcode: We present new non-LTE modelling of the helium spectrum emitted by quiescent solar prominences. The calculations are made in the frame of a one-dimensional plane-parallel slab. The physical parameters of our models are the electron temperature, the gas pressure, the slab width, the microturbulent velocity and the height above the solar surface. In this paper, we present isothermal isobaric models for a large range of temperature and pressure values. This work brings considerable improvements over the calculations of Heasley and co-workers \citep{hmp,hm2,hm3,hm4} with the inclusion in our calculations of partial redistribution effects in the formation of the H I Lyα, Lyβ, He I λ 584 Å and He Ii λ 304 Å lines. In addition we consider detailed incident profiles for the principal transitions. The statistical equilibrium equations are solved for a 33 bound levels (He I and He Ii) plus continuum atom, and the radiative transfer equations are solved by the Feautrier method with variable Eddington factors. In this way we obtain the helium level populations and the emergent line profiles. We discuss the influence of the physical parameters on the helium level populations and on the main helium spectral lines. The effect of helium abundance in the prominence plasma is also studied. Some relations between singlet and triplet lines are given, as well as between optically thin or thick lines, He I and He Ii lines, and between the He I λ 5876 Å and H I λ 4863 Å lines. In a future work this numerical code will be used for the diagnostic of the prominence plasma by comparing the results with SUMER observations. Title: Modélisation du spectre de l'hélium dans les protubérances solaires Title: Modélisation du spectre de l'hélium dans les protubérances solaires Title: Modelling of the helium spectrum in solar prominences; Authors: Labrosse, Nicolas Bibcode: 2001PhDT.......250L Altcode: No abstract at ADS Title: A ready-made code for the computation of prominence NLTE models Authors: Gouttebroze, P.; Labrosse, N. Bibcode: 2000SoPh..196..349G Altcode: A computer code is proposed for the computation of simple NLTE models of solar prominences. These models consist of plane-parallel slabs, with constant pressure and temperature, standing vertically above the solar surface. Each model is defined by five parameters: temperature, density, geometrical thickness, microturbulent velocity and height above the solar surface. The code computes the electron density, hydrogen level populations inside the slab, and determines the line profiles and continua emitted by the slab. An example of application of this code is given. Title: Modelling of Helium Spectrum in Solar Prominences Authors: Labrosse, N.; Gouttebroze, P.; Vial, J. -C. Bibcode: 1999ESASP.448..503L Altcode: 1999mfsp.conf..503L; 1999ESPM....9..503L No abstract at ADS Title: Modelling Of Helium Spectrum In Solar Prominences Authors: Labrosse, N.; Gouttebroze, P. Bibcode: 1999ESASP.446..399L Altcode: 1999soho....8..399L We present NLTE calculations for the neutral and ionized Helium spectrum in quiescent solar prominences. The Hydrogen and Helium atoms are multi-level model atoms, including for Helium the three stages of ionization. Departures from LTE are allowed for each level. We investigate the formation of lines and continuum within the frame of one-dimensional, isothermal and isobaric static slab models. The numerical code used for these calculations allows also the study of Partial Redistribution effects for several lines. The computation results are compared first with former works to see the improvements in the numerical and theoretical treatment, and then with SOHO observations of quiescent prominences at helium wavelengths. A study of the prominence plasma parameters thus can be made.