explanation blue bibcodes open ADS page with paths to full text
Author name code: arnaud
ADS astronomy entries on 2022-09-14
author:"Arnaud, Jean"
---------------------------------------------------------
Title: Extinction and Sky Brightness at Dome C
Authors: Faurobert, M.; Arnaud, J.; Vernisse, Y.
2012EAS....55..365F Altcode:
We have installed a small telescope to monitor the sky brightness
around the sun at the French-Italian station Concordia at Dome
C in Antarctica. Previous campaigns have been performed with the
same instrument at Haleakala in Hawai and Sunspot in New Mexico. We
compare here the results of the first year of the campaign at Dome C
(2008) to the purest sky observed at Haleakala. We show that Dome C
is an outstanding site for coronal observations. Compared to Haleaka,
it appears to be more transparent, and to contain less aerosols. Its
water vapour content is also significantly smaller. These results
still have to be confirmed by the analysis of the 2009 and 2010 data.
---------------------------------------------------------
Title: Sunlight refraction in the mesosphere of Venus during the
transit on June 8th, 2004
Authors: Tanga, P.; Widemann, T.; Sicardy, B.; Pasachoff, J. M.;
Arnaud, J.; Comolli, L.; Rondi, A.; Rondi, S.; Sütterlin, P.
2012Icar..218..207T Altcode: 2011arXiv1112.3136T
Many observers in the past gave detailed descriptions of the telescopic
aspect of Venus during its extremely rare transits across the Solar
disk. In particular, at the ingress and egress, the portion of the
planet’s disk outside the Solar photosphere has been repeatedly
perceived as outlined by a thin, bright arc (“aureole”). Those
historical visual observations allowed inferring the existence of
Venus’ atmosphere, the bright arc being correctly ascribed to the
refraction of light by the outer layers of a dense atmosphere. On June
8th, 2004, fast photometry based on electronic imaging devices allowed
the first quantitative analysis of the phenomenon. Several observers
used a variety of acquisition systems to image the event - ranging from
amateur-sized to professional telescopes and cameras - thus collecting
for the first time a large amount of quantitative information on this
atmospheric phenomenon. In this paper, after reviewing some elements
brought by the historical records, we give a detailed report of the
ground based observations of the 2004 transit. Besides confirming the
historical descriptions, we perform the first photometric analysis of
the aureole using various acquisition systems. The spatially resolved
data provide measurements of the aureole flux as a function of the
planetocentric latitude along the limb. A new differential refraction
model of solar disk through the upper atmosphere allows us to relate
the variable photometry to the latitudinal dependency of scale-height
with temperature in the South polar region, as well as the latitudinal
variation of the cloud-top layer altitude. We compare our measurements
to recent analysis of the Venus Express VIRTIS-M, VMC and SPICAV/SOIR
thermal field and aerosol distribution. Our results can be used a
starting point for new, more optimized experiments during the 2012
transit event.
---------------------------------------------------------
Title: Measurement of Aureole and Suppression of Internal Stray
Light of Aureole Photometer
Authors: Liu, Nian-Ping; Liu, Yu; Shen, Yun-Deng; Zhang, Xue-Fei;
Cao, Wen-Da; Arnaud, Jean
2011ChA&A..35..428L Altcode:
A modern aureole photometer (AP) was developed for the site survey
inWest China, in preparation for the installation of future large solar
equipments. The performance of this new AP was tested in preliminary
observations, and a lot of sky brightness data were accumulated at
a few sites in Yunnan Province. The result of data analysis shows
that the aureole near the noon time on Jiaozi Snow Mountain is as
low as a few millionths of the intensity at the solar disk center,
indicating the low internal stray light level of our instrument. The
internal stray light of the AP comes mainly from two parts: the edge
diffraction of the ferrule for fixing the ND4 filter in the front end
of the telescope tube, causing the stray light distributed in the inner
region of the field of view, and the edge diffractions of the diaphragms
placed inside the telescope tube, causing the stray light distributed in
the outer region of the field of view. In order to suppress the stray
light of the latter part, the experiment to change the aperture size
of an additional diaphragm was performed. The result shows that the
stray light in the outer region of the field of view can be effectively
suppressed by reducing properly the aperture size of the diaphragm.
---------------------------------------------------------
Title: Measurement of Sky Brightness and Suppression of Scattering
in Sky Brightness Monitor
Authors: Liu, N. P.; Liu, Y.; Shen, Y. D.; Zhang, X. F.; Cao, W. D.;
Arnaud, J.
