Author name code: vial
ADS astronomy entries on 2022-09-14
author:"Vial, Jean-Claude"
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Title: Linking Small-scale Solar Wind Properties with Large-scale
Coronal Source Regions through Joint Parker Solar Probe-Metis/Solar
Orbiter Observations
Authors: Telloni, Daniele; Zank, Gary P.; Sorriso-Valvo, Luca;
D'Amicis, Raffaella; Panasenco, Olga; Susino, Roberto; Bruno, Roberto;
Perrone, Denise; Adhikari, Laxman; Liang, Haoming; Nakanotani, Masaru;
Zhao, Lingling; Hadid, Lina Z.; Sánchez-Cano, Beatriz; Verscharen,
Daniel; Velli, Marco; Grimani, Catia; Marino, Raffaele; Carbone,
Francesco; Mancuso, Salvatore; Biondo, Ruggero; Pagano, Paolo; Reale,
Fabio; Bale, Stuart D.; Kasper, Justin C.; Case, Anthony W.; de Wit,
Thierry Dudok; Goetz, Keith; Harvey, Peter R.; Korreck, Kelly E.;
Larson, Davin; Livi, Roberto; MacDowall, Robert J.; Malaspina, David
M.; Pulupa, Marc; Stevens, Michael L.; Whittlesey, Phyllis; Romoli,
Marco; Andretta, Vincenzo; Deppo, Vania Da; Fineschi, Silvano; Heinzel,
Petr; Moses, John D.; Naletto, Giampiero; Nicolini, Gianalfredo;
Spadaro, Daniele; Stangalini, Marco; Teriaca, Luca; Capobianco,
Gerardo; Capuano, Giuseppe E.; Casini, Chiara; Casti, Marta; Chioetto,
Paolo; Corso, Alain J.; Leo, Yara De; Fabi, Michele; Frassati,
Federica; Frassetto, Fabio; Giordano, Silvio; Guglielmino, Salvo L.;
Jerse, Giovanna; Landini, Federico; Liberatore, Alessandro; Magli,
Enrico; Massone, Giuseppe; Messerotti, Mauro; Pancrazzi, Maurizio;
Pelizzo, Maria G.; Romano, Paolo; Sasso, Clementina; Schühle, Udo;
Slemer, Alessandra; Straus, Thomas; Uslenghi, Michela; Volpicelli,
Cosimo A.; Zangrilli, Luca; Zuppella, Paola; Abbo, Lucia; Auchère,
Frédéric; Cuadrado, Regina Aznar; Berlicki, Arkadiusz; Ciaravella,
Angela; Lamy, Philippe; Lanzafame, Alessandro; Malvezzi, Marco;
Nicolosi, Piergiorgio; Nisticò, Giuseppe; Peter, Hardi; Solanki,
Sami K.; Strachan, Leonard; Tsinganos, Kanaris; Ventura, Rita; Vial,
Jean-Claude; Woch, Joachim; Zimbardo, Gaetano
Bibcode: 2022ApJ...935..112T
Altcode:
The solar wind measured in situ by Parker Solar Probe in the very
inner heliosphere is studied in combination with the remote-sensing
observation of the coronal source region provided by the METIS
coronagraph aboard Solar Orbiter. The coronal outflows observed near
the ecliptic by Metis on 2021 January 17 at 16:30 UT, between 3.5 and
6.3 R ⊙ above the eastern solar limb, can be associated
with the streams sampled by PSP at 0.11 and 0.26 au from the Sun,
in two time intervals almost 5 days apart. The two plasma flows
come from two distinct source regions, characterized by different
magnetic field polarity and intensity at the coronal base. It follows
that both the global and local properties of the two streams are
different. Specifically, the solar wind emanating from the stronger
magnetic field region has a lower bulk flux density, as expected,
and is in a state of well-developed Alfvénic turbulence, with low
intermittency. This is interpreted in terms of slab turbulence in the
context of nearly incompressible magnetohydrodynamics. Conversely,
the highly intermittent and poorly developed turbulent behavior of the
solar wind from the weaker magnetic field region is presumably due to
large magnetic deflections most likely attributed to the presence of
switchbacks of interchange reconnection origin.
Title: Empirical relations between the intensities of Lyman lines
of H and He+
Authors: Gordino, M.; Auchère, F.; Vial, J. -C.; Bocchialini, K.;
Hassler, D. M.; Bando, T.; Ishikawa, R.; Kano, R.; Kobayashi, K.;
Narukage, N.; Trujillo Bueno, J.; Winebarger, A.
Bibcode: 2022A&A...657A..86G
Altcode: 2022arXiv220101519G
Context. Empirical relations between major UV and extreme UV spectral
lines are one of the inputs for models of chromospheric and coronal
spectral radiances and irradiances. They are also needed for the
interpretation of some of the observations of the Solar Orbiter
mission.
Aims: We aim to determine an empirical relation between
the intensities of the H I 121.6 nm and He II 30.4 nm Ly-α lines.
Methods: Images at 121.6 nm from the Chromospheric Lyman-Alpha
Spectro Polarimeter (CLASP) and Multiple XUV Imager (MXUVI) sounding
rockets were co-registered with simultaneous images at 30.4 nm from the
EIT and AIA orbital telescopes in order to derive a spatially resolved
relationship between the intensities.
Results: We have obtained
a relationship between the H I 121.6 nm and He II 30.4 nm intensities
that is valid for a wide range of solar features, intensities, and
activity levels. Additional SUMER data have allowed the derivation of
another relation between the H I 102.5 nm (Ly-β) and He II 30.4 nm
lines for quiet-Sun regions. We combined these two relationships to
obtain a Ly-α/Ly-β intensity ratio that is comparable to the few
previously published results.
Conclusions: The relationship
between the H I 121.6 nm and He II 30.4 nm lines is consistent with the
one previously obtained using irradiance data. We have also observed
that this relation is stable in time but that its accuracy depends on
the spatial resolution of the observations. The derived Ly-α/Ly-β
intensity ratio is also compatible with previous results.
Title: The first coronal mass ejection observed in both visible-light
and UV H I Ly-α channels of the Metis coronagraph on board Solar
Orbiter
Authors: Andretta, V.; Bemporad, A.; De Leo, Y.; Jerse, G.; Landini,
F.; Mierla, M.; Naletto, G.; Romoli, M.; Sasso, C.; Slemer, A.;
Spadaro, D.; Susino, R.; Talpeanu, D. -C.; Telloni, D.; Teriaca, L.;
Uslenghi, M.; Antonucci, E.; Auchère, F.; Berghmans, D.; Berlicki,
A.; Capobianco, G.; Capuano, G. E.; Casini, C.; Casti, M.; Chioetto,
P.; Da Deppo, V.; Fabi, M.; Fineschi, S.; Frassati, F.; Frassetto,
F.; Giordano, S.; Grimani, C.; Heinzel, P.; Liberatore, A.; Magli, E.;
Massone, G.; Messerotti, M.; Moses, D.; Nicolini, G.; Pancrazzi, M.;
Pelizzo, M. -G.; Romano, P.; Schühle, U.; Stangalini, M.; Straus,
Th.; Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Aznar
Cuadrado, R.; Bruno, R.; Ciaravella, A.; D'Amicis, R.; Lamy, P.;
Lanzafame, A.; Malvezzi, A. M.; Nicolosi, P.; Nisticò, G.; Peter,
H.; Plainaki, C.; Poletto, L.; Reale, F.; Solanki, S. K.; Strachan,
L.; Tondello, G.; Tsinganos, K.; Velli, M.; Ventura, R.; Vial, J. -C.;
Woch, J.; Zimbardo, G.
Bibcode: 2021A&A...656L..14A
Altcode:
Context. The Metis coronagraph on board Solar Orbiter offers a new
view of coronal mass ejections (CMEs), observing them for the first
time with simultaneous images acquired with a broad-band filter in
the visible-light interval and with a narrow-band filter around the
H I Ly-α line at 121.567 nm, the so-called Metis UV channel.
Aims: We show the first Metis observations of a CME, obtained on 16
and 17 January 2021. The event was also observed by the EUI/FSI imager
on board Solar Orbiter, as well as by other space-based coronagraphs,
such as STEREO-A/COR2 and SOHO/LASCO/C2, whose images are combined here
with Metis data.
Methods: Different images are analysed here
to reconstruct the 3D orientation of the expanding CME flux rope using
the graduated cylindrical shell model. This also allows us to identify
the possible location of the source region. Measurements of the CME
kinematics allow us to quantify the expected Doppler dimming in the
Ly-α channel.
Results: Observations show that most CME features
seen in the visible-light images are also seen in the Ly-α images,
although some features in the latter channel appear more structured
than their visible-light counterparts. We estimated the expansion
velocity of this event to be below 140 km s−1. Hence,
these observations can be understood by assuming that Doppler dimming
effects do not strongly reduce the Ly-α emission from the CME. These
velocities are comparable with or smaller than the radial velocities
inferred from the same data in a similar coronal structure on the
east side of the Sun.
Conclusions: The first observations by
Metis of a CME demonstrate the capability of the instrument to provide
valuable and novel information on the structure and dynamics of these
coronal events. Considering also its diagnostics capabilities regarding
the conditions of the ambient corona, Metis promises to significantly
advance our knowledge of such phenomena.
Movies are available at https://www.aanda.org
Title: First light observations of the solar wind in the outer corona
with the Metis coronagraph
Authors: Romoli, M.; Antonucci, E.; Andretta, V.; Capuano, G. E.; Da
Deppo, V.; De Leo, Y.; Downs, C.; Fineschi, S.; Heinzel, P.; Landini,
F.; Liberatore, A.; Naletto, G.; Nicolini, G.; Pancrazzi, M.; Sasso,
C.; Spadaro, D.; Susino, R.; Telloni, D.; Teriaca, L.; Uslenghi,
M.; Wang, Y. -M.; Bemporad, A.; Capobianco, G.; Casti, M.; Fabi, M.;
Frassati, F.; Frassetto, F.; Giordano, S.; Grimani, C.; Jerse, G.;
Magli, E.; Massone, G.; Messerotti, M.; Moses, D.; Pelizzo, M. -G.;
Romano, P.; Schühle, U.; Slemer, A.; Stangalini, M.; Straus, T.;
Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Auchère,
F.; Aznar Cuadrado, R.; Berlicki, A.; Bruno, R.; Ciaravella, A.;
D'Amicis, R.; Lamy, P.; Lanzafame, A.; Malvezzi, A. M.; Nicolosi,
P.; Nisticò, G.; Peter, H.; Plainaki, C.; Poletto, L.; Reale, F.;
Solanki, S. K.; Strachan, L.; Tondello, G.; Tsinganos, K.; Velli,
M.; Ventura, R.; Vial, J. -C.; Woch, J.; Zimbardo, G.
Bibcode: 2021A&A...656A..32R
Altcode: 2021arXiv210613344R
In this work, we present an investigation of the wind in the solar
corona that has been initiated by observations of the resonantly
scattered ultraviolet emission of the coronal plasma obtained with
UVCS-SOHO, designed to measure the wind outflow speed by applying
Doppler dimming diagnostics. Metis on Solar Orbiter complements the
UVCS spectroscopic observations that were performed during solar
activity cycle 23 by simultaneously imaging the polarized visible
light and the H I Lyman-α corona in order to obtain high spatial and
temporal resolution maps of the outward velocity of the continuously
expanding solar atmosphere. The Metis observations, taken on May 15,
2020, provide the first H I Lyman-α images of the extended corona
and the first instantaneous map of the speed of the coronal plasma
outflows during the minimum of solar activity and allow us to identify
the layer where the slow wind flow is observed. The polarized visible
light (580-640 nm) and the ultraviolet H I Lyα (121.6 nm) coronal
emissions, obtained with the two Metis channels, were combined in
order to measure the dimming of the UV emission relative to a static
corona. This effect is caused by the outward motion of the coronal
plasma along the direction of incidence of the chromospheric photons
on the coronal neutral hydrogen. The plasma outflow velocity was then
derived as a function of the measured Doppler dimming. The static
corona UV emission was simulated on the basis of the plasma electron
density inferred from the polarized visible light. This study leads
to the identification, in the velocity maps of the solar corona, of
the high-density layer about ±10° wide, centered on the extension
of a quiet equatorial streamer present at the east limb - the coronal
origin of the heliospheric current sheet - where the slowest wind
flows at about 160 ± 18 km s−1 from 4 R⊙
to 6 R⊙. Beyond the boundaries of the high-density layer,
the wind velocity rapidly increases, marking the transition between
slow and fast wind in the corona.
Title: High-resolution observations of prominence plume formation
with the new vacuum solar telescope
Authors: Xue, Jian-Chao; Vial, Jean-Claude; Su, Yang; Li, Hui; Xu,
Zhi; Su, Ying-Na; Zhou, Tuan-Hui; Li, Zhen-Tong
Bibcode: 2021RAA....21..222X
Altcode:
Prominence plumes are evacuated upflows that emerge from bubbles
below prominences, whose formation mechanism is still unclear. Here
we present a detailed study of plumes in a quiescent prominence using
the high-resolution Hα filtergrams at the line center as well as line
wing at ± 0.4 Å from the New Vacuum Solar Telescope. Enhancements of
brightening, blue shifts, and turbulence at the fronts of plumes are
found during their formation. Some large plumes split at their heads and
finger-shaped structures are formed between them. Blue-shifted flows
along the bubble-prominence interface are found before and during the
plume formation. Our observations are consistent with the hypothesis
that prominence plumes are related to coupled Kelvin-Helmholtz and
Rayleigh-Taylor (KH/RT) instabilities. Plume splittings and fingers are
evidence of RT instability, and the flows may increase the growth rate
of KH/RT instabilities. However, the significant turbulence at plume
fronts may suggest that the RT instability is triggered by the plumes
penetrating into the prominence. In this scenario, extra mechanisms
are necessary to drive the plumes.
Title: White-light Continuum Observation of the Off-limb Loops of
the SOL2017-09-10 X8.2 Flare: Temporal and Spatial Variations
Authors: Zhao, Junwei; Liu, Wei; Vial, Jean-Claude
Bibcode: 2021ApJ...921L..26Z
Altcode: 2021arXiv211014130Z
Observations of the Sun's off-limb white-light (WL) flares offer rare
opportunities to study the energy release and transport mechanisms
in flare loops. One of the best such events was SOL2017-09-10, an
X8.2 flare that occurred near the Sun's west limb on 2017 September
10 and produced a WL loop system lasting more than 60 minutes and
reaching an altitude higher than 30 Mm. The event was well observed
by a suite of ground- and space-based instruments, including the
Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI)
that captured its off-limb loops in WL continuum near Fe I 6173 Å,
and the Atmospheric Imager Assembly (SDO/AIA) that observed its
ultraviolet (UV) and extreme-ultraviolet (EUV) counterparts. We
found quasi-periodic pulsations in the WL and UV emissions at the
flare loop-top with a period around 8.0 minutes. Each pulsation
appears to have an EUV counterpart that occurs earlier in time and
higher in altitude. Despite many similarities in the WL and UV images
and light curves, the WL flux at the loop-top continues to grow for
about 16 minutes while the UV fluxes gradually decay. We discuss the
implication of these unprecedented observations on the understanding
of the enigmatic off-limb WL flare emission mechanisms.
Title: High-Resolution Observations of Prominence Plume Formation
with the New Vacuum Solar Telescope
Authors: Xue, Jianchao; Vial, Jean-Claude; Li, Hui; Xu, Zhi; Su,
Yang; Su, Yingna
Bibcode: 2021cosp...43E.972X
Altcode: 2021arXiv210501293X
Prominence plumes are evacuated upflows that emerge from bubbles
below prominences, whose formation mechanism is still unclear. Here
we present a detailed study of plumes in a quiescent prominence
using the high--resolution H$\alpha$ spectral images from the New
Vacuum Solar Telescope (NVST). Enhancements of brightening, blue
shifts, and turbulence at the fronts of plumes are found during their
formation. Some large plumes split at their heads and finger-shaped
structures (type--I) are formed between them. At the late phases of
the plumes, (type--II) fingers appear along the plume boundary where
flows are strong. We found the flows along the prominence boundary
occur before the plume formation. Our observations are consistent
with the hypothesis that prominence plumes are related to coupled
Kelvin--Helmholtz and Rayleigh--Taylor (KH/RT) instabilities. Plume
splits and fingers are evidence of RT instability, and the flows
along prominence boundary may increase the growth rate of KH/RT
instabilities. A difference from previous explanation is that the RT
instability is probably triggered by the plumes penetrating into the
prominence. The significant turbulence at plume fronts is likely due
to the collision between plumes and the prominence, and the fingers
probably result from the KH/RT instabilities at the boundary of
plumes and the prominence or the flows. Other causes of the plumes
are discussed, including possible contribution of spicules underneath
the prominence.
Title: Multiwavelength quiescent prominence spectroscopic observations
Authors: Zhang, Ping; Vial, Jean-Claude; Feng, Li; Curdt, Werner;
Zapior, Maciej
Bibcode: 2021cosp...43E1770Z
Altcode:
In the frame of the SUMER-IRIS HOP 334 campaign in March-April 2017,
joint prominence observations have been performed with IRIS (Mg II
h and k), SUMER (L-alpha) and HSFA2 ( Ondřejov Observatory) in Ca
II K, H-beta and H-alpha. We proceeded first with the difficult
task of coalignment i.e. identifying the pixels of the different
slits corresponding to the same solar region observed at the same
time. The selected profiles photometrically calibrated have been found
non-reversed.Through the use of the NLTE radiative transfer code
PRODOP available at MEDOC/IAS, we tentatively derive the 1D model
fitting all observed profiles. The observed Lalpha profile found to
be larger than the isothermal modelled one requires the addition of
a PCTR. Some basic thermodynamical parameters are consequently derived.
Title: Observations of Solar Spicules at Millimeter and Ultraviolet
Wavelengths
Authors: Bastian, T.; De Pontieu, B.; Shimojo, M.; Iwai, K.;
Alissandrakis, C.; Nindos, A.; Vial, J. C.; White, S. M.
Bibcode: 2020AGUFMSH004..08B
Altcode:
Solar spicules are a ubiquitous chromospheric phenomenon in which
multitudes of dynamic jets with temperatures of order 104
K extend thousands of kilometers into the solar atmosphere. Recent
progress has been made refining the observational characteristics
of spicules using the Hinode Solar Optical Telescope (SOT) and the
Interface Region Imaging Spectrograph (IRIS) observations at optical
and ultraviolet wavelengths, respectively. Two types of spicule
have been identified. Type I spicules, prevalent in solar active
regions, have upward speeds of order 25 km/s and lifetimes of 3-7
min. They may be the limb counterpart to shock-wave-driven fibrils
commonly seen against the solar disk in active regions. In contrast,
type II spicules, more common in quiet regions and coronal holes,
display upward speeds of 50-150 km/s, lifetimes of 30-110 s, and
appear to be partially heated to temperatures of 105 K and
higher. These observations have provoked intense interest in spicules
and have led to proposals that type II spicules play a central role
as a source of hot plasma in the corona. Nevertheless, their role in
mass and energy transport between the lower and upper layers of the
solar atmosphere remains an outstanding problem. Here, we report
imaging observations of solar spicules at millimeter wavelengths using
the Atacama Large Millimeter-submillimeter Array (ALMA) with arcsecond
angular resolution. Continuum millimeter wavelength radiation forms
under conditions of local thermodynamic equilibrium, thereby providing a
complementary tool to UV lines, which form under non-LTE conditions. The
observations were made on 2018 December 24-25 at λ=1.25 mm and λ=3
mm. The ALMA observations pose special challenges, particularly at
1.25 mm, where the limited field of view of the instrument motivated
us to use a novel mosaic imaging technique: multiple pointings were
assembled to form a single map with an angular resolution of 1" x 0.7"
on a cadence of roughly 2 min. In contrast, we were able to image at 3
mm continuously, with a map cadence of 2 s and an angular resolution of
2.3" x 1.3". We compare and contrast the morphology and dynamics
of mm-λ observations of spicules with those obtained by IRIS at UV
wavelengths and place constraints on spicule temperatures and masses
using the joint millimeter-wavelength observations.
Title: First results from combined EUI and SPICE observations of
Lyman lines of Hydrogen and He II
Authors: Teriaca, L.; Aznar Cuadrado, R.; Giunta, A. S.; Grundy, T.;
Parenti, S.; Auchere, F.; Vial, J. C.; Fludra, A.; Berghmans, D.;
Carlsson, M.; Harra, L.; Hassler, D.; Long, D.; Peter, H.; Rochus,
P. L.; Schühle, U.; Buchlin, E.; Caldwell, M.; Caminade, S.; DeForest,
C.; Fredvik, T.; Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp,
E.; Kucera, T. A.; Mueller, D.; Schmutz, W. K.; Sidher, S.; Smith, P.;
Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
Bibcode: 2020AGUFMSH0360003T
Altcode:
The Solar Orbiter spacecraft carries a powerful set of remote
sensing instruments that allow studying the solar atmosphere with
unprecedented diagnostic capabilities. Many such diagnostics require
the simultaneous usage of more than one instrument. One example of that
is the capability, for the first time, to obtain (near) simultaneous
spatially resolved observations of the emission from the first three
lines of the Lyman series of hydrogen and of He II Lyman alpha. In fact,
the SPectral Imaging of the Coronal Environment (SPICE) spectrometer
can observe the Lyman beta and gamma lines in its long wavelength
(SPICE-LW) channel, the High Resolution Lyman Alpha (HRI-LYA) telescope
of the Extreme Ultraviolet Imager (EUI) acquires narrow band images in
the Lyman alpha line while the Full Disk Imager (FSI) of EUI can take
images dominated by the Lyman alpha line of ionized Helium at 30.4 nm
(FSI-304). Being hydrogen and helium the main components of our star,
these very bright transitions play an important role in the energy
budget of the outer atmosphere via radiative losses and the measurement
of their profiles and radiance ratios is a fundamental constraint to
any comprehensive modelization effort of the upper solar chromosphere
and transition region. Additionally, monitoring their average ratios
can serve as a check out for the relative radiometric performance of
the two instruments throughout the mission. Although the engineering
data acquired so far are far from ideal in terms of time simultaneity
(often only within about 1 h) and line coverage (often only Lyman beta
was acquired by SPICE and not always near simultaneous images from all
three telescopes are available) the analysis we present here still
offers a great opportunity to have a first look at the potential of
this diagnostic from the two instruments. In fact, we have identified
a series of datasets obtained at disk center and at various positions
at the solar limb that allow studying the Lyman alpha to beta radiance
ratio and their relation to He II 30.4 as a function of the position
on the Sun (disk center versus limb and quiet Sun versus coronal holes).
Title: The Solar Orbiter SPICE instrument. An extreme UV imaging
spectrometer
Authors: SPICE Consortium; Anderson, M.; Appourchaux, T.; Auchère, F.;
Aznar Cuadrado, R.; Barbay, J.; Baudin, F.; Beardsley, S.; Bocchialini,
K.; Borgo, B.; Bruzzi, D.; Buchlin, E.; Burton, G.; Büchel, V.;
Caldwell, M.; Caminade, S.; Carlsson, M.; Curdt, W.; Davenne, J.;
Davila, J.; Deforest, C. E.; Del Zanna, G.; Drummond, D.; Dubau,
J.; Dumesnil, C.; Dunn, G.; Eccleston, P.; Fludra, A.; Fredvik, T.;
Gabriel, A.; Giunta, A.; Gottwald, A.; Griffin, D.; Grundy, T.; Guest,
S.; Gyo, M.; Haberreiter, M.; Hansteen, V.; Harrison, R.; Hassler,
D. M.; Haugan, S. V. H.; Howe, C.; Janvier, M.; Klein, R.; Koller,
S.; Kucera, T. A.; Kouliche, D.; Marsch, E.; Marshall, A.; Marshall,
G.; Matthews, S. A.; McQuirk, C.; Meining, S.; Mercier, C.; Morris,
N.; Morse, T.; Munro, G.; Parenti, S.; Pastor-Santos, C.; Peter, H.;
Pfiffner, D.; Phelan, P.; Philippon, A.; Richards, A.; Rogers, K.;
Sawyer, C.; Schlatter, P.; Schmutz, W.; Schühle, U.; Shaughnessy,
B.; Sidher, S.; Solanki, S. K.; Speight, R.; Spescha, M.; Szwec, N.;
Tamiatto, C.; Teriaca, L.; Thompson, W.; Tosh, I.; Tustain, S.; Vial,
J. -C.; Walls, B.; Waltham, N.; Wimmer-Schweingruber, R.; Woodward,
S.; Young, P.; de Groof, A.; Pacros, A.; Williams, D.; Müller, D.
Bibcode: 2020A&A...642A..14S
Altcode: 2019arXiv190901183A; 2019arXiv190901183S
Aims: The Spectral Imaging of the Coronal Environment (SPICE)
instrument is a high-resolution imaging spectrometer operating at
extreme ultraviolet wavelengths. In this paper, we present the concept,
design, and pre-launch performance of this facility instrument on the
ESA/NASA Solar Orbiter mission.
Methods: The goal of this paper
is to give prospective users a better understanding of the possible
types of observations, the data acquisition, and the sources that
contribute to the instrument's signal.
Results: The paper
discusses the science objectives, with a focus on the SPICE-specific
aspects, before presenting the instrument's design, including optical,
mechanical, thermal, and electronics aspects. This is followed by a
characterisation and calibration of the instrument's performance. The
paper concludes with descriptions of the operations concept and data
processing.
Conclusions: The performance measurements of the
various instrument parameters meet the requirements derived from the
mission's science objectives. The SPICE instrument is ready to perform
measurements that will provide vital contributions to the scientific
success of the Solar Orbiter mission.
Title: The Solar Orbiter EUI instrument: The Extreme Ultraviolet
Imager
Authors: Rochus, P.; Auchère, F.; Berghmans, D.; Harra, L.; Schmutz,
W.; Schühle, U.; Addison, P.; Appourchaux, T.; Aznar Cuadrado,
R.; Baker, D.; Barbay, J.; Bates, D.; BenMoussa, A.; Bergmann, M.;
Beurthe, C.; Borgo, B.; Bonte, K.; Bouzit, M.; Bradley, L.; Büchel,
V.; Buchlin, E.; Büchner, J.; Cabé, F.; Cadiergues, L.; Chaigneau,
M.; Chares, B.; Choque Cortez, C.; Coker, P.; Condamin, M.; Coumar,
S.; Curdt, W.; Cutler, J.; Davies, D.; Davison, G.; Defise, J. -M.;
Del Zanna, G.; Delmotte, F.; Delouille, V.; Dolla, L.; Dumesnil, C.;
Dürig, F.; Enge, R.; François, S.; Fourmond, J. -J.; Gillis, J. -M.;
Giordanengo, B.; Gissot, S.; Green, L. M.; Guerreiro, N.; Guilbaud,
A.; Gyo, M.; Haberreiter, M.; Hafiz, A.; Hailey, M.; Halain, J. -P.;
Hansotte, J.; Hecquet, C.; Heerlein, K.; Hellin, M. -L.; Hemsley, S.;
Hermans, A.; Hervier, V.; Hochedez, J. -F.; Houbrechts, Y.; Ihsan,
K.; Jacques, L.; Jérôme, A.; Jones, J.; Kahle, M.; Kennedy, T.;
Klaproth, M.; Kolleck, M.; Koller, S.; Kotsialos, E.; Kraaikamp, E.;
Langer, P.; Lawrenson, A.; Le Clech', J. -C.; Lenaerts, C.; Liebecq,
S.; Linder, D.; Long, D. M.; Mampaey, B.; Markiewicz-Innes, D.;
Marquet, B.; Marsch, E.; Matthews, S.; Mazy, E.; Mazzoli, A.; Meining,
S.; Meltchakov, E.; Mercier, R.; Meyer, S.; Monecke, M.; Monfort,
F.; Morinaud, G.; Moron, F.; Mountney, L.; Müller, R.; Nicula, B.;
Parenti, S.; Peter, H.; Pfiffner, D.; Philippon, A.; Phillips, I.;
Plesseria, J. -Y.; Pylyser, E.; Rabecki, F.; Ravet-Krill, M. -F.;
Rebellato, J.; Renotte, E.; Rodriguez, L.; Roose, S.; Rosin, J.;
Rossi, L.; Roth, P.; Rouesnel, F.; Roulliay, M.; Rousseau, A.; Ruane,
K.; Scanlan, J.; Schlatter, P.; Seaton, D. B.; Silliman, K.; Smit,
S.; Smith, P. J.; Solanki, S. K.; Spescha, M.; Spencer, A.; Stegen,
K.; Stockman, Y.; Szwec, N.; Tamiatto, C.; Tandy, J.; Teriaca, L.;
Theobald, C.; Tychon, I.; van Driel-Gesztelyi, L.; Verbeeck, C.;
Vial, J. -C.; Werner, S.; West, M. J.; Westwood, D.; Wiegelmann, T.;
Willis, G.; Winter, B.; Zerr, A.; Zhang, X.; Zhukov, A. N.
Bibcode: 2020A&A...642A...8R
Altcode:
Context. The Extreme Ultraviolet Imager (EUI) is part of the remote
sensing instrument package of the ESA/NASA Solar Orbiter mission
that will explore the inner heliosphere and observe the Sun from
vantage points close to the Sun and out of the ecliptic. Solar Orbiter
will advance the "connection science" between solar activity and the
heliosphere.
Aims: With EUI we aim to improve our understanding
of the structure and dynamics of the solar atmosphere, globally as well
as at high resolution, and from high solar latitude perspectives.
Methods: The EUI consists of three telescopes, the Full Sun Imager and
two High Resolution Imagers, which are optimised to image in Lyman-α
and EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere
up to corona. The EUI is designed to cope with the strong constraints
imposed by the Solar Orbiter mission characteristics. Limited telemetry
availability is compensated by state-of-the-art image compression,
onboard image processing, and event selection. The imposed power
limitations and potentially harsh radiation environment necessitate
the use of novel CMOS sensors. As the unobstructed field of view of
the telescopes needs to protrude through the spacecraft's heat shield,
the apertures have been kept as small as possible, without compromising
optical performance. This led to a systematic effort to optimise the
throughput of every optical element and the reduction of noise levels
in the sensor.
Results: In this paper we review the design
of the two elements of the EUI instrument: the Optical Bench System
and the Common Electronic Box. Particular attention is also given to
the onboard software, the intended operations, the ground software,
and the foreseen data products.
Conclusions: The EUI will
bring unique science opportunities thanks to its specific design,
its viewpoint, and to the planned synergies with the other Solar
Orbiter instruments. In particular, we highlight science opportunities
brought by the out-of-ecliptic vantage point of the solar poles,
the high-resolution imaging of the high chromosphere and corona,
and the connection to the outer corona as observed by coronagraphs.
Title: Metis: the Solar Orbiter visible light and ultraviolet
coronal imager
Authors: Antonucci, Ester; Romoli, Marco; Andretta, Vincenzo; Fineschi,
Silvano; Heinzel, Petr; Moses, J. Daniel; Naletto, Giampiero; Nicolini,
Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Berlicki, Arkadiusz;
Capobianco, Gerardo; Crescenzio, Giuseppe; Da Deppo, Vania; Focardi,
Mauro; Frassetto, Fabio; Heerlein, Klaus; Landini, Federico; Magli,
Enrico; Marco Malvezzi, Andrea; Massone, Giuseppe; Melich, Radek;
Nicolosi, Piergiorgio; Noci, Giancarlo; Pancrazzi, Maurizio; Pelizzo,
Maria G.; Poletto, Luca; Sasso, Clementina; Schühle, Udo; Solanki,
Sami K.; Strachan, Leonard; Susino, Roberto; Tondello, Giuseppe;
Uslenghi, Michela; Woch, Joachim; Abbo, Lucia; Bemporad, Alessandro;
Casti, Marta; Dolei, Sergio; Grimani, Catia; Messerotti, Mauro;
Ricci, Marco; Straus, Thomas; Telloni, Daniele; Zuppella, Paola;
Auchère, Frederic; Bruno, Roberto; Ciaravella, Angela; Corso,
Alain J.; Alvarez Copano, Miguel; Aznar Cuadrado, Regina; D'Amicis,
Raffaella; Enge, Reiner; Gravina, Alessio; Jejčič, Sonja; Lamy,
Philippe; Lanzafame, Alessandro; Meierdierks, Thimo; Papagiannaki,
Ioanna; Peter, Hardi; Fernandez Rico, German; Giday Sertsu, Mewael;
Staub, Jan; Tsinganos, Kanaris; Velli, Marco; Ventura, Rita; Verroi,
Enrico; Vial, Jean-Claude; Vives, Sebastien; Volpicelli, Antonio;
Werner, Stephan; Zerr, Andreas; Negri, Barbara; Castronuovo, Marco;
Gabrielli, Alessandro; Bertacin, Roberto; Carpentiero, Rita; Natalucci,
Silvia; Marliani, Filippo; Cesa, Marco; Laget, Philippe; Morea, Danilo;
Pieraccini, Stefano; Radaelli, Paolo; Sandri, Paolo; Sarra, Paolo;
Cesare, Stefano; Del Forno, Felice; Massa, Ernesto; Montabone, Mauro;
Mottini, Sergio; Quattropani, Daniele; Schillaci, Tiziano; Boccardo,
Roberto; Brando, Rosario; Pandi, Arianna; Baietto, Cristian; Bertone,
Riccardo; Alvarez-Herrero, Alberto; García Parejo, Pilar; Cebollero,
María; Amoruso, Mauro; Centonze, Vito
Bibcode: 2020A&A...642A..10A
Altcode: 2019arXiv191108462A
Aims: Metis is the first solar coronagraph designed for a
space mission and is capable of performing simultaneous imaging of the
off-limb solar corona in both visible and UV light. The observations
obtained with Metis aboard the Solar Orbiter ESA-NASA observatory
will enable us to diagnose, with unprecedented temporal coverage and
spatial resolution, the structures and dynamics of the full corona
in a square field of view (FoV) of ±2.9° in width, with an inner
circular FoV at 1.6°, thus spanning the solar atmosphere from 1.7
R⊙ to about 9 R⊙, owing to the eccentricity
of the spacecraft orbit. Due to the uniqueness of the Solar Orbiter
mission profile, Metis will be able to observe the solar corona
from a close (0.28 AU, at the closest perihelion) vantage point,
achieving increasing out-of-ecliptic views with the increase of the
orbit inclination over time. Moreover, observations near perihelion,
during the phase of lower rotational velocity of the solar surface
relative to the spacecraft, allow longer-term studies of the off-limb
coronal features, thus finally disentangling their intrinsic evolution
from effects due to solar rotation.
Methods: Thanks to a novel
occultation design and a combination of a UV interference coating of
the mirrors and a spectral bandpass filter, Metis images the solar
corona simultaneously in the visible light band, between 580 and 640
nm, and in the UV H I Lyman-α line at 121.6 nm. The visible light
channel also includes a broadband polarimeter able to observe the
linearly polarised component of the K corona. The coronal images in
both the UV H I Lyman-α and polarised visible light are obtained at
high spatial resolution with a spatial scale down to about 2000 km
and 15 000 km at perihelion, in the cases of the visible and UV light,
respectively. A temporal resolution down to 1 s can be achieved when
observing coronal fluctuations in visible light.
Results: The
Metis measurements, obtained from different latitudes, will allow for
complete characterisation of the main physical parameters and dynamics
of the electron and neutral hydrogen/proton plasma components of the
corona in the region where the solar wind undergoes the acceleration
process and where the onset and initial propagation of coronal mass
ejections (CMEs) take place. The near-Sun multi-wavelength coronal
imaging performed with Metis, combined with the unique opportunities
offered by the Solar Orbiter mission, can effectively address crucial
issues of solar physics such as: the origin and heating/acceleration
of the fast and slow solar wind streams; the origin, acceleration,
and transport of the solar energetic particles; and the transient
ejection of coronal mass and its evolution in the inner heliosphere,
thus significantly improving our understanding of the region connecting
the Sun to the heliosphere and of the processes generating and driving
the solar wind and coronal mass ejections.
Conclusions: This
paper presents the scientific objectives and requirements, the overall
optical design of the Metis instrument, the thermo-mechanical design,
and the processing and power unit; reports on the results of the
campaigns dedicated to integration, alignment, and tests, and to
the characterisation of the instrument performance; describes the
operation concept, data handling, and software tools; and, finally,
the diagnostic techniques to be applied to the data, as well as a brief
description of the expected scientific products. The performance of the
instrument measured during calibrations ensures that the scientific
objectives of Metis can be pursued with success. Metis website:
http://metis.oato.inaf.it
Title: New Light on an Old Problem of the Cores of Solar Resonance
Lines
Authors: Judge, Philip G.; Kleint, Lucia; Leenaarts, Jorrit;
Sukhorukov, Andrii V.; Vial, Jean-Claude
Bibcode: 2020ApJ...901...32J
Altcode: 2020arXiv200801250J
We reexamine a 50+ yr old problem of deep central reversals predicted
for strong solar spectral lines, in contrast to the smaller reversals
seen in observations. We examine data and calculations for the resonance
lines of H I, Mg II, and Ca II, the self-reversed cores of which form
in the upper chromosphere. Based on 3D simulations, as well as data for
the Mg II lines from the Interface Region Imaging Spectrograph (IRIS),
we argue that the resolution lies not in velocity fields on scales in
either of the micro- or macroturbulent limits. Macroturbulence is ruled
out using observations of optically thin lines formed in the upper
chromosphere, and by showing that it would need to have unreasonably
special properties to account for critical observations of the Mg
II resonance lines from the IRIS mission. The power in "turbulence"
in the upper chromosphere may therefore be substantially lower than
earlier analyses have inferred. Instead, in 3D calculations horizontal
radiative transfer produces smoother source functions, smoothing out
intensity gradients in wavelength and in space. These effects increase
in stronger lines. Our work will have consequences for understanding
the onset of the transition region, for understanding the energy in
motions available for heating the corona, and for the interpretation
of polarization data in terms of the Hanle effect applied to resonance
line profiles.
Title: The synergy between the payloads on the ASO-S mission
Authors: Vial, Jean-Claude
Bibcode: 2019RAA....19..166V
Altcode:
This paper addresses the improved science resulting from joint
observations performed by the different instruments onboard the Advanced
Space-based Solar Observatory (ASO-S) mission along with ancillary
instruments on missions flying at the same time. It first describes
the three major instruments along with their stated objectives. Then it
presents some basic science issues concerning jointly observed flares,
coronal mass ejections (CMEs) and eruptive prominences (EPs). Each
physical candidate (magnetic reconnection, instability, hard X-ray
emission and magnetic coronal field topology) is discussed in terms
of its signature and identification with ASO-S instrumentation. The
importance of Lyα detection and non-LTE modeling is stressed. Some
instrumental and science challenges are briefly discussed.
Title: Elemental composition in quiescent prominences
Authors: Parenti, S.; Del Zanna, G.; Vial, J. -C.
Bibcode: 2019A&A...625A..52P
Altcode: 2019arXiv190500871P
Context. The first ionization potential (FIP) bias is currently used
to trace the propagation of solar features ejected by the wind and
solar eruptions (coronal mass ejections). The FIP bias also helps us to
understand the formation of prominences, as it is a tracer for the solar
origin of prominence plasma.
Aims: This work aims to provide
elemental composition and FIP bias in quiescent solar prominences. This
is key information to link these features to remnants of solar eruptions
measured in-situ within the heliosphere and to constrain the coronal or
photospheric origin of prominence plasma.
Methods: We used the
differential emission measure technique to derive the FIP bias of two
prominences. Quiet Sun chromospheric and transition region data were
used to test the atomic data and lines formation processes. We used
lines from low stage of ionization of Si, S, Fe, C, N, O, Ni, Mg, and
Ne, constraining the FIP bias in the range 4.2 ≤ log T ≤ 5.8. We
adopted a density-dependent ionization equilibrium.
Results:
We showed that the two prominences have photospheric composition. We
confirmed a photospheric composition in the quiet Sun. We also
identified opacity and/or radiative excitation contributions to the
line formation of a few lines regularly observed in prominences.
Conclusions: With our results we thus provide important elements for
correctly interpreting the upcoming Solar Orbiter/SPICE spectroscopic
data and to constrain prominence formation.
Title: Elemental composition in quiescent prominences
Authors: Parenti, Susanna; Del Zanna, Giulio; Vial, Jean-Claude
Bibcode: 2019shin.confE.182P
Altcode:
The first ionization potential (FIP) bias is currently used to trace the
propagation of solar features ejected by the wind and solar eruptions
(coronal mass ejections). The FIP bias also helps us to understand
the formation of prominences, as it is a tracer for the solar origin
of prominence plasma. This work aims to provide elemental composition
and FIP bias in quiescent solar prominences. This is key information
to link these features to remnants of solar eruptions measured in-situ
within the heliosphere and to constrain the coronal or photospheric
origin of prominence plasma. We used the differential emission measure
technique to derive the FIP bias of two prominences observed with
SOHO/SUMER. Quiet Sun chromospheric and transition region data were
used to test the atomic data and lines formation processes. We used
lines from low stage of ionization of Si, S, Fe, C, N, O, Ni, Mg, and
Ne, constraining the FIP bias in the range 4.2 < log T< 5.8. We
adopted a density-dependent ionization equilibrium. We showed that
the two prominences have photospheric composition. We also identified
opacity and/or radiative excitation contributions to the line formation
of a few lines regularly observed in prominences. With our results
we thus provide important elements for correctly interpreting the
upcoming Solar Orbiter/SPICE spectroscopic data and to constrain
prominence formation.
Title: Some relationships between radiative and atmospheric quantities
through 1D NLTE modeling of prominences in the Mg II lines
Authors: Vial, J. -C.; Zhang, P.; Buchlin, É.
Bibcode: 2019A&A...624A..56V
Altcode:
Context. With more than four years of IRIS observations, and in order
to avoid building customized diagnostics for each observation, it is
useful to derive some simple relations between spectra and physical
quantities. This is even more useful for the k and h lines of Mg
II, which require complex non-local-thermodynamic-equilibrium NLTE
treatments.
Aims: The aim of this work concerning prominences
is to correlate observable spectral features in h and k lines of Mg II
to physical quantities such as the density and the emission measure
(EM) in the same way as similar correlations have been obtained in
the hydrogen lines. In this way, and within approximations done on
some parameters such as temperature, it is possible to build pixel by
pixel an IRIS map of the above-mentioned quantities.
Methods:
In order to simplify and shorten the modeling, we chose to compute
one-dimensional (1D) isothermal and isobaric models that are treated
with the PROM7 NLTE code available at MEDOC (IAS). We built a set of
models with large ranges of temperature, pressure, and thickness. At
all altitudes considered, we paid attention to the exact computation
of the incident radiation. Then we compared the emergent Mg II h and k
intensities with the corresponding hydrogen and electron densities and
EMs.
Results: From the NLTE computation, we derive correlations
between the k and h emergent intensities on one hand and the densities
and EM on the other hand. With some assumptions on the temperature,
we obtain a unique relation between the k (and h) intensities and the
EM that should be useful for deriving either the hydrogen and electron
densities or the effective thickness of an observed prominence.
Conclusions: From NLTE modeling, we have provided a relationship
between observable integrated intensities of the Mg II resonance
lines and prominence plasma EM, which will contribute to a first-order
analysis of long time series of spectroscopic observations, for example,
with IRIS. We anticipate building more complex relations between the
profiles and other plasma quantities.
Title: Launch of a CME-associated eruptive prominence as observed
with IRIS and ancillary instruments
Authors: Zhang, P.; Buchlin, É.; Vial, J. -C.
Bibcode: 2019A&A...624A..72Z
Altcode:
Aims: In this paper we focus on the possible observational
signatures of the processes which have been put forward for explaining
eruptive prominences. We also try to understand the variations in the
physical conditions of eruptive prominences and estimate the masses
leaving the Sun versus the masses returning to the Sun during eruptive
prominences.
Methods: As far as velocities are concerned, we
combined an optical flow method on the Atmospheric Imaging Assembly
(AIA) 304 Å and Interface Region Imaging Spectrograph (IRIS). Mg II
h&k observations in order to derive the plane-of-sky velocities
in the prominence, and a Doppler technique on the IRIS Mg II h&k
profiles to compute the line-of-sight velocities. As far as densities
are concerned, we compared the absolute observed intensities with values
derived from non-local thermodynamic equilibrium radiative transfer
computations to derive the total (hydrogen) density and consequently
compute the mass flows.
Results: The derived electron
densities range from 1.3 × 109 to 6.0 × 1010
cm-3 and the derived total hydrogen densities range from
1.5 × 109 to 2.4 × 1011 cm-3
in different regions of the prominence. The mean temperature is
around 1.1 × 104 K, which is higher than in quiescent
prominences. The ionization degree is in the range of 0.1-10. The
total (hydrogen) mass is in the range of 1.3 × 1014-3.2
× 1014 g. The total mass drainage from the prominence
to the solar surface during the whole observation time of IRIS is
about one order of magnitude smaller than the total mass of the
prominence. The movie associated to Fig. 2 is available at https://www.aanda.org
Title: Preface
Authors: Engvold, Oddbjørn; Vial, Jean-Claude; Skumanich, Andrew
Bibcode: 2019sgsp.bookD..17E
Altcode:
No abstract at ADS
Title: Chapter 14 - Challenges and Prospects for the Future
Authors: Vial, Jean-Claude; Skumanich, Andrew
Bibcode: 2019sgsp.book..463V
Altcode:
The 14 chapters (and five subchapters) of this book have addressed
only a few aspects of the many works that have been produced during the
latest decades in the domain of solar physics and that may be relevant
to stellar physics and possibly other fields in astrophysics. The
achievements result not only from the proximity of our star, which
allows for detailed and comprehensive observations but also from the
many questions that have arisen and have been answered through the
implications of physics and sometimes have led to the stimulation of a
"new" physics. We do not include the summaries and conclusions of
these 14 chapters here. We simply focus on a few points (challenges and
prospects) that may be of interest for future progress and discoveries
in solar and stellar physics. As is shown here, we also allow ourselves
to point out that some authors of the book, including ourselves, may
have some different views on a few topics, a fact of life in science. We
address the various issues with the two following questions in mind:
Where and how is solar progress foreseen? What are the mutual benefits
in the solar-stellar connection?
Title: The Sun as a Guide to Stellar Physics
Authors: Engvold, Oddbjørn; Vial, Jean-Claude; Skumanich, Andrew
Bibcode: 2019sgsp.book.....E
Altcode:
No abstract at ADS
Title: Effects of resonant scattering of the Si IV doublet near 140
nm in a solar active region
Authors: Gontikakis, C.; Vial, J. -C.
Bibcode: 2018A&A...619A..64G
Altcode:
Aims: In a previous study we analysed the C IV 1548.189 Å and
1550.775 Å lines observed with the Solar Ultraviolet Measurements
of Emitted Radiation (SUMER), showing cases where the 1548.189 Å
spectral profile was noticeably different from the 1550.775 Å one,
profiles that we dubbed differentially shaped profiles. We explained
this differential behaviour by an important radiative contribution,
affecting multiple plasma motions happening at the instrument
sub-resolution scale. In the present study we examine more general
cases where radiative effects may contribute to the emission from
the transition region of an active region. Here we analyse the
lines Si IV 1393.757 Å and 1402.772 Å observed with the Interface
Region Imaging Spectrograph (IRIS).
Methods: We study active
region NOAA 12529, observed with IRIS on 18 April 2016. Using sorting
techniques we selected individual profiles for which the intensity line
ratio 1393.757 Å/1402.772 Å is significantly higher or lower than
2 and we also tracked differentially shaped profiles. We analyse the
physical conditions that create these profiles and in some cases we
estimate electron densities.
Results: We found more than 4000
individual profiles with line ratios higher than 2, about 500 profiles
for which the line ratio is in the range 1.3-1.6, and 15 differentially
shaped profiles. Line ratios higher than 2, are found along loops, and
mostly at the y = 250 to 300″ part of the plage. There, we estimated
the incident radiation and derived electron densities that can vary
from 109 to a few times 1011 cm-3,
depending on the plasma temperature. For the low line ratios, the
sources are concentrated at the periphery of the active region plage,
mostly along fibrils and present optical depths, τ, between 1.5 and
3. in most cases. The electron densities calculated from these Si IV
profiles are comparable with electron densities derived using the
O IV 1399.766 Å-1401.163 Å ratios.
Conclusions: We found
that about 2.4% of the individual profiles for which we can perform
a Gaussian fit present a line ratio higher than 2. In profiles with
a high line ratio, the resonant scattering appears to be due to the
combination of an average incident radiation field with a relatively
low local electron density and not due to the vicinity of an ephemeral
strong light source. As far as low intensity ratios are concerned,
non-negligible optical depths are found at the edge of the plage,
near the footpoints of fibrils that are oriented towards quiet
Sun areas, where the electron density can be as high as (7 - 9) ×
1011 cm-3 if we assume a plasma in ionization
equilibrium. The movie associated to Fig. 3 is only available at https://www.aanda.org
Title: First high-resolution look at the quiet Sun with ALMA at 3mm
Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos,
S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu,
T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V.
Bibcode: 2018A&A...619L...6N
Altcode: 2018arXiv181005223N
We present an overview of high-resolution quiet Sun observations,
from disk center to the limb, obtained with the Atacama Large
millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun
regions were observed at a resolution of up to 2.5″ by 4.5″. We
produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full-disk
solar images. The images show well the chromospheric network, which,
based on the unique segregation method we used, is brighter than the
average over the fields of view of the observed regions by ∼305
K while the intranetwork is less bright by ∼280 K, with a slight
decrease of the network/intranetwork contrast toward the limb. At 3
mm the network is very similar to the 1600 Å images, with somewhat
larger size. We detect, for the first time, spicular structures,
rising up to 15″ above the limb with a width down to the image
resolution and brightness temperature of ∼1800 K above the local
background. No trace of spicules, either in emission or absorption,
is found on the disk. Our results highlight the potential of ALMA for
the study of the quiet chromosphere.
