Author name code: henoux
ADS astronomy entries on 2022-09-14
author:"Henoux, Jean-Claude"
------------------------------------------------------------------------
Title: Flare line impact polarization. Na D2 589 nm line polarization
in the 2001 June 15 flare
Authors: Hénoux, J. C.; Karlický, M.
Bibcode: 2013A&A...556A..95H
Altcode:
Context. The impact polarization of optical chromospheric lines
in solar flares is still being debated. For this reason, additional
observations and improved flare atmosphere models are needed still.
Aims: The polarization-free telescope THEMIS used in multiline 2
MulTiRaies (MTR) mode allows accurate simultaneous linear polarization
measurements in various spectral lines.
Methods: In the 2001
June 15 flare, Hα, Hβ, and Mg D2 lines linear impact polarization
was reported as present in THEMIS 2 MTR observations. In this paper,
THEMIS data analysis was extended to the Na D2 line. Sets of I ± U
and I ± Q flare Stokes S 2D-spectra were corrected from dark-current,
spectral-line curvature and from transmission differences. Then, we
derived the linear polarization degree P and polarization orientation
angle α 2D-spectra. No change in relative positioning could be found
that would reduce the Stokes parameters U and Q values. No V and I
crosstalks could explain our results either.
Results: The Na
D2 line is linearly polarized with a polarization degree exceeding 5%
at some locations. The polarization was found to be radial at outer
ribbons edges, and tangential at their inner edges. This orientation
change may be due to differences in electron distribution functions
on the opposite borders of flare chromospheric ribbons. Electron beams
propagating along magnetic field lines, together with return currents,
could explain both radial and tangential polarization. At the inner
ribbon edges, intensity profile-width enlargements and blueshifts
in polarization profiles are observed. This suggests chromospheric
evaporation. Appendix A is available in electronic form at http://www.aanda.org
Title: Multi-wavelength analysis of the impact polarization of 2001
June 15th solar flare .
Authors: Xu, Z.; Hénoux, J. C.
Bibcode: 2007MmSAI..78...77X
Altcode:
We report here the impact polarization of the Halpha , Hbeta and MgI
(552.8 nm) lines during an M6.3 solar flare observed on 2001 June 15th
with the THEMIS telescope in the multi-wavelength spectropolarimetric
mode. Typical spectral intensity and polarization profiles are
presented. All of these lines are linearly polarized and polarization
degree vary 3% - 6% at line center. The directions of polarization
are either parallel or perpendicular to the local transverse magnetic
field, which are investigated by simultaneous observation of FeI
(630.2 nm). The polarization islands are located at the edges of flare
kernels. After eliminating scattering, Zeeman effect and intensity
gradient, as possible origin of the observed polarization, this
polarization is interpreted as due either to low energy proton beam
or to the return current associated with electron beams.
Title: First Results of Mg I (3p 1P1-4d
1D2) Line Linear Impact Polarization during
the Solar Flare on 2001 June 15
Authors: Xu, Z.; Henoux, J. C.; Chambe, G.; Petrashen, A. G.; Fang, C.
Bibcode: 2006ApJ...650.1193X
Altcode:
The results of the analysis of the first spectropolarimetric
observations of the 3p 1P1-4d
1D2 Mg I line at 5528.4 Å made during a solar
flare are presented in this paper. The line is found to be polarized
with a polarization degree at the line center that reaches up to 3%
and a direction of polarization nearly parallel to the local transverse
magnetic field. After eliminating scattering, the Zeeman effect, and the
intensity gradient as possible origins of the observed polarization,
this polarization is interpreted as due either to a low-energy proton
beam or to the return current associated with electron beams.
Title: Multiwavelength analysis of the impact polarization of 2001
June 15 solar flare
Authors: Xu, Z.; Henoux, J. C.; Chambe, G.; Fang, C.
Bibcode: 2006cosp...36...49X
Altcode: 2006cosp.meet...49X
The linear polarization of H alpha H beta and MgI lines have been
found during the rise phase of soft X-ray emission of an M6 3 flare on
June 15th 2001 observed by THEMIS telescopes in the multi-wavelength
spectropolarimetric mode Here the linear polarization signals of MgI
line 5528 A are reported for the first time The polarization of these
three lines has a good spatial correspondence and is located at the
edges of flare kernels The maximum polarization degree of H alpha and
H beta lines can reach 4 - 6 at the line center and near line wings
For MgI line the polarization degree can exceed 3 5 concentrating
in the line center Polarization directions are not random but either
parallel or perpendicular to the local transverse magnetic field in
a large degree The origin of the observed short-time polarization is
discussed here with respect to the bombardment on the solar atmosphere
by low-energy protons or high-energy electrons associated with return
current
Title: Multiwavelength Analysis of the Impact Polarization of 2001
June 15 Solar Flare
Authors: Xu, Z.; Hénoux, J. -C.; Chambe, G.; Karlický, M.; Fang, C.
Bibcode: 2005ApJ...631..618X
Altcode:
We report here on the temporal and spatial evolution of the
impact polarization of the Hα and Hβ lines during an M6.3 solar
flare observed on 2001 June 15 with the THEMIS telescope in the
multiwavelength spectropolarimetric mode. Typical spectral intensity
and polarization profiles are presented. Both lines are linearly
polarized. The Hαline degree of polarization exceeds 4% at line
center and in the near line wings. The Hβ line is also linearly
polarized, with a degree of polarization reaching 6%. The directions
of polarization are either parallel or perpendicular to the local
transverse magnetic field (i.e., either radial or tangential because the
transverse magnetic field is directed almost in the flare-to-disk center
direction). However, contrary to Hα, the Hβ polarization direction
is radial only. The Hα and Hβ polarization islands are located at the
edges of flare kernels. Only for radial polarization are these islands
cospatial. No Hβ polarization is found at the places where tangential
Hα polarization is present. The origin of the observed polarization is
discussed. Bombardment by low-energy protons or high-energy electrons
associated with return currents can explain the radial polarization
observed in the lowest flare kernel. The tangential Hα polarization
observed in the surge near the upper flare location is interpreted
as due to the electric current at the origin of the electromagnetic
force that lifts the surge.
Title: Information on particle acceleration and transport derived
from solar flare spectropolarimetry
Authors: Xu, Z.; Hénoux, J. -C.; Chambe, G.; Karlický, M.; Fang, C.
Bibcode: 2005AdSpR..35.1841X
Altcode:
The hydrogen H α line has been found to be linearly polarized at
some locations and times during a June 15th 2001 flare observed with
THEMIS. This flare was accompanied by radio pulses and hard X-ray
emission. Linear polarization is below the noise level in the flare
kernels. However, it is present at the edges of these kernels, in
the line center and near wings where the polarization degree exceeds
4%. The directions of polarization are not random but close within
±15° to the tangential and radial directions. This polarization can
be due either to electron beams and their associated return currents
or to electron and proton beams.
Title: Spectropolarimetric diagnostics of non-thermal particles in
the solar chromosphere
Authors: Xu, Z.; Fang, C.; Henoux, J. -C.
Bibcode: 2004cosp...35..278X
Altcode: 2004cosp.meet..278X
Linear impact polarization of chromospheric lines has already
been observed in the impulsive phase of solar flares, which
can be interpreted as the results of the bombardment of an
anisotropic non-thermal particle beam in the atmosphere. Using the
spectropolarimetric observations of THEMIS, we have measured the
degrees and the directions of the polarization from Hα and CaII
8542 Stokes line profiles of Ellerman Bombs, bright points and faint
flares, which occur mainly in the solar lower atmosphere. We attempt
to explore the main characters of the non-thermal energetic particles
from its effect on the impact linear polarization of the chromospheric
lines. The existence of this polarization due to non-thermal particles
can provide the evidence of reconnection in the solar lower atmosphere.
Title: What have we learned on non-thermal particle acceleration
and transport by optical spectropolarimetry
Authors: Hénoux, J. -C.; Karlicky, M.; Xu, Z.; Fang, C.
Bibcode: 2004cosp...35..647H
Altcode: 2004cosp.meet..647H
Most of the information on non-thermal particles is derived from
hard X-ray, gamma-ray or radio observations. Optical spectroscopic
polarimetry provides complementary information on the particle nature
and velocity distributions. Information is also provided on their
propagation conditions at chromospheric level. We will report here
on the information derived from measurements of the impact linear
polarization made in the Halpha and Hbeta lines with the French-Italian
solar telescope THEMIS.
Title: First detection of return currents in solar flares by
spectropolarimetry with THEMIS
Authors: Hénoux, J. -C.; Karlický, M.
Bibcode: 2003A&A...407.1103H
Altcode:
Using THEMIS French-Italien telescope with the MTR mode, the Hydrogen
Hα and Hβ lines have been observed to be linearly polarized up to a
few percent by impact during the impulsive phase of two solar flares
associated with high-frequency radio pulses. Two privileged directions
of linear polarization are present, respectively radial (in the disk
center to flare direction) and tangential (perpendicular to the radial
direction). This 90 degree change in the linear polarization direction
is interpreted as due to the chromospheric return current generated
by the penetration of a non-thermal electron beam into the chromosphere.
Title: Impact Polarization: A Diagnostic Test for Non-thermal
Particles at Chromospheric Level During Solar Flares
Authors: Hénoux, J. C.; Vogt, E.; Sahal-Bréchot, S.; Karlichký,
M.; Feautrier, N.; Fárník, F.; Chambe, G.; Balanca, C.
Bibcode: 2003ASPC..307..480H
Altcode:
No abstract at ADS
Title: Is it possible to accelerate ions in collapsing magnetic traps?
Authors: Somov, B. V.; Hénoux, J. -C.; Bogachev, S. A.
Bibcode: 2002AdSpR..30...55S
Altcode:
A coronal hard X-ray source observed by Yohkoh during solar flares
can be interpreted under assumption that a fast plasma outflow from a
reconnecting current sheet creates a shock wave above loops of strong
magnetic field. Since the HXR source is located in the upstream side,
rather than in the downstream side of the shock, this provides a new
opportunity of particle acceleration — the two-step acceleration
of electrons and ions. The first step is acceleration by the strong
electric field present inside the current sheet. The second step is fast
'adiabatic heating' inside the collapsing magnetic trap. We demonstrate
some possibilities of ion acceleration in collapsing traps.
Title: Impact polarization as a diagnostic for non-thermal particles
in solar flares
Authors: Vogt, E.; Sahal-Bréchot, S.; Hénoux, J. -C.
Bibcode: 2002ESASP.477..191V
Altcode: 2002scsw.conf..191V
Observations of linear polarization of lines (mainly Hα) during solar
flares have been reported. The orientation (predominantly radial) and
magnitude of the Hα polarization (about 5%) suggest an interpretation
as impact polarization by low energy (<200 keV) non-thermal protons,
which are not accessible by more direct diagnostic observations,
such as hard X-rays (for non-thermal electrons) or gamma-ray lines
(for high energy protons, above a few MeV) which will be observed by
the HESSI spacecraft, soon to be launched by NASA. Impact polarization
observations could thus provide useful complementary data for the study
of accelerated particles in flares. However, observations in a single
line such as Hα can give at best an order of magnitude estimate
of the accelerated protons number flux, so multiline polarimetric
observations, as can be done by the franco-italian THEMIS telescope,
are highly desirable.
Title: Impact Hα line polarization and return current
Authors: Karlický, M.; Hénoux, J. C.
Bibcode: 2002A&A...383..713K
Altcode:
Electron beams, bombarding the dense chromospheric layers during
solar flares, carry electric currents which need to be neutralized by
so-called return currents. Return currents are formed by background
plasma electrons having an anisotropic velocity distribution. Thus
they can generate impact Hα line polarization. First, a numerical
method of computation of the impact Hα line polarization for an
arbitrary electron distribution function is presented. Then the
polarization due to return current electrons associated with beam
electrons is computed. For low electron beam fluxes, the return
current is low and the polarization is only due to the electron beam,
i.e. it is perpendicular to the electron beam direction and it reaches
-8.0%. Increasing the return current and the beam flux leads to a
change of orientation of the polarization by 90deg and
the polarization degree can even reach a maximum of +22.4%. But this
change and the maximum of the polarization require very high electron
beam fluxes of 1.79 x 1012 and 4.8 x 1012
ergs cm-2 s-1, respectively. Therefore plasma
processes, which can reduce the high-energy flux requirement for the
polarization change observations, are briefly discussed.
Title: Solar Flares: White Light
Authors: Hénoux, J.
Bibcode: 2000eaa..bookE2296H
Altcode:
Characteristics of white light solar flares...
Title: Hα Polarization during a Well-observed Solar Flare: Proton
Energetics and Implications for Particle Acceleration Processes
Authors: Emslie, A. Gordon; Miller, James A.; Vogt, Etienne; Hénoux,
Jean-Claude; Sahal-Bréchot, Sylvie
Bibcode: 2000ApJ...542..513E
Altcode:
Observations of polarization of chromospheric lines in solar flares
can constrain the energy flux in accelerated protons. In this paper
we analyze recently reported observations of Hα linear polarization
obtained during a rather well observed flare on 1989 June 20. Modeling
of the magnitude and orientation of the Hα polarization provides
a constraint on the flux of low energy (>~200 keV) protons,
while simultaneous gamma-ray and hard X-ray observations provide
constraints on the fluxes of >~10 MeV protons and >~50 keV
electrons, respectively. These, plus information on the energetics of
the low-temperature and high-temperature thermal emissions, permit
evaluation of both the absolute and relative roles of electrons
and protons in the flare energy budget. We find that accelerated
protons with energies >~200 keV can contain a significant portion
of the total energy released during the flare, consistent with a steep
extrapolation of the proton spectrum to such relatively low energies. We
discuss these results in light of a unified electron/proton stochastic
particle acceleration model and show that the energetics are indeed
consistent with this large proton energy content.
Title: Diagnostics of non-thermal processes in chromospheric
flares --- IV. Limb flare spectra for an atmosphere bombarded by an
electron beam
Authors: Fang, C.; Hénoux, J. -C.; Ding, M. D.
Bibcode: 2000A&A...360..702F
Altcode:
Hα, Lyα, Lyβ, CaII K and λ8542 Å line profiles have been computed
for limb flares with height distributions of temperatures as given by
the semi- empirical models F1 and F2, by including
the non-thermal collisional excitation and ionization of hydrogen and
of ionized calcium that results from electron bombardment. In agreement
with observations, the computed profiles of the hydrogen lines are very
broad, especially at the height where the source function reaches its
maximum. Non-thermal effects are less pronounced for CaII lines.
Title: Hα Polarization Observations and Flare Energetics
Authors: Emslie, A. G.; Miller, J. A.; Vogt, E.; Hénoux, J. -C.;
Sahal-Bréchot, S.
Bibcode: 2000SPD....31.0253E
Altcode: 2000BAAS...32..820E
Observations of polarization of chromospheric lines in solar flares
can constrain the proton energy flux during the flare. In this paper,
we analyze recently-reported observations of Hα linear polarization
obtained during a rather well-observed flare on 1989 June 20. Modeling
of the magnitude and orientation of the Hα polarization provides
a constraint on the flux of low energy ( ~ 0.2 MeV) protons, while
simultaneous gamma-ray and hard X-ray observations provide the fluxes
of ~ 10 MeV protons, and ~ 50 keV electrons, respectively. These,
plus information on the energetics of the low-temperature and
high-temperature thermal emissions, permit evaluation of the relative
role of electrons and protons in exciting the flare plasma. We find
that above about 200 keV, accelerated protons significantly dominate
the flare energy budget, overwhelming electrons by at least two
orders of magnitude. We discuss these results in light of a unified
electron/proton stochastic particle acceleration model, and show
that the energetics are indeed consistent with the broad range of
observational data. This work was supported by NASA's Office of Space
Science and by an NSF/CNRS International Collaboration Award.
Title: On the origin of solar white-light flares
Authors: Gan, W. Q.; Hénoux, J. C.; Fang, C.
Bibcode: 2000A&A...354..691G
Altcode:
Using the Hα line intensity as a constraint, we study the role of
a chromospheric condensation and the role of non-thermal effects in
producing the continuum enhancement of white-light flares. Within
an acceptable range of Hα line intensities and electron energy
flux, it is shown that neither a chromospheric condensation nor
non-thermal effects alone can directly explain the observed continuum
enhancement. The hybrid role of both chromospheric condensation and
non-thermal effects can only lead to a Balmer jump, but still not to a
significant continuum intensity increase between 4000 and 7000 Ä. A
possible picture is discussed, that is, the Balmer jump is directly
produced by the association of a chromospheric condensation and of
non-thermal effects, while the continuum enhancement between 4000 and
7000 Ä, is indirectly produced by the condensation and the non-thermal
effects via radiative heating to the deeper photospheric layers.
Title: Optical View of Particle Acceleration and Complementarity
with HESSI
Authors: Hénoux, J. -C.
Bibcode: 2000ASPC..206...27H
Altcode: 2000hesp.conf...27H
No abstract at ADS
Title: Generation and Interaction of Electric Currents in the Quiet
Photospheric Network
Authors: Somov, B. V.; Hénoux, J. C.