2011AcASn..52..160L Altcode:
A modern Sky Brightness Monitor (SBM) was developed for the site survey
in West China for the future large solar equipment installation. The
performance of this new SBM was tested in the recent preliminary
experiments. A lot of sky brightness data had been obtained at a few
sites in Yunnan. The blue channel result shows that the sky brightness
near the noon time on Jiaozi Snow Mountain is as low as a few millionths
of the solar center intensity, indicating the low scattering level
inside our SBM instrument. The scattering is mainly from two parts:
the diffraction rings from the occulter edges, distributed in the inner
field of view but outside the occulter region containing the ND4 filter;
the diffraction from the baffle rings, distributed in the extreme edges
of the field of view. To suppress the scattering of the latter part,
experiments with different aperture sizes of baffle rings are made. The
result shows that, by mounting new baffle rings with proper aperture
size into the SBM telescope tube, diffraction in the extreme edges of
the field of view can be effectively reduced.
---------------------------------------------------------
Title: Sunspot Umbra Atmosphere from Full Stokes Inversion
Authors: Wenzel, R.; Berdyugina, S. V.; Fluri, D. M.; Arnaud, J.;
Sainz-Dalda, A.
2010ASPC..428..117W Altcode: 2010arXiv1003.5114W
Sunspots are prominent manifestations of the solar cycle and provide
key constraints for understanding its operation. Also, knowing
the internal structure of sunspots allows us to gain insights on
the energy transport in strong magnetic fields and, thus, on the
processes inside the convection zone, where solar magnetic fields
are generated and amplified before emerging at the surface on various
scales, even during solar minima. In this paper, we present results
of a spectropolarimetric analysis of a sunspot observed during the
declining phase of solar cycle 23. By inversion of the full Stokes
spectra, observed in several spectral regions in the optical at the
THEMIS facility, we infer the height dependence of physical quantities
such as the temperature and the magnetic field strength for different
sunspot regions. The simultaneous use of atomic (Fe I 5250.2 and 5250.6
Å) and highly temperature-sensitive molecular (TiO 7055 Å and MgH
5200 Å) lines allows us to improve a model of the sunspot umbra.
---------------------------------------------------------
Title: Direct measurement of the formation height difference of the
630 nm Fe I solar lines
Authors: Faurobert, M.; Aime, C.; Périni, C.; Uitenbroek, H.; Grec,
C.; Arnaud, J.; Ricort, G.
2009A&A...507L..29F Altcode:
Context: Spectral lines formed over a limited height range in either
a stellar or planetary atmosphere provide us with information about
the physical conditions within this height range. In this context,
an important quantity is the so-called line formation depth. It is
usually determined from numerical calculation of the atmospheric
opacity in the line of interest and then converted into geometrical
depth by using atmospheric models. <BR />Aims: We develop a radically
different approach, which allows us to measure directly line formation
depths from spectroscopic observations without relying on assumptions
about an atmospheric model. This method requires spatially resolved
observations, which up to now have been available only for solar
or planetary studies. We apply this method to images of the solar
granulation. <BR />Methods: The method was presented and tested
numerically in previous papers. It is based on the measurement
of the perspective shift between images at different wavelengths,
formed at different heights, when they are observed away from disk
center. Because of the Fourier transform properties, this shift gives
rise to a deterministic linear phase term in the cross spectrum of the
images. <BR />Results: The method is applied to observations of solar
quiet regions performed with the SOT spectropolarimeter on HINODE in
the Fe i line pair at 630.15 and 630.25 nm. We derive the difference
in formation heights between the two lines and its center-to-limb
variations. We show that the high sensitivity of the measurements allows
us to detect variations in the line formation heights between magnetized
and non-magnetized regions of the solar atmosphere. <BR />Conclusions:
Our results are the first direct measurements of line formation depths
in the solar photosphere. Cross spectral analysis provides us with a
new observable quantity, which may be measured with an accuracy well
bellow the spatial resolution of the observations. We recall that
the Fe i line pair at 630.15 and 630.25 nm is often used to determine
solar magnetic fields by spectropolarimetric observations and inversion
methods. The difference in the line formation heights that we measure
should be taken into account in the inversion procedures.
---------------------------------------------------------
Title: ASPIICS, a giant externally occulted coronagraph for the
PROBA-3 formation flying mission
Authors: Vivès, S.; Lamy, P.; Koutchmy, S.; Arnaud, J.