Title: Cool Material in the Hot Solar Corona and the
Chromosphere-Corona Mass Cycle
Authors: Liu, Wei; Vial, Jean-Claude; Antolin, Patrick; Sun, Xudong;
Berger, Thomas
Bibcode: 2018cosp...42E2052L
Altcode:
In the million-degree hot and tenuous solar corona, under favorable
conditions, some mass can undergo a radiative cooling instability and
condense into material of 100 times cooler in two distinct forms -
prominences and coronal rain. Being at similar temperatures, they
exhibit contrasting morphologies and behaviors: a quiescent prominence
usually consists of numerous long-lasting, filamentary downflow
threads, while coronal rain consists of transient mass blobs falling
at comparably higher speeds along well-defined, curved paths (e.g.,
guided by coronal loops). We report recent imaging and spectroscopic
observations from SDO/AIA and IRIS of a hybrid prominence-coronal
rain complex structure that suggest different magnetic environments
being responsible for such distinctions. We also present an ensemble
of observations of the so-called funnel prominences that reside near
the dips of magnetic funnels. Regardless of their morphological and
behavioral differences, a large fraction of prominence and coronal
rain material eventually falls back to the chromosphere and serves as
the return flow of the so-called chromosphere-corona mass cycle (the
other half of this cycle is the upward transport of heated mass from
the chromosphere to the corona). We estimate the downflow mass fluxes
in prominences and coronal rain, and compare them with the coronal
mass budget in this cycle and with the mass loss to the solar wind
and coronal mass ejections (CMEs). We will discuss the broad physical
implications of these observations for fundamental questions, such as
coronal heating and beyond.
Title: An analysis of simultaneous observations of a CME-associated
eruptive prominence with IRIS, AIA/SDO, EUVI/STEREO and K-COR
Authors: Zhang, Ping; Vial, Jean-Claude; Buchlin, Eric
Bibcode: 2018cosp...42E3836Z
Altcode:
We present the simultaneous observations of a CME-associated eruptive
prominence which have been made by the Interface Region Imaging
Spectrograph (IRIS), Atmospheric Imaging Assembly (AIA) of SDO, EUVI
of STEREO and the ground-based K-COR coronagraph. IRIS observations
started on 2014 May 28 at 11:25 UT, lasted for about 4.5 hours. With
the aim of deriving the velocity vector, we first combined an optical
flow method on the AIA 304 observations to compute the POS velocities
in the prominence and a Doppler technique with the IRIS observations
to compute the LOS velocities. Then we characterized the Mg h and k
profiles (time and space-dependent) and compared with the signatures
of various (1000) prominence models through NLTE radiative transfer
computations (I.A.S. PROM7 code). We paid much attention to the exact
incident radiation in various lines and continua. The model parameters
include pressure, temperature, height, thickness, radial and turbulence
velocities. Having selected the best (fitting) models, we were able
to derive the total (hydrogen) density and compute the mass flows. We
also used the STEREO observations to derive the 3D geometry of the
prominence and K-COR to derive the density later on in the process of
eruption. Applying this method to more prominences observed by IRIS
could help to reduce the large range of thermodynamic parameters in
eruptive prominences and to improve their MHD modeling.
Title: Chemical fractionation in solar prominences
Authors: Parenti, Susanna; Vial, Jean-Claude; Del Zanna, Giulio
Bibcode: 2018cosp...42E2585P
Altcode:
The First Ionization Potential (FIP) fractionation of elemental
abundances in the solar atmosphere and solar wind is a known process
which appears to vary depending on the magnetic field property and
the dynamic nature of the environment. It is generally identified
by an increase of the low FIP elements (with FIP energy below 10 eV)
compared to the high FIP elements (with respect to the photospheric
values). For instance, the low FIP element abundance is enhanced
within active regions by about a factor of 3-4, with respect to
photospheric values. A similar property is measured in the slow
solar wind. This is one of the reasons why the FIP fractionation is
used as a proxy for identifying the solar wind source regions on the
Sun, a topic of particular relevance for the upcoming Solar Orbiter
mission.Cool, low-state ionized plasma and its composition have been
measured in-situ within interplanetary Coronal Mass Ejections (ICMEs)
in only a few cases. This cool plasma has been associated to remnants
of erupting prominences. However, this association is not confirmed,
because the measurement of the composition within prominence plasma is
very difficult and poorly known. The scope of this paper is to provide
a reliable measurement of elements composition and FIP fractionation in
a prominence using the available SOHO/SUMER dataset of the prominence
atlas presented in Parenti et. al 2005. Our investigation will consider
ions formed in the prominence-corona transition region, taking into
account possible density and opacity effects in the formation of the
spectral lines.
Title: Physical conditions in a prominence eruption during its
pre-eruption and acceleration
Authors: Zhang, Ping; Vial, Jean-Claude; Buchlin, Eric
Bibcode: 2018cosp...42E3837Z
Altcode:
We rely upon the simultaneous observations of a CME-associated
eruptive prominence which have been made by the Interface Region
Imaging Spectrograph (IRIS), Atmospheric Imaging Assembly (AIA) of
SDO, EUVI of STEREO and the ground-based K-COR coronagraph. We focus
on the determination of mass flows in order to detect a possible mass
loading. In order to derive the full velocity vector, we combine an
optical flow method on the AIA 304 and IRIS SJI observations to compute
the POS velocities in the prominence and a Doppler technique with the
IRIS observations to compute the LOS velocities. Then we focus on the
determination of densities through the combination of spectroscopic
observations and NLTE modelling. We first characterize the Mg II h and
k profiles (time and space-dependent!) through a grid of 6 typical
profiles (reversed and unreversed). Then we compare them with the
signatures of hundreds of prominence models through NLTE radiative
transfer computations (I.A.S. PROM7 code). Much attention is paid to
the exact incident radiation in various lines and continua. Having
selected the best (fitting) models, we are able to derive the total
(hydrogen) density and compute the mass flows. The derivation of
physical parameters (e.g. velocity) also takes into account the STEREO
observations to derive the 3D geometry of the prominence and K-COR to
derive the density later on in the process of eruption.
Title: IRIS Observations of Spicules and Structures Near the
Solar Limb
Authors: Alissandrakis, C. E.; Vial, J. -C.; Koukras, A.; Buchlin,
E.; Chane-Yook, M.
Bibcode: 2018SoPh..293...20A
Altcode: 2018arXiv180102082A
We have analyzed Interface Region Imaging Spectrograph (IRIS)
spectral and slit-jaw observations of a quiet region near the South
Pole. In this article we present an overview of the observations, the
corrections, and the absolute calibration of the intensity. We focus
on the average profiles of strong (Mg II h and k, C II and Si IV),
as well as of weak spectral lines in the near ultraviolet (NUV) and
the far ultraviolet (FUV), including the Mg II triplet, thus probing
the solar atmosphere from the low chromosphere to the transition
region. We give the radial variation of bulk spectral parameters as
well as line ratios and turbulent velocities. We present measurements
of the formation height in lines and in the NUV continuum from which
we find a linear relationship between the position of the limb and
the intensity scale height. We also find that low forming lines,
such as the Mg II triplet, show no temporal variations above the limb
associated with spicules, suggesting that such lines are formed in a
homogeneous atmospheric layer and, possibly, that spicules are formed
above the height of 2″. We discuss the spatio-temporal
structure of the atmosphere near the limb from images of intensity as
a function of position and time. In these images, we identify p-mode
oscillations in the cores of lines formed at low heights above the
photosphere, slow-moving bright features in O I and fast-moving bright
features in C II. Finally, we compare the Mg II k and h line profiles,
together with intensity values of the Balmer lines from the literature,
with computations from the PROM57Mg non-LTE model, developed at the
Institut d' Astrophysique Spatiale, and estimated values of the physical
parameters. We obtain electron temperatures in the range of ∼8000 K
at small heights to ∼20 000 K at large heights, electron densities
from 1.1 ×1011 to 4 ×1010cm−3
and a turbulent velocity of ∼24 kms−1.
Title: EUV imager and spectrometer for LYOT and solar orbiter space
missions
Authors: Millard, Anne; Lemaire, Philippe; Vial, Jean-Claude
Bibcode: 2017SPIE10568E..0RM
Altcode:
In the 2010 horizon, solar space missions such as LYOT and Solar
Orbiter will allow high cadence UV observations of the Sun at spatial
and spectral resolution never obtained before. To reach these goals,
the two missions could take advantage of spectro-imagers. A reflective
only optical solution for such an instrument is described in this
paper and the first results of the mock-up being built at IAS are shown.
Title: Definition of a metrology servo-system for a solar imaging
fourier transform spectrometer working in the far UV (IFTSUV)
Authors: Ruiz de Galarreta Fanju, C.; Philippon, A.; Bouzit, M.;
Appourchaux, T.; Vial, J. -C.; Maillard, J. -P.; Lemaire, P.
Bibcode: 2017SPIE10564E..3ER
Altcode:
The understanding of the solar outer atmosphere requires a simultaneous
combination of imaging and spectral observations concerning the far UV
lines that arise from the high chromospheres up to the corona. These
observations must be performed with enough spectral, spatial and
temporal resolution to reveal the small atmospheric structures and to
resolve the solar dynamics. An Imaging Fourier Transform Spectrometer
working in the far-UV (IFTSUV, Figure 1) is an attractive instrumental
solution to fulfill these requirements. However, due to the short
wavelength, to preserve IFTSUV spectral precision and Signal to Noise
Ratio (SNR) requires a high optical surface quality and a very accurate
(linear and angular) metrology to maintain the optical path difference
(OPD) during the entire scanning process by: optical path difference
sampling trigger; and dynamic alignment for tip/tilt compensation
(Figure 2).
Title: The Fate of Cool Material in the Hot Corona: Solar Prominences
and Coronal Rain
Authors: Liu, Wei; Antolin, Patrick; Sun, Xudong; Vial, Jean-Claude;
Berger, Thomas
Bibcode: 2017SPD....4810501L
Altcode:
As an important chain of the chromosphere-corona mass cycle,
some of the million-degree hot coronal mass undergoes a radiative
cooling instability and condenses into material at chromospheric or
transition-region temperatures in two distinct forms - prominences
and coronal rain (some of which eventually falls back to the
chromosphere). A quiescent prominence usually consists of numerous
long-lasting, filamentary downflow threads, while coronal rain consists
of transient mass blobs falling at comparably higher speeds along
well-defined paths. It remains puzzling why such material of similar
temperatures exhibit contrasting morphologies and behaviors. We report
recent SDO/AIA and IRIS observations that suggest different magnetic
environments being responsible for such distinctions. Specifically,
in a hybrid prominence-coronal rain complex structure, we found that
the prominence material is formed and resides near magnetic null points
that favor the radiative cooling process and provide possibly a high
plasma-beta environment suitable for the existence of meandering
prominence threads. As the cool material descends, it turns into
coronal rain tied onto low-lying coronal loops in a likely low-beta
environment. Such structures resemble to certain extent the so-called
coronal spiders or cloud prominences, but the observations reported
here provide critical new insights. We will discuss the broad physical
implications of these observations for fundamental questions, such as
coronal heating and beyond (e.g., in astrophysical and/or laboratory
plasma environments).
Title: Neutral Hydrogen and Its Emission Lines in the Solar Corona
Authors: Vial, Jean-Claude; Chane-Yook, Martine
Bibcode: 2016SoPh..291.3549V
Altcode: 2016SoPh..tmp..184V; 2016arXiv160905092V
Since the Lyman-α rocket observations of Gabriel (Solar Phys.21,
392, 1971), it has been realized that the hydrogen (H) lines could be
observed in the corona and that they offer an interesting diagnostic
for the temperature, density, and radial velocity of the coronal
plasma. Moreover, various space missions have been proposed to measure
the coronal magnetic and velocity fields through polarimetry in H
lines. A necessary condition for such measurements is to benefit from a
sufficient signal-to-noise ratio. The aim of this article is to evaluate
the emission in three representative lines of H for three different
coronal structures. The computations have been performed with a full
non-local thermodynamic-equilibrium (non-LTE) code and its simplified
version without radiative transfer. Since all collisional and radiative
quantities (including incident ionizing and exciting radiation) are
taken into account, the ionization is treated exactly. Profiles are
presented at two heights (1.05 and 1.9 solar radii, from Sun center)
in the corona, and the integrated intensities are computed at heights up
to five solar radii. We compare our results with previous computations
and observations (e.g. Lα from Ultraviolet Coronal Spectrometer)
and find a rough (model-dependent) agreement. Since the Hα line is a
possible candidate for ground-based polarimetry, we show that in order
to detect its emission in various coronal structures, it is necessary
to use a very narrow (less than 2 Å wide) bandpass filter.
Title: From the Observation of Non-symmetrical Profiles of the C IV
Resonance Lines for Small Dynamic Events to their Interpretation in
Terms of Resonant Scattering in Solar Active Regions
Authors: Vial, J. C.
Bibcode: 2016AGUFMSH33A..01V
Altcode:
We present observations of small areas in solar active regions recorded
with the SUMER/SOHO spectrograph where the C IV 1548A and 1550A lines
have spectral profiles of different shapes, although they are recorded
simultaneously and at the same location. We propose to explain this
asymmetry by resonant scattering of strong incident radiation from
close-by regions, associated with relative velocities of the emitting
plasmas. We present detailed artificial spectral profiles that may
explain the observations. The profiles have been computed using several
physical parameters such as the plasma temperature and electron density
and the incident radiation on the emitting volumes. We conclude that
the study of asymmetries in the C IV 1548A, 1550A lines, and also in
different doublets (e.g. Si IV for IRIS), should include this radiative
interaction and moreover that it can be a valuable diagnostic tool for
deriving the physical conditions in solar/stellar plasmas, especially
where the radiation processes (such as flare-emission) are enhanced
at the vicinity of the observed structures.
Title: Probing the Physical Connection between Solar Prominences
and Coronal Rain
Authors: Liu, W.; Antolin, P.; Sun, X.; Vial, J. C.; Guo, L.; Gibson,
S. E.; Berger, T. E.; Okamoto, J.; De Pontieu, B.
Bibcode: 2016AGUFMSH43C2587L
Altcode:
Solar prominences and coronal rain are intimately related phenomena,
both involving cool material at chromospheric temperatures within the
hot corona and both playing important roles as part of the return flow
of the chromosphere-corona mass cycle. At the same time, they exhibit
distinct morphologies and dynamics not yet well understood. Quiescent
prominences consist of numerous long-lasting, filamentary downflow
threads, while coronal rain is more transient and falls comparably
faster along well-defined curved paths. We report here a novel, hybrid
prominence-coronal rain complex in an arcade-fan geometry observed
by SDO/AIA and IRIS, which provides new insights to the underlying
physics of such contrasting behaviors. We found that the supra-arcade
fan region hosts a prominence sheet consisting of meandering threads
with broad line widths. As the prominence material descends to the
arcade, it turns into coronal rain sliding down coronal loops with
line widths 2-3 times narrower. This contrast suggests that distinct
local plasma and magnetic conditions determine the fate of the cool
material, a scenario supported by our magnetic field extrapolations
from SDO/HMI. Specifically, the supra-arcade fan (similar to those
in solar flares) is likely situated in a current sheet, where the
magnetic field is weak and the plasma-beta could be close to unity, thus
favoring turbulent flows like those prominence threads. In contrast,
the underlying arcade has a stronger magnetic field and most likely a
low-beta environment, such that the material is guided along magnetic
field lines to appear as coronal rain. We will discuss the physical
implications of these observations beyond the phenomena of prominences
and coronal rain.
Title: Where are we with the Pending Issues of Prominence Formation,
Lifetime and Eruption?
Authors: Vial, J. C.
Bibcode: 2016AGUFMSH41E..02V
Altcode:
As shown by most recent reviews (e.g. Solar Prominences, 2015, ASSL
415), the formation, existence (and eruption) of solar prominences are
still a mystery. There are many reasons for that : their complexity
in terms of geometry and fine structure, the crucial rôle of the
magnetic field (and its difficult measurement), the mixed nature of the
plasma (neither neutral nor fully ionized), the rôle of the powerful
photospheric, chromospheric and coronal incident radiation in the energy
budget, etc ... We propose to have a review of the latest discoveries
in the field resulting from the most recent missions (such as IRIS)
and ground-based instrumentation along with NLTE and MHD modelling. We
will also address some significant results on the connection between
Eruptive Prominences and CMEs.
Title: Joint SDO and IRIS Observations of a Novel, Hybrid
Prominence-Coronal Rain Complex
Authors: Liu, Wei; Antolin, Patrick; Sun, Xudong; Gao, Lijia; Vial,
Jean-Claude; Gibson, Sarah; Okamoto, Takenori; Berger, Thomas;
Uitenbroek, Han; De Pontieu, Bart
Bibcode: 2016usc..confE..99L
Altcode:
Solar prominences and coronal rain are intimately related phenomena,
both involving cool material at chromospheric temperatures within the
hot corona and both playing important roles as part of the return flow
of the chromosphere-corona mass cycle. At the same time, they exhibit
distinct morphologies and dynamics not yet well understood. Quiescent
prominences consist of numerous long-lasting, filamentary downflow
threads, while coronal rain is more transient and falls comparably
faster along well-defined curved paths. We report here a novel, hybrid
prominence-coronal rain complex in an arcade-fan geometry observed
by SDO/AIA and IRIS, which provides new insights to the underlying
physics of such contrasting behaviors. We found that the supra-arcade
fan region hosts a prominence sheet consisting of meandering threads
with broad line widths. As the prominence material descends to the
arcade, it turns into coronal rain sliding down coronal loops with
line widths 2-3 times narrower. This contrast suggests that distinct
local plasma and magnetic conditions determine the fate of the cool
material, a scenario supported by our magnetic field extrapolations
from SDO/HMI. Specifically, the supra-arcade fan (similar to those
in solar flares; e.g., McKenzie 2013) is likely situated in a current
sheet, where the magnetic field is weak and the plasma-beta could be
close to unity, thus favoring turbulent flows like those prominence
threads. In contrast, the underlying arcade has a stronger magnetic
field and most likely a low-beta environment, such that the material
is guided along magnetic field lines to appear as coronal rain. We
will discuss the physical implications of these observations beyond
prominence and coronal rain.
Title: Automated detection, characterization, and tracking of
filaments from SDO data
Authors: Buchlin, E.; Mercier, C.; Vial, J. -C.
Bibcode: 2016usc..confE.100B
Altcode:
Thanks to the cadence and continuity of AIA and HMI observations, SDO
offers unique data for detecting, characterizing, and tracking solar
filaments, until their eruptions, which are often associated with
coronal mass ejections. Because of the requirement of short latency
when aiming at space weather applications, and because of the important
data volume, only an automated detection can be worked out. We present
the code "FILaments, Eruptions, and Activations detected from Space"
(FILEAS) that we have developed for the automated detection and
tracking of filaments. Detections are based on the analysis of AIA
30.4 nm He II images and on the magnetic polarity inversion lines
derived from HMI. Following the tracking of filaments as they rotate
with the Sun, filament characteristics are computed and a database of
filaments parameters is built. We are currently building a database
of filament detections by this code, covering the full SDO mission,
and that will be made available to the community.
Title: A small mission concept to the Sun-Earth Lagrangian L5 point
for innovative solar, heliospheric and space weather science
Authors: Lavraud, B.; Liu, Y.; Segura, K.; He, J.; Qin, G.; Temmer,
M.; Vial, J. -C.; Xiong, M.; Davies, J. A.; Rouillard, A. P.; Pinto,
R.; Auchère, F.; Harrison, R. A.; Eyles, C.; Gan, W.; Lamy, P.;
Xia, L.; Eastwood, J. P.; Kong, L.; Wang, J.; Wimmer-Schweingruber,
R. F.; Zhang, S.; Zong, Q.; Soucek, J.; An, J.; Prech, L.; Zhang,
A.; Rochus, P.; Bothmer, V.; Janvier, M.; Maksimovic, M.; Escoubet,
C. P.; Kilpua, E. K. J.; Tappin, J.; Vainio, R.; Poedts, S.; Dunlop,
M. W.; Savani, N.; Gopalswamy, N.; Bale, S. D.; Li, G.; Howard, T.;
DeForest, C.; Webb, D.; Lugaz, N.; Fuselier, S. A.; Dalmasse, K.;
Tallineau, J.; Vranken, D.; Fernández, J. G.
Bibcode: 2016JASTP.146..171L
Altcode:
We present a concept for a small mission to the Sun-Earth Lagrangian L5
point for innovative solar, heliospheric and space weather science. The
proposed INvestigation of Solar-Terrestrial Activity aNd Transients
(INSTANT) mission is designed to identify how solar coronal magnetic
fields drive eruptions, mass transport and particle acceleration that
impact the Earth and the heliosphere. INSTANT is the first mission
designed to (1) obtain measurements of coronal magnetic fields from
space and (2) determine coronal mass ejection (CME) kinematics with
unparalleled accuracy. Thanks to innovative instrumentation at a vantage
point that provides the most suitable perspective view of the Sun-Earth
system, INSTANT would uniquely track the whole chain of fundamental
processes driving space weather at Earth. We present the science
requirements, payload and mission profile that fulfill ambitious science
objectives within small mission programmatic boundary conditions.
Title: The SPICE Spectral Imager on Solar Orbiter: Linking the Sun
to the Heliosphere
Authors: Fludra, Andrzej; Haberreiter, Margit; Peter, Hardi; Vial,
Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson,
William; Gabriel, Alan; Morris, Nigel; Caldwell, Martin; Auchere,
Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.; DeForest,
Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne; Janvier, Miho;
Wimmer-Schweingruber, Robert; Griffin, Douglas; Davila, Joseph; Giunta,
Alessandra; Waltham, Nick; Eccleston, Paul; Gottwald, Alexander;
Klein, Roman; Hanley, John; Walls, Buddy; Howe, Chris; Schuehle, Udo
Bibcode: 2016cosp...41E.607F
Altcode:
The SPICE (Spectral Imaging of the Coronal Environment) instrument is
one of the key remote sensing instruments onboard the upcoming Solar
Orbiter Mission. SPICE has been designed to contribute to the science
goals of the mission by investigating the source regions of outflows
and ejection processes which link the solar surface and corona to the
heliosphere. In particular, SPICE will provide quantitative information
on the physical state and composition of the solar atmosphere
plasma. For example, SPICE will access relative abundances of ions to
study the origin and the spatial/temporal variations of the 'First
Ionization Potential effect', which are key signatures to trace the
solar wind and plasma ejections paths within the heliosphere. Here we
will present the instrument and its performance capability to attain the
scientific requirements. We will also discuss how different observation
modes can be chosen to obtain the best science results during the
different orbits of the mission. To maximize the scientific return of
the instrument, the SPICE team is working to optimize the instrument
operations, and to facilitate the data access and their exploitation.
Title: The potential of hydrogen lines for the spectropolarimetry
of the solar corona
Authors: Vial, Jean-Claude; Chane-Yook, Martine
Bibcode: 2016cosp...41E2003V
Altcode:
Neutral Hydrogen lines have been detected in the hot and ionized
solar corona as early as 1970 (Gabriel et al. 1971) and since then
with the Spartan and UVCS/SoHO space experiments. Moreover, because
of the sensitivity of the Lyman lines to the Hanle effect (Bommier
and Sahal-Brechot 1982, Trujillo Bueno et al. 2005), polarization
measurements in these lines could lead to the diagnostic of weak
magnetic fields in the corona (Derouich et al. 2010), a challenge
which has led to various space mission proposals such as LYOT/SMESE
or MASC. Our investigation concerns the computation of the emission
in 10 selected lines of Hydrogen (Lyman, Balmer, and Paschen) taking
into account the proper computation of the NonLTE H ionization and
atomic levels populations. We present the results for three different
coronal models (streamer, quiet Sun and coronal hole) in terms of
profiles and absolute intensities at altitudes varying from 1.05 to
1.9 solar radius. These spectrophotometric results could help for the
determination of the space and ground-based polarimetric instrumentation
best suited for the measurement of the coronal magnetic field.
Title: Solar abundances with the SPICE spectral imager on Solar
Orbiter
Authors: Giunta, Alessandra; Haberreiter, Margit; Peter, Hardi;
Vial, Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson, William;
Bocchialini, Karine; Gabriel, Alan; Morris, Nigel; Caldwell, Martin;
Auchere, Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.;
DeForest, Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne;
Janvier, Miho; Wimmer-Schweingruber, Robert; Griffin, Douglas; Baudin,
Frederic; Davila, Joseph; Fludra, Andrzej; Waltham, Nick; Eccleston,
Paul; Gottwald, Alexander; Klein, Roman; Hanley, John; Walls, Buddy;
Howe, Chris; Schuehle, Udo; Gyo, Manfred; Pfiffner, Dany
Bibcode: 2016cosp...41E.681G
Altcode:
Elemental composition of the solar atmosphere and in particular
abundance bias of low and high First Ionization Potential (FIP)
elements are a key tracer of the source regions of the solar wind. These
abundances and their spatio-temporal variations, as well as the other
plasma parameters , will be derived by the SPICE (Spectral Imaging
of the Coronal Environment) EUV spectral imager on the upcoming
Solar Orbiter mission. SPICE is designed to provide spectroheliograms
(spectral images) using a core set of emission lines arising from ions
of both low-FIP and high-FIP elements. These lines are formed over
a wide range of temperatures, enabling the analysis of the different
layers of the solar atmosphere. SPICE will use these spectroheliograms
to produce dynamic composition maps of the solar atmosphere to be
compared to in-situ measurements of the solar wind composition of
the same elements (i.e. O, Ne, Mg, Fe). This will provide a tool to
study the connectivity between the spacecraft (the Heliosphere) and
the Sun. We will discuss the SPICE capabilities for such composition
measurements.
Title: Automated detection, characterization, and tracking of
filaments from SDO data
Authors: Buchlin, Eric; Vial, Jean-Claude; Mercier, Claude
Bibcode: 2016cosp...41E.258B
Altcode:
Thanks to the cadence and continuity of AIA and HMI observations, SDO
offers unique data for detecting, characterizing, and tracking solar
filaments, until their eruptions, which are often associated with
coronal mass ejections. Because of the requirement of short latency
when aiming at space weather applications, and because of the important
data volume, only an automated detection can be worked out. We present
the code "FILaments, Eruptions, and Activations detected from Space"
(FILEAS) that we have developed for the automated detection and tracking
of filaments. Detections are based on the analysis of AIA 30.4 nm He
II images and on the magnetic polarity inversion lines derived from
HMI. Following the tracking of filaments as they rotate with the Sun,
filament characteristics are computed and a database of filaments
parameters is built. We present the algorithms and performances of the
code, and we compare its results with the filaments detected in Hα and
already present in the Heliophysics Events Knowledgebase. We finally
discuss the possibility of using such a code to detect eruptions in
real time.
Title: Non-symmetrical profiles of the C IV 1548A and 1550A lines for
small dynamic events and their interpretation in terms of resonant
scattering in solar active region
Authors: Gontikakis, Costis; Vial, Jean-Claude
Bibcode: 2016cosp...41E.702G
Altcode:
We present observations of small areas in solar active regions
recorded with the SUMER/SOHO spectrograph where the C IV 1548A and
1550A lines have spectral profiles of different shapes, although they
are recorded simultaneously and at the same location. This asymmetry
may be explained by resonant scattering associated with relative
velocities of the emitting plasmas. We present detailed artificial
spectral profiles that may explain the observations. The profiles have
been computed using several physical parameters such as the plasma
temperature and electron density and/or the incident radiation on
the emitting volumes. We conclude that the study of asymmetries in
the C IV 1548A, 1550A lines, and also in different doublets, can be
a valuable diagnostic tool for deriving the physical conditions in
solar/stellar plasmas, especially where the radiation processes (such as
flare-emission) are enhanced at the vicinity of the observed structures.
Title: Evidence of scattering effects influenced by plasma flows in
C VI 1548 Å, 1550 Å spectral lines emitted from the Sun
Authors: Gontikakis, C.; Vial, J. -C.
Bibcode: 2016A&A...590A..86G
Altcode:
Aims: We search for, and study, individual spectral profiles
where the complex shape of the C iv 1548 Å line is different from
the shape of the simultaneously recorded C iv 1550 Å line. Such an
asymmetry is not expected for line emission resulting from collisional
excitation. Therefore we propose an explanation of these observations
through the differential effect of velocity fields on resonant
scattering.
Methods: We analyse spectra recorded with the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) on the Solar and
Heliospheric Observatory (SOHO) over active region, NOAA 8541 as well
as a second data set on the quiet Sun. We perform Gaussian fits on the
individual profiles with two or three Gaussian functions. Moreover,
we parameterize the profile asymmetries by calculating the intensity
ratios I1548/I1550, from the derived Gaussian
functions. We also calculate artificial spectral profiles emitted from
two plasma volumes, which have different line of sight motions and
where the plasma emission is influenced by resonant scattering.
Results: We locate three small regions in NOAA 8541 which have spectral
asymmetries. There the profiles have two or three spectral components,
with different intensity ratios. Artificial profiles show that two
plasma volumes, having distinct velocities relative to the observer,
may reproduce the observed profiles, under the influence of resonant
scattering.
Conclusions: Asymmetric profiles, found in an active
region, can be used as a diagnostic for the importance of resonant
scattering in transition region plasma.
Title: Observed IRIS Profiles of the h and k Doublet of Mg II and
Comparison with Profiles from Quiescent Prominence NLTE Models
Authors: Vial, Jean-Claude; Pelouze, Gabriel; Heinzel, Petr; Kleint,
Lucia; Anzer, Ulrich
Bibcode: 2016SoPh..291...67V
Altcode: 2015SoPh..tmp..173V
With the launch of the Interface Region Imaging Spectrograph (IRIS)
mission, it is now possible to obtain high-resolution solar prominence
spectra and to begin to distinguish the contributions of the many
(apparent or not) threads that structure prominences. We aim at
comparing unique observations obtained in the Mg II h and k lines of a
polar crown prominence with the radiative outputs from one-dimensional
models built with non-local-thermodynamic equilibrium codes (Heinzel et
al.Astron. Astrophys.564, A132, 2014). We characterize the profiles
obtained through thorough calibration procedures, with attention
paid to the absolute values, full-width at half-maximum, and the
ratio of k to h intensities. We also show that at the top of some
structures, line-of-sight velocities of about 9 kms−1 can
be detected. We find a range of static, low-pressure, low-thickness,
low-temperature models that could fit k or h observed values, but that
cannot satisfy the low observed k/h ratio. We investigate whether these
low values might be explained by the inclusion of horizontal flows in
small-scale threads. These flows are also necessary in another class
of models, where the pressure is kept low but thickness and temperature
are increased up to the observed thickness and up to 15 000 K.
Title: Hydrogen Ly-α and Ly-β full Sun line profiles observed with
SUMER/SOHO (1996-2009)
Authors: Lemaire, P.; Vial, J. -C.; Curdt, W.; Schühle, U.;
Wilhelm, K.
Bibcode: 2015A&A...581A..26L
Altcode:
Context. Accurate hydrogen spectra emitted by the entire solar disc in
the Ly-α and Ly-βlines are valuable for deriving the distribution and
the behaviour of atomic hydrogen in the heliosphere, for understanding
the UV emissions of solar type stars better, and finally for estimating
the solar energy input that mainly initiates the chemical processes
occurring in the planetary and cometary outer atmospheres.
Aims:
In this paper we want to accurately determine the irradiance solar
spectral profiles of Ly-α and Ly-β and their evolution through the
solar activity cycle 23.
Methods: The SUMER/SOHO spectrometer is
a slit spectrometer that is only able to analyse a small part of the
solar image. Consequently, we used the scattered light properties of
the telescope to obtain average spectra over the solar disc. Then the
profile is calibrated using the SOLSTICE/UARS and TIMED/SEE irradiance
spectra.
Results: We obtained a set of irradiance Ly-α and
Ly-β solar spectra with a 0.002 nm resolution through the solar
activity cycle 23. In each line a relation between the integrated
profile and the line centre intensity was obtained.Knowing the line
irradiance, it is possible to deduce the central line profile intensity,
a critical input into the interplanetary and planetary oxygen and
hydrogen fluorescent processes.
Conclusions: The observation
of H i Ly-α and Ly-β line profiles by SUMER/SOHO during the cycle
23 allows analysis of the evolution of their characteristics and
accurate determination of UV radiation input into the solar system. Profiles are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/581/A26
Title: VizieR Online Data Catalog: Sun hydrogen Lyman irradiance
lines profiles (Lemaire+, 2015)
Authors: Lemaire, P.; Vial, J. -C.; Curdt, W.; Schuhle, U.; Wilhelm, K.
Bibcode: 2015yCat..35810026L
Altcode:
Set of irradiance Ly-α and Ly-β solar spectra with a 0.002nm
resolution through the solar activity cycle 23. The wavelength distance
from line center is given every 0.001nm. (2 data files).
Title: First High-resolution Spectroscopic Observations of an Erupting
Prominence Within a Coronal Mass Ejection by the Interface Region
Imaging Spectrograph (IRIS)
Authors: Liu, Wei; De Pontieu, Bart; Vial, Jean-Claude; Title, Alan
M.; Carlsson, Mats; Uitenbroek, Han; Okamoto, Takenori J.; Berger,
Thomas E.; Antolin, Patrick
Bibcode: 2015ApJ...803...85L
Altcode: 2015arXiv150204738L
Spectroscopic observations of prominence eruptions associated with
coronal mass ejections (CMEs), although relatively rare, can provide
valuable plasma and three-dimensional geometry diagnostics. We report
the first observations by the Interface Region Imaging Spectrograph
mission of a spectacular fast CME/prominence eruption associated with
an equivalent X1.6 flare on 2014 May 9. The maximum plane-of-sky and
Doppler velocities of the eruption are 1200 and 460 km s-1,
respectively. There are two eruption components separated by ∼200
km s-1 in Doppler velocity: a primary, bright component
and a secondary, faint component, suggesting a hollow, rather than
solid, cone-shaped distribution of material. The eruption involves
a left-handed helical structure undergoing counterclockwise (viewed
top-down) unwinding motion. There is a temporal evolution from upward
eruption to downward fallback with less-than-free-fall speeds and
decreasing nonthermal line widths. We find a wide range of Mg ii k/h
line intensity ratios (less than ∼2 expected for optically-thin
thermal emission): the lowest ever reported median value of 1.17
found in the fallback material, a comparably high value of 1.63 in
nearby coronal rain, and intermediate values of 1.53 and 1.41 in
the two eruption components. The fallback material exhibits a strong
(\gt 5σ ) linear correlation between the k/h ratio and the Doppler
velocity as well as the line intensity. We demonstrate that Doppler
dimming of scattered chromospheric emission by the erupted material
can potentially explain such characteristics.
Title: The Balmer Lines of He II in the Blue Wing of the Hydrogen
Lyman α Line Observed in a Quiescent Prominence
Authors: Vial, J. -C.; Eurin, G.; Curdt, W.
Bibcode: 2015SoPh..290..381V
Altcode:
We revisit the prominence observations in the Lyman α line of Curdt
et al. (Astron. Astrophys.511, L4, 2010) and focus on the bump in the
blue wing of the line, which we identify with He II Balmer lines. We
determine the transition candidates, derive an upper limit for the
width of the profile and an associated non-thermal velocity close to 0
km s−1, with the assumption that the kinetic temperature
is equal to the formation temperature. We compare the total intensity
with the corresponding H Lyman α intensity and find a ratio much
lower than that measured by Ebadi, Vial, and Ajabshirizadeh (Solar
Phys.257, 91, 2009) in other Lyman lines. We confirm this result with
observations performed by Schwartz et al. (private communication,
2014), we discuss a possible interpretation, and suggest that this
issue needs to be addressed closely in future observations.
Title: Solar Prominences
Authors: Vial, Jean-Claude; Engvold, Oddbjørn
Bibcode: 2015ASSL..415.....V
Altcode:
No abstract at ADS
Title: Historical Background and Introduction
Authors: Vial, Jean-Claude
Bibcode: 2015ASSL..415....1V
Altcode:
Forty and twenty years after the two books published by Einar
Tandberg-Hanssen (Solar prominences (Geophysics and astrophysics
monographs), Vol. 12. Dordrecht: D. Reidel Publishing Co., 1974; The
nature of solar prominences, astrophysics and space science library,
Vol. 199. Dordrecht: Kluwer Academic Publishers, 1995) on solar
prominences, it is time to update our knowledge and understanding
of these fascinating solar structures. After a brief history which
overviews first eclipse observations (drawings and then photography),
spectrographic, coronagraphic and later on polarimetric measurements,
the chapter presents samples of the most spectacular results of the last
two decades, obtained whether from space or on the ground. It discusses
the contents of the book in order to encourage the reader to dip into
the following 17 chapters which provide comprehensive and detailed
observations, information about the methods used, and interpretation of
the results on the basis of the latest theoretical and modelling works.
Title: Instant: An Innovative L5 Small Mission Concept for Coordinated
Science with Solar Orbiter and Solar Probe Plus
Authors: Lavraud, B.; Liu, Y. D.; Harrison, R. A.; Liu, W.;
Auchere, F.; Gan, W.; Lamy, P. L.; Xia, L.; Eastwood, J. P.;
Wimmer-Schweingruber, R. F.; Zong, Q.; Rochus, P.; Maksimovic, M.;
Temmer, M.; Escoubet, C. P.; Kilpua, E.; Rouillard, A. P.; Davies,
J. A.; Vial, J. C.; Gopalswamy, N.; Bale, S. D.; Li, G.; Howard,
T. A.; DeForest, C. E.
Bibcode: 2014AGUFMSH21B4109L
Altcode:
We will present both the science objectives and related instrumentation
of a small solar and heliospheric mission concept, INSTANT:
INvestigation of Solar-Terrestrial Activity aNd Transients. It will be
submitted as an opportunity to the upcoming ESA-China S-class mission
call later this year. This concept was conceived to allow innovative
measurements and unprecedented, early determination of key properties
of Earthbound CMEs from the L5 vantage point. Innovative measurements
will include magnetic field determination in the corona thanks to
Hanle measurement in Lyman-α and polarized heliospheric imaging
for accurate determination of CME trajectories. With complementary
in situ measurements, it will uniquely permit solar storm science,
solar storm surveillance, and synergy with Solar Orbiter and Solar
Probe Plus (the ESA-China S2 mission launch is planned in 2021).
Title: First High-resolution Spectroscopic Observations by IRIS
of a Fast, Helical Prominence Eruption Associated with a Coronal
Mass Ejection
Authors: Liu, W.; De Pontieu, B.; Okamoto, T. J.; Vial, J. C.; Title,
A. M.; Antolin, P.; Berger, T. E.; Uitenbroek, H.
Bibcode: 2014AGUFMSH11D..04L
Altcode:
High-resolution spectroscopic observations of prominence eruptions and
associated coronal mass ejections (CMEs) are rare but can provide
valuable plasma and energy diagnostics. New opportunities have
recently become available with the advent of the Interface Region
Imaging Spectrograph (IRIS) mission equipped with high resolution of
0.33-0.4 arcsec in space and 1 km/s in velocity, together with the
Hinode Solar Optical Telescope of 0.2 arcsec spatial resolution. We
report the first result of joint IRIS-Hinode observations of a
spectacular prominence eruption occurring on 2014-May-09. IRIS
detected a maximum redshift of 450 km/s, which, combined with the
plane-of-sky speed of 800 km/s, gives a large velocity vector of 920
km/s at 30 degrees from the sky plane. This direction agrees with the
source location at 30 degrees behind the limb observed by STEREO-A
and indicates a nearly vertical ejection. We found two branches of
redshifts separated by 200 km/s appearing in all strong lines at
chromospheric to transition-region temperatures, including Mg II k/h,
C II, and Si IV, suggesting a hollow, rather than solid, cone in the
velocity space of the ejected material. Opposite blue- and redshifts
on the two sides of the prominence exhibit corkscrew variations both
in space and time, suggestive of unwinding rotations of a left-handed
helical flux rope. Some erupted material returns as nearly streamline
flows, exhibiting distinctly narrow line widths (~10 km/s), about
50% of those of the nearby coronal rain at the apexes of coronal
loops, where the rain material is initially formed out of cooling
condensation. We estimate the mass and kinetic energy of the ejected
and returning material and compare them with those of the associated
CME. We will discuss the implications of these observations for CME
initiation mechanisms.
Title: On the formation of Mg ii h and k lines in solar prominences
Authors: Heinzel, P.; Vial, J. -C.; Anzer, U.
Bibcode: 2014A&A...564A.132H
Altcode:
Aims: With the recent launch of the IRIS mission, it has become
urgent to develop the spectral diagnostics using the Mg ii resonance
h and k lines. In this paper, we aim to demonstrate the behavior of
these lines under various prominence conditions. Our results serve
as a basis for analysis of new IRIS data and for more sophisticated
prominence modeling.
Methods: For this exploratory work,
we use a canonical 1D prominence-slab model, which is isobaric
and may have three different temperature structures: isothermal,
PCTR-like (prominence-corona transition region), and consistent with
the radiative equilibrium. The slabs are illuminated by a realistic
incident solar radiation obtained from the UV observations. A five-level
plus continuum Mg ii model atom is used to solve the full NLTE problem
of the radiative transfer. We use the numerical code based on the ALI
techniques and apply the partial frequency redistribution for both
Mg ii resonance lines. We also use the velocity-dependent boundary
conditions to study the effect of Doppler dimming in the case of
moving prominences. Finally, the relaxation technique is used to
compute a grid of models in radiative equilibrium.
Results:
We computed the Mg ii h and k line profiles that are emergent from
prominence-slab models and show their dependence on kinetic temperature,
gas pressure, geometrical extension, and microturbulent velocity. By
increasing the line opacity, significant departures from the complete
frequency redistribution take place in the line wings. Models with a
PCTR temperature structure show that Mg ii becomes ionized to Mg iii
in the temperature range between roughly 15 000 and 30 000 K. Doppler
dimming is significant for Mg ii resonance lines. At the velocity 300
km s-1, the line intensity decreases to about 20% of the
value for static prominences. Finally, we demonstrate the role of Mg
ii h and k radiation losses on the prominence energy balance. Their
dominant role is at lower pressures, while the losses due to hydrogen
and Ca ii dominate at higher pressures.
Title: A comparison between observed IRIS profiles of the h &
k doublet of Mg II and profiles from quiescent prominence NLTE models
Authors: Vial, Jean-Claude; Anzer, Ulrich; Heinzel, Petr; Kleint, Lucia
Bibcode: 2014cosp...40E3515V
Altcode:
With the advent of IRIS, it is now possible to investigate the cool core
of prominences through the detailed profiles of the Mg II resonance
lines with an unprecedented spatial resolution of 0.33 arcsecond. The
slit-jaw camera also allows to record the temporal evolution of the
prominence fine structure. We present IRIS observations of quiescent
prominence profiles that we analyse in terms of reversal (if any),
width, k/h line ratio, prominence/ quiet Sun line ratio. Comparing these
parameters with the results of NLTE modelling (see Heinzel et al. 2014),
we can derive thermodynamic parameters of the cool prominence plasma,
along with the (line-of-sight) velocities and mass flows.
Title: INSTANT: INvestigation of Solar-Terrestrial Associated
Natural Threats
Authors: Lavraud, Benoit; Vial, Jean-Claude; Harrison, Richard; Davies,
Jackie; Escoubet, C. Philippe; Zong, Qiugang; Auchere, Frederic; Liu,
Ying; Bale, Stuart; Gopalswamy, Nat; Li, Gang; Maksimovic, Milan;
Liu, William; Rouillard, Alexis
Bibcode: 2014cosp...40E1758L
Altcode:
The INSTANT mission will tackle both compelling solar and heliospheric
science objectives and novel space weather capabilities. This is
allowed by combining innovative and state-of-the-art instrumentation
at an appropriate off-Sun-Earth line location on an orbit lagging
the Earth around the Sun, near the L5 Lagrangian point. It is an
affordable mission that tackles major objectives of the European and
Chinese communities in terms of space physics and space weather. The
science objectives are: 1. What is the magnetic field magnitude and
topology in the corona? 2. How does the magnetic field reconfigure
itself during CME eruptions? 3. What are the sources and links between
the slow and fast winds? 4. How do CMEs accelerate and interact in the
interplanetary medium? The mission will further allow the following
crucial space weather capabilities: 5. Three-days advance knowledge
of CIR properties that reach Earth. 6. Twelve hours to 2 days advance
warning of Earth-directed CMEs. 7. Thanks to Lyman-α observations,
first-ever capability of determining the magnetic field magnitude and
orientation of Earth-directed CMEs. The mission will be proposed in
the context of the upcoming ESA-China S-class call for mission.
Title: MASC: Magnetic Activity of the Solar Corona
Authors: Auchere, Frederic; Fineschi, Silvano; Gan, Weiqun; Peter,
Hardi; Vial, Jean-Claude; Zhukov, Andrei; Parenti, Susanna; Li, Hui;
Romoli, Marco
Bibcode: 2014cosp...40E.149A
Altcode:
We present MASC, an innovative payload designed to explore the magnetic
activity of the solar corona. It is composed of three complementary
instruments: a Hard-X-ray spectrometer, a UV / EUV imager, and a Visible
Light / UV polarimetric coronagraph able to measure the coronal magnetic
field. The solar corona is structured in magnetically closed and
open structures from which slow and fast solar winds are respectively
released. In spite of much progress brought by two decades of almost
uninterrupted observations from several space missions, the sources and
acceleration mechanisms of both types are still not understood. This
continuous expansion of the solar atmosphere is disturbed by sporadic
but frequent and violent events. Coronal mass ejections (CMEs) are
large-scale massive eruptions of magnetic structures out of the corona,
while solar flares trace the sudden heating of coronal plasma and the
acceleration of electrons and ions to high, sometimes relativistic,
energies. Both phenomena are most probably driven by instabilities
of the magnetic field in the corona. The relations between flares
and CMEs are still not understood in terms of initiation and energy
partition between large-scale motions, small-scale heating and
particle acceleration. The initiation is probably related to magnetic
reconnection which itself results magnetic topological changes due to
e.g. flux emergence, footpoints motions, etc. Acceleration and heating
are also strongly coupled since the atmospheric heating is thought to
result from the impact of accelerated particles. The measurement of
both physical processes and their outputs is consequently of major
importance. However, despite its fundamental importance as a driver
for the physics of the Sun and of the heliosphere, the magnetic field
of our star’s outer atmosphere remains poorly understood. This
is due in large part to the fact that the magnetic field is a very
difficult quantity to measure. Our knowledge of its strength and
orientation is primarily based on extrapolations from photospheric
observations, not from direct measurements. These extrapolations
require strong assumptions on critical but unobserved quantities and
thus fail to accurately reproduce the complex topologies inferred
from remote-sensing observations of coronal structures in white
light, EUV, and X-rays. Direct measurements of the coronal magnetic
field are also clearly identified by the international heliophysics
community as a key element susceptible to lead to major breakthroughs
in the understanding of our star. MASC is thus designed to answer
the following top-level scientific questions: 1. What is the global
magnetic field configuration in the corona? 2. What is the role of
the magnetic field in the triggering of flares and CMEs? 3. What is
the role of the magnetic field in the acceleration mechanisms of the
solar winds? 4. What is the energy spectrum and in particular what are
the highest energies to which charged particles can be accelerated in
the solar corona? MASC will address these fundamental questions with
a suite of instruments composed of an X-ray spectrometer, a UV / EUV
imager, and a coronagraph working in the visible and at Lyman alpha. The
spectrometer will provide information on the energetics of solar flares,
in particular at very high energies of accelerated particles. The
UV / EUV imager will provide constraints on the temperature of the
flaring and non-flaring corona. The coronagraph will provide the number
density of free electrons in the corona, maps of the outflow velocity
of neutral hydrogen, and measurements of the coronal magnetic field,
via the Hanle effect. These measurements will be performed at all
steps of the flare-CME processes, thus providing a detailed picture
of the solar coronal dynamics in the quiet and eruptive periods.
Title: Automated detection, characterization, and tracking of
filaments from SDO data
Authors: Buchlin, Eric; Vial, Jean-Claude; Mercier, Claude; Goujon,
Jean-Baptiste
Bibcode: 2014cosp...40E.425B
Altcode:
Thanks to the cadence and continuity of AIA and HMI observations, SDO
offers unique data for detecting, characterizing, and tracking solar
filaments, until their eruptions, which are often associated with
coronal mass ejections. Because of the requirement of short latency
when aiming at space weather applications, and because of the important
data volume, only an automated detection can be worked out. We present
the code "FILaments, Eruptions, and Activations detected from Space"
(FILEAS) that we have developed for the automated detection and tracking
of filaments. Detections are based on the analysis of AIA 30.4 nm He
II images and on the magnetic polarity inversion lines derived from
HMI. Following the tracking of filaments as they rotate with the Sun,
filament characteristics are computed and a database of filaments
parameters is built. We present the algorithms and performances of
the code, and we compare its results with the filaments detected in
Halpha and already present in the Heliophysics Events Knowledgebase. We
finally discuss the possibility of using such a code to detect eruptions
in real time.