Bibcode: 1999ESASP.448..659S
Altcode: 1999ESPM....9..659S; 1999mfsp.conf..659S
No abstract at ADS
Title: Acceleration Of Photoelectrons In A Return-Current Electric
Field And Ha Polarization
Authors: Karlický, Marian; Hénoux, Jean-Claude
Bibcode: 1999ESASP.446..369K
Altcode: 1999soho....8..369K
Chromospheric hydrogen Balmer Ha and Hb lines have been found to be
linearly polarized in the gradual phase of some solar flares. This
impact polarization is believed to be caused by low energy protons
(E< 200 keV). However, we still must examine if low energy electrons
(E< 200 eV) with an anisotropic velocity distribution function, if
presents, could also generate impact polarisation . In a recent paper
by H noux and Karlicky (1999), the evolution, in chromospheric layers,
of the ve-locity distribution function of high energy photoelectrons
produced by flare X-ray irradiation, was studied. A significant
anisotropy was found. However, due to the dominance of local electrons
in the line formation process, the resulting impact polarization
was one order of magnitude lower than ob-served. In this paper,
we look for the change of the photoelectrons anisotropy that could
result from the pre-sence of a return-current electric field. A 1-D
test particle code is used for computating both the re-turn-current
electric field generated by monoenergetic electron beams in flaring
chromospheric layers and the evolution of the photoelectron distribution
function. Using a 100 keV electron beam with a density of 2 and the MAVH
flare atmosphere, it is found that, at chromospheric level, low-energy
photoelectrons (E at 150 eV), produced by flare X-ray irradiation, can
be accelerated by the return-current electric field. This acceleration
is very sensi-tive to the exact density and temperature profile of the
solar atmosphere and the resulting effect as generation of impact Ha
polarization is discussed.
Title: Physics of Thin Flux Tubes in a Partially Ionized Atmosphere
Authors: Hénoux, J. -C.; Somov, B. V.
Bibcode: 1999ASPC..184...55H
Altcode:
We discuss basic features of the thin magnetic flux-tube generation by
vortex-type motions of the weakly ionized plasma near the temperature
minimum in the solar atmosphere.
Title: Observations of linear polarization in the H_alpha line during
two solar flares
Authors: Vogt, Etienne; Hénoux, Jean-Claude
Bibcode: 1999A&A...349..283V
Altcode:
Two chromospheric flares were observed in Meudon using an H_alpha
flare polarimeter on 17() th July 1982 and 20() th June 1989. A
careful reduction of the data sets has been done in order to remove
the false polarization signals induced by atmospheric turbulence. In
each event, linear polarization directed towards the disk center with a
polarization degree of the order of 5% is detected. This polarization is
correlated in time with the maximum of soft X-ray emission. One event
also shows polarization parallel to the solar limb at the moment of
maximum hard X-ray emission but with a poor signal to noise ratio. We
interpret this polarization as impact polarization, resulting from the
excitation of hydrogen atoms by anisotropic particles. The tangential
polarization could be due to a beam of energetic electrons moving
vertically. However, the best candidates to explain both tangential
and radial polarization are beams of energetic protons with an energy
below 100 keV entering into the chromosphere. The variation of the
polarization direction could result from a modification of the magnetic
topology during the flare.
Title: A spectropolarimetric estimate of energy deposition into the
chromosphere during solar flares
Authors: Kazantsev, S. A.; Karlicky, M.; Petrashen', A. G.; Hénoux,
J. -C.
Bibcode: 1999ARep...43..340K
Altcode:
The dependence of the degree of polarization of Hα and Hβ emission in
the solar chromosphere during solar flares on the energy of an incident
proton beam is calculated assuming that the origin of the observed
linear polarization is collisional. Estimates of the lower boundary
for the energy of the proton beam are obtained using a model for the
kinetics of the propagation of fast protons inside solar-flare magnetic
loops together with spectropolarimetric Hα and Hβ observations.
Title: Velocity distribution function anisotropy of soft X-ray
generated photoelectrons and resulting Hα polarization in solar
flares
Authors: Hénoux, J. -C.; Karlický, M.
Bibcode: 1999A&A...341..896H
Altcode:
Soft X-rays irradiation of the solar atmosphere during solar
flares generates photoelectrons which have an anisotropic velocity
distribution. Using a 1-D test particle code, the anisotropy of the
photoelectrons velocity distribution is derived, and the maximum
degree of linear polarization in the hydrogen Hα and Hβ lines that
photoelectrons could generate by impact is estimated. Over a band
pass of 0.75 and 0.5 Angstroms, the net polarization degree expected
in both lines is predicted not to exceed 0.2%. Therefore, soft X-ray
irradiation cannot explain the one order of magnitude higher degree
of linear polarization observed in solar flares.
Title: Impact polarization of the Hα line during solar flares
Authors: Vogt, E.; Hénoux, J. -C.; Sahal-Bréchot, S.
Bibcode: 1999ASSL..243..431V
Altcode: 1999sopo.conf..431V
No abstract at ADS
Title: The NOAA AR 6718 magnetic field extrapolation with localized
current filaments.
Authors: Karlický, M.; Démoulin, P.; Aulanier, G.; van
Driel-Gesztelyi, L.; Hénoux, J. C.; Jirička, K.
Bibcode: 1999joso.proc...97K
Altcode:
The 3-D extrapolation of magnetic field lines of the July 11, 1991
Kitt Peak magnetogram shows a differential magnetic field shear in
the NOAA 6718 active region. A new combined extrapolation technique,
which includes localized current filaments is suggested and applied in
modelling of this shear. First, the potential field extrapolation is
made and then force-free current paths for several current filaments
in specific positions are computed. It is shown that with the electric
current increase the localized magnetic field shear is increasing. The
total electric current in 16 current filaments is considered up to
1.2×1012A.
Title: Coronal Abundances
Authors: Fludra, A.; Saba, J. L. R.; Henoux, J. -C.; Murphy, R. J.;
Reames, D. V.; Lemen, J. R.; Strong, K. T.; Sylwester, J.; Widing,
K. G.
Bibcode: 1999mfs..conf...89F
Altcode:
Flare X-Ray Measurements from BCS Calcium Abundance Fe/H and Fe/Ca
Abundance Relative Abundances of Ar. Ca. and Fe in Flares Factors
Affecting Abundance Determinations from X-Ray Spectra FCS Abundances
FCS Active-Region Abundances Abundance Variability in Active Regions
Impact of Resonance Scattering Assessment of FCS Active-Region Abundance
Results FCS Flare Abundance Studies Coronal CI/S and Ar/S Measurements
Dem Studies of Flare Abuncances Determination of Solar Abundances
by Solar Flare γ-Ray Spectrometry γ-Ray Spectral Analysis γ-Ray
Results Solar Energetic Particles Major Proton Events CIR Events from
Coronal Holes Impulsive Flare Events Theory of Abundance Fractionation
Gravitational Settling Pressure Gradient and Stationary Diffusion
Ion-Neutral Separation Due to Currents Ion-Neutral Separation Due to
Electromagnetic Forces Discussion Summary
Title: Multi-Wavelength Analysis of the Flare on 2 October 1993
Authors: Fang, C.; Tang, Y. H.; Hénoux, J. -C.; Huang, Y. R.; Ding,
M. D.; Sakurai, T.
Bibcode: 1998SoPh..182..163F
Altcode:
By use of Yohkoh hard X-ray flux and soft X-ray images, and of vector
magnetograms and 2D spectral observations, a 1N/C6.5 flare observed on
2 October 1993 is analysed in detail. Evidence is provided not only
morphologically but also quantitatively that the dynamics at kernels
A and C of the flare in the impulsive phase were controlled mainly by
electron beam bombardment, while the heating of kernel B is mainly due
to heat conduction. By plotting the energy gradient of the electron
energy flux as a function of energy for the various spectral indexes
observed during the flare, the acceleration mechanism is found to be
such that there is a constant energy E0, close to 20 keV,
for which the electron flux d F1/dE is constant. It is shown
that such a conclusion can be reached more directly by using the photon
flux, which in that case must be constant for E=E0, whatever
the value of the power index. This result implies also that the electron
spectrum is represented by a power law and that the X-ray photons are
produced in a thick target. Instantaneous momentum balance is shown to
exist between the upflowing soft X-ray-emitting and the downflowing
Hα- emitting plasma at the kernels of the flare. The observed Hα
red asymmetry is well reproduced by the non-LTE computation, with the
down-moving condensation included. The observation of the magnetic
field suggests that the flare was triggered probably by magnetic
flux emergence.
Title: Spectropolarimetric studies of H alpha emission
in "solar moustaches": Observations and calculation of the Stokes
parameters
Authors: Kazantsev, S. A.; Firstova, N. M.; Kashapova, L. K.; Bulatov,
A. V.; Petrashen', A. G.; Henoux, J. -C.
Bibcode: 1998ARep...42..702K
Altcode:
The results of spectropolarimetric observations of three solar
`moustaches' carried out on the Large Vacuum Solar Telescope of
Baikal Observatory of the Institute of Solar-Terrestrial Physics are
presented. The observed degree of polarization varies from 2-13%. The
direction of the plane of polarization for a moustache with moderate
intensity is tangential, and is radial for the weakest moustache. In
the brightest moustache, the plane of polarization is close to radial
at the line center, and is tangential in the wings.
Title: A possible mechanism for the Hα broad wings emission of
Ellerman bombs
Authors: Henoux, J. -C.; Fang, C.; Ding, M. D.
Bibcode: 1998A&A...337..294H
Altcode:
In this paper, the non-thermal emission of Lyalpha , Lybeta and Hα
lines generated through charge exchange by protons accelerated in
the low chromosphere and moving with a small pitch angle around an
horizontal magnetic field has been computed. Computations have been
done for observations made at the center of the solar disk, i.e. in a
situation where the solar magnetic field is perpendicular to the line
of sight, for non zero pitch angles. In such conditions, the photons
emitted through charge exchange are Doppler shifted symmetrically in
both wings of the lines. The Hα far line wing intensities increase
significantly, making possible to reproduce the characteristics of
the spectra of Ellerman bombs. Thus it is proposed that a proton beam
accelerated in the low chromosphere, and losing its energy there,
is a viable candidate for explaining the observed EB spectra.
Title: Spectropolarimetric studies of H alpha emission in
"solar moustaches": Energy of the excited electron beam
Authors: Kazantsev, S. A.; Firstova, N. M.; Petrashen', A. G.; Henoux,
J. =C.
Bibcode: 1998ARep...42..707K
Altcode:
Spectropolarimetric observations of the Hα emission of `solar
moustaches' are used to estimate the energy of the beam of electrons
that is assumed to give rise to the observed polarization during
its shock excitation of an ensemble of hydrogen atoms in the solar
chromosphere.
Title: FIP Fractionation: Theory
Authors: Hénoux, Jean-Claude
Bibcode: 1998SSRv...85..215H
Altcode:
In this review, the main models of ion-neutral frationation leading to
an enhancement of the low FIP to high FIP abundance ratio in the corona
or in the solar wind, are presented. Models based on diffusion parallel
to the magnetic field are discussed; they are highly dependent on the
boundary conditions. The magnetic field, that naturally separates ions
from neutrals moving perpendicular to the field lines direction, when
the ion-neutral frequency becomes lower than the ion gyrofrequency,
is expected to play an active role in the ion-neutral separation. It
is then suggested that ion-neutral fractionation is linked to the
formation of the solar chromosphere, i.e. in magnetic flux-tubes at
a temperature between 4000 and 6000 K.
Title: Line profiles in moustaches produced by an impacting energetic
particle beam
Authors: Ding, M. D.; Henoux, J. -C.; Fang, C.
Bibcode: 1998A&A...332..761D
Altcode:
The Hα line profile in moustaches is characterized by enhanced wings
and a deep central absorption. We explore the possibility that such a
profile may be due to the effect of energetic particles bombarding the
atmosphere. Computations show that the characteristics of moustache
line profiles can be qualitatively reproduced in two extreme cases,
either injection from the corona of high energy particles (ga 60 keV
electrons or ga 3 MeV protons) or injection in a low-lying site, in
middle chromosphere or deeper, of less energetic particles ( ~ 20 keV
electrons or ~ 400 keV protons). The requirements on the energy and on
the depth of the injection site of energetic particles are reduced in
the case of observations close to the solar limb. The role of protons
of energies below 1 MeV is slightly less significant than that of
deka-keV electrons in the case of a high particle injection site,
but such protons remain to be viable candidates in the case of lower
particle injection sites and of observations at larger heliocentric
angles. Observations at various wavelengths are needed to find which
of these hypotheses is convenient for explaining a given event.
Title: Non-thermal hydrogen line emission caused by an oblique
incident proton beam through charge exchange
Authors: Zhao, X.; Fang, C.; Henoux, J. -C.
Bibcode: 1998A&A...330..351Z
Altcode:
In this paper, formulae are given for computing the non-thermal emission
of superthermal hydrogen atoms generated through charge exchange by
the bombardment of the solar atmosphere by an oblique incident proton
beam with a given pitch angle. Specifically, we discuss the non-thermal
emission of hydrogen in Lyalpha , Lybeta , and Hα lines and find that
the profiles of these lines are quite different from the ones caused by
bombardment by a proton beam moving vertically. The intensity and the
asymmetry of the non-thermal emission profiles strongly depend on the
beam pitch angle alpha and on the angle theta between the direction
of magnetic field and the line of sight. By computing the thermal
emission under the semi-empirical flare atmospheric models F1, F2, and
the quiet-Sun atmospheric model C, we compare the relative importance
of thermal and non-thermal emission. For the Hα line, the non-thermal
emission, with the proton flux used, is too small to be detectable; for
the Lyalpha line, the contribution of non-thermal emission to the line
wings is smaller than the one of a vertical beam; while for the Lybeta
line, line wing enhancement and broadening are significant. Thus, Lybeta
line is a good diagnostic tool for non-thermal proton beam bombardment.
Title: A study of activity in interacting sunspot groups
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Hénoux, J. -C.
Bibcode: 1998PAICz..88...13S
Altcode:
No abstract at ADS
Title: Application to Astrophysics of Collisional Polarization
Spectroscopy
Authors: Hénoux, J. -C.; Vogt, E.
Bibcode: 1998PhST...78...60H
Altcode:
Collisional polarization specroscopy brings unique information on
the anisotropies of the velocity distribution function of energetic
particles, allowing the identification of these particles and
the evaluation of the energy flux they carry. The application of
collisional polarization spectro-scopy is still limited to Solar
Physics. Chromospheric hydrogen Balmer lines Hα and Hβ have been found
to be linearly polarized in solar flares. The polarization seems to
be associated with enhanced soft X-ray emission and is found to be in
the flare to disk center direction. In the hypothesis where particles
are accelerated higher in the solar corona, protons of energy lower
than 1MeV are found to be the best candidates to explain the observed
polarization. The significant degree of polarization of a few per cent
observed may also indicate a low local acceleration site but still
requires the acceleration of protons in the 10 to 100keV energy range.
Title: Particle Beam Diagnostics Based on UV and Optical Spectra of
Solar Flares (invited)
Authors: Fang, C.; Ding, M. D.; Hénoux, J. C.
Bibcode: 1998asct.conf..497F
Altcode:
No abstract at ADS
Title: FIP Fractionation: Theory
Authors: Hénoux, J. -C.
Bibcode: 1998sce..conf..215H
Altcode:
No abstract at ADS
Title: Quasi-separatrix layers in solar flares. II. Observed magnetic
configurations.
Authors: Demoulin, P.; Bagala, L. G.; Mandrini, C. H.; Henoux, J. C.;
Rovira, M. G.
Bibcode: 1997A&A...325..305D
Altcode:
We show that the location of Hα or OV flare brightenings is related
to the properties of the field-line linkage of the underlying magnetic
region. The coronal magnetic field is extrapolated from the observed
photospheric field assuming a linear force-free field configuration
in order to determine the regions of rapid change in field-line
linkage, called "quasi-separatrix layers" or QSLs. They are open
layers that behave physically like separatrices: breakdown of ideal
magnetohydrodynamics and release of free magnetic-energy may occur
at these locations when their thickness is small enough. A feature
common to all the flaring regions studied is found to be the presence
of QSLs where Hα flare kernels are observed. The brightenings are
along restricted regions of very thin QSLs; an upper bound of their
thickness is 1Mm but it is several order of magnitude smaller in most
of the cases. These places coincide in general with zones where the
longitudinal field component is greater than 100G. These results allow
us to constrain present models of solar flares and localise where a
break-down of ideal MHD can occur. The studied flares are found to be
fed in general by only one electric current loop, but they imply the
interaction of two magnetic bipoles. The extrapolated coronal field
lines involved in the process have their photospheric footpoints
located at both sides of QSLs, as expected in recent 3D magnetic
reconnection models.