2009AdSpR..43.1007V Altcode:
Formation flying opens new perspectives for coronal physics, and
allow to conceive giant, externally occulted coronagraphs using a
two-component space system with the external occulter on one spacecraft
and the optical instrument on the other spacecraft. ASPIICS (Association
de Satellites Pour l'Imagerie et l'Interférométrie de la Couronne
Solaire) is a mission proposed to ESA in the framework of the PROBA-3
program of formation flying which is presently in phase A, to exploit
this technique for coronal observations. ASPIICS is composed of a
single coronagraph which performs high spatial resolution imaging of
the corona as well as 2-dimensional spectroscopy of several emission
lines from the coronal base out to 3 R<SUB>⊙</SUB>. The selected
lines allow to address different coronal regions: the forbidden
line of Fe XIV at 530.285 nm (coronal matter), Fe IX/X at 637.4 nm
(coronal holes), HeI at 587.6 nm (cold matter). An additional broad
spectral channel will image the white light corona so as to derive
electron densities. The classical design of an externally occulted
coronagraph is adapted to the detection of the very inner corona
as close as 1.01 R<SUB>⊙</SUB> and the addition of a Fabry-Perot
interferometer using a so-called " étalon". This paper is dedicated
to the description of the optical design and its critical components:
the entrance optics and the Fabry-Pérot interferometer. ASPIICS will
address the question of coronal heating and of the role of waves by
characterizing propagating fluctuations (waves and turbulence) in the
solar wind acceleration region and by looking for oscillations in the
intensity and Doppler shift of spectral lines. The combined imaging
and spectral diagnostics capabilities available with ASPIICS will
allow to map the velocity field of the corona both in the sky plane
(directly on the images) and along the line-of-sight by measuring
the Doppler shifts of emission lines. We will attempt to determine
how the different components of the solar wind, slow and fast are
accelerated. ASPIICS will observe the corona during the maximum of
solar activity, insuring the detection of many Coronal Mass Ejections
(CMEs). By rapidly alternating high resolution imaging and spectroscopy,
CMEs will be thoroughly characterized. In addition, ASPIICS will attempt
to characterize the topology of the magnetic field in the corona.
---------------------------------------------------------
Title: Hanle effect in the solar Ba II D2 line: a diagnostic tool
for chromospheric weak magnetic fields
Authors: Faurobert, M.; Derouich, M.; Bommier, V.; Arnaud, J.
2009A&A...493..201F Altcode: 2008arXiv0811.1180F
Context: The physics of the solar chromosphere depends in a crucial way
on its magnetic structure. However there are presently very few direct
magnetic field diagnostics available for this region. <BR />Aims:
Here we investigate the diagnostic potential of the Hanle effect
on the Ba II D2 line resonance polarization for the determination
of weak chromospheric turbulent magnetic fields. <BR />Methods:
The line formation is described with a non-LTE polarized radiative
transfer model taking into account partial frequency redistribution
with an equivalent two-level atom approximation, in the presence of
depolarizing collisions and the Hanle effect. We investigate the line
sensitivity to temperature variations in the low chromosphere and
to elastic collision with hydrogen atoms. We compare center-to-limb
variations of the intensity and linear polarization profiles observed
at THEMIS in 2007 to our numerical results. <BR />Results: We show that
the line resonance polarization is very strongly affected by partial
frequency redistribution effects both in the line central peak and
in the wings. Complete frequency redistribution cannot reproduce the
polarization observed in the line wings. The line is weakly sensitive
to temperature differences between warm and cold components of the
chromosphere. The effects of elastic collisions with hydrogen atoms and
of alignment transfer due to multi-level coupling with the metastable
^2D{5/2} levels have been studied in a recent paper showing that they
depolarize the ^2P{3/2} level of the line. In the conditions where
the line is formed we estimate the amount of depolarization due to
this mechanism as a factor of 0.7 to 0.65. If we first neglect this
effect and determine the turbulent magnetic field strength required to
account for the observed line polarization, we obtain values between
20 G and 30 G. We show that this overestimates the magnetic strength
by a factor between 1.7 and 2. Applying these correction factors
to our previous estimates, we find that the turbulent magnetic field
strength is between 10 G and 18 G. <BR />Conclusions: Because of its low
sensitivity to temperature variations, the solar Ba II D2 line appears
as a very good candidate for the diagnosis of weak magnetic fields in
the low chromosphere (z ≥ 900 km) by means of the Hanle effect.
---------------------------------------------------------
Title: European Projects of Solar Diameter Monitoring
Authors: Sigismondi, Costantino; Bianda, Michele; Arnaud, Jean
2008AIPC.1059..189S Altcode:
Three projects dealing with solar diameter evolution are presently
in development. Historical and contemporary eclipses and planetary
transits data collection and analysis, to cover potentially the
last 5 centuries with an accuracy of few hundreds of arcsecond on
diameter's measurements. The French space mission PICARD with a
few milliarcseconds accuray. With PICARD-SOL instruments located
at the plateau of Calern the role of the atmosphere in ground-based
measurements will be clarified. CLAVIUS is a Swiss-Italian project
based on drift-scan method, free from optical distortions, where hourly
circles transits will be monitored with fast CMOS sensors in different
wavebands. The will run at IRSOL Gregory-Coudé telescope.
---------------------------------------------------------
Title: Sunspot Model Atmosphere from Inversion of Stokes Profiles
Authors: Wenzel, R.; Berdyugina, V. S.; Fluri, D. M.; Arnaud, J.;
Sainz Dalda, A.
2008ESPM...12.2.24W Altcode:
We present results of a spectropolarimetric analysis of sunspots. By
inversion of full Stokes spectra observed in serveral spectral regions
in the optical at the THEMIS facility we infer the height dependence of
physical quantities such as the temperature, LOS velocity and magnetic
field for different sunspot regions. The wide spectral range and
the use of TiO and MgH transitions, which are extremely temperature
sensitive and can be treated in LTE even in higher layers, allow us
to extend and improve a sunspot model atmosphere.