Title: On the nature of the prominence - corona transition region
Authors: Parenti, Susanna; Vial, Jean-Claude
Bibcode: 2014IAUS..300...69P
Altcode:
Due to the complexity of their environment, prominences properties are
still a matter of controversy. Prominences cool and dense plasma is
suspended in the hot corona by a magnetic structure poorly known. Their
thermal insulation from the corona results in a thin geometrical
interface called prominence-corona-transition-region (PCTR). Here we
will review the main properties of such a region as derived primarily
from observations. We will introduce the thermal structure properties,
describe the fine structure together with the Doppler-shift and width
properties of lines of the emitting plasma. We will introduce the
proposed interpretations of such observations and the limits of our
knowledge imposed by the present instrumentation. We will conclude
with a perspective for the future observations of the PCTR.
Title: The EUV photosphere- corona interface from eclipses to study
the origin of low- FIP elements and the root of the basis of the
chromosphere
Authors: Bazin, Cyrille; Veselovsky, Igor; Vial, Jean-Claude; Tavabi,
Ehsan; Serge, Koutchmy
Bibcode: 2014cosp...40E.236B
Altcode:
We use the full occultation of the Sun by the Moon to study the upper
solar atmosphere with flash spectra free of any parasitic light from
the disc. A radial resolution of 40 km is obtained from unique images
in many emission lines seen as crescents of the low atmosphere. The
natural motion of the lunar limb probes the photosphere - corona
interface where the solar magnetic field emerges. High cadence CCD
slitless flash spectra obtained before and after the eclipse totality
(in 2008, 2009, 2010, 2012, and 2013) show that the over-abundance of
the low First Ionisation Potential elements (low FIP) like FeII, TiII,
BaII, etc. comes from the interface layers close to the temperature
minimum. For the 1st time, the solar edge is defined by considering
the “true” continuum analysed outside of faint emission lines at
heights ranging from 0.2 to 0.6 Mm. We also measure the helium shells
of He I 4713Å and of He II 4686Å (Paschen alpha, optically thin high
FIP lines), starting at the height of 0.8 Mm. Enhancements of the high
FIP lines (H beta, He I and He II) are found at altitudes lower than
0.8 Mm above the limb from new 2013 spectra. The extensions of the
helium shells are compared in equatorial and Polar Regions. The widths
of the lines are evaluated for the 1st time. The light curves I = f(h)
corresponding to low FIP ions are measured for different positions of
the low solar atmosphere. The scale heights correspond to radial density
gradients allowing temperature evaluations in case of the hydrostatic
assumptions. We also demonstrate some density gradient analogies
between the photosphere- corona and the prominence-corona interface
using the Ti II lines as a marker. The effect of the magnetic field
emergence for supplying mass to the corona through low FIP elements
is discussed. A simultaneously obtained 193 SDO/AIA processed image
is used to discuss what the coronal extensions are.
Title: On the development of a Fourier Transform Spectrometer for
Solar Physics
Authors: Ruiz de Galarreta, Claudia; Vial, Jean-Claude; Appourchaux,
Thierry; Philippon, Anne
Bibcode: 2014cosp...40E2793R
Altcode:
The origin and the evolution of the different structures that inhabit
beyond the Sun’s photosphere, as well as the processes involved in
the dynamics and the heating of the corona remain quite unknown. The
inextricable complexity of the physical phenomena that govern the solar
outer atmosphere is accompanied by the lack of suitable data adapted to
the scientific need. Indeed, the interpretation and the models of the
mechanisms that connect the exchanges between the chromosphere and the
corona depend on critical observational parameters. It is for example
essential to measure broad bands of vertical temperature and density
ranges that fit the multiple spatial and temporal scales that are
characteristic of the different events that take place in the Sun. The
understanding of the dynamics of the plasma must be also based on the
Doppler analysis of the observed scene. That implies the ability to
combine time resolved spectroscopic and imaging technologies. Moreover,
space is the place to observe the far UV corona and that implies a
real technical challenge. Despite excellent advances in technology and
instrumentation, the study of the Sun in the far UV is a fairly recent
science. To date, no solar space mission could provide a combined and
simultaneous diagnostic of both observables in the spectral range of
interest. It is because of these expectations that the study of a
new device called IFTSUV (the acronym of Imaging Fourier Transform
Spectrometer working in the far UV) is presented in this paper. We
start from the definition of the scientific requirements that lead to
the technical choice, the first objective of this study is to develop
a preliminary instrumental model of the IFTSUV. The overall technical
and design specifications are based in theoretical calculations that
have been expressed in terms of spectral accuracy, image quality and
signal to noise ratio. Throughout the identification of difficult
points, the realization of a servo-metrology system to control the
sampling mirror appears naturally as an intrinsic need of proof of
concept. Indeed, the wavenumbers from the raw spectra are set by the
interferogram. That implies that acquisition must be rigorously constant
and that the sampling steps must be known with high accuracy. Therefore,
the mockup of a metrological solution that has been developped at IAS
will is also presented. The results on the damonstrator that validate
and converge to the optimization and prototyping of a system that could
be integrated in a space based application will be discussed. Finally we
propose a discussion on the possible future space mission opportunities
in which this innovative project could be framed.
Title: The LYOT+ UV/EUV instrumentation for measuring the magnetic
field in the corona
Authors: Auchère, Frederic; Vial, Jean Claude
Bibcode: 2013EGUGA..1513788A
Altcode:
The solar corona is the seat of a variability which involves basic
processes of plasma-magnetic field interaction in the universe,
while also being a source of disturbances for spacecraft, technology,
and possibly for human beings. Of special interest are coronal mass
ejections (CMEs) with their associated Eruptive Prominences (EPs). Since
they are basically driven by instabilities of the magnetic field in the
corona, the measurement of the magnetic field before, after (and during)
the event is critical in the corona. Also of interest for these studies
and the source of the solar wind, the radial velocity of the plasma is a
critical parameter to be determined. We present a new proposal to CNES
called LYOT+ which meets the above-mentioned objectives: measurement
of the coronal magnetic field up to 2 solar radii, of the electron
density and the radial velocity. These measurements are complemented
by EUV images of the underlying corona providing plasma diagnostic and
magnetic field morphology. We describe the proposed combination of EUV
imager and VUV and visible coronagraph. A main feature of the proposed
instrumentation is the extended overlap of the fields-of-view of both
instruments. In our presentation, we focus on the polarimetric concept
which leads to the determination of the magnetic field through the
Hanle effect. We also mention the extensive studies already performed
in designing the instrumentation and testing parts of it. In summary,
science, instrumentation and constraints on missions on which LYOT+
could be implemented, are presented.
Title: Nature and Variability of Plasmas Ejected by the Sun
Authors: Vial, J. -C.
Bibcode: 2013LNP...857...15V
Altcode:
The Sun not only emits radiation in the whole electromagnetic spectrum
but also sends in the interplanetary medium plasmas of different natures
(energy, continuous, or episodic flows, etc.) which contribute to its
(small) mass loss. The escaping material when properly oriented may
impact on the Earth magnetic environment with cascading effects on
the Earth atmosphere. The continuous flow known as the solar wind is
actually made of two categories, slow and fast winds. We discuss their
properties, sources, and the mechanisms at work through the two types
of models (fluid and particles). We describe the sporadic mass losses
for the three main typical events: flares, prominence ejection, and
coronal mass ejection. We discuss a possible unifying scenario which
takes into account these three manifestations of magnetic disruption. We
also extend the investigation to the whole heliosphere. Our conclusion
proposes a few goals concerning the diagnostic and the understanding
of the plasmas ejected by the Sun, along with the space missions which
could provide some answers.
Title: LEMUR: Large European module for solar Ultraviolet
Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
Thomas; Winter, Berend; Young, Peter
Bibcode: 2012ExA....34..273T
Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
The solar outer atmosphere is an extremely dynamic environment
characterized by the continuous interplay between the plasma and the
magnetic field that generates and permeates it. Such interactions play a
fundamental role in hugely diverse astrophysical systems, but occur at
scales that cannot be studied outside the solar system. Understanding
this complex system requires concerted, simultaneous solar observations
from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
high spatial resolution (between 0.1'' and 0.3''), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
from the chromosphere to the flaring corona), and the capability of
measuring magnetic fields through spectropolarimetry at visible and
near-infrared wavelengths. Simultaneous spectroscopic measurements
sampling the entire temperature range are particularly important. These
requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload
providing a significant improvement of imaging and spectropolarimetric
capabilities in the UV, visible, and near-infrared with respect to
what is available today and foreseen in the near future. The Large
European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload
of high-resolution imaging spectrographs and cameras. LEMUR consists
of two major components: a VUV solar telescope with a 30 cm diameter
mirror and a focal length of 3.6 m, and a focal-plane package composed
of VUV spectrometers covering six carefully chosen wavelength ranges
between 170 Å and 1270 Å. The LEMUR slit covers 280'' on the Sun with
0.14'' per pixel sampling. In addition, LEMUR is capable of measuring
mass flows velocities (line shifts) down to 2 km s - 1 or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.
Title: Metrology for a solar imaging Fourier transform spectrometer
working in the far UV: from the instrumental concept to the first
experimental results
Authors: Ruiz de Galarreta Fanjul, C.; Bouzit, M.; Appourchaux, T.;
Dassas, K.; Viale, T.; Philippon, A.; Vial, J. -C.; Maillard, J. -P.
Bibcode: 2012SPIE.8450E..0DR
Altcode:
The spectroscopy of the far UV emission lines of the solar spectrum
combined with an imaging capability is essential to understand the
physics of the outer solar atmosphere. An imaging Fourier transform
spectrometer (IFTSUV) is an attractive instrumental solution to perform
such far-UV solar observations. Working in the far UV involves high
precision metrology to maintain the optical path difference (OPD) during
the entire scanning process of the interferogram. It also involves
a compact all-reflection design for UV applications. We present
the specification of a servo-system that enables dynamic tip/tilt
alignment compensation and OPD sampling measurement of the IFTSUV
scanning mirror. We also discuss the first experimental results of a
breadboard as well as the preliminary design of a space-based device.
Title: Flows in a Small Active Region as Seen by Hinode and SoHO
Authors: Boutry, C.; Buchlin, É.; Vial, J.
Bibcode: 2012ASPC..454..233B
Altcode:
We report on a multi-instrument study performed on Active Region 10943
located at Sun center on 20 Feb. 2007. We use XRT images, magnetic
field maps from SoHO/MDI and we focus on EIS spectra from which we
build maps of the Doppler shift and intensity of Fe XII 195.12 Å. We
paid a special attention to the absolute wavelength calibration taking
into account the orbital temperature effect. We observe coronal loops
between opposite polarities of the region and straight downflows seen
in faint regions.
Title: Flows at the Edge of an Active Region: Observation and
Interpretation
Authors: Boutry, C.; Buchlin, E.; Vial, J. -C.; Régnier, S.
Bibcode: 2012ApJ...752...13B
Altcode: 2012arXiv1204.1377B
Upflows observed at the edges of active regions have been proposed as
the source of the slow solar wind. In the particular case of Active
Region (AR) 10942, where such an upflow has been already observed,
we want to evaluate the part of this upflow that actually remains
confined in the magnetic loops that connect AR 10942 to AR 10943. Both
active regions were visible simultaneously on the solar disk and were
observed by STEREO/SECCHI EUVI. Using Hinode/EIS spectra, we determine
the Doppler shifts and densities in AR 10943 and AR 10942 in order to
evaluate the mass flows. We also perform magnetic field extrapolations
to assess the connectivity between AR 10942 and AR 10943. AR 10943
displays a persistent downflow in Fe XII. Magnetic extrapolations
including both ARs show that this downflow can be connected to the
upflow in AR 10942. We estimate that the mass flow received by AR 10943
areas connected to AR 10942 represents about 18% of the mass flow from
AR 10942. We conclude that the upflows observed on the edge of active
regions represent either large-scale loops with mass flowing along them
(accounting for about one-fifth of the total mass flow in this example)
or open magnetic field structures where the slow solar wind originates.
Title: Automated detection of filaments from He II images
Authors: Buchlin, E.; Mercier, C.; Vial, J. -C.
Bibcode: 2012EAS....55..175B
Altcode:
For space weather applications, it is important to understand filaments
evolution and especially their eruptions associated with coronal mass
ejections. In view of the cadence and continuity of SDO observations,
AIA and HMI offer a unique tool for such a program. Because of the
data volume and the requirement of short latency, only an automated
detection can be worked out. We present a new method for the automated
detection and tracking of filaments, based on the analysis of AIA 30.4
nm He ii images, with the capability to use also the magnetic field
measured by HMI.
Title: The solar hydrogen Lyman α to Lyman β line ratio
Authors: Lemaire, P.; Vial, J. -C.; Curdt, W.; Schühle, U.; Woods,
T. N.
Bibcode: 2012A&A...542L..25L
Altcode:
Aims: We investigate the variation in the solar hydrogen Lyman
α (Lyα) to Lyman β (Lyβ) line ratio as a function of the solar
activity by taking into account new results obtained by SoHO/SUMER
and TIMED/SEE.
Methods: We reanalyze data of quiet and active
regions previously collected with the LPSP multichannel instrument on
OSO8. We then re-examine data obtained on the solar disk with SUMER
and compare them with previous data. In a second step, we use the
full Sun H i Lyβ profiles to determine the Lyβ contribution to the
SEE profiles obtained with a 0.4 nm full width at half-maximum. The
variation in the Lyα to Lyβ line ratio is then measured for part
of the solar cycle 23 (2002-2008).
Results: We determine the
radiance line ratio of the solar H i Lyα to Lyβ line for a quiet Sun
area and the relation between the ratio of the Lyα to Lyβ irradiance
and the Lyα solar irradiance.
Title: High spatial resolution VAULT H-Lyα observations and
multiwavelength analysis of an active region filament
Authors: Vial, J. -C.; Olivier, K.; Philippon, A. A.; Vourlidas, A.;
Yurchyshyn, V.
Bibcode: 2012A&A...541A.108V
Altcode:
Context. The search for the fine structure of prominences has
received considerable new attention thanks to the Swedish Solar
Telescope (SST) Hα pictures that provide an unsurpassed spatial
resolution. Recently, it has been shown that the filaments' coronal
environment, at least for quiescent filaments, is perturbed by either
cool absorbing material (in the EUV) or an "emissivity blocking"
(actually a lack of transition region and coronal material).
Aims: The aim is to assess the fine structure in an active region
filament and to determine the nature of the EUV absorption or lack
of emission phenomena, using the very optically thick line H-Lyα,
formed at a temperature higher than Hα.
Methods: We performed
a multiwavelength study where high-resolution imaging in the H-Lyα
line (VAULT) was analysed and compared with observations of an active
region filament in Hα (BBSO) and EUV lines (EIT and TRACE).
Results: As for the SST data, small-scale structures were detected at
a typical scale of about one to two arcseconds with, for some cuts,
an indication of fine scales down to 0.4 arcsec in the optically thick
H-Lyα line. The filament intensity relative to the intensity of the
(active) region it is embedded in is about 0.2 in H-Lyα. This ratio
(Lymanα ratio intensity or "LRI") is the lowest value compared to
other lines, e.g. Hα. The filament environment was also investigated
and evidence of an UV extension was found. The comparison of spatial
cuts in different lines across the filament shows evidence of strong
absorption, and consequently of cool plasma on one side of the filament,
but not on the other (that side is obscured by the filament itself).
Conclusions: The absence of very fine structure in H-Lyα compared
to Hα is explained by the formation temperature of the H-Lyα line
(~20 000 K), where the transition regions of the thin threads begin to
merge. From the detection of H-Lyα absorption on the observable side of
the filament side, we derive the presence of absorbing (cool) material
and possibly also of emissivity blocking (or coronal void). This poses
the question whether these absorption effects are typical of active
region filaments. Appendix A is available in electronic form at
http://www.aanda.org
Title: Flows in the Vicinity of Two Active Regions as Seen by Hinode,
STEREO, and SoHO
Authors: Boutry, C.; Buchlin, E'.; Vial, J.; Régnier, S.
Bibcode: 2012ASPC..455...83B
Altcode:
We observed active region 10943 located at Sun center on February 20,
2007 and we characterized its interactions with active region 10942 by
using a multi-instrument comparison between Hinode/XRT and STEREO/SECCHI
images, magnetic field maps from SoHO/MDI, and Hinode/EIS spectra
from which we built maps of the Doppler shift and the intensity of the
Fe XII 195.12 Å line. The results are consistent with some material
exchange between the two regions separated by 400″.
Title: Kinematics and helicity evolution of a loop-like eruptive
prominence
Authors: Koleva, K.; Madjarska, M. S.; Duchlev, P.; Schrijver, C. J.;
Vial, J. -C.; Buchlin, E.; Dechev, M.
Bibcode: 2012A&A...540A.127K
Altcode: 2012arXiv1202.4541K
Aims: We aim at investigating the morphology as well as
kinematic and helicity evolution of a loop-like prominence during its
eruption.
Methods: We used multi-instrument observations from
AIA/SDO, EUVI/STEREO and LASCO/SoHO. The kinematic, morphological,
geometrical, and helicity evolution of a loop-like eruptive
prominence were studied in the context of the magnetic flux rope
model of solar prominences.
Results: The prominence eruption
evolved as a height-expanding twisted loop with both legs anchored
in the chromosphere of a plage area. The eruption process consisted
of a prominence activation, acceleration, and a phase of constant
velocity. The prominence body was composed of counter-clockwise twisted
threads around the main prominence axis. The twist during the eruption
was estimated at 6π (3 turns). The prominence reached a maximum height
of 526 Mm before contracting to its primary location and was partially
reformed in the same place two days after the eruption. This ejection,
however, triggered a coronal mass ejection (CME) observed in LASCO
C2. The prominence was located in the northern periphery of the CME
magnetic field configuration and, therefore, the background magnetic
field was asymmetric with respect to the filament position. The physical
conditions of the falling plasma blobs were analysed with respect to
the prominence kinematics.
Conclusions: The same sign of the
prominence body twist and writhe, as well as the amount of twisting
above the critical value of 2π after the activation phase indicate that
possibly conditions for kink instability were present. No signature
of magnetic reconnection was observed anywhere in the prominence body
and its surroundings. The filament/prominence descent following the
eruption and its partial reformation at the same place two days later
suggest a confined type of eruption. The asymmetric background magnetic
field possibly played an important role in the failed eruption. Movies showing the temporal evolution are available in electronic
form at http://www.aanda.org
Title: Solar magnetism eXplorer (SolmeX). Exploring the magnetic
field in the upper atmosphere of our closest star
Authors: Peter, Hardi; Abbo, L.; Andretta, V.; Auchère, F.; Bemporad,
A.; Berrilli, F.; Bommier, V.; Braukhane, A.; Casini, R.; Curdt,
W.; Davila, J.; Dittus, H.; Fineschi, S.; Fludra, A.; Gandorfer, A.;
Griffin, D.; Inhester, B.; Lagg, A.; Landi Degl'Innocenti, E.; Maiwald,
V.; Sainz, R. Manso; Martínez Pillet, V; Matthews, S.; Moses, D.;
Parenti, S.; Pietarila, A.; Quantius, D.; Raouafi, N. -E.; Raymond, J.;
Rochus, P.; Romberg, O.; Schlotterer, M.; Schühle, U.; Solanki, S.;
Spadaro, D.; Teriaca, L.; Tomczyk, S.; Trujillo Bueno, J.; Vial, J. -C.
Bibcode: 2012ExA....33..271P
Altcode: 2011arXiv1108.5304P; 2011ExA...tmp..134P
The magnetic field plays a pivotal role in many fields of
Astrophysics. This is especially true for the physics of the solar
atmosphere. Measuring the magnetic field in the upper solar atmosphere
is crucial to understand the nature of the underlying physical
processes that drive the violent dynamics of the solar corona—that
can also affect life on Earth. SolmeX, a fully equipped solar space
observatory for remote-sensing observations, will provide the first
comprehensive measurements of the strength and direction of the
magnetic field in the upper solar atmosphere. The mission consists
of two spacecraft, one carrying the instruments, and another one in
formation flight at a distance of about 200 m carrying the occulter to
provide an artificial total solar eclipse. This will ensure high-quality
coronagraphic observations above the solar limb. SolmeX integrates two
spectro-polarimetric coronagraphs for off-limb observations, one in
the EUV and one in the IR, and three instruments for observations on
the disk. The latter comprises one imaging polarimeter in the EUV for
coronal studies, a spectro-polarimeter in the EUV to investigate the low
corona, and an imaging spectro-polarimeter in the UV for chromospheric
studies. SOHO and other existing missions have investigated the emission
of the upper atmosphere in detail (not considering polarization),
and as this will be the case also for missions planned for the near
future. Therefore it is timely that SolmeX provides the final piece of
the observational quest by measuring the magnetic field in the upper
atmosphere through polarimetric observations.
Title: Synthetic differential emission measure curves of prominence
fine structures. II. The SoHO/SUMER prominence of 8 June 2004
Authors: Gunár, S.; Parenti, S.; Anzer, U.; Heinzel, P.; Vial, J. -C.
Bibcode: 2011A&A...535A.122G
Altcode:
Aims: This study is the first attempt to combine the prominence
observations in Lyman, UV, and EUV lines with the determination of the
prominence differential emission measure derived using two different
techniques, one based on the inversion of the observed UV and EUV lines
and the other employing 2D non-LTE prominence fine-structure modeling
of the Lyman spectra.
Methods: We use a trial-and-error method
to derive the 2D multi-thread prominence fine-structure model producing
synthetic Lyman spectra in good agreement with the observations. We then
employ a numerical method to perform the forward determination of the
DEM from 2D multi-thread models and compare the synthetic DEM curves
with those derived from observations using inversion techniques.
Results: A set of available observations of the June 8, 2004
prominence allows us to determine the range of input parameters, which
contains models producing synthetic Lyman spectra in good agreement
with the observations. We select three models, which represent this
parametric-space area well and compute the synthetic DEM curves for
multi-thread realizations of these models. The synthetic DEM curves
of selected models are in good agreement with the DEM curves derived
from the observations.
Conclusions: We show that the evaluation
of the prominence fine-structure DEM complements the analysis of the
prominence hydrogen Lyman spectra and that its combination with the
detailed radiative-transfer modeling of prominence fine structures
provides a useful tool for investigating the prominence temperature
structure from the cool core to the prominence-corona transition region.
Title: Hydrogen Lyα and Lyβ Radiances and Profiles in Polar
Colornal Holes
Authors: Tian, Hui; Teriaca, Luca; Curdt, Werner; Vial, Jean-Claude
Bibcode: 2011shin.confE.166T
Altcode:
The hydrogen Lyα plays a dominant role in the radiative energy
transport in the lower transition region, and is important for
the studies of transition-region structure as well as solar wind
origin. We investigate the Lyα profiles obtained by the Solar
Ultraviolet Measurement of Emitted Radiation spectrograph on the
Solar and Heliospheric Observatory spacecraft in coronal holes and
the quiet Sun. In a subset of these observations, the Hi Lyβ, Si III,
and Ovi lines were also (quasi-)simultaneously recorded. We find that
the distances between the two peaks of Lyα profiles are larger in
coronal holes than in the quiet Sun, indicating a larger opacity in
coronal holes. This difference might result from the different magnetic
structures or the different radiation fields in the two regions. Most
of the Lyβ profiles in the coronal hole have a stronger blue peak,
in contrast to those in quiet-Sun regions while in both regions the
Lyα profiles are stronger in the blue peak. Although the asymmetries
are likely to be produced by differential flows in the solar atmosphere,
their detailed formation processes are still unclear. The radiance ratio
between Lyα and Lyβ decreases toward the limb in the coronal hole,
which might be due to the different opacity of the two lines. We also
find that the radiance distributions of the four lines are set by a
combined effect of limb brightening and the different emission level
between coronal holes and the quiet Sun.
Title: Automated detection of filaments in SDO data
Authors: Buchlin, É.; Mercier, C.; Engin, S.; Parenti, S.; Vial,
J. -C.
Bibcode: 2010sf2a.conf..297B
Altcode:
Solar eruption can eject billions of tons of plasma to the
interplanetary space, with geophysical effects and impacts on human
activities. The time constraints for space weather application as well
as the huge volume of data that needs to be analyzed, especially since
the launch of SDO, imply that the detection of solar filaments and their
eruptions must be automated. Most current detection codes use Hα data,
which are not available frequently enough for these applications. We
present a new detection code that we have developed at IAS and that uses
the high spatial and temporal-resolution SDO/AIA He II 30.4 nm data.
Title: Turbulence in the Solar Atmosphere and Solar Wind
Authors: Petrosyan, A.; Balogh, A.; Goldstein, M. L.; Léorat, J.;
Marsch, E.; Petrovay, K.; Roberts, B.; von Steiger, R.; Vial, J. C.
Bibcode: 2010SSRv..156..135P
Altcode: 2010SSRv..tmp..117P
The objective of this review article is to critically analyze turbulence
and its role in the solar atmosphere and solar wind, as well as to
provide a tutorial overview of topics worth clarification. Although
turbulence is a ubiquitous phenomenon in the sun and its heliosphere,
many open questions exist concerning the physical mechanisms of
turbulence generation in solar environment. Also, the spatial and
temporal evolution of the turbulence in the solar atmosphere and solar
wind are still poorly understood. We limit the scope of this paper
(leaving out the solar interior and convection zone) to the magnetized
plasma that reaches from the photosphere and chromosphere upwards to
the corona and inner heliosphere, and place particular emphasis on
the magnetic field structures and fluctuations and their role in the
dynamics and radiation of the coronal plasma. To attract the attention
of scientists from both the fluid-dynamics and space-science communities
we give in the first two sections a phenomenological overview of
turbulence-related processes, in the context of solar and heliospheric
physics and with emphasis on the photosphere-corona connection and
the coupling between the solar corona and solar wind. We also discuss
the basic tools and standard concepts for the empirical analysis and
theoretical description of turbulence. The last two sections of this
paper give a concise review of selected aspects of oscillations and
waves in the solar atmosphere and related fluctuations in the solar
wind. We conclude with some recommendations and suggest topics for
future research.
Title: Definition of an imaging spectrometer meeting the needs of
UV solar physics
Authors: Ruiz de Galarreta Fanjul, C.; Philippon, A.; Vial, J. -C.;
Lemaire, P.; Maillard, J. -P.; Buisset, C.; Appourchaux, T.;
Auchère, F.
Bibcode: 2010SPIE.7732E..36R
Altcode: 2010SPIE.7732E..99R
The study of the outer solar atmosphere requires combining imaging
and spectroscopy in the UV lines formed in the high chromosphere,
the transition region and the corona. We start from the science
requirements and we define the instrumental specifications in terms
of field-of-view (FOV), spatial, temporal and spectral resolution and
bandpass. We propose two different all-reflection optical architectures
based on interferometric techniques: Spatial Heterodyne Spectroscopy
(SHS); and Imaging Transform Spectrometer (IFTS). We describe the
different set-ups and compare the potential performances of the two
types of solutions, and discuss their feasibility. We conclude that
IFTS appears to be the best solution, meeting the needs of UV solar
physics. However, we point out the many difficulties to be encountered,
especially as far as metrology is concerned.
Title: Physics of Solar Prominences: I—Spectral Diagnostics and
Non-LTE Modelling
Authors: Labrosse, N.; Heinzel, P.; Vial, J. -C.; Kucera, T.; Parenti,
S.; Gunár, S.; Schmieder, B.; Kilper, G.
Bibcode: 2010SSRv..151..243L
Altcode: 2010SSRv..tmp...34L; 2010arXiv1001.1620L
This review paper outlines background information and covers recent
advances made via the analysis of spectra and images of prominence
plasma and the increased sophistication of non-LTE ( i.e. when there is
a departure from Local Thermodynamic Equilibrium) radiative transfer
models. We first describe the spectral inversion techniques that have
been used to infer the plasma parameters important for the general
properties of the prominence plasma in both its cool core and the
hotter prominence-corona transition region. We also review studies
devoted to the observation of bulk motions of the prominence plasma and
to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically
thick at certain wavelengths. Therefore, complex non-LTE models become
necessary. We thus present the basics of non-LTE radiative transfer
theory and the associated multi-level radiative transfer problems. The
main results of one- and two-dimensional models of the prominences and
their fine-structures are presented. We then discuss the energy balance
in various prominence models. Finally, we outline the outstanding
observational and theoretical questions, and the directions for future
progress in our understanding of solar prominences.
Title: Hanle signatures of the coronal magnetic field in the linear
polarization of the hydrogen Lα line
Authors: Derouich, M.; Auchère, F.; Vial, J. C.; Zhang, M.
Bibcode: 2010A&A...511A...7D
Altcode: 2009arXiv0912.5068D
Aims: This paper is dedicated to the assessment of the validity
of future coronal spectro-polarimetric observations and to prepare their
interpretation in terms of the magnetic field vector.
Methods:
We assume that the polarization of the hydrogen coronal Lα line is
due to anisotropic scattering of an incident chromospheric radiation
field. The anisotropy is due to geometrical effects but also to the
inhomogeneities of the chromospheric regions which we model by using
Carrington maps of the Lα. Because the corona is optically thin, we
fully consider the effects of the integration over the line-of-sight
(LOS). As a modeling case, we include a dipolar magnetic topology
perturbed by a non-dipolar magnetic structure arising from a prominence
current sheet in the corona. The spatial variation of the hydrogen
density and the temperature is taken into account. We determine the
incident radiation field developed on the tensorial basis at each
point along the LOS. Then, we calculate the local emissivity vector
to obtain integrated Stokes parameters with and without coronal
magnetic field.
Results: We show that the Hanle effect is an
interesting technique for interpreting the scattering polarization of
the Lαλ1216 line in order to diagnose the coronal magnetic field. The
difference between the calculated polarization and the zero magnetic
field polarization gives us an estimation of the needed polarimetric
sensitivity in future polarization observations. We also obtain
useful indications about the optimal observational strategy.
Conclusions: Quantitative interpretation of the Hanle effect on the
scattering linear polarization of Lα line can be a crucial source
of information about the coronal magnetic field at a height over the
limb h < 0.7 R⊙. Therefore, one needs the development
of spatial instrumentation to observe this line. Present address:
Colorado Research Associates Division, NorthWest Research Associates,
Inc., 3380 Mitchell Ln., Boulder, CO 80301, USA.
Title: Space solar missions
Authors: Vial, Jean-Claude
Bibcode: 2010IAUS..264..459V
Altcode:
In the frame of Symposium 264 which concerns Solar and Stellar
Variability we address the space solar missions devoted to the various
aspects of solar activity. We describe them in three time categories:
missions ready for launch, missions which will operate in the 2012-2015
time frame and ambitious missions to be launched after 2015. We focus
on the contributions of these missions according to the following
criteria: Understanding mechanisms of activity, Improving detection
and characterisation, Working out some prediction. Major activity
contributors and manifestations are addressed: Coronal Mass Ejections,
Flares, Solar winds, Magnetism (including dynamo), Irradiance.
Title: Discussion with the HMI Team representative
Authors: Vial, Jean-Claude
Bibcode: 2010cosp...38.2865V
Altcode: 2010cosp.meet.2865V
Discussion with the HMI Team representative after her presentation
Title: Automated detection of filaments and their eruptions from
AIA and HMI/SDO data
Authors: Buchlin, Eric; Mercier, Claude; Vial, Jean-Claude
Bibcode: 2010cosp...38.2862B
Altcode: 2010cosp.meet.2862B
The superior temporal, spatial and spectral range of AIA on SDO provides
a completely new view of the dynamic nature of coronal loops. In this
paper, we will examine preliminary results of a number of loop examples
as their evolution is followed closely in time and space across the
AIA filters. The implications of these observational results on the
heating and cooling mechanisms operating will be discussed.
Title: The SDO data centre at IDOC/MEDOC in France
Authors: Parenti, Susanna; Bocchialini, Karine; Soubrie, Elie;
Auchere, Frederic; Ballans, Herv; Buchlin, Eric; Gabriel, Alan;
Mercier, Claude; Poulleau, Gilles; Vial, Jean-Claude
Bibcode: 2010cosp...38.2888P
Altcode: 2010cosp.meet.2888P
The IDOC/MEDOC centre at the Institut d'Astrophysique Spatiale (IAS,
Université Paris 11/CNRS) has a long experience in solar data archiving
and distribution, including almost 15 years of data from SOHO, STEREO
and TRACE. The center is now expanding its activity and becoming a
Pˆle Thématique Solaire of the CNES and INSU/CNRS. Part of the new
activities of the centre will be linked to the arrival of the enormous
volume of the new SDO data. The center will be one of the three European
centers to receive and redistribute the data to the community. It will
also be the only European site to permanently store about 10% of the
data (mainly from AIA). In continuity with its previous activities,
SDO data will be included in the data visualization tool FESTIVAL
and it will provide new services, like tools for the solar feature
identification (filaments, EUV intensity fluctuations). We will present
an overview of the facilities and activities of the centre in relation
to the SDO data.
Title: Discussion with EVE PI
Authors: Vial, Jean-Claude
Bibcode: 2010cosp...38.2872V
Altcode: 2010cosp.meet.2872V
Discussion with EVE PI after his presentation
Title: Large-scale Extreme-Ultraviolet Disturbances Associated with
a Limb Coronal Mass Ejection
Authors: Dai, Y.; Auchère, F.; Vial, J. -C.; Tang, Y. H.; Zong, W. G.
Bibcode: 2010ApJ...708..913D
Altcode:
We present composite observations of a coronal mass ejection (CME)
and the associated large-scale extreme-ultraviolet (EUV) disturbances
on 2007 December 31 by the Extreme-ultraviolet Imager (EUVI) and COR1
coronagraph on board the recent Solar Terrestrial Relations Observatory
mission. For this limb event, the EUV disturbances exhibit some typical
characteristics of EUV Imaging Telescope waves: (1) in the 195 Å
bandpass, diffuse brightenings are observed propagating oppositely
away from the flare site with a velocity of ~260 km s-1,
leaving dimmings behind; (2) when the brightenings encounter the
boundary of a polar coronal hole, they stop there to form a stationary
front. Multi-temperature analysis of the propagating EUV disturbances
favors a heating process over a density enhancement in the disturbance
region. Furthermore, the EUVI-COR1 composite display shows unambiguously
that the propagation of the diffuse brightenings coincides with a
large lateral expansion of the CME, which consequently results in a
double-loop-structured CME leading edge. Based on these observational
facts, we suggest that the wave-like EUV disturbances are a result of
magnetic reconfiguration related to the CME liftoff rather than true
waves in the corona. Reconnections between the expanding CME magnetic
field lines and surrounding quiet-Sun magnetic loops account for the
propagating diffuse brightenings; dimmings appear behind them as a
consequence of volume expansion. X-ray and radio data provide us with
complementary evidence.
Title: Discussion with AIA PI
Authors: Vial, Jean-Claude
Bibcode: 2010cosp...38.2860V
Altcode: 2010cosp.meet.2860V
Discussion with the PI after his presentation
Title: Poster session
Authors: Vial, Jean-Claude
Bibcode: 2010cosp...38.2870V
Altcode: 2010cosp.meet.2870V
Poster presentation
Title: Hydrogen Lyα and Lyβ Radiances and Profiles in Polar
Coronal Holes
Authors: Tian, Hui; Teriaca, Luca; Curdt, Werner; Vial, Jean-Claude
Bibcode: 2009ApJ...703L.152T
Altcode: 2009arXiv0909.0735T
The hydrogen Lyα plays a dominant role in the radiative energy
transport in the lower transition region, and is important for
the studies of transition-region structure as well as solar wind
origin. We investigate the Lyα profiles obtained by the Solar
Ultraviolet Measurement of Emitted Radiation spectrograph on the
Solar and Heliospheric Observatory spacecraft in coronal holes and the
quiet Sun. In a subset of these observations, the H I Lyβ, Si III,
and O VI lines were also (quasi-)simultaneously recorded. We find
that the distances between the two peaks of Lyα profiles are larger
in coronal holes than in the quiet Sun, indicating a larger opacity in
coronal holes. This difference might result from the different magnetic
structures or the different radiation fields in the two regions. Most
of the Lyβ profiles in the coronal hole have a stronger blue peak,
in contrast to those in quiet-Sun regions while in both regions the
Lyα profiles are stronger in the blue peak. Although the asymmetries
are likely to be produced by differential flows in the solar atmosphere,
their detailed formation processes are still unclear. The radiance ratio
between Lyα and Lyβ decreases toward the limb in the coronal hole,
which might be due to the different opacity of the two lines. We also
find that the radiance distributions of the four lines are set by a
combined effect of limb brightening and the different emission level
between coronal holes and the quiet Sun.
Title: Solar source of energetic particles in interplanetary space
during the 2006 December 13 event
Authors: Li, C.; Dai, Y.; Vial, J. -C.; Owen, C. J.; Matthews, S. A.;
Tang, Y. H.; Fang, C.; Fazakerley, A. N.
Bibcode: 2009A&A...503.1013L
Altcode: 2013arXiv1305.5593L
An X3.4 solar flare and a fast halo coronal mass ejection (CME)
occurred on 2006 December 13, accompanied by a high flux of energetic
particles recorded both in near-Earth space and at ground level. Our
purpose is to provide evidence of flare acceleration in a major solar
energetic particle (SEP) event. We first present observations from
ACE/EPAM, GOES, and the Apatity neutron monitor. It is found that the
initial particle release time coincides with the flare emission and
that the spectrum becomes softer and the anisotropy becomes weaker
during particle injection, indicating that the acceleration source
changes from a confined coronal site to a widespread interplanetary
CME-driven shock. We then describe a comprehensive study of the
associated flare active region. By use of imaging data from HINODE/SOT
and SOHO/MDI magnetogram, we infer the flare magnetic reconnection
rate in the form of the magnetic flux change rate. This correlates in
time with the microwave emission, indicating a physical link between
the flare magnetic reconnection and the acceleration of nonthermal
particles. Combining radio spectrograph data from Huairou/NOAC,
Culgoora/IPS, Learmonth/RSTN, and WAVES/WIND leads to a continuous
and longlasting radio burst extending from a few GHz down to several
kHz. Based on the photospheric vector magnetogram from Huairou/NOAC
and the nonlinear force free field (NFFF) reconstruction method,
we derive the 3D magnetic field configuration shortly after the
eruption. Furthermore, we also compute coronal field lines extending
to a few solar radii using a potential-field source-surface (PFSS)
model. Both the so-called type III-l burst and the magnetic field
configuration suggest that open-field lines extend from the flare
active region into interplanetary space, allowing the accelerated and
charged particles escape.
Title: Electron density in the quiet solar coronal transition region
from SoHO/SUMER measurements of S VI line radiance and opacity
Authors: Buchlin, E.; Vial, J. -C.
Bibcode: 2009A&A...503..559B
Altcode: 2009arXiv0906.1367B
Context: The steep temperature and density gradients that are measured
in the coronal transition region challenge the model interpretation
of observations.
Aims: We derive the average electron density
< ne > in the region emitting the S vi lines. We use
two different techniques, which allow us to derive linearly-weighted
(opacity method) and quadratically-weighted (emission measure method)
electron density along the line-of-sight, to estimate a filling factor
or derive the layer thickness at the formation temperature of the
lines.
Methods: We analyze SoHO/SUMER spectroscopic observations
of the S vi lines, using the center-to-limb variations in radiance,
the center-to-limb ratios of radiance and line width, and the radiance
ratio of the 93.3-94.4 nm doublet to derive the opacity. We also
use the emission measure derived from radiance at disk center.
Results: We derive an opacity τ0 at S vi 93.3 nm line
center of the order of 0.05. The resulting average electron density
< {ne}>, under simple assumptions concerning the
emitting layer, is 2.4 × 1016 m-3 at T = 2 ×
105 K. This value is higher than (and inconsistent with)
the values obtained from radiance measurements (2 × 1015
m-3). The last value corresponds to an electron pressure
of 10-2 Pa. Conversely, taking a classical value for the
density leads to a too high value of the thickness of the emitting
layer.
Conclusions: The pressure derived from the emission
measure method compares well with previous determinations. It implies
a low opacity of between 5 × 10-3 and 10-2. It
remains unexplained why a direct derivation leads to a much higher
opacity, despite tentative modeling of observational biases. Further
measurements in S vi and other lines emitted at a similar temperature
should be completed, and more realistic models of the transition region
need to be used.
Title: The He II Lines in the Lyman Series Profiles of Solar
Prominences
Authors: Ebadi, H.; Vial, J. -C.; Ajabshirizadeh, A.
Bibcode: 2009SoPh..257...91E
Altcode:
The hydrogen and helium lines are the most prominent lines in the solar
prominences spectra. Observations with the SUMER spectrometer onboard
SOHO showed that there are weak lines in the blue wings of the Lyman
series which affect their profiles. They were all identified as He II
lines in the Lyman series wings, except for the Lα line whose profile
was affected by the use of an attenuator. The He II lines are the even
Balmer lines of the He II system, a set of lines that we complete with
the odd ones. We characterize them by comparison with the blue wings of
the Lyman series in order to improve the H Lyman series observations
and modeling, on one hand and to provide He II lines observations for
further combined H - He I - He II modeling, on the other hand.
Title: Polarimetry of the Lα Line for Coronal Magnetic Field
Diagnostic
Authors: Derouich, M.; Auchère, F.; Vial, J. C.; Millard, A. A.
Bibcode: 2009ASPC..405..389D
Altcode:
Measurement and physical interpretation of the scattering polarization
of the Extreme-ultraviolet (EUV) and Far-UV (FUV) spectral lines
provide a largely unexplored diagnostic of coronal magnetic field. In
this context, we present the LYOT (LYman Orbiting Telescope) project
that makes it possible to observe the Lα λ1216 line polarization
in the solar corona. Because the corona is optically thin, it
is necessary to consider the effects of the integration over the
line-of-sight (LOS). The LOS effects have been usually addressed for
non polarimetric studies where the unknown is a scalar quantity (the
intensity) but not a Stokes vector. Previous studies investigating the
coronal polarization are generally concerned with a local position of
the scattering center and a deterministic magnetic field (see Raouafi
et al.~2002 for a measurement and interpretation of the O VI λ 1032
line polarization). Here, we perform computations that test whether
a LOS integrated Hanle effect can be detected in order to access to
the magnetic field topology.
Title: Diagnostics of active and eruptive prominences through hydrogen
and helium lines modelling
Authors: Labrosse, N.; Vial, J. -C.; Gouttebroze, P.
Bibcode: 2008AnGeo..26.2961L
Altcode: 2008arXiv0804.4625L
In this study we show how hydrogen and helium lines modelling can be
used to make a diagnostic of active and eruptive prominences. One
motivation for this work is to identify the physical conditions
during prominence activation and eruption. Hydrogen and helium
lines are key in probing different parts of the prominence structure
and inferring the plasma parameters. However, the interpretation of
observations, being either spectroscopic or obtained with imaging, is
not straightforward. Their resonance lines are optically thick, and
the prominence plasma is out of local thermodynamic equilibrium due
to the strong incident radiation coming from the solar disk. In view
of the shift of the incident radiation occuring when the prominence
plasma flows radially, it is essential to take into account velocity
fields in the prominence diagnostic. Therefore we need to investigate
the effects of the radial motion of the prominence plasma on hydrogen
and helium lines. The method that we use is the resolution of the
radiative transfer problem in the hydrogen and helium lines out of
local thermodynamic equilibrium. We study the variation of the computed
integrated intensities in H and He lines with the radial velocity of
the prominence plasma. We can confirm that there exist suitable lines
which can be used to make a diagnostic of the plasma in active and
eruptive prominences in the presence of velocity fields.
Title: The Lyman-alpha Line in Active and Eruptive Solar Prominences
Authors: Labrosse, N.; Vial, J. -C.
Bibcode: 2008ESPM...12.3.17L
Altcode:
We investigate the effects of radial motions on the Ly-alpha emission
in moving prominences under various temperature and pressure conditions
and for various prominence masses. The ability to compute the Ly-alpha
line intensity in active and erupting prominences with our non-LTE
radiative transfer code is especially relevant to VAULT and to
the LYOT instrument on SMESE. In the case of erupting prominences,
high-cadence imaging as anticipated from LYOT/SMESE, will allow us
to observe the dimming of the line as the prominence expands in the
radial direction. In conjunction with our non-LTE radiative transfer
code, the diagnostic of the thermodynamical plasma parameters and the
velocity field can be done. This should provide new constraints for
models of filament and prominence eruptions.
Title: Properties of the quiet solar coronal transition region from
full-Sun SoHO/SUMER S VI
Authors: Buchlin, E.; Vial, J.
Bibcode: 2008ESPM...122.117B
Altcode:
A series of full-Sun SoHO/SUMER observations of the quiet Sun in the
transition region lines S VI 933 and 944 (as well as Ly epsilon) has
been performed during year 1996. We use this unique data set to derive
the opacity of the S VI lines by different methods (following Dumont et
al. 1983), taking advantage from the availability of full-Sun data and
of the S VI doublet: 1. using the center-to-limb variations of S
VI 933 radiance and peak spectral radiance, 2. using the center-to-limb
variations of S VI 933 line width and radiance, and 3. using the S VI
944 - 933 radiance or spectral radiance ratio at disk center. We then
deduce an average value for the density in the S VI emitting region
(in the coronal transition region). By comparing this value to the
average square density obtained by an Emission Measure analysis,
we get a tentative estimate of the filling factor in this region.
Title: The HeII (and DI) Lines in the Lyman Series of Solar
Prominences
Authors: Vial, J. -C.; Ebadi, H.; Ajabshirizadeh, A.
Bibcode: 2008ESPM...12.2.20V
Altcode:
The hydrogen lines are the most prominent lines in solar prominence
spectra. Observations with the SUMER spectrometer on board SoHO showed
that there are weak emission lines in the blue wings of the Lyman
series which affect their profiles. We identified them as D I and
He II lines in the Lyman alpha profile and He II lines in the upper
Lyman series wings. The He II lines are identified as Balmer lines
of He II. We attempt to characterize these lines in the blue wings
of the Lyman series and consequently to provide supplementary He II
information for further He I-He II non-LTE modelling.
Title: Developing a CME-Associated Phenomena Catalog for SDO
Authors: Wills-Davey, M. J.; Davey, A. R.; Vial, J.
Bibcode: 2008AGUSMSP51B..12W
Altcode:
With the anticipated launch of the Solar Dynamics Observatory (SDO),
we have embarked on the development of an automated detection scheme
which will correlate and catalog CME-associated phenomena with CME
observations from existing coronagraphs. Observing primarily using the
Atmospheric Imaging Assembly (AIA), the SDO CME catalog will focus on
various aspects of CME initiation and development, including automated
measurement of coronal dimming regions at CME onset, the detection of
filament eruptions in near-real time, and the automated tracking of
CME fronts in coronagraph data.
Title: A Time-Evolving 3D Method Dedicated to the Reconstruction of
Solar Plumes and Results Using Extreme Ultraviolet Data
Authors: Barbey, Nicolas; Auchère, Frédéric; Rodet, Thomas; Vial,
Jean-Claude
Bibcode: 2008SoPh..248..409B
Altcode: 2008SoPh..tmp...65B; 2008arXiv0802.0113B
An important issue in the tomographic reconstruction of the solar poles
is the relatively rapid evolution of the polar plumes. We demonstrate
that it is possible to take into account this temporal evolution in
the reconstruction. The difficulty of this problem comes from the fact
that we want a four-dimensional reconstruction (three spatial dimensions
plus time) whereas we only have three-dimensional data (two-dimensional
images plus time). To overcome this difficulty, we introduce a model
that describes polar plumes as stationary objects whose intensity varies
homogeneously with time. This assumption can be physically justified
if one accepts the stability of the magnetic structure. This model
leads to a bilinear inverse problem. We describe how to extend linear
inversion methods to these kinds of problems. Studies of simulations
show the reliability of our method. Results for SOHO/EIT data show
that we can estimate the temporal evolution of polar plumes to improve
the reconstruction of the solar poles from only one point of view. We
expect further improvements from STEREO/EUVI data when the two probes
will be separated by about 60°.
Title: Polarisation and magnetic depolarization of the Lyman-alpha
line in the corona : the line-of-sight effects
Authors: Vial, Jean-Claude; Derouich, Moncef; Auchere, Frederic;
Zhang, Mei
Bibcode: 2008cosp...37.3340V
Altcode: 2008cosp.meet.3340V
In view of the importance of measuring coronal magnetic field and of
the capability of measuring linear polarization in the Lyman α line
with the LYOT coronagraph on board the SMESE mission, we carried out
some calculations of the degrees of depolarization resulting from the
presence of a magnetic field. Our calculation is based on a simple
magnetic field model where a current sheet in the field represents
a solar prominence. We focus in this study on the effect of the
line-of-sight integration at various locations in the corona on the
polarizing/depolarizing properties. Other magnetic configurations are
also considered and are under the study.
Title: Solar prominence properties derived from the UV-EUV SUMER
spectral atlas
Authors: Parenti, S.; Vial, J. -C.; Lemaire, P.
Bibcode: 2008AdSpR..41..144P
Altcode:
In this paper, we summarize the work done to build a UV-EUV spectral
atlas of a prominence and we introduce some recent scientific
results obtained from these data. For this work we used SOHO/SUMER
data covering the full wavelength range accessible by the instrument
(from about 800 to 1600 Å), when a prominence and the quiet Sun (used
as spectral reference) were observed in October 1998. We present here
only a fraction of the data, which results in the analysis of more
than 600 spectral lines, including some new identifications. Here we
also present the differential emission measure obtained from the data,
both for the quiet Sun and the prominence. The main differences in
characteristics are discussed.