Title: Evidence of Magnetic Reconnection from Hα, Soft X-Ray and
Photospheric Magnetic Field Observations
Authors: Mandrini, C. H.; DÉmoulin, P.; BagalÁ, L. G.; Van
Driel-Gesztelyi, L.; HÉnoux, J. C.; Schmieder, B.; Rovira, M. G.
Bibcode: 1997SoPh..174..229M
Altcode:
A conventional view of magnetic reconnection is mainly based on
the 2-D picture of an X-type neutral point, or on the extension of
it to 3-D, and it is thought to be accompanied by flux transport
across separatrices (places where the field-line mapping is
discontinuous). This view is too restrictive when we realize the variety
of configurations that are seen flaring. We designed an algorithm,
called Source Method (SM), to determine the magnetic topology of
active regions (ARs). The observed photospheric field was extrapolated
to the corona using subphotospheric sources and the topology was
defined by the link between these sources. Hα flare brightenings
were found to be located at the intersection with the chromosphere
of the separatrices so defined. These results and the knowledge we
gained on the properties of magnetic field-line linkage, led us to
generalize the concept of separatrices to `quasi-separatrix layers'
(QSLs) and to design a new method (`quasi-separatrix layers method',
QSLM) to determine the magnetic topology of ARs. QSLs are regions where
the magnetic field-line linkage changes drastically (discontinuously
when they behave like separatrices) and the QSLM can be applied to ARs
where the photospheric field has been extrapolated using any kind of
technique. In this paper we apply the QSLM to observed flaring regions
presenting very different configurations and also to a decaying AR where
a minor phenomenon, like an X-ray bright point (XBP), is observed. We
find that the locations of flare and XBP brightenings are related to the
properties of the field-line linkage of the underlying magnetic region,
as expected from recent developments of 3-D magnetic reconnection. The
extrapolated coronal field lines representing the structures involved
in the analyzed events have their photospheric footpoints located
at both sides of QSLs. Our results strongly support the hypothesis
that magnetic reconnection is at work in various coronal phenomena,
ranging from the less energetic ones to large-scale eruptions.
Title: Polarization of the hydrogen Halpha_ line in solar
flares: contribution of the different radiative and collisional
processes.
Authors: Vogt, E.; Sahal-Brechot, S.; Henoux, J. C.
Bibcode: 1997A&A...324.1211V
Altcode:
Linear polarization of the Halpha_ line of hydrogen has
been observed in solar flares. The observed polarization degree
can be as high as 10% for a flare located near the limb and a one
minute integration time. This polarization is currently explained
as anisotropic collisional excitation of the n=3 level by vertical
beams of protons with an energy greater than a few keV. Transfer of
population between the Zeeman excited states by the local protons with
an isotropic velocity distribution may reduce the polarization expected
from the beam bombardment only. The amplitude of this effect has been
computed by solving the statistical equilibrium equations for a 9-level
hydrogen atom (all the levels of n=1, 2,3 including fine structure)
for three different atmospheric models. The different collisional and
radiative processes for populating and depopulating the Zeeman sublevels
have been taken into account: excitation and deexcitation by collisions
with the protons of the beam and with the local electrons and protons,
excitation by the local Lyalpha_, Lybeta_
and Halpha_ radiation, and deexcitation by spontaneous
emission. It has been found that the polarization is not destroyed but
reduced by a factor two to ten. Beams of non-thermal particles can be,
as assumed previously, at the origin of the observed polarization,
however, to get a significant degree of polarization, the flux of these
particles must be significantly higher than that originally expected.
Title: Can we Extrapolate a Magnetic Field when its Topology is
Complex?
Authors: DÉmoulin, P.; HÉnoux, J. C.; Mandrini, C. H.; Priest, E. R.
Bibcode: 1997SoPh..174...73D
Altcode:
In order to understand various solar phenomena controlled by the
magnetic field, such as X-ray bright points, flares and prominence
eruptions, the structure of the coronal magnetic field must be
known. This requires a precise extrapolation of the photospheric
magnetic field. Presently, only potential or linear force-free
field approximations can be used easily. A more realistic modelling
of the field is still an active research area because of well-known
difficulties related to the nonlinear mixed elliptic-hyperbolic nature
of the equations. An additional difficulty arises due to the complexity
of the magnetic field structure which is caused by a discrete partition
of the photospheric magnetic field. This complexity is not limited
to magnetic regions having magnetic nulls (and so separatrices)
but also occurs in those containing thin elongated volumes (called
Quasi-Separatrix Layers) where the photospheric field-line linkage
changes rapidly. There is a wide range for the thickness of such layers,
which is determined by the character (bipolar or quadrupolar) of the
magnetic region, by the sizes of the photospheric field concentrations
and by the intensity of the electric currents. The aim of this paper
is to analyse the recent nonlinear force-free field extrapolation
techniques for complex coronal magnetic fields.
Title: Determination of proton beam energy from data of
spectropolarimetric studies of Hα-emission of th esolar
chromosphere, as carried out at the Paris Observatory
Authors: Kazantsev, S. A.; Petrashen', A. G.; Henoux, J. -C.
Bibcode: 1997OptSp..82..627K
Altcode:
No abstract at ADS
Title: Spectroscopolarimetric Sensing of Energy Deposition Into the
Chromosphere during Solar Flares - I. Observations
Authors: Firstova, N. M.; Hénoux, J. -C.; Kazantsev, S. A.; Bulatov,
A. V.
Bibcode: 1997SoPh..171..123F
Altcode:
Measurements of linear polarization in hydrogen Hα and Hβ lines,
made with the Large Solar Vacuum Telescope of Baikal Astrophysical
Observatory and Automated Solar Telescope of Sayan Solar Observatory,
affiliated with the Russian Institute of Solar and Terrestrial Physics,
are reported in this paper. Short-term polarization associated with
solar flares is found to be present in active regions. There is
a significant tendency for the Hα polarization vector to be radial,
i.e., in the flare-to-disk-center direction. This polarization may be
due to atmospheric bombardment by hecta keV protons. On the other hand,
the polarization vector is found to be perpendicular to the radial
direction at some locations where the line profile has a typical
mustache shape suggesting a bombardment by energetic electrons. The
Hβ line is also linearly polarized. However, no preferential direction
of polarization is found in this line, which is formed more deeply in
the solar atmosphere.
Title: The photospheric dynamo. I. Physics of thin magnetic flux
tubes.
Authors: Henoux, J. C.; Somov, B. V.
Bibcode: 1997A&A...318..947H
Altcode:
In a previous paper (Henoux and Somov, 1991A&A...241..613H) it
has been shown that, in an initially weak magnetic field, a radial
inflow of neutrals can generate azimuthal DC currents, and that an
azimuthal velocity field can create radial DC currents leading to
the circulation of vertical currents. The effects of such azimuthal
velocity field on the intensity and topology of electric currents
flowing in thin magnetic flux tubes is now investigated in detail in
this paper. Two systems of currents flowing in opposite direction are
created connected at photospheric level by transverse currents. The
electromagnetic forces produced by these currents play a significant
role in the structure and dynamics of flux tubes. Even for moderate
values of the azimuthal photospheric velocities, the currents created
are strong enough to prevent by the pinch effect an opening of the flux
tube with height; despite the decrease of the ambient gas pressure with
height, the thin flux tube extends into the solar atmosphere above the
temperature minimum region. In the internal current shell, the rise from
the photosphere of a partially ionized gas is found to have two main
effects: (a) the upflow of this gas associated to a leak of neutrals
across magnetic field lines leads to an increase of the ionization
degree with altitude typical for the chromosphere, and brings above
the temperature minimum region an energy flux comparable to the flux
required for chromospheric heating, (b) the outflow of neutrals that
takes place at the chromospheric level across magnetic field lines,
and leads to ion-neutral separation, may explain the observed abundance
anomalies in the corona by enhancing in the upper part of the tube
the abundances of elements of low ionization potential. Upward motions
are also present between the two current systems outside the internal
cylindrical current. Their velocity is high enough to lift the matter
to an altitude characteristic of spicules.
Title: Spectral Diagnostics of the Energetic Particles in Solar Flares
Authors: Fang, C.; Ding, M. D.; Henoux, J. C.; Gan, W. Q.
Bibcode: 1996JKASS..29..295F
Altcode:
No abstract at ADS
Title: Quasi-Separatrix Layers and Their Relationship with Solar
Flares
Authors: Bagala, L. G.; Mandrini, C. H.; Rovira, M. G.; Demoulin,
P.; Henoux, J. C.
Bibcode: 1996RMxAC...4Q..90B
Altcode:
No abstract at ADS
Title: Quasi-Separatrix Layers in Simple Magnetic Configurations
Authors: Mandrini, C. H.; Demoulin, P.; Henoux, J. C.; Priest, E.
Bibcode: 1996RMxAC...4Q.104M
Altcode:
No abstract at ADS
Title: The Viability of Energetic Protons as an Agent for Atmospheric
Heating during the Impulsive Phase of Solar Flares
Authors: Emslie, A. Gordon; Henoux, Jean-Claude; Mariska, John T.;
Newton, Elizabeth K.
Bibcode: 1996ApJ...470L.131E
Altcode:
Recent observations of gamma -ray line intensities in solar flares
results have led to the suggestion that the energy content in
accelerated protons may rival that of accelerated electrons. However,
simply having a large energy content in accelerated protons is not
sufficient to ensure an important role for protons in driving the
response of the atmosphere to flare energy input: a viable model
must also deposit a large fraction of the particle energy at the top
of the chromosphere to account for the large increase in soft X-ray
emission measure that characterizes the main phase of a flare. While
hard X-ray producing electrons indeed deposit a sufficient amount of
energy at the appropriate depths in the atmosphere, only protons with
a characteristic energy of order 1 MeV do likewise. It is intriguing
that a characteristic energy of just this value has been obtained
through independent analysis of gamma -ray line intensities. However,
it must be noted that protons of this energy do not have a signature
in hard X-rays, leading us to conclude that a substantial fraction of
the flare energy budget must still reside in deka-keV electrons. In
order to complete the global energetic picture, further corroborating
observational diagnostics for MeV protons are desirable. In this Letter,
we discuss such suitable observations.
Title: Proton transport in a magnetic loop and Hα impact line
linear polarization.
Authors: Karlicky, M.; Henoux, J. -C.; Smith, D.
Bibcode: 1996A&A...310..629K
Altcode:
Using a 1-D test particle model with 350000 numerical protons,
we study the evolution of the proton distribution function in a
magnetic loop. A continuous injection of low-energy 200-1500keV
protons with a distribution function proportional to a E^-3^
power-law is considered. The acceleration region is assumed to be
at the top of a flare loop where the protons are injected into a
cone of pitch angles centered along the loop axis. The computations
are made for a static loop of length 20880km with the parameters
in the chromosphere corresponding to the VAL-C model of the solar
atmosphere. Coulomb collisions, mirroring, and Alfven wave scattering
in an intermediate regime (W_a_^tot^=10^-1^erg/cm^3^) relative to
prior analyses corresponding to saturated scattering are taken into
consideration. The proton distribution function in the chromosphere
at the Hα formation layer is computed. The resulting anisotropy of
the proton distribution function in a quasi-stationary state of proton
bombardment is analyzed from the point of view of its expected effects
on the impact linear polarization of chromospheric lines.
Title: Energetic Protons as a Form of Energy Transport During The
Impulsive Phase of Solar Flares?
Authors: Emslie, A. G.; Henoux, J. -C.; Mariska, J. T.; Newton, E. K.
Bibcode: 1996AAS...188.2601E
Altcode: 1996BAAS...28..857E
Recent results based on hard X-ray and gamma-ray observations of solar
flares have suggested that the energy content in accelerated protons
may rival that of accelerated electrons. However, simply having a large
energy content in accelerated protons is not sufficient to ensure an
important role for protons in driving the response of the atmosphere to
flare energy input: a viable model must also deposit a large fraction
of the particle energy at the top of the chromosphere, to account for
the large increase in soft X-ray emission measure that characterizes
the main phase of a flare. While hard X-ray-producing electrons indeed
deposit a sufficient amount of energy at the appropriate depths in the
atmosphere, we show that only protons with a characteristic energy of
order 1 MeV do likewise. Since protons of this energy do not have a
signature in hard X-rays, we conclude that a substantial fraction of the
flare energy budget must indeed reside in deka-keV electrons. In order
to complete the global energetic picture, observational diagnostics
for MeV protons are required; suitable observations are discussed. This
work was supported by the NASA Office of Space Science and by the NSF
International Programs Division.
Title: Spectropolarimetry of solar flare based on measurements of
the H beta hydrogen line
Authors: Kazantsev, S. A.; Petrashen', A. G.; Firstova, N. M.; Henoux,
J. -C.
Bibcode: 1996OptSp..80..635K
Altcode:
No abstract at ADS
Title: Quasi-Separatrix layers in solar flares. I. Method.
Authors: Demoulin, P.; Henoux, J. C.; Priest, E. R.; Mandrini, C. H.
Bibcode: 1996A&A...308..643D
Altcode:
Magnetic reconnection is usually thought to be linked to the presence
of magnetic null points and to be accompanied by the transport of
magnetic field lines across separatrices, the set of field lines where
the mapping of field lines is discontinuous. In view of the variety
of observed flaring configurations, we show that this view is too
restrictive. Instead, Priest and Demoulin (1995) have explored a way
of generalising the concept of separatrices to magnetic configurations
without field-line linkage discontinuities. They propose that magnetic
reconnection may also occur in 3D in the absence of null points at
"quasi-separatrix layers" (QSLs), which are regions where there is
drastic change in field-line linkage. In previous studies we have shown
that solar flare kernels are linked to the topology of the active-region
magnetic field. The observed photospheric field was extrapolated to
the corona using subphotospheric magnetic sources and the topology was
defined by the magnetic linkage between these sources, the method being
called SM (for Source Method). In this paper we define a new method,
called QSLM (for Quasi-Separatrix Layers Method), which finds the
location of QSLs above the photosphere. It is designed to be applied to
any kind of magnetic field representation, while, in the present paper,
we apply it only to simple theoretical magnetic configurations in order
to compare it with the SM. It generalises the concept of separatrices to
magnetic configurations without field-line linkage discontinuities. The
QSLM determines elongated regions that are in general located along
small portions of the separatrices defined by the SM, and in the limit
of very concentrated photospheric fields both methods give the same
result. In bipolar magnetic configurations two QSLs are found at both
sides of the inversion line, while in quadrupolar configurations four
appear. We find that there is a wide range for the thickness of the
QSLs, which is determined by the character (bipolar or quadrupolar)
of the magnetic region and by the sizes of the photospheric field
concentrations. We then show that smooth photospheric motions induce
concentrated currents at the locations defined by the QSLM. We prove
this only for initially potential configurations but, due to the form
of the equations, we conjecture that it is also valid for any kind
of initial magnetic equilibrium. We conclude that, even in bipolar
configurations, there are localized places where current build-up can
be induced by photospheric motions, leading to ideal MHD breakdown
with strong flows and magnetic energy release.
Title: Polarimetric Study of Solar Flares
Authors: Vogt, E.; Hénoux, J. C.
Bibcode: 1996SoPh..164..345V
Altcode:
The theory of impact polarization is briefly
reviewed. Spectropolarimetry provides a tool to derive the nature,
the number flux, and the main characteristics of the angular velocity
distribution function of energetic particles accelerated in solar
flares. As an exemple of application of polarimetry the spatial and
temporal characteristics of the linear polarization of the hydrogen
Hα line observed in a solar flare is presented.
Title: 3D Magnetic Reconnection: Example of an X-Ray Bright Point
Authors: Demoulin, P.; Mandrini, C. H.; van Driel-Gesztelyi, L.;
Priest, E. R.; Henoux, J. C.; Schmieder, B.
Bibcode: 1996ASPC..111...49D
Altcode: 1997ASPC..111...49D
In the classical view magnetic reconnection occurs at neutral points
and implies transport of magnetic field-lines across separatrices. The
authors show that reconnection may also occur in the absence of neutral
points at so-called "quasi-separatrix layers" (QSLs), where there is a
steep gradient in field-line linkage at the boundaries. Reconnection
occurs in QSLs where the field-line velocity becomes larger than the
allowed maximal plasma velocity or where the electric-current density
becomes too great. The authors describe both a theoretical and an
observed configuration. In the case of a simple sheared X-field they
show that even a smooth continuous shear flow, imposed at the boundary,
gives strong plasma jetting inside and parallel to the QSLs. Applying
the QSL method to an X-ray bright point observed by Yohkoh, they find
field lines in the extrapolated field which are on both sides of QSLs
and which are in good agreement with loops observed in Hα and X-rays
related to emerging flux. The evolution of the QSL width may explain
the brightness evolution of the XBP.
Title: Impact spectropolarimetry of solar flares.
Authors: Henoux, J. -C.; Vogt, E.
Bibcode: 1996joso.proc...60H
Altcode:
Hydrogen Hα spectropolarimetry provides a tool to derive the nature,
the number flux, and the main characteristics of the angular velocity
distribution function of energetic particles accelerated in solar
flares. As an example of application, the main characteristics of the
linear polarization of the hydrogen Hα line observed in a solar flare
are briefly presented.