---------------------------------------------------------
Title: Apodized apertures for solar coronagraphy
Authors: Carlotti, Alexis; Aime, Claude; Arnaud, Jean; Faurobert,
Marianne; Ferrari, André; Grec, Catherine; Ricort, Gilbert
2008SPIE.7014E..15C Altcode: 2008SPIE.7014E..38C
An apodized aperture should make it possible to observe the solar corona
without the need of a Lyot coronagraph. We show in this communication
that Sonine functions are much better apodizers for the observation
of the solar corona than the generalized prolate spheroidal functions
previously proposed. For a perfect circular aperture of diameter
unity operated in space, a simple Sonine apodization of the form (1 -
4r<SUP>2</SUP>), with |r| <= 1/2 should sufficiently reduce the
diffraction halo produced by the solar disc to observe the corona
very close to the solar limb (a few arcsec). The throughput is just
one third of the clear aperture.
---------------------------------------------------------
Title: First Direct Detection of Magnetic Fields in Starspots and
Stellar Chromospheres
Authors: Berdyugina, S. V.; Fluri, D. M.; Afram, N.; Suwald, F.;
Petit, P.; Arnaud, J.; Harrington, D. M.; Kuhn, J. R.
2008ASPC..384..175B Altcode: 2008csss...14..175B; 2007astro.ph..3559B
Here we report on the first detection of circular polarization in
molecular lines formed in cool magnetic regions (starspots) and in
chromospheric emission lines formed in hot plages on the surfaces
of active stars. <P />Our survey of G-K-M stars included young
main-sequence dwarfs and RS~CVn-type giants and subgiants. All
stars were found to possess surface magnetic fields producing
Stokes V LSD signals in atomic lines of 0.05% to 0.5%. Several stars
clearly showed circular polarization in molecular lines of 0.1% to
1%. The molecular Stokes V signal is reminiscent of that observed in
sunspots. Chromospheric magnetic fields were detected on most active
targets in Stokes~V profiles of emission lines with peak polarization
up to 2%. The observed molecular circular polarization on M dwarfs
indicates single-polarity magnetic fields covering at least 10% of
the stellar disk. Smaller signals on K stars imply that their magnetic
fields are apparently weaker, more entangled than on M dwarfs, or more
diluted by the bright photosphere.
---------------------------------------------------------
Title: Detection of an Extended Near-Sun Neutral Helium Cloud from
Ground-based Infrared Coronagraph Spectropolarimetry
Authors: Kuhn, J. R.; Arnaud, J.; Jaeggli, S.; Lin, H.; Moise, E.
2007ApJ...667L.203K Altcode:
Sensitive spectropolarimetric observations from the Haleakala SOLARC
coronagraph and infrared imaging spectropolarimeter have detected an
extended diffuse surface brightness flux at the 1083 nm wavelength
of neutral helium (He I). This has the polarization signature of
light scattered by an extended He I cloud in the vicinity of the
Sun. The He I scattered surface brightness appears to be consistent
with a previous eclipse measurement and satellite observations of the
local interstellar medium (LISM) helium wind (LISW), obtained using
observations of the He I UV resonance line at 58.4 nm. The sensitivity
of the infrared coronagraphic method suggests that the LISW interaction
with the local solar wind can have observable consequences that may
yield a useful ground-based technique for studying the coronal and
interplanetary plasma.
---------------------------------------------------------
Title: Apodized apertures for solar coronagraphy
Authors: Aime, C.; Arnaud, J.; Carlotti, A.; Faurobert, M.; Ferrari,
A.; Grec, C.; Ricort, G.
2007sf2a.conf..574A Altcode:
The solar corona cannot be studied without the help of a coronagraph. A
telescope with an apodized aperture is, as described by Aime (2007),
an alternative to the classical Lyot coronagraph. A spheroidal prolate
apodization will modify the PSF of the telescope and optimize the energy
concentration in the focal plane. A strong apodization (prolatness
parameter c ≈ 10) would reduce the diffraction halo by a factor
10^5 at a cost of intensity throughput reduced at 10 %. In a site with
outstanding daytime seeing, like Dome C, this method should allow to
observe the corona extremely close to the solar limb and also, much
better than otherwise, the rich chromospheric weak emission spectrum.
---------------------------------------------------------
Title: Resonance polarization of the solar 455.4 nm BaII line:
diagnostics of chromospheric magnetic fields
Authors: Michel, C.; Faurobert, M.; Arnaud, J.; Malherbe, J. M.