Title: The Reversal Behavior of Some Hydrogen Lyman Lines in Solar
Spicules
Authors: Ajabshirizadeh, Ali; Ajabshirizadeh, Ali; Vial, Jean-Claude;
Fathi-Vavsari, Hassan; Ebadi, Hossein
Bibcode: 2008cosp...37...42A
Altcode: 2008cosp.meet...42A
Spicules are the dominant component of the quiet solar chromosphere. At
the solar limb they appear as jet-like dynamic structures extending into
the solar corona. The physical processes that generate spicules have
not yet been uniquely identified. In this work, we analyze spicules
data taken by the SUMER spectrometer on-board SoHO in the Lyman Beta
and Lyman Gamma lines. A similar analysis has been done already by
Vial et al. (2007) in Lyman alpha and Lyman beta lines. The data used
have a spatial resolution of one arcsec along the slit and a spectral
resolution of about 44 mA. We applied the standard procedures for
geometric distortion, flat- fielding and dead time corrections, which
can be found in the Solar Software (SSW) database. Our results show that
in spicules both Lyman beta and Lyman gamma line profiles are reversed
at all altitudes; on the contrary, in the prominence, the Lyman beta
and Lyman gamma line profiles are reversed only at higher altitude,
while at lower altitude they are clearly non-reversed in accordance
with Vial et al. (2007). We provide some explanation for this behavior.
Title: SMESE (SMall Explorer for Solar Eruptions): A microsatellite
mission with combined solar payload
Authors: Vial, J. -C.; Auchère, F.; Chang, J.; Fang, C.; Gan, W. Q.;
Klein, K. -L.; Prado, J. -Y.; Rouesnel, F.; Sémery, A.; Trottet,
G.; Wang, C.
Bibcode: 2008AdSpR..41..183V
Altcode:
The SMESE (SMall Explorer for Solar Eruptions) mission is a
microsatellite proposed by France and China. The payload of SMESE
consists of three packages: LYOT (a Lyman α imager and a Lyman α
coronagraph), DESIR (an Infra-red Telescope working at 35 80 and
100 250 μm), and HEBS (a High Energy Burst Spectrometer working
in X- and gamma-rays). The scientific objectives of the mission are
shortly presented. We describe the three instrumental packages and the
profile of the mission which accommodates them. With a launch around
2012 2013, the SMESE microsatellite mission will provide a unique
tool for detecting and understanding eruptions (flares and coronal
mass ejections). Observations should start around solar maximum, and
continue in the declining phase of activity, at a time when the Solar
Dynamics Observatory (SDO) should still be operating.
Title: The Ly α and Ly β Profiles in Solar Prominences and
Prominence Fine Structure
Authors: Vial, J. -C.; Ebadi, H.; Ajabshirizadeh, A.
Bibcode: 2007SoPh..246..327V
Altcode: 2007arXiv0710.1433V
Ly α and Ly β line profiles in a solar prominence were observed with
high spatial and spectral resolution with SOHO/SUMER. Within a 60-arcsec
scan, we measure a very large variety of profiles: not only reversed
and nonreversed profiles but also red-peaked and blue-peaked ones in
both lines. Such a spatial variability is probably related to both
the fine structure in prominences and the different orientations of
mass motions. The usage of integrated-intensity cuts along the SUMER
slit allowed us to categorize the prominence in three regions. We
computed average profiles and integrated intensities in these
lines in the range 2.36 - 42.3 W m−2 sr−1
for Ly α and 0.027 - 0.237 W m−2 sr−1
for Ly β. As shown by theoretical modeling, the Ly α/Ly β ratio
is very sensitive to geometrical and thermodynamic properties of
fine structure in prominences. For some pixels, and in both lines,
we found agreement between observed intensities and those predicted
by one-dimensional models. But a close examination of the profiles
indicated a rather systematic disagreement concerning their detailed
shapes. The disagreement between observations and thread models (with
ambipolar diffusion) leads us to speculate about the importance of
the temperature gradient between the cool and coronal regions. This
gradient could depend on the orientation of field lines as proposed
by Heinzel, Anzer, and Gunár (Astron. Astrophys.442, 331, 2005).
Title: Flare magnetic reconnection and relativistic particles in
the 2003 October 28 event
Authors: Li, C.; Tang, Y. H.; Dai, Y.; Fang, C.; Vial, J. -C.
Bibcode: 2007A&A...472..283L
Altcode: 2007arXiv0706.3648L
An X17.2 solar flare occurred on 2003 October 28, accompanied by
multi-wavelength emissions and a high flux of relativistic particles
observed at 1 AU. We present the analytic results of the TRACE, SOHO,
RHESSI, ACE, GOES, hard X-ray (INTEGRAL satellite), radio (Ondeřejov
radio telescope), and neutron monitor data. It is found that the
inferred magnetic reconnection electric field correlates well with the
hard X-ray, gamma-ray, and neutron emission at the Sun. Thus the flare's
magnetic reconnection probably makes a crucial contribution to the
prompt relativistic particles, which could be detected at 1 AU. Since
the neutrons were emitted a few minutes before the injection of protons
and electrons, we propose a magnetic-field evolution configuration to
explain this delay. We do not exclude the effect of CME-driven shock,
which probably plays an important role in the delayed gradual phase
of solar energetic particles.
Title: Prominence and quiet-Sun plasma parameters derived from FUV
spectral emission
Authors: Parenti, S.; Vial, J. -C.
Bibcode: 2007A&A...469.1109P
Altcode:
Context: A solar prominence and the quiet-Sun (QS) were observed
with SOHO/SUMER in October 1999. With this dataset we built the
first comprehensive UV spectral atlas in the range 800-1250 Å for a
prominence, thus complementing the existing reference atlases for the
QS.
Aims: This is a detailed study based on the information
in this atlas, with the aim of deriving the plasma parameters in
two distinct regions. The large amount of information available
allows us to establish these parameters with lower uncertainty than
in previous studies, leading to reference values for theoretical
investigations.
Methods: The measured lines' FWHM were used
to derive the distribution of the non-thermal velocities at various
temperatures. The lines intensities were used to derive the electron
densities at temperatures of 7 × 104 K and the differential
emission measure.
Results: The comparison with the QS shows
lower velocities in the prominence for temperature T with log~T <
5.4. The velocities derived in the highest part of the prominence
show a lower gradient with the temperature. The value obtained for
the electron density indicates a low pressure prominence. We conclude
with a discussion of the energy budget in the prominence. Table
1 is only available in electronic form at http://www.aanda.org
Title: Spectral Diagnostics of Active Prominences
Authors: Labrosse, N.; Gouttebroze, P.; Vial, J. -C.
Bibcode: 2007ASPC..368..337L
Altcode: 2006astro.ph.11488L
Active prominences exhibit plasma motions, resulting in difficulties
with the interpretation of spectroscopic observations. These solar
features being strongly influenced by the radiation coming from
the solar disk, Doppler dimming or brightening effects may arise,
depending on which lines are observed and on the velocity of the
plasma. Interlocking between the different atomic energy levels and
non local thermodynamic equilibrium lead to non-trivial spectral line
profiles, and this calls for complex numerical modeling of the radiative
transfer in order to understand the observations. We present such a
tool, which solves the radiative transfer and statistical equilibrium
for H, He I, He II, and Ca II in moving prominences where radial plasma
motions are taking place. It is found that for isothermal, isobaric
prominence models, the He II resonance lines are very sensitive to the
Doppler effect and thus show a strong Doppler dimming. The Ca II lines
Doppler effect for the prominence models considered here. We illustrate
how the code makes it possible to retrieve the plasma thermodynamic
parameters by comparing computed and observed line profiles of
hydrogen and helium resonance lines in a quiescent prominence. This
new non-LTE radiative transfer code including velocities allows us
to better understand the formation of several lines of importance in
prominences, and in conjunction with observations, infer the prominence
plasma thermodynamic properties and full velocity vector.
Title: Effect of motions in prominences on the helium resonance
lines in the extreme ultraviolet
Authors: Labrosse, N.; Gouttebroze, P.; Vial, J. -C.
Bibcode: 2007A&A...463.1171L
Altcode: 2006astro.ph..8221L
Context: Extreme ultraviolet resonance lines of neutral and ionised
helium observed in prominences are difficult to interpret as the
prominence plasma is optically thick at these wavelengths. If mass
motions are taking place, as is the case in active and eruptive
prominences, the diagnostic is even more complex.
Aims: We aim
at studying the effect of radial motions on the spectrum emitted by
moving prominences in the helium resonance lines and at facilitating the
interpretation of observations, in order to improve our understanding
of these dynamic structures.
Methods: We develop our non-local
thermodynamic equilibrium radiative transfer code formerly used
for the study of quiescent prominences. The new numerical code is
now able to solve the statistical equilibrium and radiative transfer
equations in the non-static case by using velocity-dependent boundary
conditions for the solution of the radiative transfer problem. This
first study investigates the effects of different physical conditions
(temperature, pressure, geometrical thickness) on the emergent helium
radiation.
Results: The motion of the prominence plasma induces
a Doppler dimming effect on the resonance lines of He I and He II. The
velocity effects are particularly important for the He II λ 304 Å line
as it is mostly formed by resonant diffusion of incident radiation under
prominence conditions. The He I resonance lines at 584 and 537 Å also
show some sensitivity to the motion of the plasma, all the more when
thermal emission is not too important in these lines. We also show
that it is necessary to consider partial redistribution in frequency
for the scattering of the incident radiation.
Conclusions: .This
set of helium lines offers strong diagnostic possibilities that can be
exploited with the SOHO spectrometers and with the EIS spectrometer on
board the Hinode satellite. The addition of other helium lines and of
lines from other elements (in particular hydrogen) in the diagnostics
will further enhance the strength of the method. Figures [see
full text], [see full text] and [see full text] are only available in
electronic form at http://www.aanda.org
Title: A Contribution to the Understanding of Chromospheric
Oscillations
Authors: Baudin, F.; Ibarra, E.; Avrett, E. H.; Vial, J. -C.;
Bocchialini, K.; Costa, A.; Lemaire, P.; Rovira, M.
Bibcode: 2007SoPh..241...39B
Altcode:
We present SUMER/SOHO UV measurements of chromospheric oscillations
of intensity, velocity, and linewidth observed in C I, S I, O I, and
C II lines, which are formed in the altitude range from 1000 km to
2000 km above τ500=1. Oscillations in lines originating
at similar altitudes exhibit different behaviors which we discuss in
terms of the formation of the lines.
Title: Coronal Turbulence And Intermittency From Solar Orbiter
Observations
Authors: Buchlin, É.; Vial, J. -C.
Bibcode: 2007ESASP.641E..23B
Altcode:
Turbulent motions and magnetic fields are a key component of coronal
heating mechanisms. They are indeed likely to produce the small scales
at which the mechanisms such as reconnection are efficient enough. The
properties of turbulence (and the associated intermit- tency) may thus
have an influence on the energy dissipation in the corona, and need to
be characterized from observations. Although turbulence is omnipresent
from the Sun to the heliosphere, good observations of MHD turbulence
have not yet been performed in the corona, in lines emitted at high
temperature, where the heating actually occurs. We propose a study
of coordinated EUS- EUI-VIM observations, with better resolution and
counting statistics than ever before, whose main goal is to get and
interpret the spatial statistics (spectra and structure functions)
of the velocity field in lines emitted at high temperatures (log10
T ≥ 6.4), together with the plasma and magnetic environment of the
observed region. These statistics will help us understand the precise
role of coronal turbulence in the coronal heating processes.
Title: SMESE: A SMall Explorer for Solar Eruptions
Authors: Vial, J. -C.; Auchère, F.; Chang, J.; Fang, C.; Gan, W. Q.;
Klein, K. -L.; Prado, J. -Y.; Trottet, G.; Wang, C.; Yan, Y. H.
Bibcode: 2007AdSpR..40.1787V
Altcode:
The SMall Explorer for Solar Eruptions (SMESE) mission is a
microsatellite proposed by France and China. The payload of SMESE
consists of three packages: LYOT (a Lyman α imager and a Lyman α
coronagraph), DESIR (an Infra-Red Telescope working at 35-80 and
100-250 μm), and HEBS (a High-Energy Burst Spectrometer working in
X- and γ-rays). The status of research on flares and coronal mass
ejections is briefly reviewed in the context of on-going missions such
as SOHO, TRACE and RHESSI. The scientific objectives and the profile of
the mission are described. With a launch around 2012-2013, SMESE will
provide a unique tool for detecting and understanding eruptions (flares
and coronal mass ejections) close to the maximum phase of activity.
Title: EUI, The Ultraviolet Imaging Telescopes Of Solar Orbiter
Authors: Hochedez, J. -F.; Appourchaux, T.; Defise, J. -M.; Harra,
L. K.; Schühle, U.; Auchère, F.; Curdt, W.; Hancock, B.; Kretzschmar,
M.; Lawrence, G.; Leclec'h, J. -C.; Marsch, E.; Mercier, R.; Parenti,
S.; Podladchikova, E.; Ravet, M. -F.; Rochus, P.; Rodriguez, L.;
Rouesnel, F.; Solanki, S.; Teriaca, L.; Van Driel, L.; Vial, J. -C.;
Winter, B.; Zhukov, A.
Bibcode: 2007ESASP.641E..33H
Altcode:
The scientific objectives of Solar Orbiter rely ubiquitously on EUI,
its suite of solar atmosphere imaging telescopes. In the configuration
discussed here, EUI includes three co-aligned High Resolution Imagers
(HRI) and one Full Sun Imager (FSI). FSI and two HRIs observe in extreme
ultraviolet passbands, dominated by coronal emission. Another HRI is
designed for the hydrogen Lyman α radiation in the far UV, imaging the
Chromosphere and the lower Transition Region. The current EUI design
and some of its development challenges are highlighted. EUI profits from
co-rotation phases, solar proximity and departure from the ecliptic. In
synergy with the other S.O. payload, EUI probes the dynamics of the
solar atmosphere, provides context data for all investigations and helps
to link in-situ and remote-sensing observations. In short, it serves all
four top-level goals of the mission. For these reasons, the EUI suite
is keenly anticipated in the European scientific community and beyond.
Title: Modeling the Radiative Signatures of Turbulent Heating in
Coronal Loops
Authors: Parenti, S.; Buchlin, E.; Cargill, P. J.; Galtier, S.; Vial,
J. -C.
Bibcode: 2006ApJ...651.1219P
Altcode:
The statistical properties of the radiative signature of a coronal loop
subject to turbulent heating obtained from a three-dimensional (3D)
magnetohydrodynamics (MHD) model are studied. The heating and cooling of
a multistrand loop is modeled and synthetic spectra for Fe XII 195.12,
Fe XV 284.163, and Fe XIX 1118.06 Å are calculated, covering a wide
temperature range. The results show that the statistical properties
of the thermal and radiative energies partially reflect those of the
heating function in that power-law distributions are transmitted,
but with very significant changes in the power-law indices. There is
a strong dependence on the subloop geometry. Only high-temperature
radiation (~107 K) preserves reasonably precise information
on the heating function.
Title: The Helium Spectrum in Erupting Solar Prominences
Authors: Labrosse, N.; Vial, J. C.; Gouttebroze, P.
Bibcode: 2006IAUJD...3E..47L
Altcode: 2006astro.ph..9511L
Even quiescent solar prominences may become active and sometimes
erupt. These events are occasionally linked to coronal mass
ejections. However we know very little about the plasma properties
during the activation and eruption processes. We present the first
computations of the helium line profiles emitted by an eruptive
prominence. We follow the approach of Gontikakis et al. (1997) who
computed the hydrogen spectrum in moving prominences. The prominence
is modelled as a plane-parallel slab standing vertically above the
solar surface and moving upward as a solid body. The helium spectrum is
computed with a non local thermodynamic equilibrium radiative transfer
code. The effect of Doppler dimming / brightening is investigated in
the resonance lines of He I and He II formed in the EUV, as well as on
the He I 10830 Å and He I 5876 Å lines. We focus on the line profile
properties and the resulting integrated intensities. We also study the
effect of frequency redistribution in the formation mechanisms of the
resonance lines. It is shown that the helium lines are very sensitive
to Doppler dimming effects. Together with the hydrogen lines they offer
the possibility of a powerful diagnostic of the active and eruptive
prominence plasma. We discuss the results in view of observations
provided by SOHO, and by the upcoming EUS spectrometer on SOLAR-B.
Title: What We Have Learned about Prominences and Filaments from
SOHO/SUMER and CDS Spectral Observations
Authors: Heinzel, P.; Schmieder, B.; Vial, J. -C.
Bibcode: 2006ESASP.617E..65H
Altcode: 2006soho...17E..65H
No abstract at ADS
Title: Rotational Tomography of the Solar Corona-Calculation of the
Electron Density and Temperature
Authors: Barbey, Nicolas; Auchère, Frédéric; Rodet, Thomas;
Bocchialini, Karine; Vial, Jean-Claude
Bibcode: 2006ESASP.617E..82B
Altcode: 2006soho...17E..82B
No abstract at ADS
Title: Looking for Signature of Coronal Heating in the Radiative
Emission of a Coronal Loop
Authors: Parenti, S.; Buchlin, E.; Cargill, P. J.; Caltier, S.; Vial,
J. -C.
Bibcode: 2006ESASP.617E.104P
Altcode: 2006soho...17E.104P
No abstract at ADS
Title: The Pending Issue of the Solar Fine Structure of Prominences
Authors: Vial, J. -C.
Bibcode: 2006ESASP.617E.163V
Altcode: 2006soho...17E.163V
No abstract at ADS
Title: The Helium Spectrum in Moving Solar Prominences
Authors: Labrosse, N.; Gouttebroze, P.; Vial, J. -C.
Bibcode: 2006ESASP.617E.134L
Altcode: 2006soho...17E.134L
No abstract at ADS
Title: SMESE: a combined UV-IR-X-gamma solar mission
Authors: Millard, Anne A.; Auchere, Frederic; Fang, Cheng; Gan,
Weiqun; Molodij, Guillaume; Prado, Jean-Yves; Rouesnel, Frederic;
Semery, Alain; Trottet, Gerard; Vial, Jean-Claude; Yan, Yihua; Wu, Ji
Bibcode: 2006SPIE.6266E..0JM
Altcode: 2006SPIE.6266E..15M
SMESE (SMall Explorer For the study of Solar Eruptions) is a
Franco-Chinese microsatellite mission. The scientific objectives of
SMESE are the study of coronal mass ejections and flares. Its payload
consists of three instrument packages : LYOT, DESIR and HEBS. LYOT is
composed of a Lyman α (121.6 nm) coronagraph, a Lyman α disk imager
and a far UV disk imager. DESIR is an infrared telescope working at 35
μm and 150 μm. HEBS is a high energy burst spectrometer working in
X rays and γ rays covering the 10 keV to 600 MeV range. SMESE will
be launched around 2011, providing a unique opportunity of detecting
and understanding eruptions at the maximum activity phase of the solar
cycle in a wide range of energies. The instrumentation on board SMESE
is described in this paper.
Title: IFTSUV: an imaging Fourier transform spectrometer in UV for
the next solar space missions
Authors: Millard, Anne A.; Lemaire, Philippe; Vial, Jean-Claude
Bibcode: 2006SPIE.6266E..2GM
Altcode: 2006SPIE.6266E..72M
The study of the Sun in the UV spectral domain is essential for
a better understanding of the physical processes taking place in
the solar atmosphere. The main tools for this study are imagers
and spectrometers. Nevertheless, the analysis of imagery data is
rapidly limited unless spectral information is available, and the
association of spectrometers and imagers is limited by the lack of
coherence between the instruments. Therefore, the design of an imaging
spectrometer in UV is a priority for solar physicists. In the far UV,
only all reflective optical systems can be used thus an imaging Fourier
transform spectrometer (IFTS) is the ideal candidate for the realization
of such an instrument. The performances of an IFTS are given by the
modulation efficiency. Theoretical study of performances and scientific
objectives lead to technical and operating specifications. A mock-up of
an IFTSUV has been built at IAS to validate the working principle. Its
optical design and alignment are described in this paper. The first
results are shown and discussed. Planned modifications of the design
are also discussed.
Title: Plasma diagnostic of a solar prominence from hydrogen and
helium resonance lines
Authors: Labrosse, N.; Vial, J. -C.; Gouttebroze, P.
Bibcode: 2006sf2a.conf..549L
Altcode: 2006astro.ph..9643L
We present the first comparison of profiles of H et He resonance lines
observed by SUMER with theoretical profiles computed with our non-LTE
radiative transfer code. We use the HI Lyman β, HI Lyman ɛ, and He
I λ 584 Å lines. Our code allows us to obtain the plasma parameters
in prominences in conjunction with a multi-line, multi-element set
of observations. The plasma temperature in the prominence core is ∼
8600 K and the pressure is 0.03 dyn cm-2. The Lyβ line is
formed in a higher temperature region (more than 11,000 K).
Title: A statistical study of SUMER spectral images: events,
turbulence, and intermittency
Authors: Buchlin, E.; Vial, J. -C.; Lemaire, P.
Bibcode: 2006A&A...451.1091B
Altcode: 2005astro.ph.11042B
We analyze a series of full-Sun observations performed with the
SoHO/SUMER instrument between March and October 1996. Some parameters
(radiance, shift and width) of the S vi 93.3 nm , S vi 94.4 nm ,
and Ly \varepsilon line profiles were computed on board. Radiances
and line-of-sight velocities in a large central region of the Sun
are studied statistically: distributions of solar structures, field
Fourier spectra and structure functions are obtained. The structures
have distributions with power-law tails, the Fourier spectra of the
radiance fields also display power laws, and the normalized structure
functions of the radiance and velocity fields increase at small
scales. These results support the idea of the existence of small
scales, created by turbulence, and of intermittency of the observed
fields. These properties may provide insight into the processes needed
for heating the transition region, or, if confirmed in the corona,
the corona itself. The difficulties encountered in this analysis,
especially for the velocity data, underline the need for sensitive
ultraviolet imaging spectrometers.
Title: New perspectives on prominences as observed by SOHO/SUMER
Authors: Schmieder, B.; Vial, J. -C.; Heinzel, P.
Bibcode: 2006sf2a.conf..563S
Altcode:
We summarize the results of our prominence and filament studies
based on extensive spectral observations with SOHO/SUMER and CDS
instruments. During the past decade we have gathered several sets
of UV and EUV spectral data, containing various emission lines of
different species. Our main objective was to better understand the
formation of hydrogen Lyman lines and continuum (using the results
of complex non-LTE transfer simulations). However we have also
analysed also UV and EUV lines formed under transition-region and
coronal conditions. Some highlights of our studies are: reproduction
of Lyman-line profiles with partial redistribution, understanding the
role of prominence-corona interface in the formation of Lyman-line
cores, establishing the effect of the magnetic-field orientation
on the shape of Lyman lines, discovery of EUV filament extensions
(invisible in the Hα line) and their explanation, reconstruction of
a 3D topology of the filament using EUV coronal lines, temperature
diagnostics based on measurements of the hydrogen Lyman continuum,
proper explanation of a prominence darkening detected in coronal lines.
Title: A New Way to look at Observations with EGSO
Authors: Aboudarham, J.; Scholl, I.; Fuller, N.; Csillaghy, A.;
Bentley, R. D.; Antonucci, E.; Ciminiera, L.; Finkelstein, A.; Ipson,
S.; Messerotti, M.; Pike, D.; Vial, J. C.; Zharkova, V.
Bibcode: 2006IAUS..233..229A
Altcode:
The European Grid of Solar Observations (EGSO) is a Solar virtual
observatory (see Hill et al., 2002). It has been funded through the 5th
Framework Program of the European Community. A dozen of laboratories,
mixing Solar Physics and Information Technology, in Great Britain,
France, Italy and Swiss have been involved in this project during
3 years. A grid accessing several dozens of databases and archives
scattered all around the world has been developped as well as a Solar
Event Catalogue and a Solar Feature Catalogue. The original aspect
of this work consists in the possibility not only to search through
the characteristics of observations, but also search for available
data corresponding to specific kinds of events. So it is now very
important to be able to follow the Sun 24 hours a day in order to
enrich the events database for future queries. More informations on
EGSO, catalogues and user interface can be accessd through the web
site: http://www.egso.org/
Title: European Grid of Solar Observations (EGSO)
Authors: Aboudarham, J.; Scholl, I.; Csillaghy, A.; Bentley, R. D.;
Antonucci, E.; Ciminiera, L.; Finkelstein, A.; Ipson, S.; Messerotti,
M.; Pike, D.; Vial, J. C.; Zharkova, V.
Bibcode: 2006ihy..conf...18A
Altcode:
The EGSO project addresses the problem of combining heterogeneous
data into a single "virtual" solar data resource. Wider access to
other catalogues is enabled, including both pre-existing lists and
new compilations generated using feature-recognition techniques on
existing data. Scientists are also able to perform much richer data
searches, based on solar events. Informations concerning EGSO can be
found at http://www.egso.org/
Title: A brief introduction to SMESE mission
Authors: Wang, C.; Fang, C.; Gan, W.; Prado, J. -Y.; Trottet, G.;
Vial, J. -C.; Yan, Y.; Auchere, F.; Chang, J.; Molodi, G.
Bibcode: 2006ilws.conf..211W
Altcode:
Small Exploration for Solar Eruptions (SMESE) is a joint mission
between France and China to investigate the two main types of eruption
events on the Sun: Coronal Mass Ejections (CME) and solar flares,
and their relationship. SMESE will provide a set of unprecedented
and complementary measurements including Ly-alpha imager, Ly-alpha
coronagraph, EUV imager, Detection of Solar Infra red radiation,
Hard X-ray/gamma ray spectrometry. SMESE aims to study, among others,
the CME triggering mechanism and its acceleration in the corona, the
particle acceleration by CME and solar flare, the physical association
of the CME and solar flare etc. SMESE will be launched in the next
solar maximum between 2010-2012.
Title: Can we finally solve the problems of "Coronal Heating " and
"Solar Wind Acceleration" in the Cosmic Vision era ?
Authors: Maksimovic, M.; Appourchaux, T.; Aulanier, G.; Chust, T.;
Dudok de Wit, T.; Klein, K. L.; Krasnoselskikh, V.; Louarn, P.; Roux,
A.; Vial, J. C.
Bibcode: 2006cosp...36.2999M
Altcode: 2006cosp.meet.2999M
Since the discovery of the corona s million-degree temperature in the
1940s and the supersonic solar wind in the early 1960s major efforts
have been made to discover the physical mechanisms that could explain
these two observations These efforts have led to a tremendous increase
in our knowledge of our neighbour star the inner heliosphere and the
Sun-Earth connections Unfortunately these efforts haven t allowed to
provide a definitive answer to these questions Why such a situation On
one hand the remote-sensing strategy has tried to probe the coronal
properties by basically analysing the photons emitted or absorbed
by the Sun s atmosphere With this regards limitations occur on both
theoretical ground physics of the coupling between photons and plasma
and experimental ground limited number of observables such as spectral
lines or the hardly solvable problem of the line of sight integration
On the other hand solar wind in-situ measurements have had access to
the very detailed state of the local plasma properties full particles
velocity distribution functions observations of the electromagnetic
plasma fluctuations over a huge frequency range but at locations
far from the corona and the solar wind acceleration regions Moreover
it has been realized more recently that the magnetic field plays a
fundamental role in shaping the low corona and channelling the energy
inputs Unfortunately the measurement of the full magnetic vector in
the corona is a very difficult enterprise and this lack of information
hampers all on-going modelling efforts Given
Title: SMESE, a SMall Explorer for the Study of solar Eruptions
Authors: Vial, J. -C.; Auchère, F.; Chang, J.; Fang, C.; Gan, W. Q.;
Molodij, G.; Prado, J. -Y.; Trottet, G.; Wang, C.; Yan, Y. H.
Bibcode: 2006cosp...36.3287V
Altcode: 2006cosp.meet.3287V
The SMESE Small Explorer for the Study of solar Eruptions mission is
a microsatellite proposed by France and China The payload of SMESE
consists of three packages LYOT a suite of two UV and EUV imagers and
a Lyman alpha coronagraph DESIR an Infra-Red Telescope working at 35
and 150 mu and HEBS a High Energy Burst Spectrometer working in X-
and gamma -rays The status of research on Coronal Mass Ejections and
flares will be briefly recalled in the context of on-going missions
such as SOHO TRACE and RHESSI The scientific objectives and the profile
of the mission will be described With a launch around 2011 SMESE will
provide a unique tool for detecting and understanding eruptions flares
and coronal mass ejections in the maximum phase of activity when the
Solar Dynamics Observatory SDO should still be operating
Title: SMESE: a Small Explorer for the Study of Solar Eruptions
Authors: Vial, J. -C.; Auchère, F.; Chang, J.; Fang, C.; Gan, W. Q.;
Molodij, G.; Prado, J. -Y.; Trottet, G.; Wang, C.; Yan, Y. H.
Bibcode: 2006cosp...36.3294V
Altcode: 2006cosp.meet.3294V
The SMESE Small Explorer for the Study of solar Eruptions mission is
a microsatellite proposed by France and China The payload of SMESE
consists of three packages LYOT a suite of two UV and EUV imagers and
a Lyman alpha coronagraph DESIR an Infra-Red Telescope working at 35
and 150 mu and HEBS a High Energy Burst Spectrometer working in X- and
gamma -rays The status of research on Coronal Mass Ejections will be
briefly recalled in the context of on-going missions such as SOHO TRACE
and RHESSI The scientific objectives and the profile of the mission
will be described With a launch around 2011 SMESE will provide a unique
tool for detecting and understanding eruptions flares and coronal mass
ejections in the maximum phase of activity and for the determination
of the morphology of the low corona from where the solar wind originates
Title: Multiwavelength Analysis of an Active Region
Authors: Gontikakis, C.; Dara, H. C.; Zachariadis, Th. G.;
Alissandrakis, C. E.; Nindos, A.; Vial, J. -C.; Tsiropoula, G.
Bibcode: 2006SoPh..233...57G
Altcode:
We study active region NOAA 8541, observed with instruments on board
SOHO, as well as with TRACE. The data set mainly covers the transition
region and the low corona. In selected loops studied with SUMER on SOHO,
the VIII 770 Å line is systematically redshifted. In order to estimate
the plasma velocity, we combine the Doppler shifts with proper motions
(TRACE) along these loops. In the case of an ejection, apparently
caused by the emergence of a parasitic polarity, proper motions and
Doppler shifts give consistent results for the velocity. A cooler loop,
observed in the same active region with CDS, shows a unidirectional
motion reminiscent of a siphon flow. The derived electron temperature
and density along a large steady loop confirm that it cannot be
described by hydrostatic models.
Title: Solar Hydrogen Lyman Contimuum Observations with Soho/sumer
Authors: Parenti, S.; Vial, J. -C.; Lemaire, P.
Bibcode: 2005ESASP.600E..93P
Altcode: 2005ESPM...11...93P; 2005dysu.confE..93P
No abstract at ADS
Title: The Beleinos cornerstone: the Sun, the star close to Earth
Authors: Appourchaux, T.; Auchère, F.; Bocchialini, K.; Bonnet,
R. M.; Gabriel, A.; Vial, J. -C.
Bibcode: 2005ESASP.588..389A
Altcode: 2005tssc.conf..389A
No abstract at ADS
Title: Hydrogen Lyman α Profiles of AN Active Region Filament
Obtained with SUMER on SOHO
Authors: Vial, J. -C.; Boutry, C.; Wilhelm, K.
Bibcode: 2005ESASP.600E.102V
Altcode: 2005ESPM...11..102V; 2005dysu.confE.102V
No abstract at ADS
Title: Prominence atlas in the SUMER range 800-1250 Å. II. Line
profile properties and ions identifications
Authors: Parenti, S.; Vial, J. -C.; Lemaire, P.
Bibcode: 2005A&A...443..679P
Altcode:
We present a SOHO/SUMER spectral atlas in the 800-1250 Å range of
a prominence and a Quiet Sun (QS) region observed in 1999. The atlas
is produced for two separate areas of the prominence. The QS spectrum
is used as a reference. This is the first prominence atlas obtained
with high spectral resolution (≈0.044 Å). It provides information
concerning more than 550 line profiles, in terms of position, total
radiance, and FWHM, along with the ion identification. Forty new lines
have been identified with respect to previously published spectra.
Title: A new relation between the central spectral solar H I Lyman
α irradiance and the line irradiance measured by SUMER/SOHO during
the cycle 23
Authors: Emerich, Claude; Lemaire, Philippe; Vial, Jean-Claude; Curdt,
Werner; Schühle, Udo; Wilhelm, Klaus
Bibcode: 2005Icar..178..429E
Altcode:
The spectral irradiance at the center of the solar H I Lyman α
( λ=121.5664nm, referred to as Lyα in this paper) line profile
is the main excitation source responsible for the atomic hydrogen
resonant scattering of cool material in our Solar System. It has
therefore to be known with the best possible accuracy in order to
model the various Lyα emissions taking place in planetary, cometary,
and interplanetary environments. Since the only permanently monitored
solar irradiance is the total one (i.e. integrated over the whole
Lyα line profile), Vidal-Madjar [1975. Evolution of the solar Lyman
alpha flux during four consecutive years. Solar Phys. 40, 69-86] using
Orbiting Solar Observatory 5 (OSO-5) satellite Lyα data, established
a semi-empirical formula allowing him to deduce the central spectral
Lyα irradiance from the total one. This relation has been extensively
used for three decades. But, at the low altitude of the OSO-5 orbit,
the central part of the solar line profile was deeply absorbed by a
large column of exospheric atomic hydrogen. Consequently, the spectral
irradiance at the center of the line was obtained by a complex procedure
confronting the observations with simulations of both the geocoronal
absorption and the self-reversed shape of the solar Lyα profile. The
SUMER spectrometer onboard SOHO positioned well outside the hydrogen
geocorona, provided full-Sun Lyα profiles, not affected by such an
absorption [Lemaire et al., 1998. Solar H I Lyman α full disk profile
obtained with the SUMER/SOHO spectrometer. Astron. Astrophys. 334,
1095-1098; 2002. Variation of the full Sun Hydrogen Lyman α and β
profiles with the activity cycle. Proc. SOHO 11 Symposium, ESA SP-508,
219-222; 2004. Variation of the full Sun Hydrogen Lyman profiles
through solar cycle 23. COSPAR 2004 Meeting], making it—for the first
time—possible to measure the spectral and total Lyα solar irradiances
directly and simultaneously. A new relation between these two quantities
is derived in an expression that is formally similar to the previous
one, but with significantly different parameters. After having discussed
the potential causes for such differences, it is suggested that the
new relation should replace the old one for any future modeling of the
numerous Lyα absorptions and emissions observed in the Solar System.
Title: Solar hydrogen-Lyman continuum observations with SOHO/SUMER
Authors: Parenti, S.; Lemaire, P.; Vial, J. -C.
Bibcode: 2005A&A...443..685P
Altcode:
In this work we analyze the emission of the H Lyman continuum (HI
LyC) in the Quiet Sun (QS) and a solar prominence, in order to derive
information on the temperature of the emitting plasma. We used the
spectral atlas obtained with SOHO/SUMER detector A in 1999 (Parenti
et al. 2005, A&A, 443, 679). The high spectral resolution of this
instrument allows a good selection of the continuum, free from emission
lines. However, in the HI LyC wavelength domain, the data suffer from
large radiometric uncertainties, which lead us to use detector B as
a reference. We obtained electron temperatures of 8281 K ± 280 K and
7564 K ± 230 K in two separate parts of the prominence.
Title: Radiative Signatures of Coronal Loops Submitted to Turbulent
Heating
Authors: Parenti, S.; Buchlin, E.; Galtier, S.; Vial, J. -C.
Bibcode: 2005ESASP.592..523P
Altcode: 2005soho...16E..97P; 2005ESASP.592E..97P
No abstract at ADS
Title: Formation flyers applied to solar coronal observations:
the ASPICS mission
Authors: Vives, S.; Lamy, P.; Auchere, F.; Vial, J. -C.; Koutchmy,
S.; Arnaud, J.; Prado, J. -Y.; Frassetto, F.; Naletto, G.
Bibcode: 2005SPIE.5901..305V
Altcode:
Classical externally-occulted coronagraphs are presently limited in
their performances by the distance between the external occulter and
the front objective. The diffraction fringe from the occulter and the
vignetted pupil which degrades the spatial resolution prevent observing
the inner corona inside typically 2-2.5 solar radii. Formation flyers
open new perspectives and allow to conceive giant, externally-occulted
coronagraphs using a two-component space system with the external
occulter on one spacecraft and the optical instrument on the
other spacecraft at approximately 100 m from the first one. ASPICS
(Association de Satellites Pour l'Imagerie Coronographique Solaire)
is a mission proposed to CNES in the framework of their demonstration
program of formation flyers which is presently under study to exploit
this technique for coronal observations. In the baseline concept,
ASPICS includes three coronagraphs operating in three spectral
domains: the visible continuum (K-corona brightness), the HI Lyman
alpha emission line at 121.6 nm, and the HeII emission line at 30.4
nm. Their unvignetted fields of view extend from 1.1 to 3.2 solar radii
with a typical spatial resolution of 3 arcsec. In order to connect
coronal activity to photospheric events, ASPICS further includes
two disk imagers. The first one is devoted to the HI Lyman alpha
emission line. The second one is a multi-channel instrument similar to
SOHO/EIT and devoted to the HeII (30.4 nm), FeIX/X (17.1 nm) and FeXII
(19.5 nm) emission lines. Two concepts of the space system are under
consideration: a symmetric configuration where the disk imagers and
the external occulter are on one spacecraft and the coronagraphs on
the other, an asymmetric configuration where the external occulter is
on one spacecraft and the scientific instruments are regrouped on the
other one.
Title: EGSO - A maturing VO for Solar Physics
Authors: Bentley, R. D.; Scholl, I.; Csillaghy, A.; Aboudarham, J.;
Antonucci, E.; Gurman, J.; Hill, F.; Pike, D.; Vial, J.; Zharkova, V.
Bibcode: 2005AGUSMSH43B..01B
Altcode:
The European Grid of Solar Observations, EGSO, is a Grid test-bed
funded under the Information Societies Thematic Priority of the European
Commission's Fifth Framework Programme (FP5). In the case of EGSO, the
application chosen was the use of Grid technology to establish a virtual
observatory for solar physics, and the project addresses the generic
problem of how to provide access to a distributed, heterogeneous data
set for a scattered user community. In order to identify observations
that match a user's search criteria, EGSO has been building an
environment that will support complex searches. Because of the absence
of the metadata needed to tie the heterogeneous data together, EGSO has
placed emphasis on the provision of databases that can be accessed from
the Internet through special providers. The provision of appropriate
metadata is of extreme importance in establishing a virtual observatory,
and the approach used can be adapted to facilitate the inclusion of
any data, including non-solar data. We report on the capabilities of
EGSO and discuss experience gained in creating the facility. We also
discuss how EGSO has been working with other virtual observatories that
support the solar, heliospheric and space plasma communities in order
to try to achieve interoperability between the numerous data sets. We
highlight what we consider are the most profitable ways of doing this.
Title: EUV imaging spectrometer for the Solar Orbiter mission
Authors: Millard, A. A.; Lemaire, P.; Vial, J. -C.
Bibcode: 2005AdSpR..36.1411M
Altcode:
The results from missions such as Yohkoh, Trace or SOHO have advanced
our understanding of the solar corona and heliosphere, but also have
raised many new questions. Measurements at higher spatial resolution
and cadence are needed, some regions such as the solar poles or
the inner heliosphere remain unexplored. The Solar Orbiter mission
addresses those questions. UV imaging spectrometers may be included
in the remote sensing instruments package for this mission. Fourier
transform spectrometry (FTS) is an ideal solution for imaging systems
as there is no need to scan the region of interest with a slit to
get a 2D map, and the spectral range covered is only limited by the
bandpass of the filter and the maximum optical path difference that
can be obtained. FTS systems also allow to make observations at high
cadence (100 Hz). Working in the far UV (below 200 nm) requires the use
of reflective only optical systems. A solution for such an instrument
has been designed at IAS and a mock-up has been built in order to test
and validate the working principle. The first results of the alignment
phase are shown.
Title: Variation of the full Sun hydrogen Lyman profiles through
solar cycle 23
Authors: Lemaire, P.; Emerich, C.; Vial, J. -C.; Curdt, W.; Schühle,
U.; Wilhelm, K.
Bibcode: 2005AdSpR..35..384L
Altcode:
The hydrogen Lyman (Lyα, 121.267 nm and Lyβ, 102.572 nm) lines are
important contributors to the solar extreme ultra violet (EUV) flux
which illuminates the upper Earth’s atmosphere. From high resolution
spectral observations performed with the solar ultraviolet measurement
of emitted radiations (SUMER) spectrometer on the Solar and Heliospheric
Observatory (SOHO), the detailed profiles of these two lines have been
obtained. Some insights into the variation of the shape of the profiles,
sampled throughout the present solar cycle 23, are given and discussed.
Title: Solar Orbiter: A unique opportunity for investigating
small-scale physical processes at work in the magnetic solar
atmosphere
Authors: Vial, J. -C.
Bibcode: 2005AdSpR..36.1375V
Altcode:
With knowledge gained from the recent ULYSSES, SOHO, TRACE and other
missions, a great deal of progress has been made in our understanding
of the structure and dynamics of the various regions of the solar
atmosphere: e.g., transition region and "quiet" corona, coronal holes
and active region loops. However, no clear conclusions can yet be
drawn about the fundamental processes that determine the existence
and the underlying physics of these regions, especially their
observed high temperature and flows. The lack of adequate spatial
resolution has limited the study of the continuum between cool/hot,
source/sink, and magnetic/non-magnetic regions. We consider here,
magnetic reconnection as an example of the basic processes that are
most likely involved at many different scales in heating and particle
acceleration. Starting with a possible mechanism for reconnection
(flux emergence), we consider different remote-sensing signatures of
reconnection: flows, field rearrangement, impulsive heating, particle
acceleration, wave generation, propagation and dissipation. We discuss
their small-scale properties derived from current measurements and ways
to improve their observation. We also consider how remote sensing and
in situ measurements could be coordinated. To demonstrate how these
advances might be achieved, we discuss the potential for discoveries
offered by the Solar Orbiter, resulting notably from its relatively
high spatial resolution and its capacity to observe for a substantial
time in co-rotation with the Sun.
Title: Coronal Magnetometry
Authors: Arnaud, J.; Faurobert, M.; Grec, G.; Vial, J. -C.
Bibcode: 2005EAS....14...95A
Altcode:
Magnetic fields emerging in the solar atmosphere control the structure,
dynamics and heating of the solar corona. Those fields remain
essentially unattainable with present low corona instrumentation. We
present the most direct way of magnetic field remote measurements
in the internal corona, namely visible and infrared coronal emission
lines magnetometry and we explain why Dome C should be investigated as
a likely outstanding site for such observations. We develop a strategy
towards a large aperture coronal magnetometer at Dome C in the context
of the other main instrumental projects underway for solar physics.
Title: Modelling the Radiative Signatures of Turbulent Heating in
Coronal Loops
Authors: Parenti, S.; Buchlin, E.; Galtier, S.; Vial, J. -C.
Bibcode: 2004ESASP.575..497P
Altcode: 2004soho...15..497P
No abstract at ADS
Title: Solving Science Use Cases that relate to the Sun and
Heliosphere with EGSO
Authors: Bentley, R. D.; Scholl, I.; Csillaghy, A.; Aboudarham,
J.; Antonucci, E.; Gurman, J. B.; Hill, F.; Pike, D.; Vial, J.;
Zharkova, V.
Bibcode: 2004AGUFMSH21B0415B
Altcode:
The European Grid of Solar Observations (EGSO) is a grid testbed
funded by the European Commission's Fifth Framework Programme under
its Information Society Technologies (IST) thematic priority. The
project started in 2002 and is designed to provide enhanced access to
solar and related data around the world. The EGSO grid is composed
of two main components, Roles to set up the grid and, catalogs and
registries to allow roles to answer users queries. Catalogs are made
of lists of observations, events and features (a new service provided
by EGSO). Registries are built from these catalogs and organized in
order to enhance search capabilities. EGSO is working closely with
other virtual observatory (VO) projects in the solar physics and
related domains. This includes the US Virtual Solar Observatory (VSO)
and the Collaborative Sun-Earth Connector (CoSEC). More recently we
have been working with the Virtual Space Plasma Observatory (VSPO) and
have contact with the Virtual Heliospheric Observatory (VHO). Through
discussions with future missions, and within the new IAU Working
Group on ``International Data Access'' (Solar and Heliospheric),
the VOs are studying ways of ensuring interoperability from the
``sun to dirt''. This type of integrated access will be particularly
important to missions such as STEREO and Living Witha Star. In this
paper we will report the current status of EGSO, demonstrate how the
catalogs and registries model serves within the user interface, and
show how the user can retrieve solar and heliospheric data to match
a scientific query. EGSO Release 4 is now being Beta-tested by users
and anyone interested should view the Web page detailing all the EGSO
capabilities under http://www.egso.org/demo
Title: Simplified simulations of MHD
Authors: Buchlin, É.; Velli, Marco; Galtier, Sébastien; Vial,
Jean-Claude
Bibcode: 2004sf2a.conf...91B
Altcode: 2004sf2a.confE.334B
Because of the wide range of scales involved in MHD turbulence, a
statistical approach may become necessary to keep a global view of this
complex phenomenon. In particular, in the framework of the heating of
the solar corona, the smallest events are not directly detectable by the
current instruments but may be integrated to a statistical study. From
the numerical point of view, the contradictory needs for computing speed
and good description of MHD solutions may be addressed by simplified
models, which keep the most possible of the complex and non-linear
physics of the MHD equations but run sufficiently fast to produce
statistics of fields, of structures, and of "events". We propose
two such models which have been originally developed to represent
coronal loops (with forcing and Alfvén wave reflection at the loop's
foot-points), but which may be adapted to represent any region with
a dominant large-scale magnetic field. The first model consists of a
set of cellular automata, in which the non-linear terms of the MHD
equations are modelled by a threshold dynamics on current density
(Buchlin et al. A&A, 2003). In the second model, the cellular
automata are replaced by shell-models of MHD, so as to reach a greater
range of wavenumbers and to model more realistically the non-linear
couplings between modes at different scales. The results obtained
with these models will be presented and consequences of this study
for observational statistics and for theory of MHD turbulence will
be discussed.
Title: Imagerie et spectrométrie dans l'UV pour les missions
spatiales solaires LYOT et Solar Orbiter
Authors: Millard, A.; Lemaire, P.; Vial, J. -C.
Bibcode: 2004JPhy4.119..235M
Altcode:
A l'horizon 2010, les missions spatiales solaires LYOT et Solar Orbiter
permettront d'effectuer des observations du soleil (disque et couronne)
dans l'UV à des résolutions spatiale et temporelle jamais réalisées
auparavant. Pour atteindre ce but, les deux missions utiliseront en
particulier des spectro-imageurs. La longueur d'onde de travail impose
un schéma optique original uniquement en réflexion et utilisant des
réseaux de diffraction. Le concept d'un tel instrument est décrit ici,
et l'avancement de la maquette réalisée à l'IAS sont présentés.
Title: Prominence corona transition region plasma diagnostics from
SOHO observations
Authors: Cirigliano, D.; Vial, J. -C.; Rovira, M.
Bibcode: 2004SoPh..223...95C
Altcode:
New results concerning prominence observations and in particular
the prominence-corona transition region (PCTR) are presented. In
order to cover a temperature range from 2 × 104 to 7 ×
105 K, several emission lines in many different ionization
states were observed with SUMER and CDS on board SOHO. EM and DEM were
measured through the whole PCTR. We compared the prominence DEM with
the DEM from other solar structures (active region, coronal hole and the
chromosphere-corona transition region (CCTR)). We notice a displacement
of the prominence DEM minimum towards lower temperatures with respect
to the minimum of the other structures. Electron density and pressure
diagnostics have been made from the observed C III lines. Local
electron density and pressure for T ∼ 7 × 104 K are
respectively log Ne = 9.30−0.34+0.30
and 0.0405−0.014+0.012. Extrapolations over the
entire PCTR temperature range are in good agreement with previous SOHO
results (Madjarska et al., 1999). We also provide values of electron
density and pressure in two different regions of the prominence (center
and edge). The Doppler velocity in the PCTR shows a trend to increase
with temperature (at least up to 30 km s -1 at T ∼ 7 × 104
K), an indication of important mass flows. A simple morphological model
is proposed from density and motion diagnostics. If the prominence is
taken as a magnetic flux tube, one can derive an opening of the field
lines with increasing temperature. If the prominence is represented
as a collection of threads, their number increases with temperature
from 20 to 800. Derived filling factors can reach values as low as
10−3 for a layer thickness of the order of 5000 km. The
variation of non-thermal velocities is determined for the first time,
in the temperature range from 2 × 104 to 7 × 105
K. The quite clear similarity with the CCTR non-thermal velocities
would indicate that heating mechanisms in the PCTR could be the same
as in the CCTR (wave propagation, turbulence MHD).
Title: EUV imager and spectrometer for Lyot and Solar Orbiter space
missions
Authors: Millard, Anne; Lemaire, Philippe; Vial, Jean-Claude
Bibcode: 2004ESASP.554..351M
Altcode: 2004icso.conf..351M
In the 2010 horizon, solar space missions such as LYOT and Solar
Orbiter will allow high cadence UV observations of the Sun at spatial
and spectral resolution never obtained before. To reach these goals,
the two missions could take advantage of spectro-imagers. A reflective
only optical solution for such an instrument is described in this
paper and the first results of the mock-up being built at IAS are shown.