Title: Effects on Non-Thermal Particles on the UV and Optical Spectra
of Solar Flares
Authors: Henoux, J. -C.; Fang, C.
Bibcode: 1996mpsa.conf..561H
Altcode: 1996IAUCo.153..561H
No abstract at ADS
Title: Constraints on flare models set by the active region magnetic
topology Magnetic topology of AR 6233.
Authors: Mandrini, C. H.; Demoulin, P.; Rovira, M. G.; de La
Beaujardiere, J. -F.; Henoux, J. C.
Bibcode: 1995A&A...303..927M
Altcode:
We present a detailed analysis of the magnetic topology of AR 6233
on two consecutive days (August 28 and 29, 1990) and compare the
location of the magnetic separatrices and separators with off-band
Hα observations and other flare manifestations, such as intense
nonthermal electron precipitation and high coronal pressure sites,
for two flares that occured on these days. Since for one of the days
of our analysis we have two magnetograms covering fields of view with
different scale lengths, we analyzed the dependence of the topology
of the region of interest on the presence of external magnetic field
concentrations. We have found that considering these concentrations
does not modify the location of separatrices in the region. Because
transverse magnetograms indicate that strong magnetic shear is present
along the longitudinal inversion line where flare brightenings are
located, the observed photospheric magnetic field is modeled in an
approach in which a combination of sources with current-free and non
current-free magnetic field is used. This model allows us to obtain a
better fit between the observed and modeled transverse field, then we
find a closer relationship between separatrices and flare features. The
results of a current-free and of a linear force-free approach are also
shown for comparison. As in other flaring regions studied previously,
chromospheric flare brightenings are found on separatrices. The
topological structure obtained for these flares is rather complex. We
find that the connectivity of field lines may change drastically
from one edge of a ribbon to the other. Electron precipitation and
high coronal pressure sites, and some photospheric intense currents
are also found in the immediate vicinity of separatrices. The early
kernels of August 28 flare are found closer to the separatrices of
the nonpotential field, while the later are closer to those of the
potential field. All these results agree with the hypothesis that
magnetic energy is stored in field-aligned currents and released due
to magnetic field reconnection, with a noticeable relaxation of the
field, either at the separator region or on separatrices.
Title: A Topological Approach to Understand a Multiple-Loop Solar
Flare
Authors: Bagalá, L. G.; Mandrini, C. H.; Rovira, M. G.; Démoulin,
P.; Hénoux, J. C.
Bibcode: 1995SoPh..161..103B
Altcode:
We analyze the UV and X-ray data obtained by the SMM satellite for
the flare starting at 02:36 UT on November 12, 1980 in AR 2779. From
a detailed revision of the OV emission, we find that the observations
are compatible with energy being released in a zone above the magnetic
inversion line of the AR intermediate bipole. This energy is then
transported mainly by conduction towards the two distant kernels located
in the AR main bipole. One of these kernels is first identified in
this paper. Accelerated particles contribute to the energy transport
only during the impulsive phase.
Title: Models for explaining the observed spatial variation of
element abundances - a review
Authors: Henoux, J. -C.
Bibcode: 1995AdSpR..15g..23H
Altcode: 1995AdSpR..15...23H
Recent results on the spatial dependence of low and high-FIP (First
Ionization Potential) element abundances in the sun, and on the fine
structure of this FIP dependence, are briefly discussed. Existing
models of FIP fractionation are reviewed. The main models are based on
ion-neutral separation in a magnetic field and they differ fundamentally
by the nature of the forces - gravity pressure or electric forces -
acting on the particles - neutrals or ions - that cross the lines of
force. These models predict an enhancement of low-FIP elements at the
coronal level. However, a quantitative prediction of the resulting
coronal abundances is still not possible. Abundance enhancements
of ^3He and of heavy elements observed in solar energetic particles
accelerated in impulsive flares are also quoted, and the most recent
particle acceleration theories are briefly presented. In conclusion
we emphasize the need to understand the origin of coronal abundances
in order to obtain clues on mechanisms for chromospheric formation.
Title: The Electrical Current Structure Associated with Solar Flare
Electrons Accelerated by Large-Scale Electric Fields
Authors: Emslie, A. Gordon; Henoux, Jean-Claude
Bibcode: 1995ApJ...446..371E
Altcode:
We consider the scenario in which the high-energy electrons responsible
for hard X-ray production in the impulsive phase of solar flares are
accelerated by a large-scale direct electric field. We point out that
both Ampere's and Faraday's laws require that the current pattern
associated with the accelerated electrons be highly filamented,
with the degree of filamentation dependent on the assumed structure
of the preflare current pattern. Recognizing that cospatial return
currents are not permitted in such models, we consider the closure
of the current pattern using a cross-field drift of protons at the
chromospheric footpoints of the elementary magnetic flux tubes. We
demonstrate that there is a sufficient rate of ionization (both
collisional and radiative) and recombination to create and absorb,
respectively, the necessary electron fluxes, and we also demonstrate
that pressure gradients in the chromosphere are adequate to drive the
opposite flows of protons and hydrogen atoms against the frictional
forces there. We further argue that the current closes within a
vertical layer of order the thickness of the current channel, i.e.,
a few meters, and that this layer is most likely situated at the
base of the transition region, where the conductivity tensor first
becomes roughly isotropic. A possible diagnostic of this model is the
polarization of the Hα line produced by an unequal population of the
n = 3 hydrogen atom sublevels in the presence of the anisotropic proton
distribution function commensurate with the above current structure.
Title: Hydrogen line spectra of a nonthermal proton beam. due to
charge exchange in solar flares
Authors: Fang, C.; Feautrier, N.; Henoux, J. -C.
Bibcode: 1995A&A...297..854F
Altcode:
Using more recent values of the atomic parameters and a more refined
atmospheric model, the nonthermal line emission resulting from
proton-hydrogen charge exchange has been recomputed. Confirming the
results of Canfield & Chang (1985), the hydrogen Hα nonthermal
line emission was found too small to be detectable. On the other hand,
the nonthermal emission in the red wings of the Lyα and Lyβ lines
is significantly high and can be used as a diagnostic of low energy
protons. However, this emission is at least one order of magnitude
lower than the value derived by Canfield and Chang.
Title: Determination of the energy of the proton beam formed in a
solar flare on the basis of spectropolarimetric data
Authors: Kazantsev, S. A.; Firstova, N. M.; Petrashen', A. G.; Henoux,
J. -C.; Bulatov, A. V.
Bibcode: 1995OptSp..78..655K
Altcode:
No abstract at ADS
Title: Diagnostics of non-thermal processes in chromospheric
flares. III. Lyα and Lyβ spectra for an atmosphere bombarded by
electron or proton beams.
Authors: Henoux, J. C.; Fang, C.; Gan, W. Q.
Bibcode: 1995A&A...297..574H
Altcode:
The Lyα and Lyβ line profiles, including the nonthermal excitation
and ionization of hydrogen by electron or proton bombardment, have
been computed for atmospheres with the temperature distributions of the
semi-empirical models F_1_ and F_2_. These computations indicate that
the intensities at the line wings are greatly enhanced by nonthermal
effects, especially for an electron beam bombardment. These effects are
the most obvious when the coronal column mass is relatively small. Thus,
nonthermal effects should be the most pronounced just at the beginning
of the impulsive phase. After the maximum of the impulsive phase,
due to a fast increase of the coronal column mass, these effects will
rapidly decrease.
Title: Semi-Empirical Models of the White-Light Flare on October
24, 1991
Authors: Fang, C.; Henoux, J. C.; Ju, Hu; Yin-Zhang, Xue; Xiu-Fa,
Gao; Qi-Jun, Fu
Bibcode: 1995SoPh..157..271F
Altcode:
On October 24, 1991, a white-light flare was observed both from space
and from the ground. A multi-waveband spectral analysis shows that
the peak time of the continuum emission coincides well with that of
a radio burst at 2840 MHz and with the hard X-ray emission. Three
semi-empirical models, corresponding to the pre-flare condition and to
the peak time of continuum emission both with and without non-thermal
excitation and ionization of hydrogen by an electron beam, have been
obtained. The results indicate that there is fast heating both in the
chromosphere and the photosphere. Some evidence is given that this WLF
is very likely a result of bombardment by an electron beam. By taking
into account non-thermal effects, the chromospheric temperature of
the semi-empirical model is significantly reduced.
Title: Current Closure in the Impulsive Phase of Solar Flares
Authors: Emslie, A. G.; Hénoux, J. -C.
Bibcode: 1995SPD....26.1313E
Altcode: 1995BAAS...27..989E
No abstract at ADS
Title: Polarization spectroscopy of ionized gases
Authors: Kazantsev, Sergei A.; Henoux, Jean-Claude
Bibcode: 1995ASSL..200.....K
Altcode: 1995psig.book.....K
No abstract at ADS
Title: Impact spectropolarimetry in the hydrogen Hα line: present
atomic data and astrophysical applications
Authors: Kazantev, S. A.; Feautrier, N.; Henoux, J. C.; Liaptsev,
A. V.; Luchinkina, V. V.
Bibcode: 1994A&ARv...6....1K
Altcode:
The physics of impact polarization is briefly reviewed in this
paper. Methods for derivating the impact spectropolarimetric
parameters relevant for the formation of Hα linear polarization are
summarized. Spectropolarimetric techniques can provide information
on the velocity distribution function of energetic particles. Since
the most advanced application of this technique to astrophysics is
in solar flare physics, recent results achieved by its application to
particles accelerated in solar flares are presented.
Title: Energy Release in Solar Flares
Authors: Brown, John C.; Correia, Emilia; Farnik, Frantisek; Garcia,
Howard; Henoux, Jean-Claude; Larosa, Ted N.; Machado, Marcos E.;
Nakajima, Hiroshi; Priest, Eric R.
Bibcode: 1994SoPh..153...19B
Altcode:
Team 2 of the Ottawa FLARES 22 Workshop dealt with observational and
theoretical aspects of the characteristics and processes of energy
release in flares. Main results summarized in this article stress
the global character of the flaring phenomenon in active regions, the
importance of discontinuities in magnetic connectivity, the role of
field-aligned currents in free energy storage, and the fragmentation
of energy release in time and space.
Title: Energy Transport and Dynamics
Authors: Schmieder, B.; Peres, G.; Enome, S.; Falciani, R.; Heinzel,
P.; Hénoux, J. C.; Mariska, J.; Reale, F.; Rilee, M. L.; Rompolt, B.;
Shibasaki, K.; Stepanov, A. V.; Wülser, J. P.; Zarro, D.; Zharkova, V.
Bibcode: 1994SoPh..153...55S
Altcode:
We report findings concerning energy transport and dynamics in flares
during the impulsive and gradual phases based on new ground-based and
space observations (notably fromYohkoh). A preheating sometimes occurs
during the impulsive phase. CaXIX line shifts are confirmed to be
good tracers of bulk plasma motions, although strong blue shifts are
not as frequent as previously claimed. They often appear correlated
with hard X-rays but, forsome events, the concept that electron beams
provide the whole energy input to the thermal component seems not
to apply. Theory now yields: new diagnostics of low-energy proton
and electron beams; accurate hydrodynamical modeling of pulse beam
heating of the atmosphere; possible diagnostics of microflares (based
on X-ray line ratio or on loop variability); and simulated images of
chromospheric evaporation fronts. For the gradual phase, the continual
reorganization of magnetic field lines over active regions determines
where and when magnetic reconnection, the mechanism favoured for energy
release, will occur. Spatial and temporal fragmentation of the energy
release, observed at different wavelengths, is considered to be a
factor as well in energy transport and plasma dynamics.
Title: Evolution of Active Regions Leading to Flares
Authors: Schmieder, B.; Demoulin, P.; Henoux, J. -C.; Driel-Gesztelyi,
L. V.; Mandrini, C.; Rovira, M.
Bibcode: 1994kofu.symp..297S
Altcode:
We model observed longitudinal magnetic fields obtained in Potsdam,
Meudon, MSFC Hunstville by a series of magnetic sources located
below the photosphere. H_alpha flare kernels are found situated on
intersecting separatrices (surfaces delimiting regions of different
magnetic connectivities). We deduce that energy release occurs
mainly at the separator by magnetic reconnection. Evidence for both
neutralized and un-neutralized currents are observed in different
flaring regions. Moreover we have found two photospheric currents of
opposite sign, linked in the corona by field lines, at the border of
flare kernels.
Title: Are magnetic null points important in solar flares ?
Authors: Demoulin, P.; Henoux, J. C.; Mandrini, C. H.
Bibcode: 1994A&A...285.1023D
Altcode:
When they are present, null points (points where the 3 components of
the magnetic field vanish) determine the topology of the magnetic
field configuration. It has been suggested that the presence of
nulls is related to flares, and that they settle the region where
the energy is released by magnetic reconnection. Since solar flares
are initially coronal events, nulls should be located above the
photosphere. Therefore, we investigate the location of nulls in
configurations formed by a parasitic and a main bipole (4 magnetic
sources). For both potential and linear-force free field approaches,
we have found that a null was present in the corona only when the two
bipoles were nearly antiparallel. The flaring regions analysed here
are those where the magnetic topology has been related to flare kernels
in previous papers. These observations show that flares occur for any
horizontal orientation of the parasitic bipole to the main one, having
only in particular cases a null in the extrapolated field. When a null
is present, it can be at any place along the separator and it is not
necessarily related to the region where the energy is released. These
results are found both in the subflares and the intense X-ray flares
studied. Examples of observed configurations that can be analysed
with 2D or 3D models are presented. We conclude that nulls above the
photosphere are not needed for flaring but that the spatial properties
of the coronal field still determines the location where reconnection
takes place. Results are discuss in the context of present understanding
of 3D reconnection.
Title: Observational support of reconnection in solar flares
Authors: Démoulin, P.; Hénoux, J. C.; Schmieder, B.; Mandrini,
C. H.; Rovira, M. G.; Somov, B.
Bibcode: 1994SSRv...68..129D
Altcode:
We present a detailed analysis of the magnetic topology of flaring
active region. TheH α kernels are found to be located at the
intersection of the separatrices with the chromosphere when the shear,
deduced from the fibrils or/and transverse magnetic field direction,
is taken into account. We show that the kernels are magnetically
connected by field lines passing close to the separator. We confirm,
for other flares, previous studies which show that photospheric current
concentrations are located at the borders of flare ribbons. Moreover
we found two photospheric current concentrations of opposite sign,
linked in the corona by field lines which follow separatrices. These
give evidence that magnetic energy is released by reconnection processes
in solar flares.
Title: Interpretation of multiwavelength observations of November 5,
1980 solar flares by the magnetic topology of AR 2766
Authors: Demoulin, P.; Mandrini, C. H.; Rovira, M. G.; Henoux, J. C.;
Machado, M. E.
Bibcode: 1994SoPh..150..221D
Altcode:
We present a detailed analysis of the magnetic topology of AR 2776
together with Hα UV, X-rays, and radio observations of the November
5, 1980 flares in order to understand the role of the active region
large-scale topology on the flare process. As at present the coronal
magnetic field is modeled by an ensemble of sub-photospheric sources
whose positions and intensities are deduced from a least-square fit
between the computed and observed longitudinal magnetic fields. Charges
and dipole representations are shown to lead to similar modeling of
the magnetic topology provided that the number of sources is great
enough. However, for AR 2776, departure from a potential field has to
be taken into account, therefore a linear force-free field extrapolation
is used.
Title: Space and time distribution of hard X-ray emission in a loop
at the beginning of a flare
Authors: Karlicky, Marian; Henoux, Jean-Claude
Bibcode: 1994A&A...283..202K
Altcode:
Using a 1-D hybrid model of the electron bombardment in flare
loops, we study not only the evolution of densities, plasma
velocities and temperatures in the loop, but also the temporal and
spatial evolution of hard X-ray emission. In the present paper
a continuous bombardment by electrons isotropically accelerated
at the top of flare loop with a power-law injection distribution
function is considered. The computations included the effects of the
return-current that reduces signifcantly the depth of the chromospheric
layer which is evaporated. These computations were made to study
the contribution of various processes - chromospheric evaporation,
mirroring and high pitch angle of superthermal electrons - to the
hard X-ray emission at the top of a loop at the very beginning of
flares. Therefore the present modelling was made with superthermal
electron parameters coresponding to the classical resistivity regime
for an input energy flux of superthermal electrons of 109 erg
cm-2/sec. Chromospheric evaporation density waves generated
at both feet of the loop propagate up to the top, where they collide
and cause a temporary electron density enhancement. Electron mirroring
at magnetic mirrors increases the population of superthermal electrons
at the top loop. These two processes lead to hard X-ray emission at
the top of the loop and dominate over the effect of high pitch-angle
superthermal electrons.
Title: Observational characteristics of explosive events
Authors: Hénoux, J. -C.; Dere, K. P.