2007sf2a.conf..607M Altcode:
The BaII resonance line at 455.4 nm is formed in the low solar
chromopshere. It is significantly linearly polarized outside active
regions and close to the solar limb. This so-called resonance
polarization is sensitive to the Hanle effect of weak magnetic
fields. We report on numerical simulations of the intensity and
resonance polarization profiles in the line and in the adjacent
continuum, in the quiet solar atmosphere and we compare them to
observations performed at the Jean Rosch refractor at the Pic du Midi
Observatory. In the simulations we take into account non-LTE multilevel
coupling, multiple scattering and partial frequency redistribution, and
we neglect the hyperfine structure of the odd isotopes. This allows to
model the central part of the line core and the wings quite well. Then
we investigate the diagnostic potential of the line core polarization
for weak unresolved magnetic fields in the low chromosphere. We find
that the observed polarization rates are in good agreement with the
simulations if we take into account the Hanle effect of weak magnetic
fields on the order of 60 to 75 Gauss.
---------------------------------------------------------
Title: The Prolate Apodized Solar Coronagraph
Authors: Aimé, C.; Arnaud, J.; Carlotti, A.; Faurobert, M.; Ferrari,
A.; Grec, C.; Ricort, G.
2007lyot.confE..40A Altcode:
We present the project of a new solar coronagraph that makes it possible
to observe the solar corona very close to the solar limb, without
using Lyot's mask and stop technique. The high dynamic capability is
obtained using a strongly apodized aperture. A good choice for the
aperture transmission is the generalized prolate spheroidal function
of prolateness coefficient c on the order of 10. Such an instrument
operated in space, could reduce the diffraction halo produced by the
Sun by a factor 100 000, at the cost of an intensity throughput of 10
%. The classical resolution, in terms of equivalent width of the PSF,
is reduced by a factor of about 1.7 while the MTF of the telescope
becomes similar to a Gaussian function with unchanged cut-off frequency
D/lambda. The telescope design is an unobstructed circular aperture
and the variable transmission produced directly at the entrance
window. This concept, although demanding in terms of mechanical and
optical achievements, is preferred to the more classical re-imaging
of a clear aperture and subsequent apodisation, for image quality
concerns. It does not need a wide field telescope and may take advantage
of adaptive optics for ground based observations. It is expected that
such a system should give much better images than the classical Lyot
coronagraph very close to the solar limb. Such observations should
give access to coronal heating processes expected to occur close to
the solar surface, and provide information on Coronal Mass Ejections
mechanisms at work in the very low corona.
---------------------------------------------------------
Title: Chromospheric and Prominence Physics with the ASPIICS Formation
Flying Coronagraph
Authors: Lamy, P.; Vivès, S.; Koutchmy, S.; Arnaud, J.
2007ASPC..368..639L Altcode:
Classical externally-occulted coronagraphs are presently limited in
their performances by the distance between the external occulter and
the front objective. The diffraction fringe from the occulter and
the vignetted pupil which degrades the spatial resolution prevent
observing the inner corona inside typically 2--2.5 solar radii
(R<SUB>⊙</SUB>). Formation flying opens new perspectives and allow to
conceive giant, externally-occulted coronagraphs using a two-component
space system with the external occulter on one spacecraft and the
optical instrument on the other spacecraft. ASPIICS (Association
de Satellites Pour l'Imagerie et l'Interférométrie de la Couronne
Solaire) is a mission proposed to ESA in the framework of the PROBA-3
program of formation flying which is presently under study, to exploit
this technique for coronal observations. ASPIICS is composed of a
single coronagraph which performs high spatial resolution imaging of
the corona as well as 2-dimensional spectroscopy of several emission
lines (in particular the forbidden line of Fe XIV at 530.285 nm) from
the coronal base out to 3 R<SUB>⊙</SUB>. The classical design of an
externally occulted coronagraph is adapted to the detection of the very
inner corona, and the addition of a Fabry-Pérot interferometer. By
tuning the position of the occulter spacecraft, it will be possible to
reach the chromosphere and the upper part of the spicules. Filtergrams
on the helium D3 line or even better, the hydrogen Hβ line (which is
optically thin contrary to Hα) will give access to the “cold corona”,
and could allow measuring the chromospheric prolateness.
---------------------------------------------------------
Title: First observations of the second solar spectrum with spatial
resolution at the Lunette Jean Rösch
Authors: Malherbe, J. -M.; Moity, J.; Arnaud, J.; Roudier, Th.