Title: A New Relation between Central and Total Solar H I Lyman-α
Irradiances, as measured by SOHO during Solar Cycle 23 (1996-2003)
Authors: Emerich, C.; Lemaire, P.; Vial, J. -C.; Curdt, W.; Schüle,
U.; Wilhelm, K.
Bibcode: 2004AAS...204.9802E
Altcode: 2004BAAS...36..984E
The spectral irradiance at the center of the solar H Ly-α line profile
is the main excitation source responsible for the atomic hydrogen
resonant scattering in cool material. It has therefore to be known
with the best possible accuracy to model the H Ly-α emissions taking
place in planetary, cometary and interplanetary environments. On
the other hand, the only permanently monitored solar irradiance is
the total one - either measured by near-Earth satellites, or deduced
from its correlation with solar activity indexes. It is the reason why
Vidal-Madjar (1975) using OSO-5 satellite H Ly-α data, established a
semi-empirical formula allowing to deduce the central H Ly-α irradiance
from the integrated one. This relation has been extensively used for
three decades. In fact, at the low altitude of the OSO-5 orbit, the
observed central part of the solar line profiles was deeply absorbed by
a large column of exospheric atomic hydrogen. Consequently, the solar
line center irradiances were not measured directly, but obtained by
confronting the measurements with simulations of both the geocoronal
absorption and the self-reversed shape of the central solar profile
itself. On the contrary, the SOHO/SUMER spectrometer orbiting well
outside the H geocoronal envelope (at the L1 Sun-Earth Lagrange point),
provided full Sun H Ly-α profiles, exempt from any central geocoronal
absorption (Lemaire et al. (1998, 2002, 2004)). This has made it
possible to directly measure the central H Ly-α solar irradiances
as a function of the integrated ones, during eight years of Solar
Cycle 23. The newly obtained relation confirms the general trend of
the previous one, but it is characterized by significantly different
coefficients. It will therefore provide new and more accurate inputs
for the future modeling of the various Ly-α emissions occurring inside
the Solar System.
Title: Flare observation of the Sun as a star by SUMER/SOHO in the
hydrogen Lyman continuum
Authors: Lemaire, P.; Gouttebroze, P.; Vial, J. -C.; Curdt, W.;
Schühle, U.; Wilhelm, K.
Bibcode: 2004A&A...418..737L
Altcode:
During the execution of the programme ``Sun as a star'', while the
SUMER (Solar Ultraviolet Emission of Emitted Radiation)/SOHO (SOlar and
Heliospheric Observatory) slit was collecting the scattered radiation
from the telescope mirror far away from the solar disk image, a class
X5.3/3b flare erupted on the solar disk, on 25 August 2001. During
the first phase of the flare a relative increase of a few percent was
detected at the head of the hydrogen Lyman continuum. After correction
from the instrumental parameters, the relative signal increase is 70%
at the head of the Lyman continuum (910 Å), and 190% in the C II 904
Å multiplet. Accounting for the area of the flare region, the local
increase of the radiance of the Lyman continuum and of the C II lines
is estimated to be a factor of several thousands. We compare this
result with other solar observations and models. Appendix A is
only available in electronic form at http://www.edpsciences.org
Title: Prominence atlas in the SUMER range 800 1250 Å:
I. Observations, data reduction and preliminary results
Authors: Parenti, S.; Vial, J. -C.; Lemaire, P.
Bibcode: 2004SoPh..220...61P
Altcode:
The aim of this work is to build an EUV-UV spectral catalogue of a
prominence. Here we focus on the preparatory work for the final result
and we give an example of the results obtained. As a first step, we
present the information needed for a full understanding of the results
that will form the final entire catalogue. The data are composed of a
full SUMER spectrum in the range 800-1250 Å of a prominence observed
on 8 October 1999. A quiet-Sun area was also observed in the same
spectral range in order to have a reference spectrum. Beside the
standard corrections, we give details of the estimated stray light
and the wavelength calibration of both datasets. We also present a
short list of lines as an example of the results from the line-fitting
procedure we applied to the data. For each line we give the measured
position, the total intensity and the FWHM in the quiet Sun and at two
different spatial positions in the prominence. With a final atlas of
the prominence it will be possible to investigate several properties
of the feature such as mass motion, differential emission measure,
density, and elemental composition.
Title: Optical design of the Lyman alpha coronagraph for the LYOT
microsatellite
Authors: Vives, Sebastien; Lamy, Philippe L.; Vial, Jean-Claude
Bibcode: 2004SPIE.5171..298V
Altcode:
The LYOT (LYman Orbiting Telescope) solar mission (proposed for a CNES
micro-satellite) is composed of a disk imager and a coronagraph, both
working at Lyman-α (121.6 nm). The coronagraph is internally occulted
and all-reflective with a field-of-view of 1.2 R up to 2.5 R and high
spatial resolution (2 pixels) amounts to 5 arcsec. The optical design
is driven by the requirement to use a superpolished spherical mirror
to minimize the scattered light into the instrument. The LYOT mission
will observe the Lyman-α corona at high cadence (1 image/5 minutes)
over a period of two years.
Title: Variation of the full Sun hydrogen Lyman profiles through
solar cycle 23
Authors: Lemaire, P.; Emerich, C.; Vial, J. -C.; Curdt, W.; Schühle,
U.; Wilhelm, K.
Bibcode: 2004cosp...35..510L
Altcode: 2004cosp.meet..510L
The hydrogen Lyman (121.267 nm and 102.572 nm) lines are important
contributors to the solar EUV flux which illuminates the upper Earth's
atmosphere. From high resolution spectral observations performed with
the SUMER FUV-EUV spectrometer on SoHO, the detailed profiles of these
two lines have been obtained. Some insights into the variation of the
shape of the profiles, sampled throughout the present solar cycle 23,
are shown and discussed.
Title: UV imager and spectrometer for LYOT and Solar Orbiter space
missions
Authors: Millard, A.; Lemaire, P.; Vial, J. -C.
Bibcode: 2004cosp...35.1749M
Altcode: 2004cosp.meet.1749M
The results from missions such as Yohkoh, Trace or SOHO have advanced
our understanding of the solar corona and heliosphere, but also have
raised many new questions. Measurements at higher spatial resolution and
cadence are needed, some regions such as the solar poles or the inner
heliosphere remain unexplored. Both LYOT and Solar Orbiter mission
address those questions. UV imaging spectrometers may be included in
the remote sensing instruments packages for these missions. Fourier
transform spectrometry (FTS) is an ideal solution for imaging systems
as there is no need to scan the region of interest with a slit to
get a 2D map, and the spectral ranged covered is only limited by the
bandpass of the filter and the maximum optical path difference that
can be obtained. FTS systems also allows to make observations at high
cadence (100 Hz). Working in the far UV (below 200 nm) requires the use
of reflective only optical systems. A solution for such an instrument
has been designed at IAS and a mock-up has been built in order to test
and validate the working principle. The first results of the alignment
phase are shown.
Title: Statistical Study of SOHO/SUMER Full-Sun Images
Authors: Buchlin, E.; Vial, J. -C.; Lemaire, P.; Galtier, S.
Bibcode: 2004ESASP.547..337B
Altcode: 2004soho...13..337B
A series of full-Sun observations was performed with the SoHO/SUMER
instrument between March and October 1996. Some moments of the
S VI 93.3nm, S VI 94.4nm, and Ly line profiles were computed
on-board. Intensities and line-of-sight velocities in a large central
region of the Sun are studied statistically: histograms of intensities
are computed, as well as histograms of total intensities of "events",
and structure functions of the intensity field. Some statistics of
velocities are the first to be obtained from observational data. The
aim is to compare these statistics to results previously obtained with
SoHO/EIT and by numerical simulations of MHD. Signatures of turbulent
intermittency are also researched.
Title: Statistical properties of turbulence and intermittency in
the solar corona observed in EUV
Authors: Buchlin, E.; Vial, J. -C.; Lemaire, P.
Bibcode: 2004cosp...35.3556B
Altcode: 2004cosp.meet.3556B
Statistical properties of the fields observed on the Sun in EUV may
help to understand turbulence in the solar corona and give clues to
the processes involved in the heating of the corona to millions of
degrees. In this study, we use a series of full-Sun images obtained
in 1996 by the SUMER spectroheliograph on SoHO. Each observation
consists of eight limb-to-limb raster scans in the lines Ly ɛ, S VI
193.3 nm, and S VI 194.4 nm. Intensities, Doppler velocity shifts and
line widths were computed on-board. A context spectrum was measured
for each observation. Intensities and line-of-sight velocities data
in a large central region of the Sun are then studied statistically:
histograms of data values and of events, structure functions, and
other statistics are computed. They are compared to results obtained
by imaging instruments like SoHO/EIT and to numerical simulations of
MHD. Structure functions of the velocity field reveal that turbulence
in the corona may be intermittent.
Title: Integrated Access to Solar Data using EGSO
Authors: Bentley, R. D.; Csillaghy, A.; Scholl, I.; Vial, J. -C.;
Aboudarham, J.; Antonucci, E.; Zharkova, V. V.; Pike, C. D.
Bibcode: 2004cosp...35.3935B
Altcode: 2004cosp.meet.3935B
The European Grid of Solar Observations (EGSO) is a virtual observatory
based on Grid technology that will change the way users analyze solar
data. EGSO is funded under the IST (Information Society Technologies)
thematic priority of the European Commission's Fifth Framework Programme
(FP5). It started in March 2002 and will last for 3 years. The EGSO
Consortium comprises eleven groups from five countries in Europe
and the US, and is led by the Mullard Space Science Laboratory
of University College London. The project aims to overcome one of
the major hurdles in the analysis of solar data - finding what data
are available and retrieving those that are needed. EGSO is creating
layers of metadata catalogues that will for the first time provide the
ability to select solar data based on phenomena and events. It is also
integrating access to solar data by building a Grid including solar
archives around the world. This combination of metadata and tools for
selecting, processing and retrieving distributed and heterogeneous
solar data, will radically change the way that data are distributed
and analyzed. EGSO is collaborating closely with groups in the US who
are working on similar virtual observatory projects for the solar,
solar-terrestrial and heliospheric communities with the objective
of providing integrated access to these data. In particular, strong
synergies between the EGSO and CoSEC projects are producing innovative
ways of accessing the data that will be deployed in both projects. Since
the first release of EGSO in September 2003, members of the solar
community have been involved in product testing. The constant testing
and feedback allows us to continue to improve the quality and usability
of the system. The capabilities of the latest release (R4) will be
described, and the scientific problems that it addresses discussed.
Title: SOLAR ORBITER : a unique opportunity for investigating the
physical processes at work in the magnetic solar atmosphere
Authors: Vial, J. -C.
Bibcode: 2004cosp...35.3808V
Altcode: 2004cosp.meet.3808V
With recent ULYSSES, SOHO, TRACE (and other) missions, much progress has
been made on the issues of structuring and dynamics in various regions
of the solar atmosphere : transition region and ``quiet'' corona,
coronal holes, active region loops. However, no clear conclusion could
be drawn about the processes which determine their existence and their
physics, especially their observed high temperatures or flows. For
one reason, the lack of sufficient spatial resolution at all observed
wavelengths has prevented to study the continuity between cool/hot,
source/deposit, magnetic/non magnetic regions. For another reason, the
study of the important regions of open magnetic field (mostly located
at poles) has faced the severe drawback of observations performed from
the ecliptic plane, except for (in-situ) ULYSSES measurements at a few
A.U. We discuss the potential of discoveries offered by Solar Orbiter
resulting notably from its spatial resolution performances and its
capacity to fly above the ecliptic plane. We also stress how it is
essential that remote sensing and in-situ measurements be coordinated.
Title: A search for turbulent wave heating and acceleration signatures
with SOHO/SUMER observations : Measurements of the widths of off-limb
Iron lines
Authors: Dolla, L.; Lemaire, P.; Solomon, J.; Vial, J. -C.
Bibcode: 2003AIPC..679..351D
Altcode:
The widths of coronal ions lines may contain important information
about the energetics of the solar wind and corona. We present a
method to measure these widths, taking into account the problems of
instrumental stray light inherent to SoHO/SUMER. The Iron lines are
interesting to set an upper limit on the ``unresolved'' velocity,
that may be a signature of turbulent or wave motion in the corona.
Title: A solar cellular automata model issued from reduced MHD
Authors: Buchlin, E.; Aletti, V.; Galtier, S.; Velli, M.; Vial, J. -C.
Bibcode: 2003AIPC..679..335B
Altcode:
A three-dimensional cellular automata (CA) model inspired by the reduced
magnetohydrodynamic equations is presented to describe impulsive events
generated along a coronal magnetic loop. It consists of a set of planes,
distributed along the loop, between which the information propagates
through Alfvén waves. Statistical properties in terms of power laws are
obtained in agreement with SoHO observations of X-ray bright points of
the quiet Sun. Physical meaning and limits of the model are discussed.
Title: A simplified numerical model of coronal energy dissipation
based on reduced MHD
Authors: Buchlin, E.; Aletti, V.; Galtier, S.; Velli, M.; Einaudi,
G.; Vial, J. -C.
Bibcode: 2003A&A...406.1061B
Altcode: 2002astro.ph.12444B
A 3D model intermediate between cellular automata (CA) models and
the reduced magnetohydrodynamic (RMHD) equations is presented to
simulate solar impulsive events generated along a coronal magnetic
loop. The model consists of a set of planes distributed along a
magnetic loop between which the information propagates through Alfvén
waves. Statistical properties in terms of power-laws for energies and
durations of dissipative events are obtained, {and their} agreement
with X-ray and UV flares observations {is discussed}. The existence
of observational biases is {also} discussed.
Title: Distributions of Coronal Events: Simulations and Event
Definitions
Authors: Buchlin, Éric; Galtier, Sébastien; Velli, Marco; Vial,
Jean-Claude
Bibcode: 2003ANS...324..109B
Altcode: 2003ANS...324..P15B
No abstract at ADS
Title: The solar high-resolution imager - coronagraph LYOT mission
Authors: Vial, Jean-Claude; Song, Xueyan; Lemaire, Philippe; Gabriel,
Alan H.; Delaboudiniere, Jean-Pierre; Bocchialini, Karine; Koutchmy,
Serge L.; Lamy, Philippe L.; Mercier, Raymond; Ravet, Marie Francoise;
Auchere, Frederic
Bibcode: 2003SPIE.4853..479V
Altcode:
The LYOT (LYman Orbiting Telescope) solar mission is proposed to
be implemented on a micro-satellite of CNES (France) under phase A
study. It includes two main instruments, which image the solar disk
and the low corona up to 2.5 Ro in the H I Lyman-α line
at 121.6 nm. The spatial resolution is about 1” for the disk and
2.5” for corona. It also carries an EIT-type telescope in the He II
(30.4 nm) line. The coronagraph needs a super polished mirror at the
entrance pupil to minimize the light scattering. Gratings and optical
filters are used to select the Lyman-α wavelength. VUV cameras with
2048×2048 pixels record solar images up to every 10 seconds. The
satellite operates at a high telemetry rate (more then 100 kb/s,
after onboard data compression). The envisaged orbits are either
geostationary or heliosynchronous. Possible launch dates could be end
of 2006 - beginning of 2007.
Title: Modelo semi-empírico de protuberancia solar a partir del
diagnóstico de densidades
Authors: Cirigliano, D.; Vial, J. C.; Rovira, M.
Bibcode: 2003BAAA...46....7C
Altcode:
A partir de la observación del espectro del quintuplete de C
III alrededor de 1175 Å, se ha realizado el diagnóstico de la
densidad y presión electrónica, basado en el cálculo del cociente
de las intensidades observadas. Una vez establecida la densidad
electrónica, y con el cálculo de las velocidades Doppler, hemos
investigado el flujo de masa en la protuberancia en función de la
temperatura. Estableciendo como hipótesis la conservación del número
de partículas que ingresan y salen del cuerpo de la protuberancia, se
investiga la variación del área de un tubo de flujo semi-empírico
en función de la temperatura. A partir de dicho diagnóstico, se
examina el comportamiento del radio del tubo magnético en función
de la temperatura, los que dan cuenta de la abertura de las líneas
de campo magnético que confinan el plasma y de la divergencia del
campo magnético en diferentes alturas de la atmósfera solar.
Title: Some advances in the thermodynamic diagnostic of solar
prominences
Authors: Vial, J. -C.
Bibcode: 2003EAS.....9..133V
Altcode:
The aim of this paper is to present some recent advances in the
diagnostic of solar prominences, with an emphasis put on the results
obtained with SOHO through its six years of observations. We show the
progress made since the Hvar Reference Model in the determination of
basic thermodynamic parameters, especially in the Prominence-Corona
Transtion Region (PCTR). We address the important contribution of
``prominence seismology" for determining e.g. density and magnetic
field. We summarize the most recent comparisons between non-LTE
modelling predictions and spectra of optically thick lines. Finally, we
mention the most recent magnetic measurements which seem to challenge
the historic Hanle measurements of Leroy ([CITE]) as summarized in
Bommier et al. ([CITE]).
Title: Line profiles and intensity ratios in prominence models with
a prominence to corona interface
Authors: Labrosse, N.; Gouttebroze, P.; Heinzel, P.; Vial, J. -C.
Bibcode: 2002ESASP.506..451L
Altcode: 2002svco.conf..451L; 2002ESPM...10..451L
In this work we study the hydrogen, helium and calcium spectra
emitted by a one-dimensional prominence model in magneto-hydrostatic
equilibrium. The prominence slab consists of two parts: a cool
core where the plasma is optically thick for some lines, and a
prominence-to-corona transition region (PCTR) with a strong temperature
gradient. The models are defined by 5 parameters: temperature, pressure,
slab thickness, microturbulent velocity and altitude. We solve the NLTE
radiative transfer equations for all optically thick transitions. We
present line ratios between infrared, optical and EUV lines, as well
as line profiles. We show that the presence of a PCTR, where both
collisional and radiative excitations are important, affects H, He,
and Ca populations and emergent lines in different manners.
Title: Quiet-Sun chromospheric network evolution
Authors: Lemaire, Philippe; Vial, J. -C.; Curdt, W.; Schühle, U.;
Wilhelm, K.
Bibcode: 2002ESASP.505..477L
Altcode: 2002solm.conf..477L; 2002IAUCo.188..477L
Using the SUMER/SOHO spectrometer we have observed the same quiet-Sun
area during several days in a set of eight spectral lines of the
transition region. Line intensity maps of the rastered areas are used to
separate the interior of the supergranular cells from the network. Then,
following the evolution of the supergranular pattern, we measure the
variations of intensity and the Doppler shifts at several temperatures
of formation of the transition region. We find that the overall flow
velocity of the cell interior and the network generally decays within
ten hours, which represents a significant part of the supergranular
lifetime.
Title: Study of coronal loops using TRACE and SOHO
Authors: Gontikakis, C.; Dara, H. C.; Zachariadis, Th.; Nindos, A.;
Alissandrakis, C.; Tsiropoula, G.; Vial, J. -C.
Bibcode: 2002ESASP.505..417G
Altcode: 2002solm.conf..417G; 2002IAUCo.188..417G
We analysed coronal loops observed in many spectral lines from TRACE and
SUMER, at the active region NOAA 8541, on May 15, 1999. For the loops,
which are identified in a number of wavelengths, we try to combine
the good temporal and spatial resolution of TRACE with the spectral
information obtained by the SUMER rasters, in order to determine some
physical parameters such as temperature, flow velocity and electron
density. The morphology of the magnetic field of the loops is also
approximated by a force-free extrapolation of the photospheric magnetic
field, measured with MDI, and is compared to the loop morphology.
Title: Prediction of line intensity ratios in solar prominences
Authors: Gouttebroze, P.; Labrosse, N.; Heinzel, P.; Vial, J. -C.
Bibcode: 2002ESASP.505..421G
Altcode: 2002solm.conf..421G; 2002IAUCo.188..421G
Solar prominences are made of relatively cool and dense plasma
embedded in the solar corona, supported and structured by the magnetic
field. Since this plasma is definitely out of LTE, the diagnosis
of physical conditions in prominences needs the use of specific
radiative transfer (RT) codes to predict the spectrum emitted by
models and compare it to observations. For optically thin lines, the
solution of RT equations in the transition itself is not required,
but the emitted intensities depend, via the statistical equilibrium
equations, on RT in other transitions which are optically thick. We
use two different sets of models. The first one contains monolithic
models defined by 5 parameters: temperature, pressure, thickness,
microturbulent velocity and altitude above the solar surface. For
each parameter, we assume a range of variation. For each model, the
values of the 5 parameters are randomly chosen within the corresponding
range of variation. The second set contains composite models made of
multiple layers, in order to simulate the penetration of radiation into
inhomogeneous prominences. We use NLTE radiative transfer codes to
compute the intensities of the lines of hydrogen, helium and calcium
emitted by each model. So, for any couple of lines, we may obtained
their intensity ratio as a function of the 5 parameters. We discuss
the behaviour of some of these intensity ratios as a function of the
principal parameters and construct distribution diagrams, which are
compared to different published observations.
Title: MHD waves in active region filament from SOHO-THEMIS joint
observations
Authors: Régnier, S.; Solomon, J.; Vial, J. C.; Mein, P.
Bibcode: 2002ESASP.505..647R
Altcode: 2002IAUCo.188..647R; 2002solm.conf..647R
The stability of solar filaments and their implications for eruptive
events can be revealed by the existence of magnetohydrodynamic
(MHD) waves. During the MEDOC campaign on May 2000, we performed
joint observations involving SOHO and THEMIS instruments (CDS and
MSDP respectively). We analyse the modes of oscillations for several
spectral lines (Hα at 6563 Å, He I at 584 Å and Mg X at 609 Å):
intermediate (6-40 min) and short (< 5 min) periods are found and
are discusssed in terms of MHD waves. The Hα time series (MSDP) in
both line center intensity and line-of-sight Doppler shifts provide
constraints on models of filament oscillations.
Title: Soho Contribution to Prominence Science
Authors: Patsourakos, Spiros; Vial, Jean-Claude
Bibcode: 2002SoPh..208..253P
Altcode:
We present the main current issues concerning prominence studies. We
recall the large range of plasma parameters found in prominences
which makes the work of the MHD modeler more difficult. We also
summarize the capabilities of the SOHO instrumentation. We present and
discuss the most recent SOHO results concerning the determination of
temperature, densities, and velocities. We put some emphasis on the
different morphologies observed, the diagnostic capabilities of the
Lyman lines profiles when accompanied by improved non-LTE modeling,
and the information gathered from the first prominence oscillations
measured from space. We also make an account of eruptive prominences. We
finally discuss what could be done with present and future SOHO data
to improve our understanding of prominences.
Title: A SUMER spectral atlas for prominences
Authors: Parenti, Susanna; Vial, J. -C.; Lemaire, P.
Bibcode: 2002ESASP.508..327P
Altcode: 2002soho...11..327P
We present preliminary results of a study aimed at building a SUMER
atlas for prominences. Using the atlas as reference, further studies
can be addressed at deriving prominence properties, such as DEM
distribution and anomalies in element abundances. Moreover, a comparison
with previous atlas (e.g. Curdt et al., 2001) of other solar regions
can be made. An extended prominence was observed with SUMER in the
South-West solar limb in October 1999. A full spectrum was obtained
in the waveband 790 - 1600 Å. After dealing with off-limb scattered
light, the data are processed using multi-Gaussian fitting in order
to derive the spectral properties of the observed structure. These
properties are then also compared with those of the Quiet Sun area
observed in the same wavelength range.
Title: Measurement of velocity fields in prominence plasma with
SUMER/CDS on SOHO
Authors: Cirigliano, Daniela; Vial, Jean-Claude; Rovira, Marta
Bibcode: 2002ESASP.508..287C
Altcode: 2002soho...11..287C
Disk and quiescent prominence observations have been obtained with the
CDS (Coronal Diagnostic Spectrograph) and SUMER (Solar Ultraviolet
Measurement of Emitted Radiation) instruments, on board SOHO. The
purpose is to investigate the macroscopic velocities of several species
in the prominence plasma as compared to the quiet Sun velocities. To
calculate the solar disk velocities we have taken into account the
bi-modal distribution of UV structures in the quiet Sun. The macroscopic
velocities in prominences were computed from the Doppler shifts in
every line spectrum, taking those in the solar disk as reference. We
have obtained absolute values for the macroscopic velocities ranging
from 5 km/s to 40 km/s. We have also attempted to separate the central
core vs. the external border behaviours of the macroscopic velocities.
Title: Variation of the full Sun hydrogen Lyman α and β profiles
with the activity cycle
Authors: Lemaire, Philippe; Emerich, C.; Vial, J. -C.; Curdt, W.;
Schühle, U.; Wilhelm, K.
Bibcode: 2002ESASP.508..219L
Altcode: 2002soho...11..219L
Full Sun hydrogen Lyman α and β profiles obtained through the
activity cycle are needed to compare with stars, to understand the
hydrogen distribution in the heliosphere and to evaluate the processes
in the upper planetary atmospheres. Using the SUMER/SOHO telesocope
scattered light properties, we have measured the Lyman α and β
profiles at different epochs of the solar activity cycle. Here we
report modifications in the intensity and the shape of the profiles.
Title: A Solar Cellular Automata Model Issued From Reduced MHD
Authors: Buchlin, E.; Aletti, V.; Galtier, S.; Velli, M.; Vial, J. -C.
Bibcode: 2002sf2a.conf..129B
Altcode:
A three-dimensional cellular automata model inspired by the reduced
magnetohydrodynamic equations is presented to describe impulsive events
generated along a coronal magnetic loop. It consists of a set of planes,
distributed along the loop, between which the information propagates
through Alfven waves. Statistical properties in terms of power laws are
obtained in agreement with SoHO observations of X-ray bright points of
the quiet Sun. Physical meaning and limits of the model are discussed.
Title: Intermittent behavior in the transition region and the low
corona of the quiet Sun
Authors: Patsourakos, S.; Vial, J. -C.
Bibcode: 2002A&A...385.1073P
Altcode:
We present an analysis of light-curves obtained in the O IV and Ne
VIII transition region and low corona lines, that were simultaneously
recorded in a quiet Sun region by SUMER/SOHO. By using the flatness
spectrum of the observed light-curves we searched for intermittency
signatures. It was found that a significant proportion of points
in the observed area exhibit clear indications of intermittency,
irrespectively of their intrinsic intensity. Our findings give favor to
an impulsively heated transition region and corona via intermittent-type
MHD turbulence.
Title: Multiwavelength analysis of an active region observed with
SOHO and TRACE
Authors: Dara, H. C.; Gontikakis, C.; Zachariadis, Th.; Tsiropoula,
G.; Alissandrakis, C. E.; Vial, J. -C.
Bibcode: 2002ESASP.477...95D
Altcode: 2002scsw.conf...95D
We study the solar active region NOAA 8541, observed on May 15, 1999,
from 13:00 to 15:00 UT, with the instruments aboard SOHO (SUMER,
CDS, MDI) and TRACE. The SOHO observations produced a set of raster
scans of the region with a field of view of 159"×120" for SUMER and
of 244"×240" for CDS. TRACE gave a sequence of high time resolution
images for a much larger (510"×510") field of view, in several spectral
passbands, while MDI gave the photospheric full disk longitudinal
magnetic field. The data set mainly covers the transition region and
the low corona. We have used the data to construct intensity, velocity
and magnetic field maps of the region. The comparison of the intensity
images in various wavelengths with the velocity images, as well as
with the magnetic field, gives us information about the dynamical
characteristics of the observed features and their relationship to
the photospheric magnetic field.
Title: Relation between intensity and Dopplershifts in the quiet
Sun transition region
Authors: Gontikakis, C.; Dara, H. C.; Zachariadis, Th.; Alissandrakis,
C. E.; Vial, J. -C.
Bibcode: 2002ESASP.477..107G
Altcode: 2002scsw.conf..107G
In this work we used CDS and SUMER (SOHO) observations of a quiet
region (41°W 41°N) on the 28th of July 1996. The study of the
histograms of the velocities corresponding to the network and the
internetwork regions, shows that the network plasma is redshifted
with respect to the internetwork one. The shifts in the histograms
are small, but they are systematic for all lines. It should be
mentioned that the internetwork is also statistically redshifted,
with the exception of the He I line. In the low transition region the
morphology in the intensity images is different from the morphology
in the Dopplergrams. It seems that the network intensity structures
correspond to more than one in the Dopplergrams, since the latter
are quite smaller than the intensity structures. This was verified by
calculating the average autocorrelation function for intensity images
and Dopplergrams of spectral lines from SUMER and CDS. On the average,
the FWHM of the autocorrelation function of the intensity images is
two times larger than that of the corresponding Dopplergram ones.
Title: Cooling and evacuation of an active region loop complex
observed with TRACE
Authors: Tsiropoula, G.; Gontikakis, C.; Dara, H. C.; Zachariadis,
Th.; Alissandrakis, C.; Vial, J. -C.
Bibcode: 2002ESASP.477..179T
Altcode: 2002scsw.conf..179T
We analyse the temporal variation of temperature and emission measure
at the top of a coronal loop system observed with the Transition
Region and Coronal Explorer (TRACE). Loops delineate regions of highly
localized heating and are thus typically the focus of coronal heating
theories. The analyzed data consist of observations in the 171 Å and
195 Å passbands taken at a cadence of ~10 min obtained on May 15,
1999 during an observing campaign. The temperature and emission measure
diagnostic is based in the 171 Å / 195 Å filter-ratio technique. The
loop system evacuates after the plasma at the top of the loops has
cooled. Estimates of the timescales of energy losses by radiation
and by conduction clearly suggest that the cooling is mainly due to
radiation losses.
Title: Transition region quiet sun velocity field evolution
Authors: Lemaire, P.; Artzner, G.; Vial, J. -C.; Curdt, W.; Schühle,
U.; Wilhelm, K.
Bibcode: 2002AdSpR..30..487L
Altcode:
The UV/EUV SUMER spectrometer aboard SOHO can record profiles of lines
emitted by elements at different stages of ionization corresponding
to several temperatures within the transition region temperature
range. During the solar cycle minimum in July 1996, we were able to
observe the quiet Sun during five consecutive days. From the line
positions we have determined the velocity fields and follow their time
variations at different temperatures in the transition region. The line
intensity maps are used to separate supergranular cells and network and
they allow to compare the behaviors of the velocity fields evolution in
the two structures. The results are critically analyzed and discussed.
Title: Observaciones del disco solar y de una protuberancia quiescente
en radiación ultravioleta
Authors: Cirigliano, D.; Vial, J. -C.; Rovira, M.
Bibcode: 2002BAAA...45...18C
Altcode:
Observaciones del disco solar y de una protuberancia quiescente en
el rango de longitudes de onda ultravioleta fueron obtenidas con
el instrumento CDS (Coronal Diagnostic Spectrograph) y SUMER (Solar
Ultraviolet Measurements of emitted radiation) a bordo de la sonda
SOHO. El propósito es investigar las velocidades macroscópicas de
varias especies metálicas que se observan tanto en el disco solar como
en el plasma de las protuberancias. Para calcular las velocidades del
disco solar aplicamos una técnica mixta para modelar la distribución
de estructuras en UV en el Sol quieto. Las velocidades macroscópicas
en las protuberancias se calcularon a partir de los corrimientos
Doppler en cada línea espectral y luego se tomaron las del disco
solar como referencia. Obtuvimos valores absolutos para las velocidades
macroscópicas entre 5 y 40 km/seg. También detectamos comportamientos
diferentes en las velocidades de las protuberancias en el centro con
respecto a los bordes.
Title: Relationships between CME's and prominences
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Aulanier, G.;
Démoulin, P.; Thompson, B.; De Forest, C.; Wiik, J. E.; Saint Cyr,
C.; Vial, J. C.
Bibcode: 2002AdSpR..29.1451S
Altcode:
We have studied the erupting prominences which were associated with
coronal mass ejections during a series of campaigns involving both
spacecraft and ground-based observatories. The evolution of the
physical conditions within the prominences was established from Hα
and magnetic field observations. Particular attention ahs been paid
to the presence of mixed amgnetic polarity in the filament channel,
the evolution of the shear of the large-scale magnetic field, and
the existence of multiple magnetic inversion lines. We conclude that
reconnection of large-scale coronal magnetic fields is responsible
for both the CME and filament eruption.
Title: Solar orbiter, a high-resolution mission to the sun and
inner heliosphere
Authors: Marsch, E.; Antonucci, E.; Bochsler, P.; Bougeret, J. -L.;
Fleck, B.; Harrison, R.; Langevin, Y.; Marsden, R.; Pace, O.; Schwenn,
R.; Vial, J. -C.
Bibcode: 2002AdSpR..29.2027M
Altcode:
The scientific rationale of the Solar Orbiter is to provide, at high
spatial (35 km pixel size) and temporal resolution, observations of the
solar atmosphere and unexplored inner heliosphere. Novel observations
will be made in the almost heliosynchronous segments of the orbits at
heliocentric distances near 45 R⊙ and out of the ecliptic plane at
the highest heliographic latitudes of 30° - 38°. The Solar Orbiter
will achieve its wide-ranging aims with a suite of sophisticated
instruments through an innovative design of the orbit. The first
near-Sun interplanetary measurements together with concurrent remote
observations of the Sun will permit us to determine and understand,
through correlative studies, the characteristics of the solar wind
and energetic particles in close linkage with the plasma and radiation
conditions in their source regions on the Sun. Over extended periods
the Solar Orbiter will deliver the first images of the polar regions
and the side of the Sun invisible from the Earth.
Title: Solar Orbiter: a high-resolution mission to the sun and
inner heliosphere
Authors: Fleck, Bernhard; Marsch, E.; Antonucci, Ester; Bochsler,
Peter A.; Bougeret, J. L.; Harrison, R.; Marsden, R. P.; Coradini,
M.; Pace, Oscar; Schwenn, Rainer; Vial, Jean-Claude
Bibcode: 2001SPIE.4498....1F
Altcode:
The key mission objective of the Solar Orbiter is to study the Sun
from close-up (45 solar radii, or 0.21 AU) in an orbit tuned to solar
rotation in order to examine the solar surface and the space above from
a co-rotating vantage point at high spatial resolution. Solar Orbiter
will also provide images of the Sun's polar regions from heliographic
latitudes as high as 38 degrees. The strawman payload encompasses
two instrument packages: Solar remote-sensing instruments: EUV
full-sun and high resolution imager, high-resolution EUV spectrometer,
high-resolution and full-sun visible light telescope and magnetograph,
EUV and visible-light coronagraphs, radiometers. Heliospheric
instruments: solar wind analyzer, radio and plasma wave analyzer,
magnetometer, energetic particle detectors, interplanetary dust
detector, neutral particle detector, solar neutron detector. To
reach its novel orbit, Solar Orbiter will make use of low-thrust
solar electric propulsion (SEP) interleaved by Earth and Venus gravity
assists. Solar Orbiter was selected by ESA's Science Programme Committee
(SPC) in October 2000 as a Flexi-mission, to be implemented after the
BepiColombo cornerstone mission to Mercury before 2013. This paper
summarizes the science to be addressed with the Solar Orbiter, followed
by brief descriptions of the strawman payload, the mission profile,
and the spacecraft and ground segment designs.
Title: Measuring Solar Abundances
Authors: von Steiger, R.; Vial, J. -C.; Bochsler, P.; Chaussidon, M.;
Cohen, C. M. S.; Fleck, B.; Heber, V. S.; Holweger, H.; Issautier, K.;
Lazarus, A. J.; Ogilvie, K. W.; Paquette, J. A.; Reisenfeld, D. B.;
Teriaca, L.; Wilhelm, K.; Yusainee, S.; Laming, J. M.; Wiens, R. C.
Bibcode: 2001AIPC..598...13V
Altcode: 2001sgc..conf...13V
This is the rapporteur paper of Working Group 2 on Measuring Solar
Abundances. The working group presented and discussed the different
observations and methods for obtaining the elemental and isotopic
composition of the Sun, and critically reviewed their results and
the accuracies thereof. Furthermore, a few important yet unanswered
questions were identified, and the potential of future missions to
provide answers was assessed. .
Title: The polar coronal holes and the fast solar wind: Some recent
results
Authors: Patsourakos, S.; Habbal, S. -R.; Vial, J. -C.; Hu, Y. Q.
Bibcode: 2001AIPC..598..299P
Altcode: 2001sgc..conf..299P
We report on recent results on the source regions of the fast solar
wind: the Polar Coronal Holes (PCH). They concern a comparison
between the effective temperatures for a large set of different ions
obtained from observations in the inner corona of PCH and from a fast
wind numerical model based on the ion-cyclotron resonant dissipation
of high-frequency Alfvén waves. We also report on some preliminary
results from our modeling concerning the Fe/O ratio in the inner corona
in PCH. .
Title: Dopplershifts in the solar transition region
Authors: Gontikakis, C.; Dara, H. C.; Alissandrakis, C. E.;
Zachariadis, Th. G.; Vial, J. -C.
Bibcode: 2001A&A...378..257G
Altcode:
We study the dynamics of the quiet sun transition region, using
observations obtained with the SOHO CDS/NIS and SUMER spectrographs. We
examine the morphology of the network as a function of temperature and
we compare the intensity features with those of the dopplergrams. The
velocity distributions have a different behaviour for the bright
features which outline the network and the dark ones, located in
the internetwork. A redshift and a smaller standard deviation are
observed for the bright feature distributions relative to the dark
ones. It should be mentioned that the internetwork is also statistically
redshifted, with the exception of the He I line. Velocity distributions
from different lines are compared.
Title: Analysis of a UV Event in a Polar Coronal Hole
Authors: Patsourakos, Spiros; Vial, Jean-Claude
Bibcode: 2001SoPh..203...39P
Altcode:
We present observations of a UV event which occurred in a polar coronal
hole. They were obtained by SUMER on SOHO in several chromospheric and
transition region spectral lines. Its birth site was about 50 arc sec
inside the limb and in a network lane showing a net outflow before
its initiation. The event had an extension of about 5 arc sec along
the slit, a duration of about 3 min and was characterized by a large
increase of intensity together with a significant line broadening
with, however, downflows of about 50 km s−1 being
dominant. Proper motions with a velocity of about 10 km s−1
were also observed. The event appeared at middle transition (O vi)
temperatures and it simultaneously showed up in chromospheric (O i,
Ly β) and low transition region (C ii) temperatures. We discuss this
event in view of different scenarios to account for it. Our event could
be a part of the large family of quiet-Sun explosive events observed
by Ryutova and Tarbell (2000) taking place in polar coronal holes that
are triggered by magnetic reconnection in the low solar atmosphere.
Title: Multi-wavelength analysis of a solar active region loop system
with SOHO, TRACE and ground-based telescopes
Authors: Tsiropoula, G.; Gontikakis, C.; Dara, H. C.; Zachariadis,
Th. G.; Alissandrakis, C.; Vial, J. -C.
Bibcode: 2001hell.confE..40T
Altcode:
No abstract at ADS
Title: High-resolution EUV imaging and spectroscopy of the corona
Authors: Patsourakos, Spiros; Vial, J. -C.
Bibcode: 2001ESASP.493...13P
Altcode: 2001sefs.work...13P
We present a set of imagers and spectrometer which have been proposed as
a strawman payload on board the Solar Orbiter mission. The scientific
requirements of the mission are put in the context of the main issues
presently discussed in solar physics. The on-going successful space
solar missions have evidenced a very fine structuring of the solar
atmosphere and its role in various processes at work for coronal
heating, wind acceleration, flaring activity, etc. This is especially
true for magnetic reconnection which seems to proceed at many different
scales. These results point at the need of observations substantially
improving both the spatial resolution and the multi-temperature
(multi-wavelength) coverage. Solar Orbiter offers a unique opportunity
to analyze this fine structure (e.g. the internal structure of the
thin loops observed by TRACE) in closed and open fields. It will allow
for a diagnostic of regions such as the magnetic network which seems
to play a major role in the wind acceleration, in conjunction with
in-situ observations of the ejected plasma.
Title: Solar Orbiter EUV/UV wavelength selection and instrumentation -
report of Payload Splinter Group 4
Authors: Harrison, R. A.; Vial, J. -C.
Bibcode: 2001ESASP.493..151H
Altcode: 2001sefs.work..151H
We present here a summary of the discussions concerning the extreme
ultraviolet (EUV) and ultraviolet (UV) wavelength selection and
instrumentation for Solar Orbiter, held at the Tenerife meeting. These
issues were assigned to Payload Splinter Group 4 and to the Wavelength
Selection Working Group. Concerning the wavelength selection, a number
of critical wavelength ranges were highlighted and discussed. Great
emphasis was placed on good atmospheric coverage, from the chromosphere
to the hottest coronal lines. A number of wavelength ranges were
presented but the wide temperature range demands the inclusion of
wavelengths longer than 912 Å as well as prime coronal lines in
much shorter wavelength ranges, such as 170-250 Å. Regarding the
instrumentation, the group agreed that Solar Orbiter should carry both
imaging and spectroscopic capability in the EUV/UV and the two strawman
instruments were presented and discussed. A number of alternatives
were considered as were developments in technology, which could be of
use for these instruments.
Title: Solar Orbiter, a high-resolution mission to the Sun and
inner heliosphere
Authors: Marsch, E.; Harrison, R.; Pace, O.; Antonucci, E.; Bochsler,
P.; Bougeret, J. -L.; Fleck, B.; Langevin, Y.; Marsden, R.; Schwenn,
R.; Vial, J. -C.
Bibcode: 2001ESASP.493D..11M
Altcode: 2001sefs.workD..11M
Solar Orbiter will provide, at very high spatial (35 km pixel size)
and temporal resolution, novel observations of the solar atmosphere
and unexplored inner heliosphere. It will achieve its wide-ranging
scientific aims with a suite of sophisticated instruments through an
innovative orbit design. Unprecedented observations will be made in
the heliosynchronous segments of the orbits at heliocentric distances
near 45 Rsolar and out of the ecliptic plane at the highest
heliographic latitudes of 30° - 38°. The first near-Sun interplanetary
measurements together with concurrent remote-sensing observations of
the Sun and its corona will permit us to determine and understand,
through correlative studies, the characteristics of the solar wind
and energetic particles in close linkage with the plasma and radiation
conditions in the source regions on the Sun. Solar Orbiter will deliver
the first images of the polar regions and the far side of the Sun
invisible from the Earth.
Title: Searching the source regions of the fast solar wind in polar
coronal holes: some recent SOHO/eclipse results and the potential
of the Solar Orbiter
Authors: Patsourakos, Spiros; Vial, J. -C.
Bibcode: 2001ESASP.493..321P
Altcode: 2001sefs.work..321P
No abstract at ADS
Title: Oscillations in an active region filament: Observations and
comparison with MHD waves
Authors: Régnier, S.; Solomon, J.; Vial, J. C.
Bibcode: 2001A&A...376..292R
Altcode:
During the MEDOC Campaign 4, on October 1999, observations of a
solar active region filament were carried out by the SUMER/SoHO
spectrometer. A time sequence of this filament has been obtained with
a duration of 7 h 30 min and with a temporal resolution of 30 s. The
Fourier analysis of the line-of-sight Doppler velocities measured in the
584.33 Å HeI line allows us to detect oscillations in several ranges
of periodicities (short periods: less than 5 min, intermediate periods:
6-20 min, and long periods: greater than 40 min). From a theoretical
point of view, we consider the possible modes of oscillations of an
active region filament. Following \cite{joa93a}, we treat the filament
as a plasma slab embedded in a uniform magnetic field inclined at an
angle phi to the long axis of the slab. Solving the dispersion equations
for Alfvén waves and magnetoacoustic waves, primary and secondary mode
frequencies appear to be non-equidistant. For the comparison between the
observed and calculated frequencies, we outline an identification method
of the oscillation modes in the observed filament. This identification
provides a diagnostic of the filament: the angle between the magnetic
field and the long axis of the slab is estimated to be 18deg,
and the magnetic field strength B (G) is proportional to the square
root of the density rhoo (cm-3) in the slab,
B ~ 2.9 x 10-5 sqrt {rhoo}.
Title: On a mechanism of intensification of field-aligned currents
at the solar chromosphere-quiescent prominence boundaries
Authors: Nenovski, P.; Dermendjiev, V. N.; Detchev, M.; Vial, J. -C.;
Bocchialini, K.
Bibcode: 2001A&A...375.1065N
Altcode:
Field-aligned electric currents (FAC) are assumed to support various
prominence configurations and it is usually supposed that the
quiescent prominence (QP) destabilisation can be initiated by some
plasma instability. In this work we study another possibility of QP
destabilisation connected with FAC changes. Such a destabilisation may
occur when FAC flowing along a loop-shaped QP structure are intensified
by bouncing surface MHD modes, presumably generated by motions in
the photosphere under, or adjacent to, the QP. The MHD disturbances
at the prominence ``feet'' propagate upwards as Alfven waves and
surface modes. We study the possibility that the generated MHD modes,
which carry FAC, bounce in the loop-shaped QP structure, provided that
they undergo multiple reflection at the prominence feet. This is an
interesting physical situation leading to intensification of FAC and
promising to be another source of QP destabilisation.
Title: UVCS Observations of Velocity Shear at Streamer Boundaries
in the Corona
Authors: Habbal, Shadia Rifai; Woo, Richard; Vial, Jean-Claude
Bibcode: 2001SSRv...97....5H
Altcode:
Measurements of the intensities of the Ovi 1032 and 1037 Å spectral
lines in the southern solar hemisphere, from 1.5 to 5 R_s, were made
with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) in May
2000 close to solar maximum. The ratio of the intensity of the two
oxygen lines is used as a proxy for solar wind velocity in the inner
corona. White light images of the corona taken with the SOHO/LASCO-C2
during the same time period, and used to place the UVCS observations
in the context of coronal structures, show streamers extending to
high latitudes. The measured radial and azimuthal gradients of the
intensity ratio reflect strong velocity shears in the corona with the
slowest wind coinciding with the axis of streamers. Comparison of these
results with ratios measured with UVCS during solar minimum indicates
that the transition from fast to slow wind in the inner corona occurs
within 20° of the axis of streamers at both phases of the solar cycle.
Title: Quelques réflexions sur les travaux en cours de la Commission
"Système Solaire et Univers lointain" du Comité National
Authors: Vial, J. -C.
Bibcode: 2001sf2a.conf....7V
Altcode:
No abstract at ADS
Title: UVCS Observations of Velocity Shear at Streamer Boundaries
in the Corona
Authors: Habbal, Shadia Rifai; Woo, Richard; Vial, Jean-Claude
Bibcode: 2001SSRv...97....8H
Altcode:
Measurements of the intensities of the O vi 1032and 1037 Å spectral
lines in the southern solar hemisphere, from 1.5 to 5 R s,
were made with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) in
May 2000 close to solar maximum. The ratio of the intensity of the two
oxygen lines is used as a proxy for solar wind velocity in the inner
corona. White light images of the corona taken with the SOHO/LASCO-C2
during the same time period, and used to place the UVCS observations
in the context of coronal structures, show streamers extending to
high latitudes. The measured radial and azimuthal gradients of the
intensity ratio reflect strong velocity shears in the corona with the
slowest wind coinciding with the axis of streamers. Comparison of these
results with ratios measured with UVCS during solar minimum indicates
that the transition from fast to slow wind in the inner corona occurs
within 20° of the axis of streamers at both phases of the solar cycle.
Title: SOHO/SUMER observations and analysis of the hydrogen Lyman
spectrum in solar prominences
Authors: Heinzel, P.; Schmieder, B.; Vial, J. -C.; Kotrč, P.
Bibcode: 2001A&A...370..281H
Altcode:
The complete hydrogen Lyman spectrum in several prominences has been
observed with the UV spectrometer SUMER on-board the SOHO, during
the Joint Observing Programme 107, together with other space and
ground-based observatories. Based on these observations, we are able to
demonstrate, for the first time, that there exists a large variety of
intensities and shapes of Lyman lines in different prominences and in
various parts thereof. Therefore, no ``canonical'' Lyman spectrum can
be considered for modelling purposes. However, we have identified at
least two representative properties of the observed spectra: in one case
(May 28, 1999 prominence) we detected high integrated intensities and
no reversals in lines higher than Lalpha . Another prominence (June 2,
1999) exhibited quite similar integrated intensities, but all lines have
rather strongly reversed profiles. This behaviour cannot be explained in
terms of standard isothermal-isobaric models and we thus consider more
general models which are in pressure equilibrium with the magnetic field
and which have significant prominence-corona transition region (PCTR)
temperature gradients. This type of model, recently suggested by Anzer
& Heinzel (\cite{anhe99}), is capable of explaining strong emission
profiles without reversal. Based on extended non-LTE computations,
we suggest that quite different Lyman spectra mentioned above may
correspond to two types of PCTRs, one seen along the magnetic-field
lines (unreversed profiles) and the other one seen across the field
lines (reversed profiles). Finally, we again confirm the importance
of partial-redistribution (PRD) scattering processes for Lyman lines
in prominences. However, our analysis of new SUMER data also points
to a critical role of the PCTR in radiative transport in these lines.
Title: Dynamics of a Quiescent Solar Prominence Observed with the
SUMER/SOHO Instrument
Authors: Bocchialini, K.; Costa, A.; Domenech, G.; Rovira, M.; Vial,
J. C.; Wingfield, K.
Bibcode: 2001SoPh..199..133B
Altcode:
We present the results obtained from analyzing SUMER/SOHO observational
data of a quiescent solar prominence. The studied prominence is made of
complex structures. From the 1-hr data set, we derive characteristic
frequencies in terms of intensity and velocity oscillations, as
measured in 4 transition-region lines. The presence of different types
of frequencies is detected: chromospheric oscillations and intermediate
periods (6 min to 12 min). This result suggests that these oscillations
are transmitted by the magnetic fields from the chromosphere to the
transition region.