Bibcode: 1994LNP...432..203H
Altcode:
The characteristics of dynamic phenomena observed in the EUV with
the HRTS instruments, chromospheric jets and explosive events, are
reviewed here. Most of the review is devoted to explosive events that
are short duration explosions involving a plasma at 105 K. These
events are characterised by strong Doppler shifts rather than by
brightness enhancements, contrary to EUV impulsive brightenings
observed by SMM. They are presumably due to magnetic reconnection
involving unresolved fine structures of the magnetic field near the
network. The role of the density of concentrated magnetic fluxtubes
in a reconnection scenario has still to be understood.
Title: On the Role of Separatrices and Separators of Coronal Magnetic
Fields in Solar Flares
Authors: Henoux, J. C.; Somov, B. V.
Bibcode: 1994ASPC...68..258H
Altcode: 1994sare.conf..258H
No abstract at ADS
Title: Role of Electric Currents in Magnetic Flux Tube Physics
Authors: Henoux, J. C.; Somov, B. V.
Bibcode: 1994ASPC...68..158H
Altcode: 1994sare.conf..158H
No abstract at ADS
Title: Magnetic topology of a complex active region
Authors: Mandrini, C. H.; Rovira, M. G.; Démoulin, P.; de La
Beaujarière, J. -F.; Hénoux, J. C.
Bibcode: 1994BAAA...39...52M
Altcode:
We present a detailed analysis of the magnetic topology of AR 6233
on two consecutive days (August 28 and 29, 1990). We compare the
location of the magnetic separatrices and separators with off-band Hα
observations and other flare manifestations, such as intense non-thermal
electron precipitation and high coronal pressure sites, for two flares
that occurred on these days. Because transverse magnetograms indicate
that strong magnetic shear is present along the longitudinal inversion
line, where flare brightening are located, the observed photospheric
magnetic field is modeled in an approach in which a combination
of sources with current-free and non current-free magnetic held is
used. This model allows us to obtain a better ht between the observed
and modeled transverse held. Then, we find a closer relationship between
separatrices and hare features. The results of a current-free and of
a linear force-free approach are also discussed. As in other haring
regions studied previously, chromospheric flare brightening are found
on separatrices. The topological structure obtained for these flares is
rather complex and cannot be explained by classical flare models. We
find that the connectivity of field lines may change drastically from
one edge of an Ha; ribbon to the other. Electron precipitation and
high coronal pressure sites, and some photospheric intense currents
are also found in the immediate vicinity of separatrices. The early
kernels of August 28 flare are found closer to the separatrices of the
non-potential held, while the later are closer to those of the potential
held. All these results agree with the hypothesis that magnetic energy
is stored in field-aligned currents and released due to magnetic held
reconnection, with a noticeable relaxation of the held, either at the
separator region or on separatrices.
Title: Understanding Solar Active Phenomena: A Phenomenological
Approach
Authors: Machado, M. E.; Demoulin, P.; Gary, G. A.; Henoux, J. C.;
Mandrini, C. H.; Rovira, M. G.
Bibcode: 1994step.conf..125M
Altcode:
No abstract at ADS
Title: Space and Time Distribution of Hard X-Ray Emission in a Loop
at the Beginning of a Flare
Authors: Karlicky, M.; Henoux, J. -C.
Bibcode: 1994scs..conf..275K
Altcode: 1994IAUCo.144..275K
Using a new 1D hybrid model of the electron bombardment in flare
loops, the authors study not only the evolution of densities, plasma
velocities and temperatures in the loop, but also the temporal and
spatial evolution of hard X-ray emission. In this paper a continuous
bombardment by electrons isotropically accelerated at the top of flare
loop with a power-law injection distribution function is considered.
Title: Observational characteristics of explosive events.
Authors: Hénoux, J. C.; Dere, K. P.
Bibcode: 1994LNP...432..205H
Altcode: 1994LNPM...11..205H
The characteristics of dynamic phenomena observed in the EUV with
the HRTS instruments, chromospheric jets and explosive events, are
reviewed. Most of the review is devoted to explosive events that are
short duration explosions involving a plasma at 105K. These
events are characterised by strong Doppler shifts rather than by
brightness enhancements, contrary to EUV impulsive brightenings
observed by SMM. They are presumably due to magnetic reconnection
involving unresolved fine structures of the magnetic field near the
network. The role of the density of concentrated magnetic fluxtubes
in a reconnection scenario has still to be understood.
Title: Magnetic reconnection as a mechanism for solar flares
Authors: Bagala, L. G.; Rovira, M. G.; Mandrini, C. H.; Demoulin,
P.; Henoux, J. C.
Bibcode: 1994iaf..conf.....B
Altcode:
In this paper we summarize the results of our quantitative analysis of
the 3D magnetic topology of several active regions (ARs). We show that
the flare brightenings in different wavelengths (H-alpha, UV, X-rays)
are located at the intersection of separatrices with the chromospheric
plane. Flare kernels are magnetically connected by field lines passing
close to the separator in different types of configurations. We also
find that photospheric current concentrations are associated with flare
brightenings and can be linked in the corona by field lines following
separatrices, supporting the hypothesis that magnetic energy is stored
in field-aligned currents. Since magnetic reconnection is expected to
take place at the separator region or on separatrices, these results
strongly suggest that this is the process driving energy release in
solar flares.
Title: Electron acceleration due to beam flux increase in a converging
magnetic field
Authors: Karlicky, M.; Henoux, J. -C.
Bibcode: 1993A&A...278..627K
Altcode:
The effects of the magnetic field mirroring and backscattering of beam
electrons in a time varying return-current electric field are studied
with a 1-D hybrid test particle model of the electron bombardment in
flare loops. These effects are analyzed for monoenergetic electron
beams with an energy flux increasing with time, for different widths
of their pitch-angle distribution. The consequence of a weak linear
increase of the magnetic field from the apex to the feet of the
loop is considered. The number and therefore the role of mirroring
electrons are increasing with the broadening of the pitch-angle
distribution. While in the case of bombardment by an unidirectional
beam only few particles are reflected by back-scattering in the dense
layers of the loop and then accelerated in the return-current electric
field, in the case of a broader pitch-angle distribution of beams
much more electrons are mirrored and accelerated. Part of them are
accelerated to energies higher than the initial ones. Consequently,
a collisionless return-current is formed, which decreases the beam
return-current losses. The possible role of these effects in the solar
flare scenario is shortly discussed.
Title: Multiwavelength Observations and Magnetic Field Modelling of
a Solar Flare
Authors: Bagala, L. G.; Rovira, M. G.; Mandrini, C. H.; Demoulin,
P.; Henoux, J. C.
Bibcode: 1993RMxAA..26..135B
Altcode:
No abstract at ADS
Title: Spectropolarimetric determination of the energy contribution
to the optically active region of the chromosphere
Authors: Kazantsev, S. A.; Petrashen, A. G.; Firstova, N. M.; Hénoux,
J. C.
Bibcode: 1993OptSp..75..382K
Altcode:
No abstract at ADS
Title: Return current losses in pulse beam heating of the solar
atmosphere
Authors: Karlický, Marian; Hénoux, Jean-Claude
Bibcode: 1993AdSpR..13i.195K
Altcode: 1993AdSpR..13..195K
The influence of return current losses on pulse beam heating of the
solar atmosphere is studied using a 1 D-hybrid code. While heating
of the coronal plasma by the penetrating electron beam is obtained,
as expected, strong return current losses of beam electrons at the
resistivity jump in the transition region are also found. The electron
beam energy is deposited at greater heights in the solar atmosphere
than in the case of pure collisional losses. At the starting time
of the flare, due to a strong return current heating, a very steep
transition region is formed where upwards and downwards plasma flows
are generated. However, this state has a transitory character. The
atmosphere is heated and a channel of hot, low resistivity plasma
is formed, by which the following electron beams can penetrate more
easily to deep chromospheric levels, where they are then thermalized.
Title: Sites of flares and filaments in solar active regions
Authors: Schmieder, B.; van-Driel, L.; Hofmann, A.; Démoulin, P.;
Hénoux, J. C.; Hagyard, M.
Bibcode: 1993AdSpR..13i.119S
Altcode: 1993AdSpR..13..119S
We applied a method developed to derive from magnetic field data the
location of energy release in solar active regions. This method has
been applied to two sets of data (June 13-15 1980 and June 23-25 1989)
using magnetograms (Meudon, MSFC, Potsdam) and Hα data (Debrecen,
MSDP Meudon). The Hα flares are located at intersections of the
separatrices with the chromosphere in places where high density currents
are observed. This supports the idea that the energy released in flares
is due to magnetic reconnection at the location of a separator and
subsequently transported to the chromosphere along field lines. It is
found that strong magnetic shear is a necessary condition for filament
formation. Magnetic shear merely determines the importance of the
flare and is certainly not a necessary condition for flare activity.
Title: Electric currents in magnetic flux-tubes
Authors: Hénoux, J. C.; Somov, B. V.
Bibcode: 1993AdSpR..13i..23H
Altcode: 1993AdSpR..13...23H
The effect on magnetic flux-tubes formation and equllibrium of the DC
currents generated in the tubes by radial and azimuthal motions are
investigated. These currents are found to be high enough to modify
significantly the horizontal and vertical pressure distribution
distribution at photospheric level. Consequently a radial variation
of pressure can also be created and maintained at chromospheric levels
leading to diffusion of neutral particles across the lines of force. The
leakage of neutrals procedures a rise of the degree of ionization in
the flux-tube and an enrichment in elements of high first ionization
potential.
Title: Diagnostics of non-thermal processes in chromospheric
flares. I. H alpha and CaII K line profiles of an atmosphere bombarded
by hecta keV electrons.
Authors: Fang, C.; Henoux, J. C.; Gan, W. Q.
Bibcode: 1993A&A...274..917F
Altcode:
The significance of non-thermal excitation and ionization of hydrogen
and CaII, by an electron beam, on the line profiles of Hα and CaII K
line has been investigated. Non-LTE Hot and CaII K line profiles have
been calculated for the temperature distributions of semi-empirical
flares models F1 and F2 (Machado et al. t980). For
reasonable values of the beam energy flux and power index, the hydrogen
lines are greatly strengthened and broadened, and an obvious central
reversal appears. The effects are weaker for the CaII K line. These
effects can be used to diagnose electron beam bombardment during a
solar flare, especially at its early phase. Any semi-empirical flare
model that does not take into account non-thermal effects overestimates
the heating of the solar atmosphere.
Title: Diagnostics of non-thermal processes in chromospheric
flares. II. H alpha and CaII K line profiles of an atmosphere
bombarded by 100 KeV-1 MeV protons.
Authors: Henoux, J. C.; Fang, C.; Gan, W. Q.
Bibcode: 1993A&A...274..923H
Altcode:
The effects on the Hα line profile of non-thermal excitation
and ionization of hydrogen by a 100 KeV- 1 MeV proton beam have
been investigated. Non-LTE Hα line profiles have been calculated
for the temperature distributions of semi- empirical flares models
F1 and F2 (Machado et al. 1980). For reasonable
values of the beam energy flux and power index, the hydrogen lines are
greatly strengthened. However, contrary to the case of an electron
bombarded atmosphere, the line is not broadened, and no central
reversal appears. These effects, alone or in conjunction with linear
polarization measurements or Lyα red wing observations, can be used
to diagnose proton beam bombardment.
Title: Evidence for magnetic reconnection in large-scale magnetic
structures in solar flares
Authors: Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C.;
Machado, M. E.; Wilkinson, L. K.
Bibcode: 1993A&A...272..609M
Altcode:
Modelling the observed vertical magnetic field of an active region (NOAA
2372) for two consecutive days, April 7 and 8, 1980, by the potential
field of an ensemble of magnetic dipoles, we derived the location of
the separatrices, surfaces that separate cells of different field line
connectivities, and of the separator which is the intersection of the
separatrices. The overall temporal evolution of the magnetic fields
and the location of the off-band Hα kernels of flares, that occurred
before the obtention of the magnetograms, support the hypothesis that
the flares were due to magnetic reconnection taking place in the main
separator of the active region. The triggering of reconnection in
a second separator appearing on April 8 by reconnection in the main
separator is strongly suggested by the observed magnetic connectivities
and the kernels locations. The location of the emerging currents on
the separatrices support the idea that flares are fed by the release
of magnetic free energy.
Title: Electron acceleration and heating in solar flares:
Interpretation of Hα signatures
Authors: Smith, D. F.; Henoux, J. C.
Bibcode: 1993SoPh..143..247S
Altcode:
Vector magnetogram, Hα, and hard X-ray observations of flares
are reviewed which show that nonthermal electron signatures in
Hα are never cospatial with regions of maximum current density
for the small number of flares analyzed, but lie to the sides of
these regions. By considering electron acceleration and transport
requirements, four conditions are found that must be fulfilled to
observe nonthermal electron signatures in Hα: (1) The plasma betaβ
≤ 0.3 in the acceleration region. (2) The energy flux of electrons
above 20 keV is greater than 1010 erg cm−2
s−1. (3) The column densityN ≤ 1020
cm−2 between the electron source and the chromosphere. (4)
The coronal pressure in the flux tube connecting to the Hα layerp
≤ 100 dyne cm−2. Condition 2 can be most easily met
in the initial stages of flares. In contrast, the only condition for
a high-pressure Hα signature isp ≥ 1000 dyne cm−2,
which is most easily met in a region of maximum current density or
heating and far enough into the flare for significant heating to have
occurred. Thus, high-pressure signatures should be expected to occur
more frequently than nonthermal electron signatures and to occur
generally later in time.
Title: Observational Evidence for Magnetic Reconnection in Solar
Flares (Invited)
Authors: Henoux, J. C.; Demoulin, P.; Mandrini, C. H.; Rovira, M. G.
Bibcode: 1993ASPC...46..333H
Altcode: 1993IAUCo.141..333H; 1993mvfs.conf..333H
No abstract at ADS
Title: Interpretación de las observaciones de fulguraciones solares
en función de la topología de la región activa
Authors: Rovira, M. G.; Mandrini, C. H.; Demoulin, P.; Henoux, J. C.;
Machado, M. E.
Bibcode: 1993BAAA...38..114R
Altcode:
Con el objeto de comprender el rol que juega la topología a gran escala
durante las fulguraciones solares, realizamos un estudio detallado de la
estructura topológica de la región activa (AR) 2776 y la comparamos
con observaciones en Hα , UV, rayos X y radio de dos fulguraciones
que tuvieron lugar el 5 de Noviembre de 1980. Como en casos anteriores
el campo magnético coronal se modeló usando un conjunto de fuentes
subfotosféricas, cuyas posiciones e intensidades se dedujeron a partir
de un ajuste por cuadrados mínimos al campo longitudinal observado. En
este caso, dado que el campo de AR 2776 no es potencial, se uso en
el modelo una extrapolación libre de fuerzas lineal. La relación
entre la posición de los cuatro abrillantamientos en Hα de distintas
fulguraciones y la topología de regiones activas cuadrupolares ha
sido estudiada anteriormente. En este caso la región es bipolar y
las fulguraciones muestran una estructura de dos bandas. Estas se
ubican sobre las separatrices cuando se tiene en cuenta el shear del
campo, deducido de la dirección de las fibrillas observadas a nivel
cromosférico. Este estudio esta de acuerdo con la hipótesis de que
la energía magnética está almacenada en corrientes alineadas con
el campo y que se libera por reconección del mismo, en la región
del separador, antes de ser transportada a la cromosfera. También es
posible que parte de la energía magnética se almacene y se libere
sobre las separatrices. La ubicación de las corrientes fotosféricas,
deducidas de los magnetogramas vectoriales, en la intersección de
las separatrices con la fotosfera concuerda con este último punto.
Title: Estabilidad de la estructura topológica de una región activa
en presencia de fuentes de campo externas
Authors: Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C.;
de La Beaujardiere, J.
Bibcode: 1993BAAA...38..115M
Altcode:
A partir de las observaciones del campo magnético longitudinal
de la región activa (AR) 6233, obtenidas en el Observatorio Mees
(Universidad de Hawaii), derivamos su estructura topológica y
estudiamos la evolución de la misma a lo largo de dos días. En
el bipolo principal de esta región se desarrollaron numerosas
fulguraciones y microfulguraciones en el período de estudio. Dado que
en este caso contamos con magnetogramas que cubren distintas escalas
espaciales, analizamos la influencia que las fuentes de campo externas
a dicho bipolo tienen sobre la estructura topológica de la zona en
donde se produjeron las fulguraciones. Esta se obtiene a partir de
un modelo del campo de AR 6233 tanto en la aproximación potencial,
como en la libre de fuerzas lineal. Nuestros resultados muestran
que la estructura topológica básica de la región de interés
permanece invariante en ambos casos. Esto justificaría el uso, debido
a limitaciones instrumentales, de magnetogramas que cubren una porción
limitada de la región activa al modelar el campo como se ha hecho en
estudios anteriores.
Title: First ionization potential fractionation.
Authors: Henoux, J. C.; Somov, B. V.