2007A&A...462..753M Altcode:
Context: A new polarimeter has been installed at the focus of the 50
cm refractor of the Lunette Jean Rösch (LJR), previously known as
Turret Dome, Pic du Midi, France, for spectroscopic observations of
weak solar magnetic fields. Fields can be derived through the Hanle
effect from the depolarization of the second solar spectrum (i.e. the
linearly polarized spectrum at the limb). <BR />Aims: We present the
first observations with spatial resolution based on the new device
performed with the large 8 m Echelle spectrograph, or recorded in
imagery mode through narrow band filters. The observations started
in April 2004, especially in the blue part of the spectrum where our
instrumentation has a particularly good efficiency. The capabilities
and the characteristics of the new instrument are briefly described. We
observed several lines of the second solar spectrum with the slit
of the spectrograph orthogonal to the limb to study the polarization
as a function of limb distance (which is related to altitude in the
atmosphere), and several spectral windows in imagery to determine
the average continuum polarization. <BR />Methods: The polarimeter
uses Nematic Liquid Crystal (NLC) technology at the primary focus
of the refractor, in spectroscopic or imagery mode. <BR />Results:
A continuous polarization profile through the limb is presented for
the photospheric SrI 460.7 nm line, the low chromospheric BaII 455.4 nm
line, and the CaI 422.7 nm line within a distance of 120´´, together
with measurements of the mean continuum polarization obtained in
imagery mode. Preliminary results of the polarization of the SrI 460.7
nm line are also shown at 40´´ from the limb, as a function of the
brightness of structures visible in the continuum (granulation). They
reveal a tendency for the polarization to be weaker in dark features
(intergranules) than in bright ones (granules), suggesting a stronger
magnetic field in intergranular lanes. As example the enigmatic and
weak polarization signal in the core of the NaD1 589.6 nm line is
presented. <BR />Conclusions: .Some aspects of the spatial variation
of the polarization with respect to the granulation pattern require
further investigation at higher spatial resolution. <P />Appendices
A-C are only available in elctronic form at http://www.aanda.org
---------------------------------------------------------
Title: Spectro-polarimetry of a sunspot simultaneously in atomic
and molecular lines.
Authors: Arnaud, J.; Berdyugina, S. V.; Fluri, D. M.; Afram, N.
2007MmSAI..78...89A Altcode:
We performed with THEMIS spectro-polarimetric observations
simultaneously in various atomic and molecular lines. We present the
observations and discuss an important aspect of spectro-polarimetric
data reduction: the recentering of the frames in the spectral
direction needed before substracting spectra to extract polarized
Stokes parameters. We conclude that THEMIS has the unique capability,
among present time large solar telescope, of providing polarization
data almost free from instrumental effects.
---------------------------------------------------------
Title: Dome C: An exceptional site for solar observations .
Authors: Arnaud, J.; Faurobert, M.; Fossat, E.
2007MmSAI..78..105A Altcode:
Dome C, on the Antarctica plateau, may be the best site on Earth
for astronomy, thanks to outstanding image quality and very pure and
cold atmosphere. This is of particular interest for solar physics,
namely for very high-resolution studies of the solar surface and
for magnetometry of the innermost solar corona. Here we review Dome
C unique atmospheric properties and present two projects aimed at
quantitatively qualify this site for solar observations.
---------------------------------------------------------
Title: Solar Coronagraphy at Dome C: Site Testing and Prospects
Authors: Arnaud, J.; Faurobert, M.; Grec, G.; Renaud, C.
2007EAS....25...81A Altcode:
Progress in our understanding of solar magnetism and activity rest to a
large part on our ability to improve spatial resolution for resolving
the solar surface magnetic fields fine structure. The solar corona
is permeated by magnetic fields emerging from the sun and, in turn,
ejects particules and magnetic field into the heliosphere. It is of
prime importance to measure the coronal magnetic field to understand
mechanisms at work in the corona. We explain why Dome C is expected to
be an outstanding site for such observations and describe the Solar
Brightness Monitor we prepare to probe sky background and aerosols
levels at this site. We also discuss coronal observations DomeC could
allow to obtain.
---------------------------------------------------------
Title: Spectro polarimetry with liquid crystals .
Authors: Malherbe, J. -M.; Roudier, Th.; Moity, J.; Mein, P.; Arnaud,
J.; Muller, R.
2007MmSAI..78..203M Altcode:
We report spectro polarimetric observations made with the spectrograph
of the Lunette Jean Rösch at Pic du Midi, France. We have tested
Ferroelectric (FLC) and Nematic (NLC) Liquid Crystals. The instrument
setup is briefly decribed, together with first observations of
magnetic fields obtained with the Multichannel Subtractive Double Pass
(MSDP). Polarization analysis of various spectral lines performed with
the single pass (SP) spectrograph in active regions or at the limb is
also presented.
---------------------------------------------------------
Title: Spectro-Polarimetry of a Sunspot in Atomic and Molecular
Lines with THEMIS
Authors: Arnaud, J.; Berdyugina, S. V.; Fluri, D. M.; Afram, N.;
Solanki, S. K.; Raouafi, N. -E.
2006ASPC..358..319A Altcode:
We present spectro-polarimetric observations of a sunspot, which were
recorded simultaneously with THEMIS in various atomic and molecular
lines. These observations include the first full Stokes measurements
of the band-head of TiO around 7055 Å.
---------------------------------------------------------
Title: Molecular Diagnostics of the Internal Structure of Starspots
and Sunspots
Authors: Afram, N.; Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.;
Lagg, A.; Petit, P.; Arnaud, J.