Title: SUMER/SOHO Observations of Long Period Oscillations in an
Active Region Filament
Authors: Régnier, S.; Solomon, J.; Vial, J. C.
Bibcode: 2001IAUS..203..307R
Altcode:
During the MEDOC campaign #4 (October 1999), we observed an active
region filament with the SUMER/SoHO spectrometer. After a global
description of the active region NOAA 8725 with several instruments
on board SoHO, we present a Fourier analysis of SUMER long time
observations. This analysis allows to detect oscillations in several
ranges of periodicities : 6-20 min, 30-40 min, and 55-150 min. We
discuss these periodicities in terms of Alfvén and magnetoacoustic
waves obtained in filament models developped by different authors. New
MEDOC campaign (May 2000) coordinated with THEMIS (Tenerife) observatory
should allow to examine the problem more closely.
Title: Solar Orbiter, a High-Resolution Mission to the Sun and
Inner Heliosphere
Authors: Marsch, E.; Antonucci, E.; Bochsler, P.; Bougeret, J. -L.;
Fleck, B.; Harrison, R.; Marsden, R.; Schwenn, R.; Vial, J. -C.
Bibcode: 2001IAUS..203..565M
Altcode:
The scientific rationale of the Solar Orbiter (SO) is to provide,
at high spatial and temporal resolution, observations of the solar
atmosphere and unexplored inner heliosphere. The most interesting and
novel observations will be made in the almost heliosynchronous segments
of the orbits at heliocentric distances near 45 Rodot and
out-of-ecliptic at the highest heliographic latitudes of 38 degrees. The
SO will achieve its many and varied aims with a suite of small and
innovative instruments through a clever choice of orbits. The first
near-Sun interplanetary measurements together with concurrent remote
observations of the Sun will permit us to determine and understand,
through correlative studies, the characteristics of the solar wind and
energetic particles in close linkage with the plasma and radiation
conditions in their source regions on the Sun. The SO will, during
the high-latitude orbital passes, provide the first observations of
the Sun's polar regions as seen from outside the ecliptic and also
measure the magnetic field at the poles.
Title: Plasma Parameters of a Prominence Observed on October 16/17
1999 by SUMER and CDS/SOHO
Authors: Madjarska, M. S.; Vial, J. -C.; Boccialini, K.; Dermendijiev,
V. N.
Bibcode: 2001IAUS..203..410M
Altcode:
The aim of our study was to confirm and enrich the results obtained
so far on dynamics and diagnostics of solar prominences. A prominence
observed on October 16/17, 1999 during MEDOC campaign # 4 in the frame
of the updated joint observing programme 09 was studied. The main
prominence plasma parameters like temperature and density were derived
as well as their changes during 8 hours of observations. The relative
line-of-sight velocities were obtained in the cool plasma material
(SUMER, Si IV, 8 104 K) and prominence-corona transition
region (SUMER, O IV, 2 105 K). Velocity and line width maps
in both CDS He I 584 Å and O V 629.73 Å were derived. A study of the
blend of O IV 1404.81 Å by Si IV 1404.77 Å and the second order line
O III 702.31 Å was made.
Title: DEM Study of Selected Quiet Sun Regions
Authors: Gontikakis, C.; Landi, E.; Dara, H. C.; Alissandrakis, C. E.;
Vial, J. -C.
Bibcode: 2001IAUS..203..390G
Altcode:
In the present work EUV spectra of quiet Sun regions, observed with
the Coronal Diagnostic Spectometer (CDS), are analysed in order to
determine the Differential Emission Measure (DEM) of selected areas
of the field of view. In particular, we study the differences between
the DEM curves of the quiet Sun cell center areas, network areas and
cell-network boundaries. The results are discussed in the light of
theoretical models for the solar upper atmospheres.
Title: Oscillations Observed in Intensity and Velocity for a
Quienscent Prominence
Authors: Bocchialini, K.; Costa, A.; Domenech, G.; Rovira, M.; Vial,
J. -C.
Bibcode: 2001IAUS..203..419B
Altcode:
We present the results obtained from analyzing SUMER/SOHO observation
data of a solar prominence. The studied prominence can be characterized
as having a complex structure. From the 1 hour data set, we derived
characteristic frequencies in terms of intensity and velocity
oscillations, for 4 transition region lines. The homogenity in the
characteristic frequencies suggests the engagemente of coronal
oscillations with the chromospheric structure. The presence of
different types of frequencies is detected: chromospheric oscillations,
intermediate periods (6min to 12min) and also long periods (25min to
51min). This result suggests that these oscillations are transmitted
by the magnetic fields.
Title: Microscale Structures on the Quiet Sun and Coronal Heating
Authors: Aletti, V.; Velli, M.; Bocchialini, K.; Einaudi, G.;
Georgoulis, M.; Vial, J. -C.
Bibcode: 2000ApJ...544..550A
Altcode:
We present some results concerning transient brightenings on the quiet
Sun, based on data from the Extreme-Ultraviolet Imaging Telescope on
board the Solar and Heliospheric Observatory. Histograms of intensity
are found to be well fitted by χ2 distributions for
small values of the intensity, while at high intensities power-law
distributions are always observed. Also, the emission presents the
same statistical properties when the resolution is downgraded by local
averaging; i.e., it appears to be self-similar down to the resolution
scale of the instruments. These properties are characteristic of
the emission from a forced turbulent system whose dissipation scale
is much smaller than the pixel dimension. On the basis of the data
presented as well as other published results and our present theoretical
understanding of MHD turbulence, we discuss the realism of the nanoflare
scenario of coronal heating.
Title: Outflow velocity of interplume regions at the base of Polar
Coronal Holes
Authors: Patsourakos, S.; Vial, J. -C.
Bibcode: 2000A&A...359L...1P
Altcode:
We report on SUMER/SOHO observations at 1.05 Rsun of a well
identified interplume region in a South Pole Coronal Hole. Combination
of Doppler shifts and Doppler dimming measurements allowed to
determine, for the first time, the total wind outflow velocity (~ 67 km
s-1) at this height. Our calculations of the outflow velocity
benefit from co-spatial and almost co-temporal observations. This large
outflow velocity is a strong argument in favour of the interplumes
being the main source of the fast solar wind. We find that the mass
flux density through the observed interplume is 4.8 10-10
g cm-2s-1 which yields 10-15 g
cm-2s-1 at 1 AU with an expansion factor of 11.
Title: Multi-wavelength study of the slow ``disparition brusque"
of a filament observed with SOHO
Authors: Schmieder, B.; Delannée, C.; Yong, Deng Yuan; Vial, J. C.;
Madjarska, M.
Bibcode: 2000A&A...358..728S
Altcode:
A mid-latitude filament was observed before and after its eruption with
SOHO (EIT, SUMER, CDS and LASCO) and with ground based observatories
(Meudon and Pic du Midi) in the context of a coordinated MEDOC
campaign in Orsay. The eruption was followed by a large Coronal
Mass Ejection well observed by LASCO. Few hours before its eruption,
the filament is partially heated (as seen in 195 Ä with EIT). The
physical conditions of the filament before its eruption have been
investigated by spectroscopic analysis of SUMER (the Lyman series L4 to
L9) and of CDS combined with the Multi-channel Subtractive Double Pass
Spectrograph (MSDP) spectra of Hα . Five hours before the eruption,
large broadenings of chromospheric and transition region lines (CDS)
were observed in the main body of the filament suggesting strong
turbulence as well as opposite Dopplershifts on each side of the
filament (Hα and He I) which could be interpreted as twist motions. The
optical thickness of the filament is rather large. During the eruption
the twist is largely developed as observed in 304 Ä. The Doppler
shifts of the filament estimated from Lyman lines are in good agreement
with the velocity of the front edge of the CME bright loop. We notice
that both, the filament and the bright loop, are deviated towards the
equator. This implies that they belong to the same global expansion
event constrained to remain in the equatorial streamer. An X-ray bright
point observed close to a filament footpoint could be the signature of
reconnection process linked to the destabilization of the filament. It
is interpreted in the framework of new MHD modeling of lateral filament
footpoints (Aulanier & Démoulin 1998).
Title: Solar Orbiter --- A High Resolution Mission to the Sun and
Inner Heliosphere
Authors: Fleck, B.; Marsch, E.; Schwenn, R.; Antonucci, E.; Bochsler,
P.; Bougeret, J. -L.; Harrison, R. A.; Marsden, R.; Vial, J. -C.
Bibcode: 2000SPD....31.0296F
Altcode: 2000BAAS...32..828F
The scientific rationale of the Solar Orbiter (SO) is to provide,
at high spatial and temporal resolution, observations of the solar
atmosphere and unexplored inner heliosphere. The most interesting and
novel observations will be made in the almost heliosynchronous segments
of the orbits at heliocentric distances near 45 Rsun and
out-of-ecliptic at heliographic latitudes of up to 38o. By
going to 45 Rsun the SO will allow remote sensing of the
solar atmosphere with unprecedented spatial resolution, and the almost
heliosynchronous orbit segments will permit us to disentangle spatial
and temporal variations in the solar wind in close linkage with the
plasma and radiation conditions in the source regions of the Sun. The
strawman payload encompasses two instrument packages: Heliospheric
Instruments --- high-res visible light telescope and magnetograph
(<40 km), high-res X-ray/EUV imager (<30 km), high-res EUV
spectrometer (<100 km), EUV and visible-light coronagraphs, solar
neutron and γ -ray detectors, radiometers. Heliospheric Instruments
--- solar wind analyzer, magnetometer, energetic particle detectors, IP
dust detector, plasma wave analyser, radio experiment, neutral particle
detector. Using solar electric propulsion (SEP) in conjunction with
multiple planet swing-by manoeuvres, it will take SO two years to reach
a perihelion of 45 Rsun at an orbital period of 149 days,
with an inclination ranging from 6.7o to 23.4o
w.r.t. the ecliptic. During an extended mission phase of about 2
years the inclination will increase to 31.7o, leading to
a maximum heliographic latitude of 38.3o. The SO was one
of the about 40 responses to the Call for Proposals for the next two
"flexi-missions" (F2 and F3) within ESA's Scientific Programme. At
its meeting on 1 March 2000, ESA's Space Science Advisory Committee
recommended the Solar Orbiter among 5 other proposals for an assessment
study. Launch is expected by the end of the decade.
Title: 3-D Magnetic Configurations for Filaments and Flares: The
Role of ``Magnetic Dips'' and ``Bald Patches''
Authors: Aulanier, G.; Schmieder, B.; van Driel-Gesztelyi, L.; Kucera,
T.; Démoulin, P.; Fang, C.; Mein, N.; Vial, J. -C.; Mein, P.; Tang,
Y. H.; Deforest, C.
Bibcode: 2000AdSpR..26..485A
Altcode:
The 3-D magnetic configuration of a filament and of a low energy
flare is reconstructed, using linear mag- netohydrostatic (lmhs)
extrapolations. In both cases, we find observational signatures
of energy release at the locations of computed ``bald patches''
separatrices, characterised by field lines which are tangent to
the photosphere.The filament was observed on Sept. 25, 1996, in Hα
with the MSDP on the German VTT, Tenerife, as well as in Si IV with
SOHO/SUMER. It is modeled as a twisted flux-tube deformed by the
magnetic polarities observed with SOHO/MDI. The shape and location of
the computed dipped field lines are in good agreement with the shape of
the filament and its feet observed in Hα. Some ``bald patches'' (BPs)
are present where the distribution of dips reaches the photosphere. We
show that some of the large scale field lines rooted in BPs can be
related to bright fine structures in Si IV. We propose that the plasma
there is heated by ohmic dissipation from the currents expected to be
present along the BP separatrices.The flare was observed on May 18,
1994, in soft X-rays with Yohkoh/SXT, and in Hα at Mitaka (Japan). The
magnetic field is directly extrapolated from a photospheric magnetogram
from Kitt Peak Observatory. The intersections with the photosphere of
the computed separatrices match well the bright Hα ribbons. The later
are associated to three BPs, with overlaying dipped field lines. We
show that enhanced densities are present in these dips, which can be
correlated with dark Hα fibrils.Both cases show the importance of
dipped field lines and BPs in the solar atmosphere. Energy release
via ohmic dissipation as well as reconnection along BP separatrices
is proposed to provide heating observed as UV brightenings in filament
channels and even as small flares
Title: Transport and Energy Conversion in the Heliosphere
Authors: Rozelot, J. P.; Klein, L.; Vial, J. -C.
Bibcode: 2000LNP...553.....R
Altcode: 2000tech.conf.....R
No abstract at ADS
Title: Solar Prominences Observed by Soho (SUMER, CDS, EIT) and
Ground-Based Observatories (GBO)
Authors: Heinzel, P.; Schmieder, B.; Vial, J. C.; Rudawy, P.
Bibcode: 2000AdSpR..25.1777H
Altcode:
We present two sets of prominence observations in higher lines
of the hydrogen Lyman series (from Lδ to L-9), together with
some other UV lines. These data have been obtained by the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) onboard the
SOHO satellite in June 1997. Coordinated observations were also taken
by other SOHO instruments: Coronal Diagnostic Spectrometer (CDS) and
Extreme-Ultraviolet Imaging Telescope(EIT) and with the coronagraph
of the Wroclaw University Observatory at Bialkóv, the spectrograph
of the Ondřejov Observatory. We demonstrate the basic characteristics
of the calibrated line profiles and compare them with the theoretical
profiles computed from isothermal-isobaric models
Title: Future Diamond UV Imagers For Solar Physics
Authors: Hochedez, J. -F.; Verwichte, E.; Bergonzo, P.; Guizard, B.;
Mer, C.; Tromson, D.; Sacchi, M.; Dhez, P.; Hainaut, O.; Lemaire,
P.; Vial, J. -C.
Bibcode: 2000PSSAR.181..141H
Altcode:
No abstract at ADS
Title: Modelling of Helium Spectrum in Solar Prominences
Authors: Labrosse, N.; Gouttebroze, P.; Vial, J. -C.
Bibcode: 1999ESASP.448..503L
Altcode: 1999mfsp.conf..503L; 1999ESPM....9..503L
No abstract at ADS
Title: Observational Signatures of Microscale Heating
Authors: Bocchialini, K.; Aletti, V.; Vial, J. -C.; Lemaire, P.
Bibcode: 1999ESASP.448..539B
Altcode: 1999ESPM....9..539B; 1999mfsp.conf..539B
No abstract at ADS
Title: Magnetic and Dynamic Evolution of an Active Region
Authors: Régnier, S.; Solomon, J.; Vial, J. C.; Amari, T.; Mickey, D.
Bibcode: 1999ESASP.448..519R
Altcode: 1999mfsp.conf..519R; 1999ESPM....9..519R
No abstract at ADS
Title: Is Flaring Activity present in the Chromospheric Network ?
Authors: Cauzzi, G.; Falchi, A.; Falciani, R.; Vial, J. C.
Bibcode: 1999ESASP.448..685C
Altcode: 1999mfsp.conf..685C; 1999ESPM....9..685C
Microflares occurring at coronal levels are one of the mechanisms
proposed for the heating and dynamics of the chromospheric
network. During a SOHO coordinated campaign, we acquired a set
of chromospheric and transition region data, at high temporal and
spatial resolution, that are suitable for such a research. We describe
the characteristics of network points at several heights in the
atmosphere. We look for the presence of signatures typical of flares,
albeit at much smaller scales. Only one, of the 11 network points
analyzed over 1 hr of observations, displays several episodes of red
asymmetry in the H_α wings. These asymmetries can be interpreted
as downward motions induced by the sudden compression of the lower
atmosphere caused by either a particle beam or a conduction front. The
analysis hence suggests that microflaring events in network points
have a low occurrence probability, or that their energy flux is still
below our observational capabilities.
Title: Structure and Dynamics in the Transition Region
Authors: Gontikakis, C. P.; Dara, H. C.; Alissandrakis, C. E.;
Zachariadis, Th. G.; Vial, J. -C.; Bastian, T.; Chiuderi Drago, F.
Bibcode: 1999ESASP.448..297G
Altcode: 1999mfsp.conf..297G; 1999ESPM....9..297G
No abstract at ADS
Title: Preface
Authors: Vial, J. -C.
Bibcode: 1999ESASP.446....1V
Altcode: 1999soho....8....1V
No abstract at ADS
Title: Multi-Instrument Study Of The Evolution Of An Active Region
Authors: Regnier, S.; Amari, T.; Solomon, J.; Vial, J. C.; Mickey, D.
Bibcode: 1999ESASP.446..571R
Altcode: 1999soho....8..571R
We follow, for about half a solar rotation, the dynamic evolution of
an acive region (AR 8151) which exhibited a single heading sunspot
and a more diffuse following magnetic flux and a filament eruption
on 12 February 1998 at 13:51. For longitudinal magnetic observations,
we use the MDI (SoHO) magnetograph and for vector magnetic fields the
IVM (Mees Solar Observatory, Hawaii). The dynamic evolution is derived
from time-sequence images in the Fe XII line (195 Angstrom) from EIT
(SoHO). Density and abundance diagnostic of the filament are obtained
from SoHO spectrometers (CDS, SUMER).
Title: Hydrogen Lyman Lines and Continuum Emission in a Polar-Crown
Prominence Observed with SUMER/SOHO
Authors: Schmieder, B.; Kucera, T.; Heinzel, P.; Vial, J. -C.
Bibcode: 1999ESASP.446..605S
Altcode: 1999soho....8..605S
We present, for the first time, a quasi-simultaneous spectroscopic
observation of the whole Lyman series of HI and continuum in a
quiescent prominence. Namely we have extended our previous study of
higher Lyman lines to lower members of the series, particularly
L-alpha and L-beta. For the latter two lines, we compare our
calibrated profiles (free of geocoronal absorption) with previous
data from OSO-8 LPSP spectrometer and (for L-alpha) from UVSP/SMM. We
demonstrate the importance of Lyman lines for studies of the base of
the prominence-corona transition region.
Title: La mission solaire SOHO: quelques résultats récents
Authors: Vial, J.
Bibcode: 1999CRASB.327.1201V
Altcode:
After more than 3 years of operations, the SOHO solar mission
has brought a large body of new results, the full exploitation of
which continues. SOHO has provided evidence of the role of magnetic
reconnection at many different spatial scales (including scales smaller
than any spatial resolution) in direct heating by the Joule effect, or
in generating MHD waves or accelerating particles. Reconnection seems
to occur very low in the atmosphere with a permanent reshuffling of
magnetic fields resulting from flux emergence at the borders of the
supergranulation network. SOHO has also demonstrated the multifluid
nature of the solar wind in the low corona where ion (and proton)
temperatures are higher than electron temperatures. This ion heating
can be explained by resonance between MHD waves and ion (and proton)
gyration around the field lines. Such conclusions (and others) will
be tested over the next few years with new observations from SOHO.
Title: 8th SOHO Workshop: Plasma Dynamics and Diagnostics in the
Solar Transition Region and Corona
Authors: Vial, J. -C.; Kaldeich-Schü, B.
Bibcode: 1999ESASP.446.....V
Altcode: 1999soho....8.....V
No abstract at ADS
Title: Plasma Diagnostics Of A Solar Prominence Observed On 12 June
1997 by EIT, Sumer And CDS
Authors: Madjarska, M. S.; Vial, J. -C.; Bocchialini, K.; Dermendjiev,
V. N.
Bibcode: 1999ESASP.446..467M
Altcode: 1999soho....8..467M
The plasma diagnostics of a quiescent prominence observed on June 12,
1997 with SUMER, CDS and EIT instruments aboard SOHO in the frame
of Joint Observing Programme 9 has been made. Two sets of SUMER
observations were taken in the four spectral lines Si IV 1393.755,
1402.770 (6-8 104 K) and O IV 1401.156, 1404.812 (1.7-2.0
105 K) at two different slit positions on the prominence
body. The relative line-of-sight velocities using both Si IV 1393.755
and 1402.770 lines are derived. The electron density (derived
from the intensity ratio of O IV 1401.156 to 1404.812 lines) in the
prominence-corona interface is determined for both slit positions. CDS
obtained 10 rasters in Si X 347.40, He I 584.33, Si X 356.04, Fe XVI
360.76, Mg IX 368.06, O V 629.73 lines covering a temperature range
from 104 to 106 K. By analysing the CDS spectra
in He I and O V ions the relative line-of-sight velocity maps with
regards to the quiet sun are derived.
Title: SOHO/SUMER observations and analysis of hydrogen Lyman lines
in a quiescent prominence
Authors: Schmieder, B.; Heinzel, P.; Vial, J. C.; Rudawy, P.
Bibcode: 1999SoPh..189..109S
Altcode:
A quiescent prominence was observed in June 1997 by instruments
onboard the SOHO spacecraft: the Solar Ultraviolet Measurements of
Emitted Radiation (SUMER), Coronal Diagnostic Spectrometer (CDS)
and Extreme-Ultraviolet Imaging Telescope (EIT), along with the
coronagraph of the Wrocław University Observatory at Bialków and
the spectrograph of the Ondřejov Observatory. We present prominence
observations in higher lines of the hydrogen Lyman series (from Lδ
to L-9), together with some other UV lines obtained by SUMER. We
extract the basic characteristics of the calibrated line profiles
of these Lyman lines and compare them with the theoretical profiles
computed from three kinds of NLTE models which also include prominence
filamentation. Our principal result is that the current NLTE models are
in principle capable of explaining the SUMER calibrated intensities
in the observed Lyman lines. We also find that in order to fit all
these lines, one has to consider a prominence-corona transition region
(PCTR) with a temperature gradient. At low pressures, higher Lyman
lines are still rather sensitive to the incident radiation which must
be carefully taken into account in the modeling. From PCTR models,
which also take into account the effect of ambipolar diffusion on the
heating, we have derived the formation depths for the Lyman series
lines. High Lyman lines seem to be formed just at the base of the PCTR.
Title: Plasma dynamics and diagnostics in the solar transition region
and corona. Proceedings.
Authors: Vial, J. -C.; Kaldeich-Schürmann, B.
Bibcode: 1999pdds.book.....V
Altcode:
No abstract at ADS
Title: The Coarse Versus The Fine Structure Of The Quiet-Sun
Chromospheric And Transition Region Network
Authors: Patsourakos, Spyridwn; Vial, J. -C.; Gabriel, A. -H.;
Bellamine, N.
Bibcode: 1999ESASP.446..537P
Altcode: 1999soho....8..537P
The chromospheric and transition region network is believed to be
the basic channel of energy and momentum that heats the corona and
accelerates the solar wind. While at spatial scales of one supergranular
cell the network appears to be more or less homogeneous, at smaller
scales it possesses a finer structure. We present here observations
made with the CDS and SUMER spectrometers on SOHO pursuing the
investigation of the coarse and the fine structure of the quiet-Sun
network. A two-dimensional autocorrelation method allowed us to
deduce the temperature-variation of network's width, while well-chosen
density-sensitive line-ratios permitted to determine its filling factor
at different temperatures. A discussion on possible implications of our
results for steady-state energy and momentum balance for the quiet-Sun
is included.
Title: Multiwavelength Analysis of Network Bright Points - Coordinated
Observations SOHO-GBO JOP No 37
Authors: Falchi, A.; Cauzzi, G.; Falciani, R.; Vial, J. -C.
Bibcode: 1999ASPC..184..261F
Altcode:
We analyze the temporal behaviour of Network Bright Points (NBPs)
using a set of data acquired during coordinated observations between
ground based observatories (mainly at the NSO/Sacramento Peak) and the
SUMER and MDI instruments onboard SOHO. We find that, at any time,
all NBPs present in the NaD_2 images are co-spatial within 1" with
locations of enhanced magnetic field density, and that not all the
NBPs identified in the low chromosphere can be identified at higher
levels. We calculate the intensity power spectrum for each NBP in
several low-chromospheric signatures, such as the red wing of Hα,
NaD_2 and Hα line center. The power spectra show no power at the 5.5
mHz frequency, while they display an enhancement at frequencies below
2 mHz, corresponding to periods between 8 and 20 minutes.
Title: Transition-Region Network Boundaries in the Quiet Sun: Width
Variation with Temperature as Observed with CDS on SOHO
Authors: Patsourakos, S.; Vial, J. -C.; Gabriel, A. H.; Bellamine, N.
Bibcode: 1999ApJ...522..540P
Altcode:
We report here the results of a study of the temperature variation
of the network boundary thicknesses in the quiet-Sun transition
region. A Fourier-based two-dimensional autocorrelation method has
been applied to 240''×240'' rasters obtained in
several transition-region lines by the CDS spectrometer on SOHO. The
quantitative variation of the network boundary width with temperature
has been obtained for the first time in a full two-dimensional field. It
appears that network boundaries have an almost constant width up to
a temperature of about 105.4 K and then fan out rapidly at
coronal temperatures. This expansion of the transition-region network
boundaries with temperature is found to be quantitatively in agreement
with earlier theoretical models of the transition region.
Title: The Role of "Magnetic Dips" and "Bald Patches" for a Filament
Observed by SOHO and GBO
Authors: Aulanier, G.; Schmieder, B.; Kucera, T.; van Driel-Gesztelyi,
L.; Démoulin, P.; Mein, N.; Vial, J. -C.; Mein, P.
Bibcode: 1999ASPC..184..291A
Altcode:
The studied filament was observed on Sept. 25, 1996, in Hα with
the MSDP on the German VTT, Tenerife, as well as in Si IV with
SOHO/SUMER. The 3-D magnetic configuration of the filament channel is
reconstructed, using linear magnetohydrostatic (lmhs) extrapolations
from a SOHO/MDI magnetogram, which is modified by a background magnetic
component constraining a twisted flux-tube. This flux-tube is deformed
by the magnetic polarities observed with SOHO/MDI. The shape and
location of the computed "dipped field lines" are in good agreement
with the shape of the filament and its feet observed in Hα. Some "bald
patches" (BPs) are present where the distribution of dips reaches the
photosphere. We find observational signatures in Si IV brightenings of
energy release at the locations of computed "bald patch separatrices",
defined by field lines which are tangent to the photosphere. We propose
that the plasma is there heated by ohmic dissipation from the expected
currents in the BP separatrices. The results show the importance of
"dipped field lines" and "bald patches" in filament channels.
Title: Coordinated Prominence Observations by SOHO and Ground-Based
Observatories
Authors: Schmieder, B.; Heinzel, P.; Vial, J. -C.; Malherbe, J. M.;
Mein, P.; Rudawy, P.; Ceppatelli, G.
Bibcode: 1999ASPC..184..296S
Altcode:
Coordinated observations obtained during the JOP12 (Joint Observing
Programme between SOHO and ground-based instruments) allow us to
analyse the physical conditions in a prominence of 5 June 1997 and
its environment in the solar corona. The arch-shaped prominence shows
either vertical or horizontal structures according to the observed
lines (Hα with the coronagraph of the Wroclaw University Observatory
at Bialków and lines in a broad temperature range by the Coronal
Diagnostic Spectrometer CDS). The less dynamic behaviour of this
prominence was shown by the persistence of bubbles in the prominence
and confirmed by the Dopplershifts measured in CDS lines and in Hα
by the Italian Panoramic Monochromator (IPM) filter on the THEMIS
telescope in Tenerife. We explain the complex morphology of this
prominence by recent 3D MHD models. Finally, we present prominence
spectra in higher lines of the hydrogen Lyman series (from Lδ to L-9),
together with some other UV lines. These data have been obtained by
the Solar Ultraviolet Measurements of Emitted Radiation (SUMER). We
demonstrate the basic characteristics of the calibrated line profiles
of Lyman lines and compare them with the theoretical profiles computed
from isothermal-isobaric models. This leads to some constraints on
the environment of the prominence.
Title: Coordinated observations between SOHO/SUMER and ground during
the 1998 total eclipse: Non-thermal line broadenings and electron
densities in a polar coronal hole
Authors: Patsourakos, S.; Vial, J. -C.; Gabryl, J. -R.; Koutchmy,
S.; Schühle, U.
Bibcode: 1999AIPC..471..285P
Altcode: 1999sowi.conf..285P
Alfvén waves represent one of the most prominent ways of heating the
solar corona and accelerating the solar wind. One of their signatures
is to broaden the spectral lines in excess of their thermal width. Here
we aim to combine observations of non-thermal broadenings measured
by SUMER in OVI (1037.6 Å) line and electronic densities derived
from white-light observations during the 1998 total eclipse. After
checking the validity of the frequently-used assumption of equal ion
and electron temperatures, we compute the variation of the non-thermal
velocity as a function of height in an interplume region within the
south polar coronal hole.
Title: Filament channel structures in a SI IV line related to a 3d
magnetic model
Authors: Kucera, T. A.; Aulanier, G.; Schmieder, B.; Mein, N.; Vial,
J. -C.
Bibcode: 1999SoPh..186..259K
Altcode:
A recent 3D magnetic model of filament support (Aulanier and Démoulin,
1998) has shown that specific morphologies derived from the model, based
on SOHO/MDI magnetograms, match quite well with the observations of a
filament observed in Hα and Ca ii lines with the German telescope VTT
in Tenerife on 25 September 1996 (Aulanier et al., 1998, 1999a). Some
predictions of this model concern the filament channel. To continue the
comparison of model and data, we have investigated the same filament
region observed in ultraviolet by the SOHO spectrometers SUMER and
CDS. The elongated EUV fine structures in the filament channel observed
in the Si iv 1393.76 Å line by SUMER have similar orientations
and locations to features predicted by the model of Aulanier et
al. (1999a). These regions are near the bases of field lines which
tangentially join to the photosphere in so called 'bald patches' and
are parts of large arcades above the filament channel. In addition,
we consider the Si iv Doppler shifts in these structures and compare
them to what might be expected from the model field structure. Our
study also suggests that the filament has a very low opacity in Si iv,
lower than that of the O v line observed by CDS.
Title: Multiresolution wavelet analysis of SUMER/SOHO observations
in a solar prominence
Authors: Blanco, S.; Bocchialini, K.; Costa, A.; Domenech, G.; Rovira,
M.; Vial, J. -C.
Bibcode: 1999SoPh..186..281B
Altcode:
We have studied through a multiresolution wavelet analysis the
oscillations in a limb prominence. Intensity fluctuations in time and
height corresponding to different lines of Si iv and O iv observed
with SUMER on board SOHO have been analyzed in the wavelet bands of
J3= 1 min 36 s to 3 min 12 s and J4=3 min 12
s to 6 min 24 s. For all species, oscillations in the J4
band were dominant. We found relevant differences between the behavior
of line D1 (1393.76 Å) corresponding to Si iv and the set
D2 (1401.16 Å), D3 (1404.81 Å), D4
(1402.77 Å) corresponding to O iv, O iv and Si iv respectively. We
also report the identification of a pulse in the intensity of the line
D1 that appears in the range of 15-20 min. This disturbance
seems to travel with a speed of about 170 km s−1.
Title: Solar Wind Outflow and the Chromospheric Magnetic Network
Authors: Hassler, Donald M.; Dammasch, Ingolf E.; Lemaire, Philippe;
Brekke, Pal; Curdt, Werner; Mason, Helen E.; Vial, Jean-Claude;
Wilhelm, Klaus
Bibcode: 1999Sci...283..810H
Altcode:
No abstract at ADS
Title: Oscillations of the upper chromosphere
Authors: Gouttebroze, P.; Vial, J. -C.; Bocchialini, K.; Lemaire,
P.; Leibacher, J. W.
Bibcode: 1999SoPh..184..253G
Altcode:
Variations of intensity and wavelength in several UV lines have been
observed with the SUMER spectroheliometer onboard SOHO, and they have
been analysed to obtain oscillation spectra and phase differences
between lines of different ions. Lines intensities of neutral or
singly ionized atoms (with temperature of formation ≤ 30 000 K)
exhibit an increase of oscillatory power between 2.5 and 7 mHz, which
may be considered as the signature of p modes. Lines of highly ionized
elements (with a temperature of formation ≥ 50 000 K) yield power
spectra which are continuously decreasing with frequency. Brightness
variations of the continuum at different wavelengths between 1000
and 1400 Å present oscillations in the same frequency range. Thus,
p modes seem to be efficiently stopped by the transition region. No
clear evidence is found for the existence of a chromospheric oscillation
mode. Phase comparisons between lines formed at different altitudes
(in particular Si i and Si ii) indicate that these lines oscillate in
phase, within the precision of the measurements.
Title: Eruptive filament of May 31, 1997, observed by SOHO.
Authors: Schmieder, B.; Heinzel, P.; Vial, J. -C.; Delaboudinière,
J. -P.; Delannée, C.
Bibcode: 1999joso.proc..147S
Altcode:
In the frame of the SUMER/CDS Joint Programme (JOP 17) the authors
have detected the four Lyman lines in an erupting filament. The
strong self-absorption in these lines, already reported for quiescent
filaments, is still present in this highly dynamical event, but the
authors observe a significant red asymmetry in the intensities of the
two peaks. They ascribe it to an upward bulk motion of the filament,
which they can actually see on a series of EIT images taken in the
Fe XII line. Both sets of observations can lead to a determination
of the velocity vector. The Doppler velocities are also derived from
other lines detected by SUMER/CDS and can be correlated with the
observations of the Pic-du-Midi MSDP obtained for this event. The
filament eruption was also well observed by other GBO instruments in
the Hα line (Meudon and Ondřejov).
Title: Outflow Velocities at the Base of a Polar Coronal Hole During
the 1998 Total Eclipse
Authors: Patsourakos, S.; Vial, J. -C.; Gabryl, J. -R.; Koutchmy,
S.; Schühle, U.
Bibcode: 1999SSRv...87..291P
Altcode:
Polar coronal holes represent the most convincing site from which the
high-speed solar wind originates. Here we report high-accuracy Doppler
shifts measured in the O VI (1037.6 Å) line obtained by SUMER on SOHO
inside an interplume region within the south polar coronal hole. We
infer limits on the outflow velocity and draw hints about the flow
geometry.
Title: Solar chromospheric structures observed in UV ressonance
lines : a multivariate analysis approach
Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C.
Bibcode: 1999CR2...322..337P
Altcode:
We present the results of a statistical analysis carried out from a data
base of 6 solar chromospheric emission lines recorded simultaneously
and with high spectral resolution. An empirical and a clustering method
for separating the different solar structures contributions have been
used and been found in a good agreement. Mean profiles corresponding to
the different populations have been built. Correlations of different
parameters for each profile allowed us to deduce different properties
of the solar chromosphere, such as the existence of magnetic canopies
and downflows in active regions.
Title: Study of solar prominences with data obtained with the SUMER
instrument on B oard SOHO satellite.
Authors: Rovira, M. G.; Costa, A.; Blanco, S.; Domenech, G.; Vial,
J. C.
Bibcode: 1998larm.confE..13R
Altcode:
The oscillations in a limb prominence have been studied through a
multiresolution wavelet analysis. We found relevant differences between
the behavior of Si IV and O IV lines. We also report the identification
of a pulse in a range between 15-20 min. This disturbance seems to
travel with a speed of about 170 km/s.
Title: Filament Observations with SOHO Sumer/cds: The Behaviour of
Hydrogen Lyman Lines
Authors: Schmieder, B.; Heinzel, P.; Kucera, T.; Vial, J. -C.
Bibcode: 1998SoPh..181..309S
Altcode:
On 21 September 1996, a filament close to an area of enhanced network
was observed with the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) spectrometer and Coronal Diagnostic Spectrometer
(CDS). CDS provided intensity, Doppler shift and linewidth maps of the
region in six lines whose temperature range covers 104 to
106 K. SUMER observations consisted of maps of the region
in four hydrogen Lyman lines (Lδ, L∈, L-6, L-7) and a Svi line
(944 Å). In all the Lyman lines we detect a central absorption
and an asymmetry in the intensity of the two peaks. First NLTE
computations indicate that such reversed Lyman profiles and their
absolute intensities can be reproduced with the existing filament models
provided that we take into account a prominence-corona transition region
(PCTR). We discuss the Lyman lines' asymmetry in terms of macroscopic
flows by comparison with the Hei line Doppler shifts observed with CDS.
Title: Solar chromospheric structures observed in UV resonance lines:
a multivariate analysis approach.
Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C.
Bibcode: 1998CRASB.326..337P
Altcode:
The authors present the results of a statistical analysis carried out
from a data base of six solar chromospheric emission lines recorded
simultaneously and with high spectral resolution. An empirical and
a clustering method for separating the different solar structure
contributions have been used and found to be in good agreement. Mean
profiles corresponding to the different populations have been
built. Correlations of different parameters for each profile allowed
one to deduce different properties of the solar chromosphere, such as
the existence of magnetic canopies and downflows in active regions.
Title: Statistical analysis of solar bright points observed with
the SOHO spacecraft.
Authors: Régnier, S.; Bocchialini, K.; Vial, J. -C.; Delaboudinière,
J. -P.; Thompson, W.
Bibcode: 1998CRASB.326..211R
Altcode: 1998CR2...326..211R
Bright points, small and short lifetime structures, appear permanently
in the atmosphere and could be associated with magnetic reconnections,
potential sources of coronal heating. Such structures have been
observed with the coronal instruments on-board SOHO and a statistical
analysis was carried out in order to find the signature of very small
scale structures.
Title: Cor-I: a coronal white-light imager for a solar probe
Authors: Vial, J. -C.; Koutchmy, S.; Habbal, S. R.
Bibcode: 1998AdSpR..21..291V
Altcode:
Solar and heliospheric observations acquired over several decades,
have shown that the corona is a highly structured medium. There is
no doubt that these structures reflect the response of the coronal
plasma - confined by the highly inhomogeneous magnetic field - to
different forms of energy input. While in-situ plasma measurements
have provided the characteristic properties of both fast and slow
solar winds, they have fallen short in connecting them to the source
regions of the wind. A near-Sun flyby mission offers an unprecedented
opportunity to explore the solar wind at distances much closer to
the Sun than ever achieved before. However, it is essential that
in-situ measurements be coordinated with simultaneous imaging of
the structures encountered in the corona. We present the concept and
design of a white-light imager called Cor-I, as a key instrument for a
near-Sun flyby mission which makes it possible to distinguish spatial
structures from temporal changes in the plasma parameters. With the
inference of the electron density from the Thomson scattered emission,
white-light measurements are also a very powerful tool for quantitative
studies of the acceleration region of the solar wind. In addition, the
proposed instrument carries the potential for discovery of transient
events and waves in these parts of the acceleration region of fast and
slow solar winds that are inaccessible to in-situ plasma instruments.
Title: SUMER/SOHO Filament Observations in Selected Lyman Lines
Authors: Schmieder, B.; Kucera, T.; Heinzel, P.; Vial, J. -C.
Bibcode: 1998ASPC..150..205S
Altcode: 1998IAUCo.167..205S; 1998npsp.conf..205S
No abstract at ADS
Title: EUV and Microwave Observations of a Filament
Authors: Chiuderi-Drago, F.; Bocchialini, K.; Lamartinie, S.;
Vial, J. -C.; Bastian, T.; Alissandrakis, C. E.; Harrison, R.;
Delaboudiniere, J. -P.; Lemaire, P.
Bibcode: 1998ASPC..150...55C
Altcode: 1998IAUCo.167...55C; 1998npsp.conf...55C
No abstract at ADS
Title: Solar Probe: The RAMSES Proposal
Authors: Le Quéau, D.; Roux, A.; Vial, J. -C.
Bibcode: 1998ESASP.417...75L
Altcode: 1998cesh.conf...75L
No abstract at ADS
Title: Quiescent filament diagnostic.
Authors: Lamartinie, S.; Bocchialini, K.; Vial, J. -C.; Chiuderi-Drago,
F.; Harrison, R.; Alissandrakis, C. E.
Bibcode: 1998joso.proc..139L
Altcode:
UV observations of a quiescent filament were performed on July 28,
1996 by SUMER and CDS, two spectrometers onboard SOHO.
Title: Solar Prominence Diagnostics (Review)
Authors: Vial, J. -C.
Bibcode: 1998ASPC..150..175V
Altcode: 1998IAUCo.167..175V; 1998npsp.conf..175V
No abstract at ADS
Title: Height variations of prominence plasma parameters
Authors: Kotrč , P.; Heinzel, P.; Vial, J. -C.; Rompolt, B.
Bibcode: 1998PAICz..88..208K
Altcode:
No abstract at ADS
Title: 3-D Modelling of a Filament Observed in Hα and with SOHO
Authors: Aulanier, G.; Schmieder, B.; Démoulin, P.; Mein, N.; van
Driel-Gesztelyi, L.; Mein, P.; Vial, J. C.; Deforest, C.
Bibcode: 1998ESASP.417..217A
Altcode: 1998cesh.conf..217A
No abstract at ADS
Title: Coronal jet turbulent activity to explain distorted emission
line
Authors: Loucif, M. L.; Ben Jaffel, L.; Koutchmy, S.; Vial, J. -C.
Bibcode: 1998ESASP.421..303L
Altcode: 1998sjcp.conf..303L
No abstract at ADS
Title: Polar jets and plasmoids:Results from JOP 57
Authors: Delannee, C.; Koutchmy, S.; Delaboudiniere, J. -P.; Hochedez,
J. -F.; Vial, J. -C.; Dara, H.; Georgakilas, A.
Bibcode: 1998ESASP.421..129D
Altcode: 1998sjcp.conf..129D
No abstract at ADS
Title: Transient Events and Their Solar Magnetic Field
Authors: Vial, J. -C.
Bibcode: 1998HiA....11..877V
Altcode:
No abstract at ADS
Title: Space solar physics : theoretical and observational issues
in the context of the SOHO mission
Authors: Vial, Jean Claude; Bocchialini, Karine; Boumier, Patrick
Bibcode: 1998LNP...507.....V
Altcode: 1998sspt.conf.....V
No abstract at ADS
Title: Filament observations with SOHO SUMER/CDS.
Authors: Schmieder, B.; Kučera, T.; Heinzel, P.; Vial, J. -C.
Bibcode: 1998joso.proc..136S
Altcode:
During a coordinated campaign between SOHO and ground-based instruments
a filament located close to the central meridian has been the target
of SUMER and CDS spectrometers on September 21, 1996.
Title: On a Possible Mechanism of Quiescent Prominence Destabilization
Authors: Nenovski, P.; Dermendjiev, V. N.; Madjarska, M. S.; Vial,
J. -C.
Bibcode: 1998ASPC..150..354N
Altcode: 1998IAUCo.167..354N; 1998npsp.conf..354N
No abstract at ADS
Title: Emission of hydrogen lines by moving solar prominences.
Authors: Gontikakis, C.; Vial, J. -C.; Gouttebroze, P.
Bibcode: 1997A&A...325..803G
Altcode:
We study the radiative transfer processes occurring in a plane-parallel
slab standing vertically above the chromosphere and moving upward
as a solid body. This structure simulates a prominence in the phase
of eruption or a quiescent prominence where the plasma presents bulk
velocities. We use partial redistribution for the description of the
resonance scattering in the hydrogen Lα and Lβ lines. We compute
the Lα, Lβ and Hα emergent line profiles of hydrogen for different
velocities. We derive the variation of the emitted intensities as a
function of the velocity for various temperatures and thicknesses. We
discuss our results in view of the diagnostic of erupting prominences
in Lyman lines that SOHO observations can provide.
Title: Spectral diagnostics for eruptive prominences
Authors: Gontikakis, C.; Vial, J. -C.; Gouttebroze, P.
Bibcode: 1997SoPh..172..189G
Altcode: 1997ESPM....8..189G
The diagnostic of eruptive prominences needs the development of
new tools. Here we propose the Lyman and Balmer lines of hydrogen,
which are important in the radiative budget. In the NLTE radiative
transfer calculations, we include the effect of the outward motion
of the structure associated with the eruption of the prominence. The
treatment of the resonance scattering of Lα and Lβ with partial
redistribution gives higher intensities, and a higher ionization than
the complete redistribution, but the two approaches converge to the same
solution as the velocity increases. As a first step in the diagnostic,
we present new results concerning the variation of the integrated
intensities of hydrogen lines with respect to the radial velocity.
Title: Formation of CA II Lines in Solar Prominences
Authors: Gouttebroze, P.; Vial, J. -C.; Heinzel, P.
Bibcode: 1997SoPh..172..125G
Altcode: 1997ESPM....8..125G
We compute the profiles of the resonance lines and infrared
triplet of ionized calcium emitted by some representative models of
prominences. These models consist of plane-parallel slabs of different
temperatures, pressures and thicknesses, standing vertically above
the solar surface. These slabs are assumed to be observed at the limb,
and to be perpendicular to the line of sight. They are irradiated by
the Sun on both sides, and the incoming intensities, at every relevant
wavelength, are taken from observations. The model atom includes 3
stages of ionization (Cai, Caii and Caiii) with 5 discrete levels for
Caii. We study the relations between emitted intensities and physical
properties of the slabs, and compare the intensities emitted in Caii and
hydrogen lines for the same set of models. As a result of ionization,
the intensity decreases more rapidly with temperature in Caii lines than
in Hi lines, so that the ratio of Caii to Hi line intensities may be
used as a temperature indicator. The intensity ratio between resonance
and infrared lines of Caii depends principally on the optical thickness
of the structure. At high pressure and low temperature, the ratio
Caii 8542Å/Hβ is found to increase with pressure. This behaviour,
which is due to the saturation of Hβ, is opposite to that found by
Heasley and Milkey (1978) for low pressures (optically thin structures).
Title: Polar Jets and Plasmoids: Preliminary Results from JOP 57
Authors: Delannée, C.; Koutchmy, S.; Delaboudiniè, J. -P.; Hochedez,
J. -F.; Vial, J. -C.; Dara, H.; Georgakilas, A.
Bibcode: 1997ESASP.404..327D
Altcode: 1997cswn.conf..327D
No abstract at ADS
Title: Dynamics of Minor Solar Activity \newline Coordinated
Observations SOHO-GBO JOP #37
Authors: Cauzzi, G.; Vial, J. C.; Falciani, R.; Falchi, A.; Smaldone,
L. A.
Bibcode: 1997ASPC..118..309C
Altcode: 1997fasp.conf..309C
We present a program for coordinated observations between ground based
observatories, mainly NSO/Sacramento Peak, and several instruments
onboard SOHO (primarily SUMER). The scientific goal is the study of
small activity phenomena, at high spatial and temporal resolution.
Title: NLTE Analysis of SUMER Filament Observations on SOHO
Authors: Heinzel, P.; Schmieder, B.; Vial, J. -C.
Bibcode: 1997ESASP.404..427H
Altcode: 1997cswn.conf..427H
No abstract at ADS
Title: Solar Magnetic Field Events related to CMEs observed with SOHO
(MDI, EIT, SUMER, LASCO)
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Wiik, J. E.; Thompson,
B.; de Forest, C.; Saint Cyr, C.; Vial, J. -C.; Nitta, N.; Simnett, G.
Bibcode: 1997IAUJD..19E..42S
Altcode:
We shall present two CMEs observed by LASCO during the minimum of
activity of the Sun. These are associated with filament disparitions
brusques (DB). CME and DB definitively seem to be consequences of global
magnetic field instability, which causes reconnection of pre-existing
field lines in the corona. We shall demonstrate how cancelling flux
and converging magnetic field in photosphere may destabilize coronal
streamers overlying one or two filament channels.
Title: Statistical Analysis of a Bright Point Observed Simultaneously
in Two Chromospheric and Transition Region Lines by SUMER
Authors: Bocchialini, K.; Vial, J. -C.; Einaudi, G.
Bibcode: 1997ESASP.404..211B
Altcode: 1997cswn.conf..211B
No abstract at ADS
Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
I. Spectra and Spectroradiometry
Authors: Wilhelm, K.; Lemaire, P.; Curdt, W.; Schühle, U.; Marsch, E.;
Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Huber,
M. C. E.; Vial, J. -C.; Kühne, M.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.; Feldman, U.; Hollandt, J.; Brekke, P.
Bibcode: 1997SoPh..170...75W
Altcode:
SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation
instrument on the Solar and Heliospheric Observatory (SOHO) - observed
its first light on January 24, 1996, and subsequently obtained a
detailed spectrum with detector B in the wavelength range from 660
to 1490 Å (in first order) inside and above the limb in the north
polar coronal hole. Using detector A of the instrument, this range
was later extended to 1610 Å. The second-order spectra of detectors
A and B cover 330 to 805 Å and are superimposed on the first-order
spectra. Many more features and areas of the Sun and their spectra
have been observed since, including coronal holes, polar plumes and
active regions. The atoms and ions emitting this radiation exist at
temperatures below 2 × 106 K and are thus ideally suited
to investigate the solar transition region where the temperature
increases from chromospheric to coronal values. SUMER can also be
operated in a manner such that it makes images or spectroheliograms
of different sizes in selected spectral lines. A detailed line profile
with spectral resolution elements between 22 and 45 mÅ is produced for
each line at each spatial location along the slit. From the line width,
intensity and wavelength position we are able to deduce temperature,
density, and velocity of the emitting atoms and ions for each emission
line and spatial element in the spectroheliogram. Because of the high
spectral resolution and low noise of SUMER, we have been able to detect
faint lines not previously observed and, in addition, to determine
their spectral profiles. SUMER has already recorded over 2000 extreme
ultraviolet emission lines and many identifications have been made on
the disk and in the corona.