Bibcode: 1992ESASP.348..325H
Altcode: 1992cscl.work..325H
The authors briefly review the existing models for FIP
fractionation. First they recall the main characteristics of the
observed abundance anomalies that must be taken into account by
FIP fractionation models. Two main models are presented. They are
all based on ion-neutral separation in a magnetic field and differ
fundamentally by the nature of the particles - neutrals or ions -
that cross the lines of force under the constraint of pressure or
electric forces. A qualitative model of FIP fractionation is described
based on a quantitative estimate of the characteristics of DC currents
generated into magnetic flux tubes and of their mechanical effects. FIP
fractionation appears as a natural consequence of the circulation
of currents in magnetic flux-tubes and it can be associated with the
formation of the solar chromosphere.
Title: Return current losses in pulse beam heating of the solar
atmosphere
Authors: Karlicky, M.; Henoux, J. -C.
Bibcode: 1992A&A...264..679K
Altcode:
A 1D-hybrid code is employed to examine the influence of return
current losses on pulse beam heating of the solar atmosphere. While
heating of the coronal plasma by the penetrating electron beam is
obtained as expected, strong return current losses of beam electrons
at the resistivity jump in the transition region are also found. The
electron beam energy is deposited at greater heights in the solar
atmosphere than in the case of pure collisional losses. At the
starting time of the flare, due to a strong return current heating,
a very steep transition region is formed where upward and downward
plasma flows are generated. The atmosphere is heated and a channel of
hot low-resistivity plasma is formed by which the following electron
beams can penetrate more easily to deep chromospheric levels where
they are then thermalized.
Title: Line polarization observed in chromospheric flares -
Calculations for electron impact excitation of H-alpha
Authors: Aboudarham, J.; Berrington, K.; Callaway, J.; Feautrier,
N.; Henoux, J. C.; Peach, G.; Saraph, H. E.
Bibcode: 1992A&A...262..302A
Altcode:
The observation of chromospheric flares accompanying coronal
flares in the sun indicates fast energy transfer between the two
layers. Polarization observed in the H-alpha and S I lines can help
to explain the nature of this energy transfer if accurate atomic data
for the line polarization is available. Calculations for H-alpha line
polarization by low-energy electron impact are presented, using the most
sophisticated collision data available to date. The theoretical results
compare well with polarization measurements dating from 1968. Low-energy
electrons with anisotropic velocity distributions could be present in
solar flares. They could be associated either with proton bombardment
or with the existence of large temperature gradients. Assuming that
the polarization of H-alpha observed in chromospheric flares is due
only to electron impact, the ratio of the two even moments J2 and J0
of the electron velocity distribution is inferred. Further, under the
hypothesis that the anisotropy is due to a high temperature gradient,
a velocity distribution function for electrons carrying a conductive
heat flux is linked to the observed polarization.
Title: Development of a Topological Model for Solar Flares
Authors: Demoulin, P.; Henoux, J. C.; Mandrini, C. H.
Bibcode: 1992SoPh..139..105D
Altcode:
The main theoretical studies of the process involved in solar flares
have been made in the two-dimensional approximation. However, the
preliminary studies made with three field components suggest that
reconnection could take place in the separatrices, the separator
(intersection of separatrices) being a privileged location for this
process. As a consequence the sites of flare kernels must be located on
the intersections of the separatrices with the photosphere. Therefore,
in order to understand the role of interacting large-scale structures
in solar flares, we have analysed the topology of three-dimensional
potential and linear force-free fields. The magnetic field has been
modelled by a distribution of charges or dipoles located below the
photosphere. This modelling permits us to define the field connectivity
by the charges or the dipoles at both ends of every field line.
Title: Reconección magnética entre estructuras a gran escala
durante fulguraciones solares
Authors: Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C.;
Machado, M. E.
Bibcode: 1992BAAA...37..112M
Altcode:
A partir del modelado del campo magnético de la región activa
NOAA 2372 se determina la ubicación de sus distintas estructuras
topológicas: separatrices y separador. Este análisis se hace
en base a observaciones del campo magnético a lo largo de tres
días. La evolución temporal del campo global y la ubicación de los
abrillantamientos en H a de varias fulguraciones, en relación con
la topología determinada, están de acuerdo con el hecho de que las
fulguraciones son el resultado del proceso de reconección que tiene
lugar en el separador principal de la región activa.
Title: The solar X-ray/cosmic gamma-ray burst experiment aboard
ULYSSES
Authors: Hurley, K.; Sommer, M.; Atteia, J. -L.; Boer, M.; Cline,
T.; Cotin, F.; Henoux, J. -C.; Kane, S.; Lowes, P.; Niel, M.
Bibcode: 1992A&AS...92..401H
Altcode:
The scientific objectives of the Ulysses solar X-ray/cosmic gamma-ray
burst experiment, and the unique features of the Ulysses mission which
will help to achieve them are described. After a discussion of the
special design constraints imposed by the mission, the sensor systems,
consisting of two CsI scintillators and two Si surface barrier detectors
covering the energy range 5-150 keV are described. Their operating
modes and inflight performance are also given.
Title: White-Light Flares
Authors: Henoux, J. C.; Aboudarham, J.
Bibcode: 1992LNP...399..118H
Altcode: 1992esf..coll..118H; 1992IAUCo.133..118H
The observed good temporal correlation between white-light flares
and hard X-ray bursts suggests that energetic electrons could be the
cause of white-light flare emission. However, even if sufficient energy
can be deposited in the chromosphere by electron bombardment, direct
collisional heating of the photosphere requires too high a flux of
electrons of a few hundred keV and does not appear plausible. We show
that nonthermal effects increase the opacity of the upper photosphere
and temperature minimum region. Then these regions are consequently
radiatively heated both by the beam-produced flare chromospheric
emission and by the quiet photospheric emission. As a consequence,
a temporary decrease of the continuum intensity ( negative flare ) is
expected. After less than 20 seconds, the radiative heating of the upper
photosphere and temperature minimum region produces a white-light flare.
Title: Interaction of Largescale Magnetic Structures in Solar Flares
Authors: Mandrini, C. H.; Demoulin, P.; Henoux, J. C.
Bibcode: 1992LNP...399...54M
Altcode: 1992IAUCo.133...54M; 1992esf..coll...54M
Modelling the observed vertical magnetic field of active region (AR)
NOAA 2372 by the potential field of an ensemble of magnetic dipoles,
we have derived the likely location of the separatrices, surfaces
that separate cells of different field line connectivities, and of
the separator which is the intersection of the separatrices. The
connectivity of every magnetic field line, which is defined by the
dipoles located at its ends, is computed by a code that, starting
from any pixel in the photospheric plane, integrates numerically the
differential equation defining a line of force towards both ends of
this line until one dipole is reached. This code allows us to obtain the
topology of the field in three dimensions. We have compared our results
with observations of a 1B/M1 flare that developed in AR 2372 on April
6, 1980 at 20:53 UT (Lin and Gaizauskas, 1987), twenty minutes before
obtaining the magnetogram. We found that four of the five off-band Ha
kernels were located near or at the separatrices. These Ha kernels
are connected by field lines that pass close to the separator. This
indicates that the flare may have resulted from the interaction of
large scale magnetic structures in the separator region. Moreover, Lin
and Gaizauskas (1987) showed that the Ha flare kernels coincided with
the peak values of the longitudinal electric current density. This
finding and the fact that no strong current and no Ha kernel are
observed at the intersection of the separator with the photosphere,
lead to the conclusion that the magnetic energy released during the
flare is mostly stored in an ensemble of currents flowing along lines of
force. Some instability, presumably due to reconnection taking place
in the separator, is likely to be the origin of the energy release
and of the observed flare.
Title: Evidence for the interaction of large scale magnetic structures
in solar flares.
Authors: Mandrini, C. H.; Demoulin, P.; Henoux, J. C.; Machado, M. E.
Bibcode: 1991A&A...250..541M
Altcode:
By modeling the observed vertical magnetic field of an active region
AR 2372 by the potential field of an ensemble of magnetic dipoles, the
likely location of the separatrices, surfaces that separates cells of
different field line connectivities, and of the separator which is the
intersection of the separatrices, is derived. Four of the five off-band
H-alpha kernels of a flare that occurred less than 20 minutes before
obtaining the magnetogram are shown to have taken place near or at
the separatrices. These H-alpha kernels are connected by field lines
that pass near the separator. This indicates that the flare may have
resulted from the interaction in the separator region of large scale
magnetic structures.
Title: Conditions for flare and filament formation in interacting
solar active regions
Authors: Schmieder, B.; Henoux, J. -C.; van Driel-Gesztelyi, L.;
Simnett, G. M.
Bibcode: 1991A&A...244..533S
Altcode:
The evolution of two interacting sunspot groups of different ages is
traced over a period of three days. The photospheric velocity field is
obtained and compared with the general evolution of the region in an
attempt to better understand the conditions that lead to flare activity
and filament formation. It is shown that the observed photospheric
motions can generate dc electric currents, which, in effect, could
lead to energy storage.
Title: Solar Flare X-Ray Observations with Ulysses
Authors: Kane, S. R.; Hurley, K.; Cotin, F.; Niel, M.; Vedrenne, G.;
Henoux, J. C.; Sommer, M.
Bibcode: 1991BAAS...23.1042K
Altcode:
No abstract at ADS
Title: Flares and filament formation due to the interaction between
two active regions
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Hénoux, J. C.;
Simnett, G.
Bibcode: 1991AdSpR..11e..95S
Altcode: 1991AdSpR..11...95S
We follow the evolution (flare activity, filament formation) of two
interacting active regions of different ages over three days, through
observations at white-light, Hα, UV, and X-ray wavelengths. We show
that the observed photospheric motions could generate DC electric
currents and that they could lead to free energy storage. Flares
were observed more-or-less simultaneously in remote locations of the
sunspot group. This suggests that the same perturbation affected an
ensemble of lines of force. Filament formation took place due to DC
current generation by photospheric shearing motions with a velocity
up to 350 m s-1.
Title: Observation and interpretation of Hα polarization in solar
flares.
Authors: Hénoux, J. C.
Bibcode: 1991sopo.work..285H
Altcode:
Impact linear polarization of the Hα chromospheric line has been
observed in some flares and reported (Hénoux et al., 1990). A new
observation made on July 17th 1982 is presented. The characteristics
of the 10 minutes time integrated polarization are similar to the
characteristics of the polarization observed in other flares, i.e. the
main direction of the polarization is close to the radial direction
and the polarization degree reaches 5%. However, in a few locations,
an higher polarization fraction as high as 15% is observed in the one
minute time integrated data. The observational method is described
and the origin of the observed polarization is discussed.
Title: Chromosphere Generation in Magnetic Flux-Tubes (With 1 Figure)
Authors: Hénoux, J. C.; Somov, B. V.
Bibcode: 1991mcch.conf..567H
Altcode:
No abstract at ADS
Title: The energy budget in active regions and flares
Authors: Henoux, J. C.
Bibcode: 1991AdSpR..11e...7H
Altcode: 1991AdSpR..11....7H
Information on the energetic balance in active regions derived from
space observations is reviewed. It suggests both a global balance
with some lag between sunspot darkening and plage brightening and
the existence of a solar-cycle modulation. Some recent models are
quoted. Recent works on the role of the global magnetic field topology
and on flare energy storage are briefly discussed. The role of large
scale structures is emphasized. Progress on the understanding of the
energy transport mechanisms in solar flares is reviewed. It includes
new observational indications of the existence of low energy protons
and confirmation of the significance of the coupling between modes
to the transport of energy. The role of the radiative transport
mechanism is underlined. Observations support for the model of
chromospheric evaporation derived from multiwavelength observations
is presented. Other possible interpretations are briefly discussed.
Title: The photospheric dynamo. I - Magnetic flux-tube generation
Authors: Henoux, J. C.; Somov, B. V.
Bibcode: 1991A&A...241..613H
Altcode:
Velocities of electrons, ions and neutrals are computed, in the
three-fluid approximation, for an axisymmetrical magnetic field. By
prescribing a radial dependence of the velocity of neutrals, in
agreement with a downflow, the radial dependence of the magnetic field
energy density is derived. This gives the radial flux of neutrals
that is required to increase the magnetic field from 0.01 G to 1000 G
inside thin magnetic flux tubes in the photosphere. The hypothesis of
local cooling by advection of ionization energy of Schatten and Mayr
(1985) is tested, and it is seen that this flux of neutrals is high
enough to affect significantly the energy balance in the tube and
to maintain the pressure gradient necessary to produce the radial
inflow of neutrals. In agreement with recent infrared observations,
the inside of the flux-tube is predicted to be cooler than the outside.
Title: Effect of Electron Beams during Solar Flares
Authors: Aboudarham, J.; Henoux, J. C.; Brown, J. C.; van den Oord,
G. H. J.; van Driel-Gesztelyi, L.; Gerlei, O.
Bibcode: 1990SoPh..130..243A
Altcode:
Electron bombardment of the solar atmosphere has two effects: one is
to enhance hydrogen recombination emission, the other is to increase
the opacity via an increase of H− population. The first
effect is the most important in the upper part of the atmosphere and
the second in the lower part. We predict that, when enhanced absorption
dominates in the part of the atmosphere where radiation originates,
there will be a decrease in the white-light emission, leading to a
`negative flare', or what we call a `Black-Light Flare'. This phenomenon
occurs only for a short duration, not more than ∼ 20 s. `Black-Light
Flares' have already been observed in the case of flare stars and we
suggest here that they could also be present on the Sun, just prior
to a White-Light Flare.
Title: Coronal Proton Transport in the Presence of Alfven Waves and
Implications for Impact Line Linear Polarization
Authors: Smith, Dean F.; Chambe, G.; Henoux, J. C.; Tamres, D.
Bibcode: 1990ApJ...358..674S
Altcode:
The transport of fast (about 1 MeV) protons in the corona is considered
when their density and ansiotropy are sufficiently large to excite
Alfven waves. The Alfven waves scatter the protons and make them
almost isotropic. The Alfven wave instability remains in a marginally
stable state in which the proton anisotropy is just large enough
to excite Alfven waves to a level which would eliminate any greater
anisotropy. The protons propagate diffusively down a coronal loop and
have a path length of order 100 times their length in the absence of
Alfven waves. This increases their Coulomb losses, and much higher
energy protons (2-20 MeV) are required initially to produce H-alpha
impact line linear polarization in the chromosphere as compared to the
case in the absence of Alfven waves (about 200 keV) for loop lengths
about 10 to the 9th cm. The interpretation of the observed polarization
becomes less direct because it depends on more poorly known parameters
than in the case of the absence of Alfven waves.
Title: Black and white flares?
Authors: Henoux, J. -C.; Aboudarham, J.; Brown, J. C.; van den Oord,
G. H. J.; van Driel-Gesztelyi, L.
Bibcode: 1990A&A...233..577H
Altcode:
It is shown that the nonthermal ionization of a solar flare atmosphere
by beam bombardment can result, in the initial stages of a flare, in
dimunitions in the continuum solar flare brightness (termed 'black
light flares'). The most favorable conditions for observing this
diagnostic phenomenon are investigated in terms of flare location and
wavelength. In terms of bombarding beam parameters, electron beams
of large peak flux are shown to be the most favorable as are target
atmospheres with minimal preheating.
Title: Hα impact polarization observed in solar flares as a
diagnostic of energy transport mechanisms.
Authors: Henoux, J. C.; Chambe, G.
Bibcode: 1990JQSRT..44..193H
Altcode:
Various mechanisms of energy transport and energy release in
solar flares create a population of energetic particles with an
anisotropic velocity distribution function. By collisional excitation,
these particles may produce linearly polarized line emission. The
characteristics of the impact polarization associated with diverse
mechanisms of energy transport are reviewed. Observations of linear
polarization at some locations of Hα filtergrams, taken at the
time of three solar flares, are reported. The polarized electric
vector is directed in the flare-to-disk-center direction. This
polarization indicates that energetic particles with anisotropic
velocity distributions are present in the high chromosphere during
solar flares. They could be either deca-eV electrons coming from the
transition zone or produced in local acceleration in weak double-layers
or deca-keV protons accelerated in the corona.
Title: Impact Line Linear Polarization as a Diagnostic of 100 keV
Proton Acceleration in Solar Flares
Authors: Henoux, J. C.; Chambe, G.; Smith, D.; Tamres, D.; Feautrier,
N.; Rovira, M.; Sahal-Brechot, S.
Bibcode: 1990ApJS...73..303H
Altcode:
The use of impact linear polarization of chromospheric lines as a
diagnostic of 100 keV protons is proposed. Observations of hard X-ray
emission are examined, noting the possibility that 100 keV proton
beams bombarding the atmosphere could create a hot thermal plasma at
the origin of X-ray emission. The application of impact linear line
polarization as a diagnostic of the existence of energetic particles
with anisotropic velocity distribution functions is described. The
mechanisms leading to an anisotropic proton distribution in the solar
chromosphere are discussed and the required initial energy and energy
flux for accelerated protons in the corona are derived. It is suggested
that it is possible to infer the original proton anisotropy in the
corona and the effect of this anisotropy on the proton energy and
proton energy flux required to reach the H-alpha-forming layers.
Title: Generation of Magnetic Fields and Electric Currents in the
Solar Photosphere
Authors: Henoux, J. C.; Somov, B. V.