2006ASPC..358..375A Altcode:
We have analyzed the usefulness of molecules as a diagnostic tool for
studying solar and stellar magnetism with the molecular Zeeman and
Paschen-Back effects. In the first part we concentrate on molecules
that are observed in sunspots such as MgH and TiO. We present calculated
molecular line profiles obtained by assuming magnetic fields of 2-3 kG
and compare these synthetic Stokes profiles with spectro-polarimetric
observations in sunspots. The good agreement between the theory and
observations allows us to turn our attention in the second part to
starspots to gain insight into their internal structure. We investigate
the temperature range in which the selected molecules can serve as
indicators for magnetic fields on highly active cool stars and compare
synthetic Stokes profiles with our recent observations.
---------------------------------------------------------
Title: Solar Spectro-Polarimetry at Pic-du-Midi/LJR
Authors: Arnaud, J.; Roudier, T.; Malherbe, M.; Moity, J.
2006ASPC..358..167A Altcode:
A modern polarization analysis package was installed in 2004 at the
50 cm Pic-du-Midi solar telescope (Lunette Jean Rösch-LJR) by one
of us (JMM) to complement LJR instrumentation which already included
a spectrograph built by Z. Mouradian (LESIA), an MSDP device built by
P. Mein (LESIA), and one La Vision CCD camera bought by R. Muller (LATT)
and installed by one of us (JMM). We describe hereafter characteristics
of the telescope and of its instrumentation and present some of the
first Zeeman and Hanle effects measurements obtained using LJR new
polarimeter.
---------------------------------------------------------
Title: Detection of the Molecular Zeeman Effect in Circular
Polarization on Cool Active Stars
Authors: Berdyugina, S. V.; Petit, P.; Fluri, D. M.; Afram, N.;
Arnaud, J.
2006ASPC..358..381B Altcode: 2007astro.ph..3560B
We report on the first ever detection of circular polarization
in molecular lines forming in magnetic regions on the surfaces
of active stars. The new observations were obtained with the
high-resolution spectro-polarimeter ESPaDOnS recently installed at the
Canada-France-Hawaii Telescope. In July 2005 we carried out a survey
of 17 G-K-M stars including active main-sequence dwarfs and RS CVn-type
giants and subgiants. All stars were found to possess surface magnetic
fields producing average atomic Stokes-V signals of 0.05% to 0.5%. Three
stars clearly showed circular polarization in molecular lines of 0.5%
to 1%. The molecular Stokes-V signal is reminiscent of that observed
in sunspots.
---------------------------------------------------------
Title: ASPIICS, a giant externally occulted coronagraph for the
PROBA-3 formation flyer mission
Authors: Vivès, S.; Lamy, P.; Koutchmy, S.; Arnaud, J.
2006cosp...36.3063V Altcode: 2006cosp.meet.3063V
Formation flyers open new perspectives and allow to conceive giant
externally-occulted coronagraphs using a two-component space system with
the external occulter on one spacecraft and the optical instrument on
the other spacecraft at approximately 100 m from the first one ASPIICS
Association de Satellites Pour l Imagerie et l Interferometrie de la
Couronne Solaire is a mission proposed to ESA in the framework of the
PROBA-3 program of formation flyers which is presently in phase A to
exploit this technique for coronal observations ASPIICS is composed of
a single coronagraph which performs high spatial resolution imaging of
the corona as well as 2-dimensional spectroscopy of several emission
lines from the coronal base out to 3 Rs The selected lines allow to
address different coronal regions the forbidden line of FeXIV at 530
285 nm coronal matter Fe IX X at 637 4 nm coronal holes HeI at 587
6 cold matter An additional broad spectral channel will image the
white light corona and derive electron densities The classical design
of an externally occulted coronagraph is adapted to the detection
of the very inner corona as close as 1 01 Rs and the addition of
a Fabry-Perot interferometer using a so-called etalon ASPIICS will
address the question of the coronal heating and the role of waves by
characterizing propagating fluctuations waves and turbulence in the
solar wind acceleration region and by looking for oscillations in the
intensity and Doppler shift of spectral lines The combined imaging
and spectral diagnostics capabilities available with ASPIICS
---------------------------------------------------------
Title: Infrared Coronal Polarimetry: Magnetometry and More
Authors: Kuhn, J.; Lin, H.; Jaeggli, S.; Arnaud, J.; Mickey, D.
2006cosp...36.1643K Altcode: 2006cosp.meet.1643K
Near-infrared spectropolarimetry of the solar corona is a powerful tool
for measuring the coronal magnetic field and even the local interstellar
wind Here we describe how sensitive imaging spectropolarimetric
observations are being obtained from the worlds largest coronagraph --
a reflecting off-axis telescope -- from the summit of Haleakala Hawai i
---------------------------------------------------------
Title: Coronal Emission Lines Linear Polarization: a Tracer of
Coronal Magnetic Fields Topology
Authors: Arnaud, J.