Title: High resolution solar ultraviolet measurements
Authors: Lemaire, P.; Wilhelm, K.; Schühle, U.; Curdt, W.; Poland,
A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Vial, J. -C.
Bibcode: 1997AdSpR..20.2249L
Altcode:
The increase of our understanding of the processes acting in the solar
corona and maintaining it is strongly dependent on the quality of the
data that are obtained to check theories. The fine structure of the
solar atmosphere seen from the photosphere and extending to the hottest
parts of the corona requires data with high resolution in all parameter
space (angular, spectral and temporal). To constrain the hypotheses that
are proposed to describe the solar corona, it is necessary to establish
an accurate energy budget taking into account the processes which are
acting from the chromosphere to the corona. Some requirements can be
established and compared with the data collected so far (or about to
be collected) with the present SUMER (Solar Utraviolet Measurements
of Emitted Radiations) instrumentation.
Title: Simulated white-light images of coronal structures as obtained
by the CORI imager on-board a solar probe
Authors: Patsourakos, S.; Vial, J. -C.
Bibcode: 1997AIPC..385..129P
Altcode: 1997recs.conf..129P
A white-light coronal imager called CORI to be implemented on a solar
probe has been proposed by Habbal et al. (1995). Its scientific
objectives concern the investigation of the solar corona and the
source of the solar wind. It is aimed as a complement to the in-situ
instruments. This paper presents some simulations of the images
that will be recorded when observing solar structures of increasing
complexity during the close encounter phase of the trajectory. These
attempts should be considered as a first step towards the assessment
of the full scientific capabilities of CORI and the definition of the
observing strategy.
Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
II. Imagery and Data Management
Authors: Lemaire, P.; Wilhelm, K.; Curdt, W.; SchÜle, U.; Marsch,
E.; Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Vial,
J. C.; KÜhne, M.; Huber, M. C. E.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.
Bibcode: 1997SoPh..170..105L
Altcode:
SUMER - Solar Ultraviolet Measurements of Emitted Radiation - is not
only an extreme ultraviolet (EUV) spectrometer capable of obtaining
detailed spectra in the range from 500 to 1610 Å, but, using the
telescope mechanisms, it also provides monochromatic images over
the full solar disk and beyond, into the corona, with high spatial
resolution. We report on some aspects of the observation programmes
that have already led us to a new view of many aspects of the Sun,
including quiet Sun, chromospheric and transition region network,
coronal hole, polar plume, prominence and active region studies. After
an introduction, where we compare the SUMER imaging capabilities to
previous experiments in our wavelength range, we describe the results
of tests performed in order to characterize and optimize the telescope
under operational conditions. We find the spatial resolution to be
1.2 arc sec across the slit and 2 arc sec (2 detector pixels) along
the slit. Resolution and sensitivity are adequate to provide details
on the structure, physical properties, and evolution of several solar
features which we then present. Finally some information is given on
the data availability and the data management system.
Title: Low Transition-Region Characteristics of Equatorial Coronal
Holes
Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C.
Bibcode: 1997ESASP.404..577P
Altcode: 1997cswn.conf..577P
No abstract at ADS
Title: Diagnostic and observations of quiescent and
Authors: Vial, J. -C.; Gontikakis, C.; Bocchialini, K.; Gouttebroze, P.
Bibcode: 1997IAUJD..19E..55V
Altcode:
We present a new diagnostic tool for investigating the plasma conditions
in a moving structure in the solar corona, such as an eruptive filament
or prominence. It relies on NLTE radiative transfer calculations and
the signatures of outward directed velocities on Lyman and Balmer lines
profiles. Preliminary observations with SUMER on SOHO are discussed.
Title: Microwave and UV observations of filaments with SOHO and
the VLA
Authors: Alissandrakis, C. E.; Drago, F.; Bastian, T.; Bocchialini,
K.; Delaboudiniere, J. -P.; Lemaire, P.; Vial, J. -C.; Harrison,
R. A.; Thompson, B.
Bibcode: 1997ASPC..118..289A
Altcode: 1997fasp.conf..289A
Observations performed in coordination between SOHO instruments and
ground-based observatories offer the unique possibility to derive
information simultaneously in several wavelengths formed at different
altitudes and/or temperatures in the solar atmosphere. The SUMER and
CDS spectrometers, the imaging telescope EIT aboard SOHO, and the VLA
provide complementary information in the UV and the radio ranges. We
illustrate such a coordination with observations of filaments in the
transition region, performed in July 1996. The observations in the UV
between 10(4) and 10(6) K provide the differential emission measure
as a function of temperature; this can be used to compute the expected
brightness temperature in the microwave range and check models of the
filament-corona transition region.
Title: First Results of SOHO's Joint Observing Programme 40
Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C.
Bibcode: 1997IAUJD..19E..38P
Altcode:
The first results of SOHO's JOP 40 are presented. This program
proposes to study the chromospheric to transition region of equatorial
coronal holes in order to derive parameters such as the temperature,
the density, using different lines formed at different altitudes,
in different places: the boundary of a coronal hole or the central
region, on the disk. The two components of the chromospheric quiet
Sun, network and internetwork, should be observed, in and out of an
equatorial coronal hole.
Title: High-Chromosphere and Low-Transition-Region Network: a
Different Organization in an Equatorial Coronal Hole?
Authors: Bocchialini, K.; Vial, J. -C.
Bibcode: 1996SoPh..168...37B
Altcode:
In order to investigate the high chromosphere and the low transition
region in a coronal hole, we have analysed Ca II, Mg II and hydrogen
resonance lines, recorded by the OSO-8 spectrometer in 1975. We
present the comparison between average profiles observed in and out
of the equatorial coronal hole which was at the center of the solar
disk between 27 and 29 November, 1975. We separate internetwork and
quiet-Sun (network+internetwork) profiles: for the internetwork, we
observe that the hydrogen and Mg II profiles recorded in the hole are
stronger than the profiles recorded out of the hole; a similar result,
but with a much lower contrast, is found for the quiet Sun. We discuss
this surprising result.
Title: Prominence Thread Models Including Ambipolar Diffusion
Authors: Fontenla, J. M.; Rovira, M.; Vial, J. -C.; Gouttebroze, P.
Bibcode: 1996ApJ...466..496F
Altcode:
We present a study of the modeling of prominence slabs. Our models
consider a collection of threads in energy balance with the surrounding
corona and submitted to illumination from the underlying chromospheric
layers. The models are isobaric, but temperature variations within
the slab occur as a result of the energy balance constraint. We
compute the non-LTE radiative transfer for a hydrogen model atom
with five bound levels. The ionization is treated consistently with
non-LTE radiative transfer and ambipolar diffusion (AD). The AD
also affects the energy balance because of the transport of hydrogen
ionization energy. We compute the emitted Lyman and Balmer spectra of
our models and compare them with the observations. We find that the
consideration of ambipolar diffusion increases the emission in Lyβ
(and higher members of the Lyman series) as compared with the other
lines. This contrasts with isothermal models that yield Lyβ emission
that is too low. However, the AD models give excessive Lyβ emission,
viz., too small a Lyα/Lyβ ratio compared with observations. We also
compute models that include a cold core in which mechanical energy is
dissipated. These models increase the Hα/Lβ ratio to values similar to
the observed values for a moderate number of threads along the line of
sight. However, these models still give too low a Lyα/Lyβ ratio. We
conclude that the prominence observations in Lyβ show intensities
that are not compatible with a steady state, field-aligned interface
between the cold prominence and the hot coronal material. Also, the
observations are not consistent with an isothermal slab isolated from
the corona. Consequently, we suggest that at the prominence-corona
interface, there is a substantial angle between the temperature gradient
and the field, although this angle is significantly smaller than 90°.
Title: Book reviews
Authors: Humphreys, R. M.; Kemp, S.; Savonije, G.; van der Hucht,
K. A.; van der Kruit, P. C.; Miley, G.; Bumba, V.; van Nieuwkoop,
J.; van Hoolst, T.; Cox, A.; Rutten, R. J.; Kleczek, J.; de Jager,
Cornelis; Jerzykiewicz, M.; Zwaan, C.; Poedts, S.; Sakai, Jun-Ichi;
Pecker, J. -C.; Heikkila, W.; de Jong, T.; Wilson, P. R.; Müller,
E. A.; Hoyng, P.; Icke, V.; Shore, S. N.; Achterberg, A.; Lucchin, F.;
Butcher, H.; Ne'Eman, Y.; Heidmann, J.; Belton, M. J. S.; de Graauw,
Th.; Waters, L. B. F. M.; Pacini, F.; Hultqvist, B.; Akasofu, S. -I.;
Vial, J. -C.; Schatzman, E.; van der Laan, H.; Cole, K. D.; Vanbeveren,
D.; Southwood, D.; van der Klis, M.; Katgert, Peter
Bibcode: 1996SSRv...76..339H
Altcode:
No abstract at ADS
Title: Cloud model with variable source function for solar Hα
structures.
Authors: Mein, N.; Mein, P.; Heinzel, P.; Vial, J. -C.; Malherbe,
J. M.; Staiger, J.
Bibcode: 1996A&A...309..275M
Altcode:
The "cloud model" used to derive the physical parameters of solar
chromospheric features is extended to the cases of non-constant
source function and of velocity gradients. This model assumes a given
relationship between the source function and the opacity of the cloud
which is derived from non-LTE modelling. An algorithm using 4 points
of the Halpha_ profile is proposed to derive the optical
thickness, the line-of-sight velocity and the dopplerwidth. The
results are compared with a 5-points inversion which does not use the
given relationship between source function and opacity. Effects of the
uncertainty about the radiation coming from the underlying chromosphere,
as well as effects of data noise, are discussed. The inversion method
is illustrated by some examples of observed profiles obtained with
the MSDP spectrograph of the VTT telescope (Teide Observatory).
Title: A Complex Diagnostic of Solar Prominences
Authors: Heinzel, P.; Bommier, V.; Vial, J. C.
Bibcode: 1996SoPh..164..211H
Altcode:
We use the polarimetric and intensity measurements of Hα and HeI
D3 lines in solar prominences to derive the true geometrical
thickness for several quiescent prominences. The electron densities,
derived from the collisional depolarization in Hα by Bommier et
al. (1994), are used to evaluate the thickness from the emission
measure. The emission measure was obtained from the theoretical
correlation with the Hα integrated intensity, according to Gouttebroze,
Heinzel, and Vial (1993). Theoretical electron densities obtained by
latter authors are also compared with those of Bommier et al. (1994) and
we find a very good agreement between them. The prominence geometrical
thickness exhibits a relatively large range of values from about 100 km
up to a few 104 km. The plasma densities vary by almost two
orders of magnitude in the observed structures, but the total column
mass in the direction perpendicular to the prominence sheet seems to
be fairly constant for the set of prominences studied.
Title: Prominence Eruption and Coronal Mass Ejections: Diagnostics
and Future Observations from SOHO
Authors: Gontikakis, C.; Vial, J. -C.
Bibcode: 1996ApL&C..34..119G
Altcode:
No abstract at ADS
Title: Two-dimensional Model of a Rotating Solar Prominence
I. Observations and Preliminary Approach
Authors: Kononovich, E. V.; Gorshkov, A. B.; Smirnova, O. B.; Kotrc,
P.; Vial, J. -C.
Bibcode: 1996ASPC...95..251K
Altcode: 1996sdit.conf..251K
No abstract at ADS
Title: SUMER - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Marsch, E.; Schühle, U.; Lemaire,
P.; Gabriel, A.; Vial, J. -C.; Grewing, M.; Huber, M. C. E.; Jordan,
S. D.; Poland, A. I.; Thomas, R. J.; Kühne, M.; Timothy, J. G.;
Hassler, D. M.; Siegmund, O. H. W.
Bibcode: 1995SoPh..162..189W
Altcode:
The instrument SUMER - Solar Ultraviolet Measurements of Emitted
Radiation is designed to investigate structures and associated dynamical
processes occurring in the solar atmosphere, from the chromosphere
through the transition region to the inner corona, over a temperature
range from 104 to 2 × 106K and above. These
observations will permit detailed spectroscopic diagnostics of plasma
densities and temperatures in many solar features, and will support
penetrating studies of underlying physical processes, including plasma
flows, turbulence and wave motions, diffusion transport processes,
events associated with solar magnetic activity, atmospheric heating,
and solar wind acceleration in the inner corona. Specifically, SUMER
will measure profiles and intensities of EUV lines; determine Doppler
shifts and line broadenings with high accuracy; provide stigmatic
images of the Sun in the EUV with high spatial, spectral, and temporal
resolution; and obtain monochromatic maps of the full Sun and the inner
corona or selected areas thereof. SUMER will be flown on the Solar
and Heliospheric Observatory (SOHO), scheduled for launch in November,
1995. This paper has been written to familiarize solar physicists with
SUMER and to demonstrate some command procedures for achieving certain
scientific observations.
Title: Some design and performance features of SUMER: solar
ultraviolet measurements of emitted radiation
Authors: Wilhelm, Klaus; Curdt, W.; Marsh, E.; Schuehle, Udo H.;
Lemaire, Philippe; Gabriel, Alan H.; Vial, J. -C.; Grewing, Michael;
Huber, Martin C.; Jordan, S. D.; Poland, Arthur I.; Thomas, Roger J.;
Kuehne, Mikhael; Timothy, J. Gethyn; Hassler, Donald M.; Siegmund,
Oswald H.
Bibcode: 1995SPIE.2517....2W
Altcode:
The instrument SUMER (solar ultraviolet measurements of emitted
radiation) is designed to investigate structures and associated
dynamical processes occurring in the solar atmosphere from the
chromosphere through the transition region to the inner corona, over a
temperature range from 104 to 2 multiplied by 106
K and above. The observations will be performed, on board SOHO (solar
and heliospheric observatory) scheduled for launch in November 1995,
by a scanning, normal-incidence telescope/spectrometer system in
the wavelength range from 500 to 1610 angstrom. Spatial resolution
requirements compatible with the pointing stability of SOHO are less
than 1000 km corresponding to about 1-arcsec angular resolution. Doppler
observations of EUV line shifts and broadenings should permit solar
plasma velocity measurements down to 1 km s-1. We report
here on some specific features of this instrument related to its
pointing as well as its spatial and spectral resolution capabilities.
Title: Solar Physics from Ground-Based Infrared and Space Observations
Authors: Vial, J. -C.
Bibcode: 1995itsa.conf..221V
Altcode:
No abstract at ADS
Title: Theoretical correlations between prominence plasma parameters
and the emitted radiation.
Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. -C.
Bibcode: 1994A&A...292..656H
Altcode:
Recently a set of 140 prominence NLTE models has been computed using
the best available numerical techniques (Gouttebroze et al. 1993,
hereafter GHV). Models are represented by one-dimensional (1D) slabs
vertically standing on the solar surface and irradiated by photospheric
and chromospheric radiation. They are parametrized by the gas pressure
and temperature (uniform), the geometrical thickness of the 1D slab,
the microturbulent velocity and the height above the solar surface. As
outputs we obtained several physical quantities and optical parameters
like the electron density, the total hydrogen density, the optical
thickness in hydrogen lines and continua, spectral line intensities
etc. (see GHV). In order to establish mutual correlations between
various plasma parameters and the basic characteristics of the
synthesized hydrogen spectrum, we construct some basic correlation
curves. A very important relation already mentioned in GHV concerns the
plasma emission measure found to be closely related to the integrated
intensity of the Balmer Hα line. We present several other correlations
which can be divided into four categories: (i) relations between
radiation properties themselves; (ii) radiation properties versus
plasma parameters; (iii) the Hα source function behaviour; and (iv)
correlations between plasma parameters. Together with the 24 presented
figures, we discuss the physical interpretation of these correlations
and we give some hints for their application to the observed data. When
appropriate, we also compare our results with existing observations.
Title: About small plasmoids propagating in the solar corona
Authors: Koutchmy, S.; Bouchard, O.; Grib, S.; November, L.; Vial,
J. -C.; Gouttebrone, P.; Koutvitsky, V.; Molodensky, M.; Solov'iev,
L.; Veselovsky, I.
Bibcode: 1994ESASP.373..139K
Altcode: 1994soho....3..139K
No abstract at ADS
Title: On the three-dimensional structure of coronal rays
Authors: Koutchmy, S.; Molodenskii, M. M.; Vial, J. -C.
Bibcode: 1994ARep...38..822K
Altcode:
No abstract at ADS
Title: The Chromospheric network dynamics as derived from the analysis
of CA II K and He I 1083 NM lines
Authors: Bocchialini, S.; Vial, J. -C.; Koutchmy, S.
Bibcode: 1994SSRv...70...57B
Altcode:
We present results of line profile analysis of observations
simultaneously performed around the Ca II K and He I (1083 nm) lines,
using the Horizontal Spectrograph of the Vacuum Tower Telescope of
NSO/SP. From the spectral analysis of a 83 min long sequence of CCD
spectra, we derive some dynamical properties of the main components
of the quiet chromosphere: i) the magnetic network, ii) the cell
interior. We present a whole set of amplitude spectra near 5 and 3
min periods for the two lines; K3 and He I velocity spectra
extending up to 100 mHz are also considered, for the first time.
Title: Solar chromospheric structures as observed simultaneously
in strong UV lines I. Observations, statistical analysis and
characteristic line profiles.
Authors: Bocchialini, K.; Vial, J. -C.
Bibcode: 1994A&A...287..233B
Altcode:
We present a set of high resolution profiles of H Lyman α and β, Mg II
h and k, Ca II H and K lines measured near the center of the solar disk
and simultaneously above different solar chromospheric structures. The
large data base provides a way of correlating different parameters in
the different lines: correlations such as Lα reversal vs intensity,
Lα vs Ca K are discussed. We notice that Mg II and Ca II have a similar
behaviour, different from Lα and β. We also discuss a classification
derived from the distribution of integrated intensities in Ca II K,
from which average profiles (for cell, network, plage) are computed
for the six lines and are compared with theoretical ones derived from
several models.
Title: Moon-based UV reflecting coronagraph
Authors: Vial, J. C.; Koutchmy, S.; Smartt, R. N.
Bibcode: 1994AdSpR..14f..43V
Altcode: 1994AdSpR..14...43V
UV observations of the solar disc, and above the limb, have evidenced
a wide range of possible diagnostics, especially in the Lα line. On
the disc, Lα traces the magnetic (sometimes unexpected) structuring of
the top of the atmosphere; out from the limb, it allows measurement of
radial velocities up to a few solar radii where most optical techniques
fail. Other diagnostics include the kinematics of ejections (e.g. CMEs,
but also small-scale rapidly evolving plasmoïds). We propose a
dual-channel reflecting coronagraph combining relatively-high angular
resolution (0.2-0.4'') with large spatial (2.5 solar radii from Sun
center) and temporal coverage. The advantages offered by a Moon-based
instrument are discussed.
Title: The solar corona from SOHO
Authors: Vial, J. -C.
Bibcode: 1994AdSpR..14d.181V
Altcode: 1994AdSpR..14..181V
The heating of the solar corona and the acceleration of the solar
wind are, after decades of observations and modelling, still open
questions. Many processes are possible in regions of strong magnetic
field, such as waves, currents, or impulsive events which involve
particles acceleration. However, no conclusion has been reached up to
now. The situation is no better in open field regions where a (quiet)
corona also exists and the wind is faster. Apart from a theoretical
effort, a coherent diagnostic of the relevant physical quantities such
as densities, temperatures, velocities and their temporal and spatial
variations, is necessary. We show how the coronal package on SOHO can
provide the temperature and height coverage adequate to understand both
small and large scale, closed and open field, solar structures. We give
examples of observing programs which address some important physical
problems. Finally, we emphasize the increase of scientific return if
the SOHO instrumentation is considered as a unique package.
Title: The SIMURIS interferometric mission: Solar physics objectives
and model payload
Authors: Dame, L.; Rutten, R. J.; Thorne, A. P.; Vial, J. C.
Bibcode: 1994AdSpR..14d.167D
Altcode: 1994AdSpR..14..167D
We describe the SIMURIS Mission with emphasis on the scientific goals
and related capabilities of the major instruments of the model payload.
Title: Dynamical Properties of the Chromosphere In and Out of the
Solar Magnetic Network
Authors: Bocchialini, Karine; Vial, Jean-Claude; Koutchmy, Serge
Bibcode: 1994ApJ...423L..67B
Altcode:
We present the results of a comparative analysis of an 83 minute
time sequence of spectra taken around the Ca II and He I 1083 lines,
near the center of the solar disk and away from active regions. We
discuss the behavior of the Fourier spectra at low frequency: 3
minute oscillations are well observed out of the network, and 5 minute
oscillation waves are prominent in the network. The 5 s sampling time
also permits the observation of the high-frequency part of the Fourier
spectra of intensity and velocity fluctuations at different heights. At
high frequencies, K2V-K2R and 1083 (velocity)
results differ when magnetic and non-magnetic regions are compared.
Title: Very High Resolution Analysis of the Dynamics of a Coronal
Plasmoid
Authors: Bouchard, O.; Koutchmy, S.; November, L.; Vial, J. -C.;
Zirker, J. B.
Bibcode: 1994scs..conf..593B
Altcode: 1994IAUCo.144..593B
The authors present the results of the analysis of a movie taken over a
small field of view in the intermediate corona at a spatial resolution
of 0.5", a temporal resolution of 1 s and a spectral passband of 7
nm. These CCD observations were made at the prime focus of the 3.6 m
aperture CFHT telescope during the 1991 total solar eclipse.
Title: 'SUMER' - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Gabriel, A. H.; Grewing, M.; Huber,
M. C. E.; Jordan, S. D.; Kuhne, M.; Lemaire, P.; Marsch, E.; Poland,
A. I.; Schuhle, U.; Thomas, R. J.; Timothy, J. G.; Vial, J. -C.
Bibcode: 1994scs..conf..619W
Altcode: 1994IAUCo.144..619W
SUMER is designed for the investigations of plasma flow characteristics,
turbulence and wave motions, plasma densities and temperatures,
structures and events associated with solar magnetic activity in the
chromosphere, the transition zone and the corona. The spatial and
spectral resolution capabilities of the instrument are considered in
some detail, and a new detector concept is introduced.
Title: Theoretical Correlations Between Various Prominence Parameters
Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. -C.
Bibcode: 1994scs..conf..439H
Altcode: 1994IAUCo.144..439H
The authors present some examples of important correlations between the
prominence plasma parameters and radiation properties. For example,
the plasma emission measure was found to be closely related to the
integrated Hα line intensity which provides a new diagnostic tool
for determination of plasma densities.
Title: Wave Properties in the Upper Chromosphere and at the Base of
the Corona
Authors: Bocchialini, K.; Vial, J. -C.; Koutchmy, S.
Bibcode: 1994scs..conf..123B
Altcode: 1994IAUCo.144..123B
From a 83 min long sequence of observations of Ca II K and He I (1083
nm) line profiles, some dynamical properties of the main components
of the quiet upper chromosphere are derived: for both the magnetic
network and the internetwork, amplitude and phase spectra of the
Doppler velocities are presented.
Title: On the Motion of Eruptive Prominences
Authors: Molodensky, M. M.; Vial, J. -C.
Bibcode: 1994scs..conf..349M
Altcode: 1994IAUCo.144..349M
The increase of current in filaments can be evidenced by the variation
of its twist. The authors show two examples of such a current increase,
the last stage of which is the filament eruption and the flare. They
suggest a theory of the equilibrium and the eruptive motion including
the interaction of the filament current with the magnetic fields of
the active region and the mirror current. They take into account the
curvature of filament.
Title: Analysis of Chromospheric Proxies of Coronal Bright Points
Authors: Bocchialini, K.; Vial, J. -C.; Koutchmy, S.; Zirker, J. B.
Bibcode: 1994ASPC...68..389B
Altcode: 1994sare.conf..389B
No abstract at ADS
Title: Solar coronal structures
Authors: Rusin, Vojtech; Heinzel, Petr; Vial, Jean-Claude
Bibcode: 1994scs..conf.....R
Altcode: 1994IAUCo.144.....R
No abstract at ADS
Title: On the 3D Solar Corona Structure
Authors: Koutchmy, S.; Molodensky, M. M.; Vial, J. -C.
Bibcode: 1994scs..conf..585K
Altcode: 1994IAUCo.144..585K
The authors consider the 3D structure of the solar corona using
eclipse observations. They use a pseudostereoscopic effect of the
rigidly rotating corona to determine the true position of the main
coronal structures: broad threads, rays and streamers. An example of
stereo-view deduced from a simple analysis of results coming from the
1991 eclipse is given. The authors conclude that large helmet streamers
are composed by the pleats of the heliosphere current sheet projected
on the plane of the sky.
Title: Observed Chromospheric Profiles Compared with Theoretical Ones
Authors: Bocchialini, K.; Gouttebroze, P.; Vial, J. -C.
Bibcode: 1994emsp.conf...49B
Altcode:
No abstract at ADS
Title: on the Three-Dimensional Structure of Coronal Rays
Authors: Koutchmy, S.; Molodenskii, M. M.; Vial, J. C.
Bibcode: 1994AZh....71..925K
Altcode:
No abstract at ADS
Title: Effects of Ambipolar Diffusion on Prominence Thread Models
Authors: Rovira, M. G.; Fontenla, J. M.; Vial, J. -C.; Gouttebroze, P.
Bibcode: 1994scs..conf..315R
Altcode: 1994IAUCo.144..315R
The authors have improved previous model calculations of the
prominence-corona transition region including the effect of the
ambipolar diffusion in the statistical equilibrium and energy balance
equations. They show its influence on the different parameters that
characterize the resulting prominence theoretical structure. They
take into account the effect of the partial frequency redistribution
in the line profiles and total intensities calculations.
Title: Analysis of the Chromospheric Proxies of Coronal Bright Points
- Preliminary Results
Authors: Bocchialini, K.; Koutchmy, S.; Vial, J. -C.; Zirker, J. B.
Bibcode: 1994emsp.conf..173B
Altcode:
No abstract at ADS
Title: Round Table on Solar Databases
Authors: Vial, J. -C.
Bibcode: 1994emsp.conf..203V
Altcode:
No abstract at ADS
Title: Congrès Européen de Physique Solaire de Catane (Sicile).
Authors: Vial, J. -C.
Bibcode: 1993LAstr.107..316V
Altcode:
Conference on «Progrès en physique solaire», Catane (Italy), 11 -
15 May 1993.
Title: Structure of coronal rays
Authors: Vial, J. -C.; Molodenskij, M. M.
Bibcode: 1993AZh....70.1092V
Altcode:
The ray structures of the corona are treated as folds and plies of
magnetic surfaces with a large gradient of electron density when
projected to the picture plane. The number of the intersections of
the rays with an arbitrary closed contour in the projection plane is
shown to be even. This allows the classification of the singular points
of the observed structures. Such a classification is performed, and
results of an analysis of singular points of the corona are presented
for the period 1936-1984.
Title: Structure of coronal rays
Authors: Vial, J. -C.; Molodenskii, M. M.
Bibcode: 1993ARep...37..551V
Altcode: 1993SvA....37..551V
No abstract at ADS
Title: Two-dimensional radiative transfer with partial frequency
redistribution. II. Application to resonance lines in quiescent
prominences
Authors: Paletou, F.; Vial, J. -C.; Auer, L. H.
Bibcode: 1993A&A...274..571P
Altcode:
Theoretical emergent profiles in the resonance lines of H I Lyman α,
Mg II h & k and Ca II H & K formed in quiescent prominences
are presented. Both partial frequency redistribution effects and
two-dimensional structure have been included in the calculations. The
prominence model consists of a static, isobaric and isothermal
freestanding slab irradiated by realistic chromospheric profiles
(080-8 observations). We compare the differences between complete (CRD)
and partial frequency redistribution (PRD). Vertical variations in the
emergent profiles are displayed, and the importance of the geometrical
effects is discussed. In addition, we have evaluated both emergent
profiles for a filament as seen over the disk, and the back-scattered
radiation towards the chromosphere.
Title: The hydrogen spectrum of model prominences.
Authors: Gouttebroze, P.; Heinzel, P.; Vial, J. C.
Bibcode: 1993A&AS...99..513G
Altcode:
The emission of hydrogen lines and continua from solar prominences is
investigated using a set of 140 simple models, covering the range of
physical conditions usually assumed for these objects. These models
are plane-parallel, isobaric and isothermal. The computations have been
carried out using a 20 level plus continuum hydrogen atom, and taking
into account the effects of partial frequency redistribution in the
Lyman-alpha and beta lines. The aim of these computations is twofold:
firstly, to describe the variations of hydrogen lines and continua
emitted by prominences when physical conditions vary. Secondly, to
provide observers with some diagnostic tool to interpret data such as
intensity ratios, line widths, etc... The results of computations are
given as mixed table-figure panels, each of them corresponding to a
given model and summarizing the associated physical parameters and
the principal features of the emitted hydrogen spectrum. Finally,
for some specific parameters (or couple of parameters), we present
figures illustrating the variations of these quantities across the
whole set of models.
Title: SUMER - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Marsch, E.; Schuehle, U.; Gabriel,
A. H.; Lemaire, P.; Vial, J. -C.; Grewing, M.; Huber, M. C. E.;
Jordan, S. D.; Poland, A. I.; Thomas, R. J.; Kuehne, M.; Timothy, J. G.
Bibcode: 1993BAAS...25.1192W
Altcode:
No abstract at ADS
Title: Stellar objectives of SIMURIS
Authors: Damé, L.; Coradini, M.; Foing, B.; Rutten, R. J.; Thorne,
A.; Vial, J. C.
Bibcode: 1993MmSAI..64..345D
Altcode:
No abstract at ADS
Title: The SIMURIS interferometric mission: solar physics objectives
and model payload (invited paper)
Authors: Damé, L.; Coradini, M.; Foing, B.; Rutten, R. J.; Thorne,
A.; Vial, J. C.
Bibcode: 1993MmSAI..64..333D
Altcode:
No abstract at ADS
Title: Quiet and active solar structures as observed at the bottom
of the transition region.
Authors: Bocchialini, K.; Vial, Jean-Claude
Bibcode: 1992ESASP.348..197B
Altcode: 1992cscl.work..197B
The authors present a set of high resolution profiles of H Lyman α
and β, Mg II h and k, Ca II H and K lines measured simultaneously
above different solar structures. The large data base provides a
way of correlating different parameters in the different lines:
Lα reversal vs intensity, Lα vs Ca K, etc... The authors notice
that Mg II and Ca II have a similar behaviour, different from Lα
and β ones. They also discuss two classifications derived from the
distribution of intensities, from which average (cell, network, plage,
sunspot) profiles are computed for the 6 lines. They compare the Ca
K results with the two-dimensional models of Solanki et al. (1991).
Title: Radiative modeling of solar prominences, two-dimensional
transfer plus partial frequency redistribution.
Authors: Paletou, F.; Vial, Jean-Claude; Auer, L. H.
Bibcode: 1992ESASP.348..225P
Altcode: 1992cscl.work..225P
The two-dimensional, PRD radiative transfer code of Auer and
Paletou (1992) has been used to compute the resonance lines of H
I, Mg II and Ca II in quiescent prominences, which are modeled as
isothermal freestanding slabs illuminated from the sides as well as
from below. Partial redistribution (PRD) and 2D effects are evidenced
and compared to complete redistribution computations for both 1D and
2D geometries. Important edge variations are fround at the bottom
and the top that should be observed with a spatial resolution of one
arcsecond. As in 1D, PRD effects allow for greater penetration of the
incident radiation into the layer. The 2D code computes both the radial
emergent intensity and the amount of radiation backscattered into the
chromosphere. It can, accordingly, be used to estimate the visibility of
filaments. It will be of special interest to build non-isothermal models
and compare e.g. the Lyα profiles with the SUMER/SOHO observations.
Title: SUMER: temperatures, densities, and velocities in the outer
solar atmosphere.
Authors: Lemaire, P.; Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel,
A. H.; Grewing, M.; Huber, M. C. E.; Jordan, S. D.; Kuehne, M.;
Marsch, E.; Poland, A. I.; Richter, A. K.; Thomas, R. J.; Timothy,
J. G.; Vial, J. C.
Bibcode: 1992ESASP.348...13L
Altcode: 1992cscl.work...13L
The SUMER instrumentation, that will be mounted on the SOHO spacecraft,
is in development under MPAE leadership. It has some capability
to improve the solar angular resolution and the spectral resolution
already obtained in the far UV to the extreme UV, corresponding to the
temperature range between 104 and a few 106K. The
authors give some insights into the SUMER spectrometer that is developed
to study the dynamics and to infer temperatures and densities of the
low corona and the chromosphere-corona transition zone in using the
50 - 160 nm wavelength range. First, they recall the SUMER scientific
goals and the technics used. Then, after a brief description of the
instrumentation the expected performances are described. The way the
observations can be conducted is emphasized and it is shown how SUMER
is operated in coordination with other SOHO instrumentations and in
cooperation with ground-based observations.
Title: Structural Characteristics of Eruptive Prominences
Authors: Demoulin, P.; Vial, J. C.
Bibcode: 1992SoPh..141..289D
Altcode:
Nowadays the primordial importance of the magnetic field for coronal
plasma physics is well known. However, its determination is only made in
cool regions, mainly the photosphere and prominences. The extrapolation
to the corona gives some indications of the magnetic structure but is
not presently sufficiently reliable. So it is important to consider
all the other observable physical effects of the magnetic field.
Title: Model payload and system design of the SIMURIS interferometric
mission
Authors: Dame, L.; Rutten, R. J.; Thorne, A. P.; Vial, J. C.
Bibcode: 1992wadc.iafcZ....D
Altcode:
SIMURIS (Solar, Solar System, and Stellar Interferometric Mission
for Ultrahigh Resolution Imaging and Spectroscopy) has been proposed
to ESA as a Mission in the context of the Space Station in November
1989 in answer to the Call for the Next Medium Size Mission (M2). It
has completed, since, an Assessment Study, and is now proceeding for
a Phase A. SIMURIS employs advanced interferometric techniques. The
payload includes two major instruments which are the Solar Ultraviolet
Network (SUN), an interferometric array of four 20-cm telescopes on
a 2-m baseline, and the Imaging Fourier Transform Spectrometer (IFTS)
which uses light from a 40-cm Gregory telescope. Both instruments have
active pointing capabilities of 3 milliarcsec stability, and SUN has,
in addition, an active cophasing control to 1/50th of a wavelength. EUV
multilayer telescopes complete the payload for diagnostics of the very
high temperature plasma. The SIMURIS model payload will be described
with emphasis on the system design of the interferometric aspects of
the instruments.
Title: "SUMER" - Solar Ultraviolet Measurements of Emitted Radiation.
Authors: Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel, A. H.;
Grewing, M.; Huber, M. C. E.; Jordan, S. D.; Kühne, M.; Lemaire, P.;
Marsch, E.; Poland, A. I.; Richter, A. K.; Thomas, R. J.; Timothy,
J. G.; Vial, J. C.
Bibcode: 1992eocm.rept..225W
Altcode:
The experiment Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) is designed for the investigations of plasma flow
characteristics, turbulence and wave motions, plasma densities
and temperatures, structures and events associated with solar
magnetic activity in the chromosphere, the transition zone and the
corona. Specifically, SUMER will measure profiles and intensities
of extreme ultraviolet (EUV) lines emitted in the solar atmosphere
ranging from the upper chromosphere to the lower corona; determine line
broadenings, spectral positions and Doppler shifts with high accuracy;
provide stigmatic images of selected areas of the Sun in the EUV with
high spatial, temporal and spectral resolution and obtain full images of
the Sun and the inner corona in selectable EUV lines, corresponding to a
temperature range from 104 to more than 1.8×106K.
Title: The fine structure of prominences.
Authors: Heinzel, P.; Vial, J. -C.
Bibcode: 1992ESASP.344...57H
Altcode: 1992spai.rept...57H
Ground-based observations evidence in prominences a fine structure both
in density and velocity fields at a subarcsec scale. The modeling of
such structures is necessary in order to account for heating and cooling
processes which depend critically on the geometry and the structure of
the magnetic field. For a rigorous treatment of the radiative losses,
one needs to solve the full NLTE problem especially in UV lines,
which are critical for the energy balance. Although some attempts
have already been made to model individual fine-structure elements,
quiescent prominences are still mostly considered as one-dimensional
structures. We discuss current improvements such as two-dimensional
geometry and bundle of threads.
Title: Evidence of plasmoid ejection in the corona from 1991 eclipse
observations with the Canada-France-Hawaii telescope
Authors: Vial, J. -C.; Koutchmy, S.; Monnet, G.; Sovka, J.; Clark,
C.; Salmon, D.; Purves, N.; Sydserff, P.; Coulder, R.; November, L.
Bibcode: 1992ESASP.344...87V
Altcode: 1992spai.rept...87V
Observations of the solar corona with a large telescope at high
altitude was fully exploited with the 3.60 m CFHT (Canada France
Hawaii Telescope) in Hawaii, during the 11 Jul. 1991 eclipse,
are reported. Different instruments set up for the eclipse and
preliminary results are given. The moving feature in the corona is
focused upon. Physical conditions in this plasmoid and its origins
are discussed. One of the four cameras installed in the primary focus
was a video charge coupled device camera with a red filter at 637
nm selecting the red line. The power of the telescope allowed for a
good signal in a pixel as small as 0.12 arcsec and a very good time
resolution. The spectral resolution as measured at the Moon limb
was better than one arcsec. During the three minute long sequence,
6000 video images were obtained. Among the fine structures recorded,
a plasmoid about 1500 km wide was seen to ascend and dilute in the
corona. Possible emission mechanisms are discussed. It was found that
both low and relatively high temperature plasmas can be confined in this
ejected plasmoid. Such a small scale phenomenon could be important for
the heating of the corona and should be observed in UV emission lines
in a wide range of temperatures. The high spatial resolution achieved
by Solar Interferometric Mission for Ultrahigh Resolution Imaging and
Spectroscopy (SIMURIS) allows to study the shape, stability and the
diagnostics of such plasmoids in the corona.
Title: Design Rationale of the Solar Ultraviolet Network / Sun
Authors: Dame, L.; Acton, L.; Bruner, M. E.; Connes, P.; Cornwell,
T. J.; Curdt, W.; Foing, B. H.; Hammer, R.; Harrison, R.; Heyvaerts,
J.; Karabin, M.; Marsch, E.; Martic, M.; Mattic, W.; Muller, R.;
Patchett, B.; Roca-Cortes, T.; Rutten, R. J.; Schmidt, W.; Title,
A. M.; Tondello, G.; Vial, J. C.; Visser, H.
Bibcode: 1992ESOC...39..995D
Altcode: 1992hrii.conf..995D
No abstract at ADS
Title: SUMER - Solar ultraviolet measurements of emitted radiation
Authors: Wilhelm, K.; Axford, W. I.; Gurdt, W.; Marsch, E.; Richter,
A. K.; Grewing, M.; Gabriel, A. H.; Lemaire, P.; Vial, J. -C.; Huber,
M. C. E.
Bibcode: 1992sws..coll..129W
Altcode:
The SUMER (solar ultraviolet measurements of emitted radiation)
experiment is described. It will study flows, turbulent motions, waves,
temperatures and densities of the plasma in the upper atmosphere of
the Sun. Structures and events associated with solar magnetic activity
will be observed on various spatial and temporal scales. This will
contribute to the understanding of coronal heating processes and the
solar wind expansion. The instrument will take images of the Sun in EUV
(extreme ultraviolet) light with high resolution in space, wavelength
and time. The spatial resolution and spectral resolving power of the
instrument are described. Spectral shifts can be determined with
subpixel accuracy. The wavelength range extends from 500 to 1600
angstroms. The integration time can be as short as one second. Line
profiles, shifts and broadenings are studied. Ratios of temperature
and density sensitive EUV emission lines are established.
Title: A solar interferometric mission for ultrahigh resolution
imaging and spectroscopy: SIMURIS
Authors: Damé, L.; Acton, L.; Bruner, M.; Connes, P.; Cornwell, T.;
Foing, B. H.; Heyvaerts, J.; Lemaire, P.; Martić, M.; Muller, R.;
Porteneuve, J.; Roca Cortés, T.; Riehl, J.; Rutten, R.; Séchaud,
M.; Smith, P.; Thorne, A. P.; Title, A. M.; Vial, J. -C.; Visser,
H.; Weigelt, G.
Bibcode: 1991AdSpR..11a.383D
Altcode: 1991AdSpR..11..383D
SIMURIS is an interferometric investigation of the very fine structure
of the solar atmosphere from the photosphere to the corona. It was
proposed to ESA /1/, November 30 1989, for the Next Medium Size
Mission - M2, and accepted in February 1990 for an Assessment Study
in the context of the Space Station. The main scientific objectives
will be outlined, and the ambitious model payload featuring the Solar
Ultraviolet Network (SUN), a 2 m long monolithic array of 4 telescopes
of Ø20 cm, and the Imaging Fourier Transform Spectrometer (IFTS),
an UV and Visible Imaging Fourier Transform Spectrometer coupled to
a Ø40 cm Gregory, described.
Title: Solar physics at ultrahigh resolution from the space station
with the Solar Ultraviolet Network (SUN)
Authors: Damé, L.; Acton, L.; Bruner, M.; Connes, P.; Cornwell,
T.; Foing, B.; Heyvaerts, J.; Lemaire, P.; Martić, M.; Muller, R.;
Roca Cortés, T.; Riehl, J.; Rutten, R.; Title, A. M.; Vial, J. -C.;
Visser, H.; Weigelt, G.
Bibcode: 1991AdSpR..11e.267D
Altcode: 1991AdSpR..11..267D
The SUN experiment is a UV and visible Space Interferometer aimed at
ultra-high resolution in the solar atmosphere. It has been proposed
to ESA as part of the SIMURIS Mission Proposal which has recently
been accepted for an Assessment Study in the framework of the
Space Station. The 4 × 20 cm telescopes of the SUN linear array are
non-redundantly placed to cover a 2 m baseline, and the instrument makes
full use of stabilized interferometry potential, the 4 telescopes being
co-aligned and co-phased on a reference field on the sun. After a brief
outline of the scientific objectives, the concept of the instrument
is described, and its image reconstruction potential is illustrated.
Title: The helioseismology experiment on the Phobos planetary
mission. Preliminary results
Authors: Frohlich, C.; Bonnet, R. M.; Bruns, A. V.; Vial, J. C.;
Delaboudiniere, J. P.; Domingo, V.; Kollath, Z.; Kotov, V. A.;
Rachkovskii, D. N.; Wehrli, Ch.; Toulain, T.; Shumko, S. M.
Bibcode: 1991BCrAO..83...18F
Altcode:
No abstract at ADS
Title: Chauffage de la couronne et de la région de transition
(solaires).
Authors: Vial, J. -C.
Bibcode: 1991sed..conf..317V
Altcode:
Contents: (1) Evidence d'une région externe chaude et morphologie
de la couronne solaire. (2) Bilan énergétique. (3) Les sources
d'énergie. (4) Couronne solaire/couronnes stellaires.
Title: The helioseismological experiment at the Phobos interplanetary
station - Preliminary results
Authors: Froehlich, C.; Bonnet, R. M.; Bruns, A. V.; Vial, J. C.;
Delaboudiniere, J. P.; Domingo, V.; Kollath, Z.; Kotov, V. A.;
Rachkovskii, D. N.; Wehrli, Ch.
Bibcode: 1991IzKry..83...22F
Altcode:
Preliminary results obtained from IPHIR (Interplanetary Helioseismology
by Irradiance Measurements), a solar irradiance experiment on board
the Soviet planetary mission Phobos-2, are presented. During the
spacecraft's flight to Mars, the instrument gathered valuable data on
tiny variations of solar irradiance over the course of six months. The
data clearly show 5-min oscillations with relative amplitudes of about
10 exp -5 and with a well-defined pattern of discrete peaks in the
power spectrum. The data of the red channel (it exhibited the lowest
degradation of sensitivity over time) reveal remarkable temporal changes
of amplitudes of discrete peaks within a period range of about 5 min,
but with excellent frequency stability.
Title: UV solar reflecting coronagraph
Authors: Smartt, R. N.; Koutchmy, S.; Vial, J. C.
Bibcode: 1990AIPC..207..578S
Altcode: 1990am...proc..578S
A dual-channel reflecting coronagraph is proposed that would provide
observations of Lα corona and chromosphere, upper transition-region
phenomena in CIV, and also helioseismology observations in the continuum
around 166 nm. Each channel would use a 104×104-UV-sensitive CCD
array. The combined velocity and magnetic field data would link
events in the chromosphere, the transition region and the corona to
an elongation of about 2.5 R0. These data would be used to study both
the global-scale and also the fine-scale properties of the corona in
terms of the physical processes that deposit energy and momentum in the
corona. Specific question to be investigated would be the origin and
morphology of CME's and other coronal transients, sources of coronal
heating, and the source(s) and dynamics of the coronal wind in the
inner coronal region.
Title: Coming: 24 hour surveillance of the sun.
Authors: Koutchmy, S.; Vial, J. -C.
Bibcode: 1990Rech...21...10K
Altcode:
No abstract at ADS
Title: Multi-Thread Structure as a Possible Solution for the L-Beta
Problem in Solar Prominences
Authors: Vial, J. -C.; Rovira, M.; Fontenla, J.; Gouttebroze, P.
Bibcode: 1990LNP...363..282V
Altcode: 1990IAUCo.117..282V; 1990doqp.coll..282V
Following the pioneering works of Heasley, Mihalas, Milkey and Poland
(see e.g. Heasley and Milkey, 1983) who built non LTE onedimensional
models of solar prominence, much attention has been paid to the
spectral signatures of the Lyman lines as observed with OSO 8 (Vial,
1982a). In spite of a better treatment of the frequency redistribution
and boundary conditions, one-dimensional low-pressure models lead to
Lyman intensities much lower than observed ones (Heinzel, Gouttebroze
and Vial, 1987). Different atomic processes of formation of hydrogen
lines (Cooper, Ballagh and Hubeny, 1988) or the inclusion of a
Prominence Corona Transition Region or PCTR (Heinzel, Gouttebroze and
Vial, 1988) have been proposed to explain this discrepancy. We present
here a different approach where the filamentary nature of prominences
which provides the hydrogen lines with different opacities, offers
their photons different escaping possibilities. The thread models
we use derive from an energy equation where radiative losses are
balanced by conductive flux (Foutenla and Rovira, 1983, 1985). We
show that no superposition of threads gives good values of Lyman a,
and H a intensities for too high and too low pressures. Solutions are
found for pressure around 0.05-0.1 dyn/cm2 and a number of threads
between 100 and 400. Two improvements have been performed: first, the
inclusion of Partial Redistribution leads to a decrease of L (and L)
intensity and models now require a higher number of threads; second,
the inclusion of the ambipolar diffusion along the steep temperature
gradient which changes the hydrogen ionization in the lower regions
(Foutenla, Avrett and Loeser, 1990). The new run of temperature and
density implies more material at low temperatures and hydrogen lines
intensities increase. A solution for the L problem can be found for
a pressure of about 0.1 dyn cm-t2. However the H intensity appears to
be rather high. Moreover, the number of threads required (about 200)
is far larger than the number derived by Zirker and Koutchmy (this
issue) and Mein (this issue) from observed H profiles. Our neglect
of the radiative interaction between threads may explain our results
(Heinzel, this issue). To conclude, these computations of non-lte
radiative transfer in realistic geometrical and physical models, appear
to be a promising path for the investigation of solar prominences.
Title: High Resolution Solar Physics from the Space Station with
Interferometric Techniques: The Solar Ultraviolet Network (SUN) -
Instrument &Objectives
Authors: Damé, L.; Acton, L.; Bruner, M.; Connes, P.; Cornwell, T.;
Foing, B.; Heyvaerts, J.; Jalin, R.; Lemaire, Ph.; Martic, M.; Moreau,
B.; Muller, R.; Roca Cortés, T.; Riehl, J.; Rutten, R.; Title, A. M.;
Vial, J. -C.; Visser, H.; Weigelt, G.
Bibcode: 1990PDHO....7..262D
Altcode: 1990dysu.conf..262D; 1990ESPM....6..262D
No abstract at ADS
Title: The Prominence / Corona Interface
Authors: Vial, J. -C.
Bibcode: 1990LNP...363..106V
Altcode: 1990IAUCo.117..106V; 1990doqp.coll..106V
The existence of cool and dense material in the hot and diluted corona
implies specific mass and energy transfers between the two media. This
is true for all steps in prominence lifetime : formation, quiescence
and disappearance. Much theoretical work has been done recently on the
formation by coronal condensation, but observational signatures are
scarce, probably because of the long duration involved. On the contrary,
the Disparition Brusque phenomenon has been observed in different
wavelengths (temperatures) and shown to be either essentially magnetic
or thermal. Line ratios have been used for the density diagnostics
of eruptive prominences and point to a small filling factor. As
for the quiet PCTR, the increase of Differential Emission Measure
at lower temperatures, extensively studied with Skylab, is still a
puzzle. With the help of both u-v (HRTS) and radio (VLA) new data,
temperature gradients have been derived. The DEM increase could be
explained by such heating process as waves or transients and also
(at low temperature) by the reduction of radiative losses in optically
thick lines. UVSP,observations on SMM indicate upflows and downflows
in the PCTR. Their positions with respect to the magnetic field
lines are unknown simply because no magnetic measurement exists in the
PCTR. There is much activity in modeling prominences as a superposition
of fine structures (threads, loops,..) in thermal equilibrium and in
comparing with the uv emission. Obviously, we now have some information
on pressure and temperature gradient in the PCTR but we do not know the
geometry, the magnetic field nor the heating process. Further decisive
progress will be made with the spectrometers and coronagraphs on SOHO.