Bibcode: 1990IAUS..138..273H
Altcode:
No abstract at ADS
Title: Negative Flares on the Sun
Authors: van Driel-Gesztelyi, L.; Brown, J. C.; Hénoux, J. -C.;
Aboudarham, J.; van den Oord, G. H. J.; Gerlei, O.; Fárnik, F.
Bibcode: 1990PDHO....7..202V
Altcode: 1990dysu.conf..202V; 1990ESPM....6..202V
The authors showed that under certain conditions at the beginning
of a solar white-light flare (WLF) event an electron beam can cause
a transient darkening before the WLF emission starts. They propose
optimal conditions for possible observation of solar negative flares and
present an observation, which may be the first identified observation
of such events.
Title: Electrodynamic conversion of energy: Magnetic field
amplification in the solar photosphere
Authors: Henoux, J. C.; Somov, B. V.
Bibcode: 1990AdSpR..10i.179H
Altcode: 1990AdSpR..10R.179H
Velocities of electrons, ions and neutrals are computed, in the
three-fluid approximation, for an axisymmetrical magnetic field. By
prescribing a radial dependence of the velocity of neutrals, in
agreement whith a downflow, the radial dependence of the magnetic
field energy density is derived. This gives the radial flux of neutrals
that is required to increase, in the photosphere, the magnetic field
from 5 Gauss to 1000 Gauss. We test the hypothesis of local cooling
by advection of ionization energy of Schatten and Mayr/1/, and find
that this flux of neutrals is high enough to affect significantly
the energy balance in the tube and to maintain the pressure gradient
necessary to produce the radial inflow of neutrals. The product of
the tube radius by the radial velocity Vr,nr being, in the
photosphere (τ5000 = 1), lower than a few 105
m.2 s.-1, the associated velocity would presumably
not exceed a few meters per second. This supports the idea of creation
of strong fields by enhancement of a preexisting magnetic field in
the photosphere, i.e. superficial creation of magnetic fluxtubes.
Title: The Solar X-Ray/Cosmic Gamma-Ray Burst Experiment Aboard the
Ulysses Mission
Authors: Hurley, K.; Sommer, M.; Paschmann, G.; Boer, M.; de Jager,
C.; Heise, J.; van Rooijen, J.; Niel, M.; Vedrenne, G.; Cline, T.;
Henoux, J. -C.
Bibcode: 1990ICRC....5...74H
Altcode: 1990ICRC...21e..74H; 1989ICRC....5...74H
No abstract at ADS
Title: Electron Beam as Origin of White-Light Solar Flares
Authors: Aboudarham, J.; Henoux, J. C.
Bibcode: 1989SoPh..121...19A
Altcode: 1989IAUCo.104...19A
We study the effect of chromospheric bombardment by an electron
beam during solar flares. Using a semi-empirical flare model, we
investigate energy balance at temperature minimum level and in the
upper photosphere. We show that non-thermal hydrogen ionization (i.e.,
due to the electrons of the beam) leads to an increase of chromospheric
hydrogen continuum emission, H− population, and absorption
of photospheric and chromospheric continuum radiation. So, the upper
photosphere is radiatively heated by chromospheric continuum radiation
produced by the beam. The effect of hydrogen ionization is an enhanced
white-light emission both at chromospheric and photospheric level, due
to Paschen and H− continua emission, respectively. We then
obtain white-light contrasts compatible with observations, obviously
showing the link between white-light flares and atmospheric bombardment
by electron beams.
Title: Flare Energy Release and Deposition
Authors: Holman, G.; Benka, S.; de La Beaujardiere, J.; Dulk, G.;
Gabriel, A.; Henoux, J. C.; Hiei, E.; Kane, S.; Klein, L.; Kuin, P.;
Larosa, T.; MacKinnon, A.; McClements, K.; Moses, D.; Ramaty, R.;
Tromans, N.; Vilmer, N.
Bibcode: 1989tnti.conf....3H
Altcode:
No abstract at ADS
Title: The Global Energy Balance in Flares
Authors: Simnett, G. M.; Linford, G. A.; Metcalf, T. R.; Henoux,
J. C.; Spicer, D. S.
Bibcode: 1989tnti.conf....4S
Altcode:
No abstract at ADS
Title: Spectroscopie des éruptions solaires: éruptions en noir
et blanc.
Authors: Henoux, J. -C.; Aboudarham, J.
Bibcode: 1989JAF....34Q...8H
Altcode:
No abstract at ADS
Title: Spectroscopy of solar flares: black and white flares.
Authors: Henoux, J. -C.; Aboudarham, J.
Bibcode: 1989musi.work...89H
Altcode:
No abstract at ADS
Title: Generation and structure of the electric currents in a flaring
activity complex
Authors: Henoux, J. C.; Somov, B. V.
Bibcode: 1987A&A...185..306H
Altcode:
Assuming the existence of organized photospheric velocity fields in an
active region, the creation of photospheric and coronal dc currents
by vortex and radial motions is studied. Vortex motions leading to
opposite temporal evolutions of the magnetic flux in old and new
centers of activity create two systems of coronal currents flowing
along the lines of force that, in the active region complex, connect
the old center of activity to the new. The magnetic energy stored in
these currents is higher than the energy of the largest flares. The
effect of radial photospheric motions is also discussed. Two systems
of coronal currents can be distinguished. They are located inside
two different magnetic cells, and interact along the separator which
is the intersection of the magnetic line surfaces that separate the
magnetic cells produced by the photospheric magnetic sources. Due
to source motions and electric current evolution, the separator may
be the location of reconnection of the magnetic field. The separator
being perpendicular to the two current systems, this reconnection may
affect the magnetic field lines of a significant fraction of the loop
current systems, interrupting the currents and quickly releasing the
stored magnetic energy.
Title: Non-thermal excitation and ionization of hydrogen in solar
flares. II - Effects on the temperature minimum region Energy balance
and white light flares
Authors: Aboudarham, J.; Henoux, J. C.
Bibcode: 1987A&A...174..270A
Altcode:
This paper is the second of a series of two papers on the effects on the
non-thermal excitation and ionization of hydrogen by electron beams on
the solar atmosphere. Here the modification of the energy balance at the
temperature minimum level and in the upper photosphere is studied. The
authors show that enhanced hydrogen ionization at the base of the
chromosphere and at the flare temperature minimum region leads to an
increase of the H- population and to enhanced absorption
of photospheric and chromospheric continuum radiation. Consequently
the upper photosphere is radiatively heated at the expense of the
chromospheric continuum radiation produced by the beam. A second
consequence of the hydrogen ionization is the increase of the white
light emission both at chromospheric and photospheric levels.
Title: REVIEW ARTICLE: Galactic ultraviolet astronomy
Authors: Vidal-Madjar, A.; Encrenaz, T.; Ferlet, R.; Henoux, J. C.;
Lallement, R.; Vauclair, G.
Bibcode: 1987RPPh...50...65V
Altcode:
No abstract at ADS
Title: Dynamo Theories of Solar Flares
Authors: Henoux, J. C.
Bibcode: 1987sman.work..109H
Altcode:
In flare models based on magnetic field reconnection, the energy is
liberated in a very thin layer. This makes difficult an explanation
of the high rate of energy release observed in solar flares. The
limitation of these models is briefly discussed. Flare models
based on the disruption of current flowing from the photosphere
to the corona have been proposed. Direct currents can be generated
by organized motions of the neutral photospheric plasma across the
magnetic field. Observations of organized photospheric velocities are
reviewed, and the main characteristics of the electric current system
are presented.
Title: Sunspots rotation and electric currents in a flaring activity
complex.
Authors: Henoux, J. C.; Somov, B. V.
Bibcode: 1987PAICz..66..153H
Altcode: 1987eram....1..153H
Assuming the existence of organised photospheric velocity fields in
an active region, the authors study the creation of photospheric and
coronal D.C. currents by vortex motions.
Title: Non-thermal excitation and ionization of hydrogen in solar
flares. I. Effects on a flaring chromosphere.
Authors: Aboudarham, J.; Henoux, J. C.
Bibcode: 1986A&A...168..301A
Altcode:
By using a semiempirical flare model and assuming that the observed
heating is produced by electron bombardment, a computation is made
of the energy flux above 20 keV that is required in the beam to
compensate for radiative losses. It is then shown that nonthermal
processes strongly increase the radiative losses in the middle
chromosphere. As a consequence, the temperature increase of existing
semiempirical flare models is shown to be overestimated in the low
chromosphere. The inclusion of nonthermal processes reduces but does
not eliminate the difference between energy gains and losses in the
middle chromosphere.Consequently, existing empirical models are not
in a static energy balance.
Title: Energy deposit at temperature minimum level and white light
flares
Authors: Aboudarham, J.; Henoux, J. C.
Bibcode: 1986A&A...156...73A
Altcode:
Empirical atmospheric models are used to estimate the energy deposit
required to heat the temperature minimum region of the quiet sun to
flare temperature. The calculations show that the necessary energy
deposit in the temperature minimum region can be accounted for by
electron bombardment. Electron beam heating of the temperature minimum
and chromospheric regions produces white light emission with an energy
output of about 5×109erg cm-2s-1. Also
the upper photosphere is heated to about 30° above its quiet sun value
by the downward radiation field. All layers from the chromosphere to
the photosphere contribute to the white light emission process. The
emission mechanisms are H- and hydrogen bound-free
emission. The authors conclude, that no in-situ energy release is
necessary to explain the heating of the temperature minimum region. An
electron bombardment can increase the temperature of this region,
and subsequently of the photosphere via radiative back heating, hence
producing a white light flare.
Title: White light flares and atmospheric modeling (Working Group
report).
Authors: Machado, M. E.; Avrett, E. H.; Falciani, R.; Fang, C.;
Gesztelyi, L.; Henoux, J. -C.; Hiei, E.; Neidig, D. F.; Rust, D. M.;
Sotirovski, P.; Svestka, Z.; Zirin, H.
Bibcode: 1986lasf.conf..483M
Altcode:
The authors give a short summary of their discussions, and a set
of recommendations which may help in the study of white light flare
emission processes.
Title: Non-thermal collisional excitation and ionization by electron
beams: Effect on the atmospheric energy balance and white-light
emission in solar flares
Authors: Aboudarham, J.; Henoux, J. C.
Bibcode: 1986AdSpR...6f.131A
Altcode: 1986AdSpR...6..131A
In the middle chromosphere and below, at the time of atmospheric
heating by electron bombardment, the electrons of a beam lose most of
their energy in inelastic collisions with neutral hydrogen. Then the
hydrogen non-thermal excitation and ionization can be more important
that the thermal one and can lead to a significant increase of the
electron number density. In the chromosphere the enhancement of the
hydrogen ionization leads to an increase of the hydrogen continuum
emission. In the temperature minimum region (TMR) the enhancement of
the electron number density produces an increase of the H-
population. Then the absorption by H- of both photospheric
radiation and chromospheric emission produced by the beam increases
the temperature of the TMR and upper photosphere. Both effects lead
to a White-Light Flare with a minimum contrast of 5% at disk center
at 600 nm.
Title: White light flares: heating of the temperature minimum region
by electron beams.
Authors: Aboudarham, Jean; Henoux, Jean-Claude
Bibcode: 1986lasf.conf..205A
Altcode: 1986lasf.symp..205A
Empirical atmospheric models are used to estimate the energy deposit
required to heat the temperature minimum region of the quiet sun to
flare temperature.
Title: Energy Release and Energy Transport Below the Transition Zone
in Solar Flares
Authors: Hénoux, J. C.; Chambe, G.; Heristchi, D.; Semel, M.;
Woodgate, B.; Shine, R.; Beckers, J.
Bibcode: 1985spit.conf..758H
Altcode:
No abstract at ADS
Title: Study of energy release in flares
Authors: Henoux, J. -C.
Bibcode: 1984AdSpR...4g.227H
Altcode: 1984AdSpR...4..227H
Recent advances in the study of energy release in Flares are
reviewed. Progress has been made in modelling coronal X-ray emission
and the chromospheric response to energy imput. These advances are
based on theoretical studies and on the comparison of complementary data
obtained from spacecraft and ground-based observatories. We first review
the modelling of the coronal flare derived from radio, X-ray and XUV
observations. Then we summarize results on the chromospheric response
to various energy imput. Observations of X-ray continuum intensity
and polarization, transition zone lines and chromospheric lines do not
show evidence of particle trapping by a turbulent front. Although they
might be in agreement with trapping and partial precipitation. White
light flares appear to result from energy deposited above the
photosphere. They are probably due to electron bombardment. The
implication of these results on the primary energy release process
are discussed and prospects for new research are presented.
Title: Magnetic Energy Storage and Release in Solar Flares
Authors: Henoux, J. C.
Bibcode: 1984apoa.conf..200H
Altcode:
Accepting the concept of the magnetic origin of solar flares the
mechanisms leading to the release of magnetic energy are reviewed.
Title: Conductive Heat Flux in the Chromosphere Derived from Line
Linear Polarization Observation
Authors: Henoux, J. -C.; Chambe, G.; Heristchi, D.; Semel, M.;
Woodgate, B.; Shine, D.; Beckers, J.
Bibcode: 1983SoPh...86..115H
Altcode:
Linear polarization in two chromospheric lines (Hα and SI 1437 A) was
observed in the gradual phase of solar flares. The polarized electric
vector is directed towards disk center.
Title: Conductive flux in flaring solar chromospheres deduced from
the linear polarization observations
Authors: Henoux, J. C.; Heristchi, D.; Chambe, G.; Woodgate, B.;
Shine, R.; Beckers, J.; Machado, M.
Bibcode: 1983A&A...119..233H
Altcode:
The linear polarization of Hα and S I 1437 Å lines produced in
impact excitation by energetic electrons with an anisotropic velocity
distribution function during solar flares is calculated. Selecting
a function which represents the velocity distribution of electrons
carrying heat flux, the relationship between conductive heat flux and
linear line polarization has been computed. The application of the
relationship between linear polarization and heat flux to the observed
degree of polarization leads to the determination of the conductive
heat flux at the top of flaring chromospheric layers. This conductive
flux is of the order of magnitude of the total radiation loss in the
chromosphere and below, which is also of the order of magnitude of
the conductive flux in the transition zone.
Title: Self-consistent models of flare heated solar chromospheres
Authors: Fang, C.; Henoux, J. C.
Bibcode: 1983A&A...118..139F
Altcode:
For the first time self consistent models of an X-ray irradiated
flaring chromosphere have been derived, together with a model of
an electron heated chromosphere. The atmospheric radiation losses
have been computed by including Lα, Lβ, LyC, Hα, Mg II and Ca
II and H- emission. The hydrogen radiation losses were
computed using complete linearization of the transfer, energy balance
and hydrostatic equilibrium equations coupled with the statistical
equilibrium equations. This method permits a substantial increase in
the accuracy of the radiation loss estimate without requiring excessive
computing time.
Title: Impact linear polarization observed in a UV chromospheric
line during a solar flare
Authors: Henoux, J. C.; Chambe, G.; Sahal, S.; Semel, M.; Woodgate,
B.; Shine, D.; Beckers, J.; Machado, M.
Bibcode: 1983ApJ...265.1066H
Altcode:
Linear polarization was observed in the S 11437 A line in bright
flaring points during the soft X-ray emission from a flare on 1980
July 15. The degree of polarization is about 25% and is detected at a
signal-to-noise ratio of 2.9. The polarized electric vector is directed
toward disk center to within 3°. This polarization could be due
to collisional excitation of S I by energetic electrons beamed in the
vertical direction. Direct excitation by a highly energetic beam of
electrons of order 10-100 keV is doubtful. We suggest that the heat flux
in the region connecting the transition zone to the high chromosphere
during the gradual phase of a flare could lead to an anisotropic
excitation. Then the observed polarization would be due to vertical
motions of the transition zone sweeping the preexisting chromosphere.
Title: The ISPM solar flare X-ray and cosmic gamma-ray burst
experiment.
Authors: Cotin, F.; de Jager, C.; Henoux, J. -C.; Heise, J.; Hilhorst,
M.; Hurley, K.; Niel, M.; Paschmann, G.; Sommer, M.; van Rooijen,
J.; Vedrenne, G.
Bibcode: 1983ESASP1050..209C
Altcode:
The ISPM solar flare X-ray and cosmic gamma-ray burst instrument
(designated the HUS experiment) consists of a pair of Cs I scintillators
and a pair of Si surface barrier detectors for measuring X-rays in
the ranges 15 - 150 and 5 - 15 keV, respectively. High-time-resolution
X-ray measurements (up to 8 ms) will be used to study X- and gamma-ray
bursts of solar and cosmic origin.
Title: Chromospheric effects of XUV radiation emitted during solar
flares
Authors: Machado, M. E.; Henoux, J. -C.
