explanation blue bibcodes open ADS page with paths to full text
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
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
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.
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 τ<SUB>3mm</SUB> ≍ 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
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.
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
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. <BR /> 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? <BR /> 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. <BR />
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 (10<SUP>11</SUP> cm<SUP>−3</SUP>) than in the inner part
of the prominence. <BR /> 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. <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202140976/olm">https://www.aanda.org</A>
---------------------------------------------------------
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.
2021A&A...653A...5P Altcode: 2021arXiv210610351P
<BR /> 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. <BR /> 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. <BR /> 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<SUP>−2</SUP>; column masses of 3.7 × 10<SUP>−8</SUP>-5
× 10<SUP>−4</SUP> g cm<SUP>−2</SUP>; a mean electron density
of 7.3 × 10<SUP>8</SUP>-1.8 × 10<SUP>11</SUP> cm<SUP>−3</SUP>;
and an ionisation degree n<SUB>HII</SUB>/n<SUB>HI</SUB> = 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. <BR /> 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. <P />Movies associated to Figs. 10 and A.1 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202140907/olm">https://www.aanda.org</A>
---------------------------------------------------------
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
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.
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
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 D<SUB>3</SUB> 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
D<SUB>3</SUB> 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 D<SUB>3</SUB> 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 D<SUB>3</SUB> 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
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.
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.
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. <BR /> Aims: Our aim is to
understand how physical conditions inside a prominence slab influence
shapes and properties of emergent Mg II line profiles. <BR /> 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). <BR /> 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. <BR />
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
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.
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.
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. <BR /> 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. <BR /> 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. <BR /> 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. <BR />
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. <P />Movie attached to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833614/olm">https://www.aanda.org</A>
---------------------------------------------------------
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.
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
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.
2018A&A...617L...6R Altcode: 2018arXiv180807797R
<BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP>-10<SUP>1</SUP>), 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<SUP>-1</SUP>
to τ ≈ 10<SUP>0</SUP>. 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
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<SUP>-1</SUP>. 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
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
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 D<SUB>3</SUB> Line
Filter on the PROBA-3/ASPIICS Coronagraph
Authors: Jejčič, S.; Heinzel, P.; Labrosse, N.; Zhukov, A. N.;
Bemporad, A.; Fineschi, S.; Gunár, S.
2018SoPh..293...33J Altcode: 2018arXiv180700155J
We determine the optimal width and shape of the narrow-band filter
centered on the He I D<SUB>3</SUB> 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 D<SUB>3</SUB> 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<SUP>−1</SUP> 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
D<SUB>3</SUB> line and the prominence VL to the visibility in a given
narrow-band filter. We also discuss possible signal contamination by Na
I D<SUB>1</SUB> and D<SUB>2</SUB> 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 D<SUB>3</SUB> line is at 30 kK
and the minimal at 100 kK, and iii) the ratio of emission in the He I
D<SUB>3</SUB> 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
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.
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. <BR /> 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. <BR /> 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. <BR />
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 × 10<SUP>4</SUP> km). Knots run
along more or less horizontal threads with velocities reaching 65 km
s<SUP>-1</SUP>. The dominant driving force is the gas pressure. <P
/>Movies associated to Figs. 1, 9, 10, and 13 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201730839/olm">http://www.aanda.org</A>
---------------------------------------------------------
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.
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. <BR /> 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. <BR /> 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 D<SUB>3</SUB> 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. <BR /> 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 k<SUB>3</SUB> Doppler shift is found to be between
±10 km s<SUP>-1</SUP> everywhere. Electron densities at a temperature
of 1.5 × 10<SUP>6</SUP> K are found to be around 10<SUP>9</SUP>
cm<SUP>-3</SUP>. 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. <BR />
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
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
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
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
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.
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. <BR
/> 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. <BR /> 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. <BR /> 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. <BR /> 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.
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
2016A&A...596A..51B Altcode: 2016arXiv161004007B
<BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP>, and speeds in the
flare excess signal of around 30 km s<SUP>-1</SUP>. <BR /> 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
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.
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 D<SUB>3</SUB> 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
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
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. <BR />
Aims: We investigate the possibility of determining flare-accelerated
non-thermal ion and/or plasma velocity distributions. <BR /> 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. <BR /> 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. <BR
/> 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.
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 D<SUB>3</SUB> 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.
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.
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.
2016A&A...587A.113L Altcode: 2016arXiv160102392L
<BR /> 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. <BR />
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. <BR /> 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. <BR /> 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.
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<SUP>-1</SUP> 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.
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.
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.
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. <BR /> 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 × 10<SUP>5</SUP> K, giving a constraint on the
properties of the heated transition region. <BR /> 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. <BR /> Results: Electron number densities of up
to 10<SUP>11.9</SUP> cm<SUP>-3</SUP> 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. <BR /> 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.
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. <BR /> 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. <BR /> 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. <BR
/> 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 n<SUB>e</SUB> = 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 n<SUB>e</SUB> 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. <P />A movie is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201425586/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Polarimetric measurements in prominences and "tornadoe"
observed by THEMIS
Authors: Schmieder, Brigitte; López Ariste, Arturo; Levens, Peter;
Labrosse, Nicolas; Dalmasse, Kévin
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 D<SUB>3</SUB> 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
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
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
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.
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/E<SUP>c</SUP> )<SUB>-δ</SUB> for
energies greater than a cutoff value of E<SUP>c</SUP>. 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.
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. <P />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.
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.
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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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.
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. <BR /> 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. <BR /> 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. <BR /> 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. <BR
/> 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.
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.
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.
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<SUP>−1</SUP> 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<SUP>−1</SUP> 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.
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. <BR /> 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. <BR /> 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. <BR /> 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<SUP>-2</SUP>, and a column mass of
2.5 × 10<SUP>-4</SUP> g cm<SUP>-2</SUP>. The corresponding theoretical
hydrogen column density (10<SUP>20</SUP> cm<SUP>-2</SUP>) 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. <P
/>The movie associated to Fig. 2 is available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Solar flares: observations vs simulations
Authors: Rubio da Costa, Fatima; Zuccarello, Francesca; Labrosse,
Nicolas; Fletcher, Lyndsay; Prosecký, Tomáš; Kašparová, Jana
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.
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.
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.
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.
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. <BR />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. <BR
/>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. <BR />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 10<SUP>26</SUP> erg s<SUP>-1</SUP> 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. <BR />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.
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. <BR />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. <BR />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. <BR />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. <BR
/>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
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.
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.
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.
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.
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.
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 H<SUB>2</SUB> Lines in Sunspots
Authors: Labrosse, N.; Morgan, H.; Habbal, S. R.; Brown, D.
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 H<SUB>2</SUB> 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 H<SUB>2</SUB> 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<SUP>+5</SUP> 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.
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.
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. <BR />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. <BR />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. <BR />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. <BR />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. <P />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.
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.<BR
/>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.<BR />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.<BR />
---------------------------------------------------------
Title: A global 2.5-dimensional three fluid solar wind model with
alpha particles
Authors: Li, Bo; Li, Xing; Labrosse, Nicolas
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.
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.
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.
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.
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<SUP>-2</SUP>. 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.
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.
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.
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 6×10<SUP>3</SUP>K
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.
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.
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
2001PhDT.......250L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A ready-made code for the computation of prominence NLTE models
Authors: Gouttebroze, P.; Labrosse, N.
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.
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.
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.