Title: Comparison of Ly-α and Ly-β interplanetary glows observed
by the Voyager ultra-violet spectrometer.
Authors: Chassefiere, E.; Lallement, R.; Bertaux, J. L.; Vial, J. C.;
Sandel, B. R.
Bibcode: 1990phoh.coll...65C
Altcode:
The comparison between Ly-α and Ly-β glows exhibits significant
discrepancies which can not be explained by radiation transfer in
the Ly-α interplanetary line. They might be due, at least partially,
to the temporal variability of the solar flux, larger at Ly-α center
than at Ly-β center.
Title: Fine structure observation in a solar prominence
Authors: Lemaire, P.; Samain, D.; Vial, J. C.
Bibcode: 1990AdSpR..10i.191L
Altcode: 1990AdSpR..10..191L
The high resolution balloon spectrograph (RASOLBA) has obtained
ultraviolet prominence spectra during its September 19th, 1986,
flight. The high resolution spectra (one arcsecond along the
30 arcseconds spectrograph slit length, and 0.0015 nm spectral
resolution within the 20 nm wavelength band) have been recorded on
film. The wavelength band was centered on the Mgll h and k (279.6
nm and 280.3 nm) resonance doublet lines inside the cross-dispersion
echelle spectrograph. The analysis of the prominence spectra shows
evidence of sheared velocities (up to 20 km/s) which very within few
arcseconds with the distance above the limb. This shear may appear
inside magnetic loops confining the prominence material. We present
the observations and a preliminary analysis of the data.
Title: Le Soleil 24 Heures Sur 24
Authors: Koutchmy, S.; Vial, J.
Bibcode: 1990Rech..217...10K
Altcode:
No abstract at ADS
Title: Réunion "SOHO-Couronne" des investigateurs français sur
les instruments coronaux de SOHO.
Authors: Vial, J. C.
Bibcode: 1989JAF....35...18V
Altcode:
No abstract at ADS
Title: 6 - 20 mars 1989: deux semaines d'intense activité pour une
seule région solaire.
Authors: Vial, J. -C.
Bibcode: 1989LAstr.103..203V
Altcode:
No abstract at ADS
Title: Protuberanzen und Beobachtungsprogramme.
Authors: Malherbe, J. -M.; Martres, M. -J.; Vial, J. -C.
Bibcode: 1989Sonne..13....8M
Altcode:
No abstract at ADS
Title: SUMER - Solar ultraviolet measurements of emitted radiation.
Authors: Curdt, W.; Wilhelm, K.; Axford, W. I.; Marsch, E.; Richter,
A. K.; Gabriel, A. H.; Lemaire, P.; Vial, J. -C.; Grewing, M.; Huber,
M. C. E.; Jordan, S. D.; Poland, A. I.; Thomas, R. J.; Timothy, J. G.
Bibcode: 1989AGAb....2...14C
Altcode: 1989amt..conf...14C
No abstract at ADS
Title: Multithread Structure as a Possible Solution for the L-beta
Problem in Solar Prominences
Authors: Vial, J. C.; Rovira, M.; Fontela, J.; Gouttebroze, P.
Bibcode: 1989HvaOB..13..347V
Altcode:
No abstract at ADS
Title: Particles and energy transport in the solar atmosphere during
solar flares.
Authors: Heristchi, D.; Raadu, M. A.; Vial, J. -C.; Malherbe, J. -M.
Bibcode: 1989sasf.confP.321H
Altcode: 1988sasf.conf..321H; 1989IAUCo.104P.321H
The proposed model of particle transport in the solar atmosphere
during flares consists in a low density plasmoid originating
deep in the atmosphere and rising under magnetic and buoyancy
forces. Confined particles are selectively released during the ascent
and their interaction with the solar atmosphere produces X and γ
bremsstrahlung. The characteristics of high energy particles released
in the interplanetary medium are found to agree with observations.
Title: The diagnostic and modelling of the solar atmosphere through
non-LTE radiative transfer: some results and prospects.
Authors: Gouttebroze, Pierre; Vial, Jean-Claude; Lemaire, P.
Bibcode: 1989mse..proc..245G
Altcode:
The authors describe new results from non-LTE radiative transfer
calculations for solar UV continua and line profiles. The new non-LTE
codes include partial frequency redistribution in the lines, moving
atmospheres with differential velocities, and can treat finite objects
with external irradiation (loops, prominences). Selected examples are
given for: (1) a static atmosphere (plage); (2) a moving atmosphere
(waves); and (3) free standing slabs (prominences).
Title: IPHIR: The helioseismology experiment on the PHOBOS mission.
Authors: Fröhlich, C.; Bonnet, R. M.; Bruns, A. V.; Delaboudinière,
J. P.; Domingo, V.; Kotov, V. A.; Kollath, Z.; Rashkovsky, D. N.;
Toutain, T.; Vial, J. C.; Wehrli, C.
Bibcode: 1988ESASP.286..359F
Altcode: 1988ssls.rept..359F
IPHIR (InterPlanetary Helioseismology by IRradiance measurements) is
a solar irradiance experiment on the USSR planetary mission PHOBOS to
Mars and its satellite Phobos. The experiment is a cooperative effort
of PMOD/WRC, LPSP, SSD/ESA, KrAO and CRIP. The sensor is a three channel
sunphotometer (SPM) which measures the solar spectral irradiance at 335,
500 and 865 nm with a precision of better than 1 ppm. A two axis solar
sensor (TASS) is added to monitor the moderate solar pointing of the
spacecraft. A microprocessor based data processing unit controls the
sensor operation, acquires the data, and performs the data compression
for the transmission at a mean rate of 1 bit/s. The two spacecrafts
have been launched on July 7th and 12th, 1988. The experiment on
PHOBOS I gathered data during 45 days before the S/C was lost, the
one on PHOBOS II is still operating. The data recovery is excellent
with virtually 100% coverage. Although the signal is disturbed by the
pointing of the spacecraft the results of a preliminary analysis in
the range of the 5-minutes oscillations demonstrate the improvement
achievable due to the fact that the time series is truly continuous
and the instrumental and sampling noise is very low.
Title: Non LTE modelling of prominences.
Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. -C.
Bibcode: 1988dssp.conf...71H
Altcode:
The authors present the results on non-LTE computations performed in
the major lines and continua of the hydrogen atom. The prominence is
represented by a slab illuminated by the neighbouring chromosphere and
corona. Classical models are recomputed and it appears that the low
pressure model represent well the observed Lα profiles. However the
Lβ-computed value is much lower than the observed one. Preliminary
computations where a transition region to the corona is included that
the Lβ line may be improved.
Title: Two Solar Observation Programmes
Authors: Marthes, M. J.; Malherbe, J. M.; Vial, J.
Bibcode: 1988scaa.conf..175M
Altcode: 1988IAUCo..98..175M
No abstract at ADS
Title: The O VI (103.2 nm) prominence profile and the
prominence-corona interface.
Authors: Vial, J. -C.
Bibcode: 1988dssp.conf..181V
Altcode:
Few lines profiles have been obtained up-to-now in the transition region
between prominences and corona (PCTR hereafter). The major source of
information has been Skylab UV intensities. Important results concern:
the presence of cool absorbing material as in the corona, the evidence
of numerous (about 8) PCTRs, the similarity between differential
emission measures of the chromosphere-corona transition region and
the PCTR, especially in increase towards lower temperatures. However
in the absence of profiles measurements, the run of temperature,
densities and microturbulence could not be derived in the PCTR.
Title: Formation of the hydrogen spectrum in quiescent prominences -
One-dimensional models with standard partial redistribution
Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. -C.
Bibcode: 1987A&A...183..351H
Altcode:
One-dimensional isothermal-isobaric static slab models are used to study
departures from complete frequency redistribution (CRD) in hydrogen
lines for quiescent solar prominences. Partial redistribution (PRD)
effects on the hydrogen L-alpha line are shown to be significant
in the near wings in addition to the far wings of L-alpha. It is
suggested that strong symmetrical peaks found in the theoretical
PRD L-alpha profiles are due to partially coherent penetration of
the incidence double-peaked solar L-alpha. The present results are
found to be consistent with OSO-8/LPSP observations and with UVSP/SMM
data. The possible interplay between the effects of lateral transport
or radiation, level-interlocking, and PRD is considered.
Title: Protubérances solaires et programmes d'observation.
Authors: Malherbe, Jean-Marie; Martres, Marie-Josephe; Vial,
Jean-Claude
Bibcode: 1987LAstr.101..321M
Altcode:
The observed characteristics of solar prominences are reviewed, and
models for the formation of filaments and for the magnetic structure
of protuberances are discussed. Data suggest that coronal filaments
are formed either by the pumping of chromospheric matter or by
condensation of the coronal plasma itself by thermal instability. The
class of Kippenhahn-Schluter models involve magnetic rings which are
bent under the influence of gravity, and the class of Kuperus-Raadu
models place prominences above a certain neutral point. Observations
of filamentary velocity fields indicate that the magnetic support of
the condensation is in quasi-static evolution. Three proposed areas
of study of prominences, the connections and exchanges of matter at
great distances, eruptive prominences, and the sudden disappearance
of prominences, are discussed.
Title: Structures fines chromosphériques: nouveaux résultats de
la caméra de la région de transition.
Authors: Foing, B. H.; Dame, L.; Vial, J. C.; Gouttebroze, P.; Martic,
M.; Bonnet, R. M.
Bibcode: 1987JAF....29...15F
Altcode:
No abstract at ADS
Title: La haute résolution en physique solaire: perspectives pour
l'avenir.
Authors: Damé, L.; Foing, B.; Vial, J. C.
Bibcode: 1987JAF....29...16D
Altcode:
No abstract at ADS
Title: Simultaneous measurements of chromospheric lines in sunspot
umbra andpenumbra.
Authors: Vial, J. -C.; Bellout, A.
Bibcode: 1987PAICz..66..215V
Altcode: 1987eram....1..215V
The author reports on simultaneous profiles measurements obtained in
the Lα, Lβ, Mg II and Ca II lines in a sunspot umbra and penumbra,
performed with the L.P.S.P. instrument on OSO 8. They aim at providing
some new information on both oscillations and thermodynamic structure
of sunspots.
Title: The OVI 103.2-NM Prominence Profile and the Prominence /
Corona Interface
Authors: Vial, J. C.
Bibcode: 1987dssp.work..181V
Altcode: 1987ASSL..150..181V
No abstract at ADS
Title: Non-Lte Modelling of Prominences
Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. C.
Bibcode: 1987dssp.work...71H
Altcode: 1987ASSL..150...71H
No abstract at ADS
Title: Observations spatiales solaires.
Authors: Vial, J. C.
Bibcode: 1987JAF....29...15V
Altcode:
No abstract at ADS
Title: Diagnostics and structure.
Authors: Vial, J. C.
Bibcode: 1986NASCP2442...89V
Altcode:
The structure of prominences and the diagnostic techniques used to
evaluate their physical parameters are reviewed and discussed.
Title: Partial redistribution effects in the formation of hydrogen
lines in quiescent prominences.
Authors: Heinzel, P.; Gouttebroze, P.; Vial, J. C.
Bibcode: 1986NASCP2442..155H
Altcode: 1986copp.nasa..155H
Departures from complete frequency redistribution (CRD) in hydrogen
lines are investigated for solar prominences. Partial redistribution
effects (PRD) are found both in the wings (their already known lowering)
and in the central part of the L alpha line; a new feature is evidenced
here: the partially coherent scattering in the near wings of the
line leads to a double-peaked profile mirroring the incident solar
radiation. With a low density model, we obtain a good agreement with
OSO 8 observed profiles. On the contrary, the PRD computed L beta
profile (lower density, no reversal) departs from the observed one,
a result which calls for more progress in terms of non-LTE transfer
and modelling.
Title: Dynamical properties of a pre-perihelion comet
tail. I. December 6, 1985 observations of P/Halley 82i.
Authors: Guerin, P.; Koutchmy, S.; Vial, J. C.
Bibcode: 1986A&A...167..395G
Altcode:
Wide field pictures of comet P/Halley 1982i obtained every hour on
December 6, 1985, have been analyzed in order to study the dynamics
of low intensity plasma structures in the tail. The deduced radial
velocities increase from 50 to 80 km s-1 over distances
of 2 to 6×106km. The measured apparent aberration angle
is interpreted as a result of a large polarward solar wind velocity
component.
Title: Non-LTE models of solar prominences
Authors: Heinzel, P.; Vial, J. C.; Gouttebroze, P.; Rompolt, B.
Bibcode: 1986CoSka..15..183H
Altcode:
The authors briefly review some representative non-LTE models of solar
prominences, developed during the past decade. Particular attention is
devoted to recent interpretation of hydrogen Lyman α line profiles
in quiescent prominences and to the solution of the non-LTE problem
for moving active prominences. Finally, the authors outline some of
the most important prospects of prominence plasma diagnostics.
Title: Emission of Lyman alpha radiation by solar coronal loops. I -
General synopsis
Authors: Gouttebroze, P.; Vial, J. C.; Tsiropoula, G.
Bibcode: 1986A&A...154..154G
Altcode:
The processes of emission of Lyman-alpha radiation by loop-like
structures embedded in the solar corona are investigated, for
a large range of physical conditions within these objects. The
coupled set of equations for radiative transfer, and hydrogen atom
level populations, ionization and pressure equilibria is solved
to obtain the emitted L-alpha intensities as functions of pressure,
temperature and size. Three different cases are treated: (1) optically
thin structures with arbitrary geometry. (2) plane-parallel slabs,
either horizontal or vertical, with arbitrary optical depth. (3)
cylindrical loops with horizontal axis, for moderate optical depths
(au is less than 1000). The importance of geometry, as well as that of
partial frequency redistribution and of the hydrogen atom's model, are
evaluated. Empirical formulae and diagrams of intensity as a function
of physical state parameters are given. The diagnostic possibilities of
Lyman-alpha filtergrams alone or in conjunction with other observations,
are discussed.
Title: On the origin of the blue continuum of white-light flares
Authors: Dame, L.; Vial, J. -C.
Bibcode: 1985ApJ...299L.103D
Altcode:
A new model for white-light flares is proposed in order to explain
the observed blue continuum (i.e., the higher contrast longward of
the Balmer jump, around 4000 A). Its broad temperature plateau between
60,000 and 90,000 K is compatible with chromospheric evaporation. The
predicted UV emission, computed here in the Si IV resonance lines
(1402 and 1393 A), is, however, too large by two orders of magnitude,
as compared to the emission from weak flares. Because of the lack of a
comprehensive set of measurements in white-light flares, the validity
of such a model is still open.
Title: Periodic Comet Halley (1982i)
Authors: Jewitt, D.; Meech, K.; Ricker, G.; Lamy, P.; Koutchmy, S.;
Vial, J. C.
Bibcode: 1985IAUC.4148....1J
Altcode:
D. Jewitt, K. Meech, and G. Ricker, Massachusetts Institute of
Technology, communicate: "Observations from McGraw-Hill Observatory
on Kitt Peak over 4 nights show variable structures in the inner
coma of P/Halley. Images were taken through broad and narrowband
interference filters using the MIT 'MASCOT' CCD camera on the 1.3-m
telescope. Jet-like structures were observed in position angles 358
and 313 on Nov. 29 UT. The jets extended 10 000 km in the plane of
the sky and had widths comparable to the atmospheric seeing. The
jets were visible in both broad and narrowband continuum filters and
are probably dust features. The jets showed no variation in position
angle or brightness in an observing interval of > 3 hr but were
absent on the preceding and following nights." Meech and Jewitt also
report: "Observations of P/Halley with the Kitt Peak 0.61-/0.91-m
Schmidt telescope (with baked IIIa-J plates and exposure times
30-60 min) show that extensive tail development has occurred within
the past month. Observations on Nov. 6-9 showed only a transient,
faint anti-solar tail (length 20' on Nov. 6.20) which faded in <
1 day. Observations on Dec. 4-8 show a persistent plasma tail (length
> 2.5 deg) displaying a classical streamer morphology. We are able
to follow knots, kinks, and streamers in the tail for up to 6 hr. The
measured speeds of 3 tail knots are 190, 216, and 240"/hr (39, 45, and
50 +/- 5 km/s along the tail, km/s), considerably less than the solar
wind speed but similar to the speeds measured in the tails of other
comets. No evidence for acceleration of the features is seen. Two
episodes of ray formation have been seen in 25 hr of observation;
the rays form in ~ 1 hr and evolve over several hr, but fade in <
18 hr. The tail as a whole shows gross brightness changes from night
to night. No dust tail is seen." P. Lamy, Laboratoire d'Astronomie
Spatiale, Marseille, and S. Koutchmy, Institut d'Astrophysique, Paris,
telex: "Four consecutive 1-hr-exposure IIIa-J hypered plates obtained
between Dec. 6.79-6.96 UT by Koutchmy and J. C. Vial with the 0.62-m
f/3 Schmidt telescope of Haute Provence Observatory show a disturbed,
narrow, plasma tail of length > 2 deg. The tail's inner part
deviates southward from the anti-solar direction by 4.8 +/- 0.7 deg;
the outer part widens and nears the anti-solar direction. The point
of bifurcation seems to move radially outward with time."
Title: Transfer of Lyman-α radiation in solar coronal loops.
Authors: Gouttebroze, P.; Vial, J. -C.; Tsiropoula, G.
Bibcode: 1985ASIC..152..359G
Altcode: 1985pssl.proc..359G
The emission and scattering of Lyman-α radiation within the loop-like
structures of the solar corona are investigated, for a large range
of physical conditions within these objects. Results from partial
and complete redistribution computations are compared. A series of
predictions, concerning line profiles, integrated intensities, and
directional diagrams are given for observation diagnosis.
Title: Le satellite S.M.M. (Solar Maximum Mission). Un observatoire
tout entier consacré à l'activité solaire.
Authors: Vial, J. -C.
Bibcode: 1984LAstr..98..211V
Altcode:
The instrumentation on-board the SMM is described, together with
data gathered up to November 1980. The SMM carries a gamma ray
spectrometer, two hard X ray spectrometers, an X ray polychromator,
an UV spectrometer polarimeter, a coronograph/polarimeter and a
radiometer. The observational data linked the eruption processes
with the appearance of parasitic magnetism, the disappearance of a
filament, plasma temperature enhancement to 50,000 K, an increase in
the 6 cm flux continuum and hard X ray emission. Measurements have
confirmed a two-stage flux acceleration, with highest temperatures
happening before peak emissions. The deeper understanding of solar
flux phenomena gained with the SMM has been due in large part to an
internationally cooperative effort to confirm space-based observations
with ground-based measurements.
Title: Simultaneous H and K Ca ii, h and k Mg ii, Lα and Lβ
H i profiles of the April 15, 1978 solar flare observed with the
OSO-8/L.P.S.P. experiment
Authors: Lemaire, P.; Choucq-Bruston, M.; Vial, J. -C.
Bibcode: 1984SoPh...90...63L
Altcode:
Solar flare observations have been performed with the multichannel
L.P.S.P. experiment on board OSO-8 NASA Satellite. Simultaneous H and K
CaII, h and k MgII, Lα and Lβ HI profiles have been recorded on the
plage just before the flare, during the flare onset and relaxation
phases. The different behaviour of line profiles and intensities
during the flare is evidenced and indicates a downward propagation
with relaxation times increasing from the upper part to the lower part
of the chromosphere related to line formation processes. Using the Hɛ
observed profile, an upper limit of 8 × 1013 cm-3
is derived for the electron density.
Title: Simultaneous H and K CAII H and K MGII L-Alpha L-Beta HI
Profiles of a Solar Flare Observed with OSO-8 L.P.S.P. Spectrometer
Authors: Lemaire, P.; Choucq-Bruston, M.; Vial, J. C.
Bibcode: 1984apoa.conf..266L
Altcode:
No abstract at ADS
Title: Dynamics of a surge observed in the C IV and H alpha lines
Authors: Schmieder, B.; Mein, P.; Vial, J. -C.; Tandberg-Hanssen, E.
Bibcode: 1983A&A...127..337S
Altcode:
Time sequences of a surge have been obtained in Active Region 2701
during a coordinated SMY program, on October 2nd, 1980, while the MSDP
spectrograph operated in H-alpha at the Meudon Solar Tower and the UVSP
spectrometer on SMM observed in the 1548 A C IV resonance line. The cold
(H-alpha) and hot (C IV) material follow the same channel, and the event
lasts about 10 min in both lines. A good correlation is found between
H-alpha and C IV velocities; radial velocities along the surge are in
the range 40-60 km/s in both cases. The observations are consistent
with the hypothesis that a pressure gradient drives the surge. The
H-alpha data seem to indicate the presence of a shock wave in the
chromosphere, while the C IV quantities (velocities, accelerations)
vary on a very short time scale. Their maxima occur at some locations
which could be interpreted as 'pinched' zones.
Title: OSO-8 observations of a quiescent prominence - A comparison
of Lyman-alpha with theoretical intensities
Authors: Heinzel, P.; Vial, J. -C.
Bibcode: 1983A&A...121..155H
Altcode:
Using simultaneous observations of hydrogen Lyman-α and Ca II K lines
obtained with the OSO 8 LPSP instrument, the authors compare Lα
emission from a quiescent prominence with those predicted from the
existing theoretical models. They use the observed relation between
Hα and Ca II K integrated intensities to obtain an estimate of
E(Hα)/E(Lα) vs. E(Hα). This ratio differs significantly from those
predicted theoretically under the assumption of complete frequency
redistribution during the scattering of Lα photons. On the other
hand, using the partial-redistribution treatment in the Lα wings,
as suggested by Milkey et al., the authors arrived at a reasonable
agreement with the corresponding theoretical curve. The possible
influence of macroscopic velocities on line ratios is briefly discussed.
Title: Structure and Physics of Solar Faculae - Part Three - the
Densities in the Chromosphere-Corona Transition Zone
Authors: Dumont, S.; Mouradian, Z.; Pecker, J. -C.; Vial, J. -C.;
Chipman, E.
Bibcode: 1983SoPh...83...27D
Altcode:
Si IV, C IV, and O VI resonance lines have been measured above quiet
and active solar regions from both pointed OSO-8 instruments. From
calibrated profiles, optical depths are computed with three different
methods. All three methods provide evidence that the opacity above
faculae is lower than above the quiet Sun.
Title: Measurements of solar transition zone velocities and line
broadening using the ultraviolet spectrometer and polarimeter on
the Solar Maximum Mission
Authors: Simon, G.; Mein, P.; Vial, J. C.; Shine, R. A.; Woodgate,
B. E.
Bibcode: 1982A&A...115..367S
Altcode:
The UVSP instrument on SMM is able to observe solar regions at two
wavelengths in the same line with a band-pass of 0.3 A. Intensity and
Doppler velocity maps are derived. It is shown that the numerical
values are sensitive to the adopted Doppler width and the range of
velocities is limited to within 30 km/sec. A method called Double
Dopplergram Determination (DDD) is described for deriving both the
Doppler width and the velocity (up to 80 km/sec), and the main sources
of uncertainties are discussed. To illustrate the method, a set of C
IV 1548 A observations is analyzed according to this procedure. The
mean C IV Doppler width measured (0.15 A) is comparable to previous
determinations. A relation is found between bright regions and
down-flows. Large Doppler widths correspond to strong velocity
gradients.
Title: Mass motions in the solar chromosphere and transition zone
Authors: Mein, P.; Simon, G.; Vial, J. C.; Shine, R. A.
Bibcode: 1982A&A...111..136M
Altcode:
A comparison is made between H-alpha and C IV observations of Active
Region 2717 on October 9, 1980. On the basis of this comparison,
it is found that upward velocities are present above sunspots in the
chromosphere-corona transition zone (20 km/s). The downward velocities
are found to be well correlated in both lines. Doppler-shift ratios
between C IV and H-alpha levels (approximately 10) are seen to be much
smaller than expected from density ratio estimates. The comparison is
seen as suggesting that flow lines are probably far from vertical in
the transition zone. It is pointed out, however, that this depends
on model densities that may not be correct. A simple method for
comparing matter flows is presented. The best fit between H-alpha and
C IV levels is obtained when C IV Doppler shifts are multiplied by
the line intensity to the power 0.5 (approximately) in order to make
allowance for density fluctuations.
Title: Structure and Physics of Solar Faculae - Part Two - the
Non-Thermal Velocity Field above Faculae
Authors: Mouradian, Z.; Dumont, S.; Pecker, J. -C.; Chipman, E.;
Artzner, G. E.; Vial, J. C.
Bibcode: 1982SoPh...78...83M
Altcode:
The OSO-8 satellite enabled us to study various characteristics of
the profiles of Si II, Si IV, C IV, and O VI lines above active areas
of the Sun, as well as above quiet areas, and to derive some physical
properties of the transition region between chromosphere and corona
(CCT): (i) The study of the lines shows a general tendency for the
microvelocity fields on the average to be nearly constant for the
heights corresponding to T > 105 K; however they seem
to slightly increase with height in quiet areas, and decrease in
active areas. (ii) A multicomponent model of the CCT is however quite
necessary, and its geometry is far from being a set of plane-parallel
columns. It is similar to an association of moving knots within the
non-moving principal component of the matter. (iii) The proportion
of mass, in the knots relative to that in the non-moving component,
is several times larger in active regions than in quiet regions. (iv)
In the knots, the non-thermal microvelocity fields are smaller in active
regions and seem to decrease for T increasing above 105 K,
contrary to what happens in the steady principal component. Of course,
we consider that microturbulence and Doppler shift are two aspects of
the same distribution of velocity.
Title: Two-dimensional nonlocal thermodynamic equilibrium transfer
computations of resonance lines in quiescent prominences
Authors: Vial, J. C.
Bibcode: 1982ApJ...254..780V
Altcode:
The two-dimensional transfer code of Mihalas, Auer and Mihalas (1978)
is used to compute emergent profiles of resonance lines of H I, Mg
II, and Ca II. The model (a uniform slab limited in two directions)
and the radiative and thermodynamic quantities are described. The
metallic line profiles are sensitive to the ionization degree, which
is fixed at a certain value. Some modifications are implemented in
the code, in particular, the true incident profiles of chromospheric
lines. A comparison is made between two-dimensional and one-dimensional
profiles. Good agreement between computed and observed profiles is
found for Ly-alpha and Ca II but not for Mg II lines.
Title: Optically thick lines in a quiescent prominence - Profiles of
Lyman-alpha, Lyman-beta /H I/, K and H /Mg II/, and K and H /Ca II/
lines with the OSO 8 LPSP instrument
Authors: Vial, J. C.
Bibcode: 1982ApJ...253..330V
Altcode:
The first set of simultaneous measurements are presented of H I
Lyman-alpha and Lyman-beta, Ca II K and H, and Mg II k and h lines
in a quiescent prominence. It is found that: (1) Ca II resonance
lines have low opacity, with an optical thickness at the center of
the K line varying between 1.4 and 3.2, and nonthermal velocities
ranging from 5 to 9 km/sec.; (2) the resonance lines of Mg II, as
measured in the whole prominence, depart from Gaussian profiles and
are unexplainably broader than the corresponding Ca II ones. The
observed Mg II and Ca II 'inverted' intensity ratios may be due to
different incident intensities ratios; and (3) the Lyman-alpha and
Lyman-beta lines of H I have the same reversals as the chromospheric
lines in bright regions, and unreversed profiles may be observed in
darker regions. The intensities are larger than the diluted incident
radiation, and the opacity reaches values of 100,000.
Title: Preflare heating of filaments
Authors: Malherbe, J. M.; Simon, G.; Mein, P.; Mein, N.; Schmieder,
B.; Vial, J. C.
Bibcode: 1982AdSpR...2k..53M
Altcode: 1982AdSpR...2...53M
Disappearances of preflare filaments have been observed on June 22,
1980 (S07,W13) (flare at 13.04 U.T.) and September 3, 1980 (flare
at 7.52 U.T.). The analysis of MSDP data (MEUDON) leads to the
followings conclusions : - Disappearances begin a few minutes before
the Hα impulsive phase. - The filaments can be seen again after the
flares. - Upwards motions occur in several points, without disturbing
significantly preëxisting downflows. Velocity maps suggest shears
or velocity loops. The filament disappearance seems to be due to
a heating mechanism beginning before the flare maximum.
Title: A surge obsrved in Hα and CIV
Authors: Schmieder, B.; Mein, P.; Vial, J. C.; Tandberg-Hanssen, E.
Bibcode: 1982AdSpR...2k.225S
Altcode: 1982AdSpR...2..225S
Simultaneous Hα (MSDP at Meudon) and C IV (UVSP aboard SMM)
measurements of Active Region 2701 were made on October 2,
1980. Isodensity and velocity maps were derived for both lines
and superposed. A good correlation was found between Hα and C IV
velocities. A surge was observed for 10 minutes. The base was located
in a bright point in CIV and Hα, and escaping matter followed the same
channel (``absorbing'' in Hα, ``emitting'' in C IV). The velocity
along the surge was about 80 kms.-1 in Hα and 100 km s-1 in C IV. A
loop appeared in C IV. We discuss the existing models and conclude
that the vertical pressure gradient was capable of driving the surge.
Title: Physical properties of the solar chromosphere deduced from
optically thick lines. I - Observations, data reduction, and modelling
of an average plage
Authors: Lemaire, P.; Gouttebroze, P.; Vial, J. C.; Artzner, G. E.
Bibcode: 1981A&A...103..160L
Altcode:
Simultaneous Ca II H and K, Mg II h and k, and H I Lyman-alpha and
Lyman-beta profiles have been recorded by the OSO-8/LPSP spectrometer on
a quiet sun area and a part of plage, McMath 13738. After data reduction
and filtering, a full set of calibrated profiles is obtained. Using
a code developed at LPSP (Gouttebroze et al., 1978), profiles
computed from VAL III model C (Vernazza et al., 1981) are compared
to observations. A specific plage model has been computed to fit the
observed profiles. This model reproduces successfully Ca II H and K,
and H I Lyman-alpha and Lyman-beta, but partly fails with Mg II h and
k. Atmospheric inhomogeneities and dynamical effects may contribute to
this discrepancy, and it is proposed that the level number entering
in the Mg II computation be increased to take account of a likely
fluorescence induced by the H I Lyman-beta radiation field.
Title: Absorption feature observed on the H Lyman-alpha solar line -
an interpretation
Authors: Artzner, G.; Cazes, S.; Emerich, C.; Vial, J. C.; Lemaire, P.
Bibcode: 1981A&A...100..205A
Altcode:
A narrow absorption feature on the red part of the solar H Lyman-alpha
profile has been observed by two instruments in 1975 and attributed
to atomic hydrogen of the nearby interplanetary gas. This hypothesis
implies that the absorption feature shifts with the position of the
earth on its orbit. New measurements above active regions at other
seasons rule out this hypothesis. On the other hand, appropriate
laboratory calibrations indicate that the absorption feature is likely
due to a ghost image of the geocoronal absorption.
Title: Lα, Lβ (of H i), k and h (of Mg ii), K and H (of Ca ii)
observations in a quiescent prominence with the OSO-8 LPSP instrument
Authors: Vial, J. C.; Martres, M. J.; Salm-Platzer, J.
Bibcode: 1981SoPh...70..325V
Altcode:
A sequence of images taken at different positions in the resonance lines
of Ca II, Mg II, and H I was obtained over a quiescent prominence
with the LPSP instrument on OSO-8. Ca II K (and H) profiles are
reconstructed at different locations in the prominence with a (10 × 5)
arc sec2 resolution. Significant variations of FWHM and line
shifts are found: FWHM range from 0.14 Å to 0.5 Å; blue shifts reach
about 14 km s-1. The ratio of K to H absolute intensities
shows a large spread around the average value of 1.2. The same ratio
for the Mg II lines in the whole prominence is higher (1.7), a fact
already noticed at the edge of an active prominence (Vial et al.,
1979). The ionization degree, as measured by the Lα/Ca K ratio, shows
noticeable variations within the prominence. The Lα intensity is about
0.3 times the intensity measured in the quiet Sun, and the Lα/Lβ
ratio is less than one half the disk value. These results indicate
important variations of the thermal conditions inside the prominence.
Title: OSO-8 Observations of CAII H and K MGII H and K Lyman-Alpha
and Lyman-Beta above a Sunspot
Authors: Kneer, F.; Scharmer, G.; Mattig, W.; Wyller, A.; Artzner,
G.; Lemaire, P.; Vial, J. C.
Bibcode: 1981SoPh...69..289K
Altcode:
Observations with the French (L.P.S.P.) experiment on board OSO-8 of
a sunspot and nearby plage region are described. The behaviour of the
emission cores of the Ca II H and K and Mg II h and k resonance lines is
very similar and the correspondence in intensity between the four lines
persists in all observed features. In contrast, the Lyman lines show
little correlation with the other lines. Their emission regions appear
broader in the spectroheliograms than the underlying sunspot structure
and must not necessarily possess a counterpart in lower layers. From
the central intensity of Lα above the umbra an electron density of
4.3 × 1010 cm-3 ≲ne*
≲2.3 × 1011 cm-3 at 20 000 K is estimated.
Title: Solar H I LY alpha far wing measurement
Authors: Jouchoux, A.; Vial, J. C.; Artzner, G. E.; Gouttebroze, P.;
Lemaire, P.
Bibcode: 1981A&A....93..415J
Altcode:
High spectral resolution photoelectric observations of the solar H I
Ly alpha far wing are presented. Measurements above active regions and
quiet sun center are compared to photographic observations of Basri
et al. (1979).
Title: Contribution à l'étude des protubérances solaires à partir
des observations effectuées sur l'instrument du LPSP à bord du
satellite OSO-8 Title: Contribution à l'étude des protubérances
solaires à partir des observations effectuées sur l'instrument du
LPSP à bord du satellite OSO-8 Title: Contribution to the study of
solar prominences from observations made on the LPSP instrument on
board the OSO-8 satellite;
Authors: Vial, Jean-Claude Jacques
Bibcode: 1981PhDT........42V
Altcode:
No abstract at ADS
Title: On VI (λ = 1032 Å) profiles in and above an active region
prominence, compared to quiet Sun center and limb profiles
Authors: Vial, J. C.; Lemaire, P.; Artzner, G.; Gouttebroze, P.
Bibcode: 1980SoPh...68..187V
Altcode:
O VI (λ = 1032 Å) profiles have been measured in and above a filament
at the limb, previously analyzed in H I, Mg II, Ca II resonance lines
(Vial et al., 1979). They are compared to profiles measured at the
quiet Sun center and at the quiet Sun limb.
Title: Microturbulence near the edge of a solar plage
Authors: Simon, G.; Mouradian, Z.; Dumont, S.; Pecker, J. C.; Artzner,
G.; Vial, J. C.
Bibcode: 1980A&A....89L...8S
Altcode:
Observations of the Ca II K line at the edge of a solar plage show
enhanced separation of the K2 peaks with respect to the measured value
inside the plage and in the quiet sun. This effect may be interpreted as
a variation of microturbulent motions at the height of formation of K2.
Title: Observations of Chromospheric Lines from OSO-8
Authors: Grossmann-Doerth, U.; Kneer, F.; Uexkuell, M.; Artzner,
G. E.; Vial, J. C.
Bibcode: 1980SoPh...66....3G
Altcode:
The line profiles of Lα, Ca II K and Mg IIk were measured with the
spectrometer of the `Laboratoire de Physique Stellaire et Planétaire'
on board of OSO-8. The results of these measurements are presented.
Title: Center-to-limb solar observations of the K2
component of the Ca II K line with the OSO 8 satellite.
Authors: Dumont, S.; Mouradian, Z.; Pecker, J. -C.; Simon, G.; Artzner,
G. E.; Vial, J. C.
Bibcode: 1980CRASB.290..365D
Altcode:
OSO 8 spectrometer measurements of the separation between emission
peaks in the K2 Ca II line across the solar disk in quiet and active
regions are presented. The center-to-limb variation in emission peak
separation is found to differ slightly for quiet and facula regions
at distances greater than 0.2 solar radii from the limb, in agreement
with previous observations. For a facula located at the solar limb,
however, the peak separation is observed to be up to 35 percent greater
than in quiet regions, indicating the presence of a region of enhanced
chromospheric turbulence surrounding the faculae.
Title: Non thermal velocities in the chromosphere-corona transition
zone of solar active regions.
Authors: Dumont, S.; Mouradian, Z.; Pecker, J. -C.; Chipman, E.;
Artzner, G.; Vial, J. -C.
Bibcode: 1980CRASB.290..317D
Altcode:
OSO 8 satellite observations of lines of the Si II, Si IV, C IV and
O VI ions in the ultraviolet spectrum of active solar regions are
considered. It is noted that for the case of pronounced physical
dispersion of the data, there is no marked systematic variation from
the center to the edge of the solar disk. The nonthermal velocities
in the transition zone are, for a given temperature, the same as for
quiet regions. In addition, the velocities tend to reach a constant
value at temperatures above 100,000 deg K, and the observed physical
dispersion is much higher than the inaccuracy of the data.
Title: Profiles of H I (Lalpha ), Mg II (h and k), Ca II (H and K)
lines of an active filament at the limb, with the LPSP instrument
aboard the OSO-8 satellite.
Authors: Vial, J. C.; Gouttebroze, P.; Artzner, G.; Lemaire, P.
Bibcode: 1979SoPh...61...39V
Altcode:
We scanned the H I Lα, Mg II h and k, Ca II K and H lines
simultaneously with the LPSP instrument on OSO-8, to investigate the low
and moderate temperature regions of an `active region filament'. The
Lα line is not reversed except for the innermost position in the
prominence. Intensity (k/h), (K/H) ratios are respectively 2 and 1.1,
indicating that the Mg II lines are optically thin, and that Ca II
K is saturated, although not clearly reversed. The results obtained
during the second sequence of observations (K saturated before Lα
for example) indicate that within the size of the slit (1″ × 10″)
we are not observing the same emitting features in the different lines.
Title: LY α and β of hi, H and K of MG ii, H and K of CA II Profiles
of a Quiescent Prominence Obtained with the LPSP Instrument of OSO-8.
Authors: Vial, J. C.; Lemaire, P.; Gouttebroze, P.
Bibcode: 1979phsp.coll...52V
Altcode: 1979IAUCo..44...52V
No abstract at ADS
Title: Profiles of H i (Lyα), MG II (h and K), CA II (h and k)
Lines in an Active Filament at the Limb, Observed with the LPSP
Instrument Onboard the OSO-8 Satellite.
Authors: Vial, J. C.; Gouttebroze, P.; Artzner, G.; Lemaire, P.
Bibcode: 1979phsp.coll..250V
Altcode: 1979IAUCo..44..250V
No abstract at ADS
Title: The solar hydrogen Lyman-beta and Lyman-alpha lines: disk
center observations from OSO 8 compared with theoretical profiles.
Authors: Gouttebroze, P.; Lemaire, P.; Vial, J. C.; Artzner, G.
Bibcode: 1978ApJ...225..655G
Altcode:
The solar La and Lfl lines of hydrogen have been measured at the center
of the disk with the LPSP spectrometer aboard OSO 8. These line profiles
are compared with theoretical profiles obtained with different solar
atmospheric models, assuming either complete or partial frequency
redistribution in scattering. The assumption of microturbulence for
the velocity fields appears insufficient to account for the profiles
of the line cores; better results are obtained with a blend of micro-
and macroturbulence, which shows the need of a generalized treatment of
the turbulent motions in the formation of these lines. If the effects
of partial redistribution are taken into account, a good fit of the
line wings requires higher temperatures, in the region under the
plateau, than in the reference atmospheric model of Vernazza, Avrett,
and Loeser. Subject headings: line formation - line profiles - Sun:
chromosphere - Sun: spectra - ultraviolet: spectra
Title: Simultaneous time-resolved observations of the H Lalpha ,
Mg k 2795 Å, and Ca K solar lines.
Authors: Artzner, G.; Leibacher, J.; Vial, J. C.; Lemaire, P.;
Gouttebroze, P.
Bibcode: 1978ApJ...224L..83A
Altcode:
No abstract at ADS
Title: Calibrated full disk solar H I Lyman-alpha and Lyman-beta
profiles.
Authors: Lemaire, P.; Charra, J.; Jouchoux, A.; Vidal-Madjar, A.;
Artzner, G. E.; Vial, J. C.; Bonnet, R. M.; Skumanich, A.
Bibcode: 1978ApJ...223L..55L
Altcode:
Resolved solar H I Ly-alpha and -beta profiles have been recorded by the
French LPSP experiment on OSO 8. Intensity observations at the center
and the limb have been combined to obtain flux-equivalent profiles
(5.46 plus or minus 30 percent and 0.078 plus or minus 25 percent
erg/sq cm per sec for Ly-alpha and -beta, respectively). Comparison of
the flux profiles with unresolved calibration rocket profiles allows
one to obtain an absolute calibration.
Title: The LPSP instrument on OSO 8. II. In-flight performance and
preliminary results.
Authors: Bonnet, R. M.; Lemaire, P.; Vial, J. C.; Artzner, G.;
Gouttebroze, P.; Jouchoux, A.; Leibacher, J. W.; Skumanich, A.;
Vidal-Madjar, A.
Bibcode: 1978ApJ...221.1032B
Altcode:
The paper describes the in-flight performance for the first 18 months of
operation of the LPSP (Laboratoire de Physique Stellaire et Planetaire)
instrument incorporated in the OSO 8 launched June 1975. By means of
the instrument, an absolute pointing accuracy of nearly one second
was achieved in orbit during real-time operations. The instrument
uses a Cassegrain telescope and a spectrometer simultaneously
observing six wavelengths. In-flight performance is discussed with
attention to angular resolution, spectral resolution, dispersion
and grating mechanism (spectral scanner) stability, scattered light
background and dark current, photometric standardization, and absolute
calibration. Real-time operation and problems are considered with
reference to pointing system problems, target acquisition, and L-alpha
modulation. Preliminary results involving the observational program,
quiet sun and chromospheric studies, quiet chromospheric oscillation
and transients, sunspots and active regions, prominences, and aeronomy
investigations are reported.
Title: Doppler Shifts measured in 0 VI line from OSO-B observations
above and in the vicinity of plage Mc Math 13738.
Authors: Lemaire, P.; Skumanich, A.; Artzner, G.; Gouttebroze, P.;
Vial, J. C.; Bonnet, R. M.; McWhirter, P.
Bibcode: 1978BAAS...10Q.440L
Altcode:
No abstract at ADS
Title: OSO-8 Radio and X-ray observations of the 19 April 1977 flare.
Authors: Skumanich, A.; Jouchoux, A.; Castelli, J.; Lemaire, P.;
Artzner, G.; Gouttebroze, P.; Vial, J. C.; Bonnet, R. M.
Bibcode: 1978BAAS...10..441S
Altcode:
No abstract at ADS
Title: EUV observations of class-C X-ray flare by the LPSP
(Laboratoire de Physique Stellaire et Planétaire du Centre National
de la Recherche Scientifique) spectrometer on OSO-8.
Authors: Jouchoux, A.; Skumanich, A.; Bonnet, R. M.; Lemaire, P.;
Artzner, G.; Leibacher, J.; Vial, J. C.; Vidal-Madjar, A.
Bibcode: 1977BAAS....9..432J
Altcode:
No abstract at ADS
Title: The LPSP experiment on OSO-8. I - Instrumentation, description
of operations, laboratory calibrations and pre-launch performances
Authors: Artzner, G.; Bonnet, R. M.; Vial, J. C.; Jouchoux, A.;
Leibacher, J.; Vidal-Madjar, A.; Lemaire, P.
Bibcode: 1977SSI.....3..131A
Altcode:
The characteristics of OSO-8, including its solar-pointed instrument
assembly and rasters, are discussed, as well as the accompanying
Laboratoire de Physique Stellaire et Planetaire (LPSP) instrumentation,
which is designed to study the solar atmosphere with high spatial,
spectral, and temporal resolution. The LPSP instrument, which consists
of two subassemblies, a Cassegrainian telescope and a spectrometer,
is described; main optical characteristics, including spectral lines
observed, and means of correcting aberrations and eliminating stray
light, are given for the spectrometer. Detectors and their capacities,
and various filter wheel configurations available for detection of
polarized light and discrimination of low orders of diffraction, are
also described. The observation program, which consists of a study of
solar prominences, flares, and dynamic and three-dimensional physical
structures of the chromosphere, as well as determination of seasonal
variations of some gases in earth's atmosphere, is reviewed. A detailed
account of pre-launch tests and calibration procedures is also given.
Title: Extreme-Ultraviolet Observations of New Cycle Sunspots with
the LPSP Spectrometer from OSO-8
Authors: Skumanich, A.; Jouchoux, A.; Artzner, G.; Bonnet, R. M.;
Leibacher, J.; Lemaire, P.; Vial, J. C.; Vidal-Madjar, A.
Bibcode: 1977BAAS....9..340S
Altcode:
No abstract at ADS
Title: On VI Profiles of Solar Quiet and Active Areas Recorded by
OSO-8 LPSP Experiment".
Authors: Lemaire, P.; Artzner, G.; Vial, J. C.; Bonnet, R. M.;
Gottebroze, P.; Jouchoux, A.; Vidal-Madjar, A.; McWhirter, P.;
Leibacher, J.; Skumainich, A.
Bibcode: 1977uxsa.coll...46L
Altcode: 1977IAUCo..43...46L
No abstract at ADS
Title: OSO-8 Observations of the EUV Chromospheric Network
Authors: Artzner, G.; Bonnet, R. M.; Leibacher, J.; Lemaire, P.;
Skumanich, A.; Vial, J. C.; Vidal-Madjar, A.
Bibcode: 1976BAAS....8..332A
Altcode:
No abstract at ADS
Title: Evolution of sunspot and active region morphology as observed
on the resonance lines of Ca+ (K, H), Mg+
(k, h), hydrogen (Lalpha , Lbeta ), and O VI from OSO-8 (LPSP).
Authors: Artzner, G.; Skumanich, A.; Bonnet, R. M.; Vidal-Madjar,
A.; Leibacher, J.; Lemaire, P.; Vial, J. C.
Bibcode: 1976BAAS....8..397A
Altcode:
No abstract at ADS
Title: Periodic temporal phenomena in the solar chromosphere as
observed from OSO-8 (LPSP).
Authors: Vial, J. C.; Leibacher, J.; Lemaire, P.; Artzner, G.; Bonnet,
R. M.; Skumanich, A.; Vidal-Madjar, A.
Bibcode: 1976BAAS....8..397V
Altcode:
No abstract at ADS
Title: Spatial variations of solar profiles of Ca+ H and
K, Mg+ h and k, and Lyman alpha and beta (H I) resonance
lines as observed from OSO-8 (LPSP).
Authors: Bonnet, R. M.; Artzner, G.; Leibacher, J.; Lemaire, P.;
Skumanich, A.; Vial, J. C.; Vidal-Madjar, A.
Bibcode: 1976BAAS....8..397B
Altcode:
No abstract at ADS
Title: Prominence Observations with the OSO-8 French Experiment
Authors: Vial, J. C.; Artzner, G.; Bonnet, R. M.; Lemaire, P.;
Leibacher, J.; Skumanich, A.; Vidalmadjar, A.
Bibcode: 1976BAAS....8..344V
Altcode:
No abstract at ADS
Title: High-Resolution Atmospheric Extinction Measurements from the
French Experiment on Board the NASA Spacecraft OSO-8
Authors: Vidal-Madjar, A.; Roble, R. G.; Mankin, W. G.; Artzner, G.;
Bonnet, R. M.; Lemaire, P.; Vial, J. C.
Bibcode: 1976ASSL...61..117V
Altcode: 1976aps..conf..117V
No abstract at ADS
Title: High resolution atmospheric extinction measurements from the
French experiment on board the NASA spacecraft OSO-8
Authors: Vidal-Madjar, A.; Artzner, G.; Bonnet, R. M.; Lemaire, P.;
Vial, J. C.; Roble, R. G.; Mankin, W. G.
Bibcode: 1976atps.proc..117V
Altcode:
The French instrument aboard OSO-8 is a multichannel, high-resolution UV
spectrometer for observing very small areas of the sun simultaneously
in the Ca II, Mg II, Lyman alpha, and Lyman beta lines. By observing
extinction through the earth atmosphere, the spectrometer studies the
three-dimensional structure and the composition of the atmosphere. The
quality of data appears to give a 500 m vertical resolution both for
O3 and O2; O3 is observed primarily from 55 to 75 km, while O2 is
observed from 85 to 200 km. Data on the hydrogen absorption present a
new method for evaluating exospheric temperature and atomic hydrogen
density at each point of the exobase.
Title: Angular Dependence of the Optical Properties of a Narrow Band
Interference Filter
Authors: Koutoumy, S.; Vial, J. -C.
Bibcode: 1973A&A....25..145K
Altcode:
Summary. An interferential filter, 2" diameter, centered around Hoc
line, has been studied. Its resolving power with unpolarized light,
is 0/ 4. 1O . The instrumental width of the spectrometer was less than
0.3 A and the field less than 10'. Wavelength shift A and half height
bandwidth variation of the I.F. are given for different incident angles
0. The beam was almost plane parallel; natural and linear polarized
light were used. The wavelength splitting was not observed up to A
10(a ). Polarization effects due to the filter are important and we
empirically deduced the following formula: II- 1 (0.0610.01)00(A) for
0 less than 5 . Key words: Hoc interference filter - polarization -
spectral transmission - instrumental technique
Title: Intensity Distribution in the LYMAN-α Line at the Solar Limb
Authors: Vial, J. C.
Bibcode: 1970IAUS...36..260V
Altcode:
No abstract at ADS