Bibcode: 1982A&A...108...61M
Altcode:
X and UV radiation emitted from the flare corona and transition zone
are shown to affect both the energy balance and ionization balance
of chromosphere layers. The effect of X-rays is most important in
producing temperature increases through the chromosphere, while it
does not affect in a substantial way the overall ionization balance of
abundant elements, with the exception of He I and, possibly, O I. UV
lines radiation, on the other hand, produces strong variations in the
ionization balance of some elements, in particular C I and Si I, and
induce non LTE effects which modify the emergent spectra. Variations
in the Si I continuum intensities at wavelengths under 1682 A are shown
to be strongly decoupled from local variations in the Planck function,
and cannot be used to derive temperature changes at the temperature
minimum level.
Title: Impact linear polarization observed in a UV chromospheric
line during a solar flare
Authors: Henoux, J. C.; Chambe, G.; Semel, M.; Woodgate, B.; Shine,
R.; Beckers, J.
Bibcode: 1982AdSpR...2k.155H
Altcode: 1982AdSpR...2..155H
Linear polarization was observed in the S I 1437Å line in bright
flaring points during the soft X-ray emission. The degree of
polarization is about 25% and is detected at a signal to noise ratio
of 2.9. The polarized electric vector is directed towards disk center
to within 3°. This polarization could be due to collisional
excitationm of S I by energetic electrons beamed in the vertical
direction. We suggest that the heat flux in the region interconnecting
the transition zone to the high chromosphere during the gradual phase
of a flare could lead to an anisotropic excitation. Then the observed
polarization would be due to vertical motions of the transition zone
sweeping the preexisting chromosphere.
Title: Horizontal distribution of the X-ray energy deposit in the
chromosphere and H alpha two ribbon flares
Authors: Henoux, J. C.; Rust, D.
Bibcode: 1980A&A....91..322H
Altcode:
The two-ribbon Hα brightening and the X-ray emitting coronal loop
arcade during the very late phase of the 29 July 1973 flare are
examined. By means of a simple geometrical model of the X-ray emitting
structures, the horizontal distribution of X-radiation is computed
for several different levels in the chromosphere. It is found that an
arcade of X-ray emitting loops, commonly found over large two-ribbon
flares, gives an energy deposit pattern in the chromosphere similar
in shape to the Hα flare emission. Isophotes of the Hα brightening
are compared to the X-ray energy deposit horizontal variation profiles
from a single loop and from an arcade of loops. The brightest 29 July
isophotes fit midway between the X-ray profiles associated respectively
with a loop and an arcade. The maximum X-ray energy deposit rate of 1.5
106 ergs cm-2 s-1 is slightly higher
than the peak Hα emission rate. It is concluded that X-ray radiation
is an important source of energy for Hz flares. There seems to be no
need for in- situ energy release in the chromosphere.
Title: The chromosphere and transition region
Authors: Canfield, R. C.; Brown, J. C.; Craig, I. J. D.; Brueckner,
G. E.; Cook, J. W.; Doschek, G. A.; Emslie, A. G.; Machado, M. E.;
Henoux, J. -C.; Lites, B. W.
Bibcode: 1980sfsl.work..231C
Altcode: 1980sofl.symp..231C
The physical processes occurring as a result of the transfer of
energy and momentum from the primary solar flare energy release site
in the corona to the underlying chromosphere and transition region
during the course of the flare are investigated through a comparison
of theoretical models and observational data. Static, dynamic and
hydrodynamic models of the lower-temperature chromospheric flare are
reviewed. The roles of thermal conduction, radiation, fast particles
and mass motion in chromosphere-corona interactions are analyzed on
the basis of Skylab UV, EUV and X-ray data, and empirical and synthetic
models of the chromospheric and upper photospheric responses to flares
are developed. The canonical model of chromospheric heating during
flares as a result of primary energy release elsewhere is found to be
justified in the chromosphere as a whole, although not entirely as the
temperature minimum, and a simplified model of horizontal chromospheric
flare structure based on results obtained is presented.
Title: Energy Release and Energy Transfer in Flares
Authors: Henoux, J. C.
Bibcode: 1980jfss.conf..210H
Altcode:
No abstract at ADS
Title: Japan-France Seminar on Solar Physics
Authors: Moriyama, F.; Henoux, J. C.
Bibcode: 1980jfss.conf.....M
Altcode:
No abstract at ADS
Title: Direct excitation of hydrogen by photoelectron and accelerated
electron collisions in solar chromospheric flares - Effects on the
profile and polarization of LY alpha
Authors: Chambe, G.; Henoux, J. -C.
Bibcode: 1979A&A....80..123C
Altcode:
Summary. The rate of direct collisional excitation of Ly by
(superthermal) photoelectrons is compared to the thermal rates. These
photoelectrons are produced via ionization of chromospheric material
(mainly helium) by XUV radiation from the overlying flare source. We
found that for intense XUV flares, with area not larger than 1018 cm2,
there exists a layer in the atmosphere where direct excitation effects
are significant, which leads to enhanced emerging intensity in the
Ly wings (for A V >3.5 A VD). These results were established by
using a-priori given models for hydrogen and thermal electrons in
flares, but the ionization of helium was independently calculated. We
then calculated the velocity distribution of the photoelectrons, and
found substantial anisotropy (the photoelectrons moving preferentially
near the horizontal) increasing with the depth in the atmosphere and
with the compactness of the XUV source. The Ly photons resulting from
photoelectrons excitation alone are linearly polarized, with a degree
increasing with the line of sight inclination, up to a value of 4.5
%, but the polarization is lost during the travel outwards, unless
practically 100% coherence in photon scattering is assumed. This
does not preclude the possibility for other lines to be polarized,
however. The other possible mechanism of direct excitation (collisions
by electron beams) is shown to produce the same qualitative effects;
in particular excitation is also due predominantly to electrons
moving at small angle with the horizontal. Key words: solar flares :
photoelectrons - accelerated electrons - Lya emission - Lyoc line :
anisotropic excitation - polarization
Title: Dynamics of an atmosphere irradiated by soft X-rays in flares.
Authors: Henoux, J.; Nakagawa, Y.
Bibcode: 1978A&A....66..385H
Altcode:
It was previously shown that the lower chromosphere can be heated
substantially by soft X-ray radiation at wavelengths of 1-300 A arising
from a high-temperature plasma in the corona during a flare. The
analysis was, however, based on the steady-state approximation. In
this paper, a more realistic dynamic response is examined utilizing
numerical calculations. Specifically, the physical parameters,
such as the temperature, emission measure, and physical size of the
X-ray source, are taken similar to the previous study; i.e., typical
values for one 1N flares. The initial atmosphere is represented by
the HSRA model atmosphere. The results indicate that with continuous
and constant irradiation by the soft X-ray flux: (1) the atmosphere
undergoes an oscillating expansion characterized by an oscillation
period of approximately 270 s before reaching a new steady state in
about 30 min; (2) in the oscillatory motions, a temperature increase
coincides with downward motions and with upward motions; and (3)
the observed time variation of the H-alpha line profile in flares
appears to be in agreement with the initial part of the oscillatory
behavior. It is noted that the oscillatory motions may not arise for
spatially as well as temporally inhomogeneous soft X-ray sources.
Title: Effects of Soft X-Ray Flux on the Lower Solar Atmospherer in
Flares (Proceedings of the Meeting `How Can Flares be Understood?',
held during the 16th General Assembly of the IAU in Grenoble, France,
on 27 August, 1976.)
Authors: Henoux, J. C.; Nakagawa, Y.
Bibcode: 1977SoPh...53..279H
Altcode:
No abstract at ADS
Title: Anisotropy and Polarization of Solar X-Ray Bursts
Authors: Henoux, J. C.
Bibcode: 1975SoPh...42..219H
Altcode:
The effects of the Compton back-scattered X-ray flux from the
photosphere on the directivity and polarization of flare X-rays between
15 keV and 150 keV are computed. The calculations are made with a thin
target model for flares of De Jager-Kundu type with electrons spiralling
downward around a vertical magnetic field and for an Isotropie source.
Title: Abstracts of papers from other journals
Authors: Namba, O.; Henoux, J. -C.
Bibcode: 1975SoPh...41..771N
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Henoux, J. C.
Bibcode: 1973SoPh...33..259H
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Henoux, J. -C.
Bibcode: 1973SoPh...31..532H
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Pasachoff, Jay M.; Uchida, Y.; Vassilyeva, G.; Henoux, J. C.
Bibcode: 1973SoPh...30..273P
Altcode:
No abstract at ADS
Title: X-rays spectroheliograms in lines of Mg xi and Mg xii
Authors: Bonnelle, C.; Senemaud, C.; Senemaud, G.; Chambe, G.;
Guionnet, M.; Henoux, J. C.; Michard, R.
Bibcode: 1973SoPh...29..341B
Altcode:
Spectroheliograms in the Lα Mg XII line and in the Mg XI resonance
(R) 1s21S0-1s2p1P1
line, intercombination (I)
1s21S0-1s2p3P1,2,
line, and the forbidden (F)
1s21S0-1s2s3S1 line,
have been obtained.
Title: Abstracts of papers from other journals
Authors: Uchida, Y.; Vassilieva, G.; Henoux, J. C.
Bibcode: 1973SoPh...29..270U
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Henoux, J. C.; Uchida, Y.; Vassilieva, G.
Bibcode: 1973SoPh...28..546H
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Shaw, M. L.; Gussmann, E. A.; Stepayan, N.; Henoux, J. C.
Bibcode: 1972SoPh...25..504S
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: De Feiter, L. D.; Pasachoff, Jay M.; Vassilyeva, G.; Gussmann,
E. A.; Vassilyeva, G. J.; Henoux, J. -C.; Uchida, Y.; Namba, O.
Bibcode: 1972SoPh...23..501D
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Henoux, J. -C.; De Feiter, L. D.; Ambroš, P.; Pasachoff,
JAY M.
Bibcode: 1972SoPh...22..252H
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Uchida, Y.; Namba, O.; Henoux, J. -C.
Bibcode: 1971SoPh...21..255U
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: De Feiter, L. D.; Vassilyeva, G.; Henoux, J. -C.; Ambrož,
Pavel
Bibcode: 1971SoPh...20..517D
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Pasachoff, Jay M.; Vassilyeva, G. J.; Henoux, J. -C.; De
Fetter, L. D.
Bibcode: 1971SoPh...19..494P
Altcode:
No abstract at ADS
Title: Isotopes of Magnesium in the Solar Atmosphere
Authors: Boyer, R.; Henoux, J. C.; Sotirovski, P.
Bibcode: 1971SoPh...19..330B
Altcode:
We have analysed MgH A2Π-X2Σ(0.0), (1.1),
(2.2), (0.1) and (1.2) absorption bands in a sunspot spectrum. By two
different methods, which are almost independent of the estimated value
of the correction for stray light, we have determined the solar isotopic
ratios of magnesium. These ratios are equal to the terrestrial ones -
24Mg∶25Mg∶26Mg = 80∶10∶10.
Title: Abstracts of papers from other journals
Authors: Henoux, J. C.
Bibcode: 1971SoPh...17..512H
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Pasachoff, Jay M.; Henoux, J. -C.; de Feiter, L. D.
Bibcode: 1971SoPh...17..277P
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Henoux, J. C.; Pasachoff, Jay M.; Vassilyeva, G. Y.
Bibcode: 1970SoPh...11..343H
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Uchida, Y.; Gussmann, E. A.; De Feiter, L. D.; Henoux,
J. -C.; Stepanyan, N. N.; Pasachoff, Jay. M.
Bibcode: 1970SoPh...11..173U
Altcode:
No abstract at ADS
Title: Abstracts of papers from other journals
Authors: Stepanyan, N.; Pasachoff, Jay M.; Ambrož, P.; Vassilyeva,
G.; Henoux, J. -C.; Fokker, A. D.; De Feiter, L. D.; Gussmann, E. A.;
Uchida, Y.; Namba, O.
Bibcode: 1969SoPh....8..491S
Altcode:
No abstract at ADS
Title: A Model of Sunspot Umbra
Authors: Henoux, J. C.
Bibcode: 1969A&A.....2..288H
Altcode:
In a preceding paper (He'noux, 1968) we have determined the temperature
of a large umbra (A,e> 100 X 10-6 Hem.), in the layers deeper than r
= 0.3. The temperature structure has been deduced from measurements of
infra-red umbral intensities, with an estimated accuracy of 60 K. In
this paper another large umbra observed the 9/21/69 is studied. The
study of proffles and equivalent widths of strong, medium or weak
atomic lines, in the visible spectral region, permits a study of the
temperature structure to higher layers and to show that umbra is in
hydrostatic equilibrium. It is supposed that umbras of large areas (A
> 100 >c 10-6 Hem.) have the same temperature, as that previously
determined for r0 > 0.3. This hypothesis is justffled in the first
chapter: it is shown (Fig. 1) that two of the three mean relative umbral
intensities deduced form the data of Makita and Morimoto (1960) must
be corrected for the effect of lines. Some corrections must be applied
also to the measurements of Kneer and Mattig (1968) (Fig. 3). These
corrected values are nearly equal to the intensities we have measured
(Tables 1 and 2). The true relative umbral intensities are computed
with the thermal law previously determined, and compared with the
observed one. In this way the stray light is determined (Table 2) as a
function of the wavelength. Thus the proffles and equivalent widths are
corrected for the stray light. In Chapter II the temperature structure
is extended from r = 0.3 up to higher layers (r = 10- ). The wings
of the strong Na 1) and Mg b lines are studied. The wings of the Na
D lines are very sensitive to temperature (Figs. 46). The temperature
structure at the optical depth r <0.3 is determined by trial, and
error until a good agreement between observed and computed Na D wings
is obtained (Fig. 4). For this purpose the atmosphere is supposed to
be in hydrostatic equilibrium. The model is then used to compute the
wings of the b lines. The agreement obtained is good too (Fig. 8). It
is shown that it is impossible to represent the observed wings with
sub-hydrostatic pressures and the temperature structure O(r0>
0.3) which is reasonably well established. In the third chapter the
equivalent widths of many ionic and atomic lines of Fe H, Cr H, Ti H, Fe
I, Cr I, Ti I are measured and computed with the model. The selection of
the unblended lines has been made by using a spectrum of the same umbra
taken with a Babinet biprism. Many ionic lines studied by Makita (1963)
and Fricke and (1965) are in fact blended with molecular lines. Their
equivalent widths are probably as weak as the values predicted by the
model. For example it is shown (half-tones 10a, b, c) that the atomic
lines of large excitation potential observed in an umbra by Makita are
in fact molecular lines. The measured equivalent widths are compared to
the values computed with the model. The computations are made with a
so called "turbulence" = 1.5 km/s; the influence of the Zeeman effect
is neglected. The agreement obtained is good in the case of medium
weak ionic lines (Tables 9) and of the ionic lines measured by Zwaan
(1965). The representation of the equivalent width of the atomic lines
is good too (Fig. 9). The model is given in Chapter IV (Tables 12,
Figs. 11-12). The transparency of the umbra is computed; it equals
the transparency of the photosphere at the same optical depth. We have
not tried to relate the geometrical depth scales of the photospheric
and umbral model, because it would have been necessary to make some
unreliable assumption about the geometrical shape of the spot or about
the curvature of the magnetic lines of force. The integrated radiative
flux is computed in function of the optical depth (Fig. 13). Oniy the
higher layers are in radiative equilibrium (Teff = 3650 K). There is
no radiative equilibrium in the layers deeper than = 1.
Title: Abstracts of papers from other journals
Authors: Pasachoff, Jay M.; Vassilyeva, G. Y.; Henoux, J. -C.;
Stepanyan, N.
Bibcode: 1968SoPh....5..588P
Altcode:
No abstract at ADS
Title: Sur une particularité de la composante π du triplet normal
dans l'ombre d'une tache
Authors: Henoux, J. C.
Bibcode: 1968SoPh....4..315H
Altcode:
No abstract at ADS
Title: Abstracts
Authors: Yassilyeva, G. Y.; Dupree, A. K.; Henoux, J. C.; Namba, O.
Bibcode: 1968SoPh....4..127Y
Altcode:
No abstract at ADS
Title: Abstracts
Authors: Henoux, J. C.; Dupree, A. K.; Stepanyan, N. N.
Bibcode: 1968SoPh....3..364H
Altcode:
No abstract at ADS
Title: Un modèle thermique de l'ombre d'une tache basé sur la
spectrophotométrie du continuum infra rouge
Authors: Henoux, J. C.
Bibcode: 1968AnAp...31..511H
Altcode:
No abstract at ADS
Title: Abstracts
Authors: Dupree, A. K.; Henoux, J. -C.; Ambož, Pavel; Gussmann,
E. A.; Vassilyeva, Galina. Y.
Bibcode: 1967SoPh....2..502D
Altcode:
No abstract at ADS
Title: Étude du triplet b du magnésium sur le disque et sur la
chromosphère
Authors: Henoux, J. C.
Bibcode: 1966AnAp...29..271H
Altcode:
No abstract at ADS
Title: Essai de détermination des intensités et des orientations
des champs magnétiques d'un groupe de taches solaires
Authors: Henoux, J. -C.
Bibcode: 1963AnAp...26..159H
Altcode:
No abstract at ADS