2005ASPC..346..145A Altcode:
Coronal Emission Lines (CEL) polarization is the only direct way to
access magnetic fields in most of the low corona (up to one solar
radius above the limb). Linear polarization CEL data were obtained by
two different experiments in the seventies, opening a first window
on the magnetic field topology. Twenty five years later, recently
built new dedicated instruments, using present time photometric
near infrared mosaic detectors, are opening a new era for coronal
magnetometry. I present what we have learned from the past observations:
the organisation of CEL polarization maps reflects the existence of
a large scale organisation of the magnetic field and CEL measured
polarization values set limits on the degree of inhomogeneity of
coronal material and magnetic field.
---------------------------------------------------------
Title: Unveiling the atmosphere of Venus during the June 2004
solar transit
Authors: Tanga, P.; Arnaud, J.; Colas, F.; Comolli, L.; Rondi, S.,
A.; Sicardy, B.; Suetterlin, P.; Unione Astrofili Italiani-“Planets"
Section Team
2005DPS....37.5718T Altcode: 2005BAAS...37.1571T
Visual and CCD observations of Venus transiting in front of the Sun
on June 8, 2004, revealed traces of the light passing through the
atmosphere of the planet. As several witness of past events have
accounted for [1][2], the event happens close to the ingress and
egress phases, when the disk of the planet is crossing the Solar
limb. The portion of atmosphere that is projected against the darker
sky background appears bright, at least in part, due to refracted
light (mainly). <P />The 2004 opportunity was the first observed by
electronic equipment. Sets of several images were acquired by widely
different instruments, at different wavelengths. <P />The images were
processed in order to subtract the sky background, and normalized. The
brightness of the atmospheric arc was measured; its spatial structure
and its variation in time are discussed. A latitude dependence of
the arc brightness is clearly detected, with an intensity maximum
close to the planet polar regions. Even comparing CCD images to
visual observations, an investigation of the variability of the arc
brightness from one event to the other encounters several difficulties,
mainly due to the evolution of instruments in time. <P />[1] F. Link,
Eclipse phenomena in Astronomy, Springer Verlag (Berlin 1969) <P />[2]
H.N. Russell, ApJ 9, 284 (1899)
---------------------------------------------------------
Title: Using Imaging Infrared Coronal Spectropolarimetry to Measure
the Near-Sun Plasma
Authors: Kuhn, J.; Lin, H.; Arnaud, J.; Jaeggli, S.
2005AGUFMSH44A..08K Altcode:
A moderate aperture ground-based coronagraph and an imaging infrared
spectropolarimeter have provided our first direct longitudinal coronal
magnetograms. This talk will describe the advantages and subtleties of
these techniques for direct coronal magnetometry. We also summarize
some of the diagnostic potential of current and likely future IR
spectropolarimetric instruments (like the Advanced Technology Solar
Telescope) for measuring the properties of the near-solar plasma.
---------------------------------------------------------
Title: Formation flyers applied to solar coronal observations:
the ASPICS mission
Authors: Vives, S.; Lamy, P.; Auchere, F.; Vial, J. -C.; Koutchmy,
S.; Arnaud, J.; Prado, J. -Y.; Frassetto, F.; Naletto, G.
2005SPIE.5901..305V Altcode:
Classical externally-occulted coronagraphs are presently limited in
their performances by the distance between the external occulter and
the front objective. The diffraction fringe from the occulter and the
vignetted pupil which degrades the spatial resolution prevent observing
the inner corona inside typically 2-2.5 solar radii. Formation flyers
open new perspectives and allow to conceive giant, externally-occulted
coronagraphs using a two-component space system with the external
occulter on one spacecraft and the optical instrument on the
other spacecraft at approximately 100 m from the first one. ASPICS
(Association de Satellites Pour l'Imagerie Coronographique Solaire)
is a mission proposed to CNES in the framework of their demonstration
program of formation flyers which is presently under study to exploit
this technique for coronal observations. In the baseline concept,
ASPICS includes three coronagraphs operating in three spectral
domains: the visible continuum (K-corona brightness), the HI Lyman
alpha emission line at 121.6 nm, and the HeII emission line at 30.4
nm. Their unvignetted fields of view extend from 1.1 to 3.2 solar radii
with a typical spatial resolution of 3 arcsec. In order to connect
coronal activity to photospheric events, ASPICS further includes
two disk imagers. The first one is devoted to the HI Lyman alpha
emission line. The second one is a multi-channel instrument similar to
SOHO/EIT and devoted to the HeII (30.4 nm), FeIX/X (17.1 nm) and FeXII
(19.5 nm) emission lines. Two concepts of the space system are under
consideration: a symmetric configuration where the disk imagers and
the external occulter are on one spacecraft and the coronagraphs on
the other, an asymmetric configuration where the external occulter is
on one spacecraft and the scientific instruments are regrouped on the
other one.
---------------------------------------------------------
Title: Coronal Magnetometry
Authors: Arnaud, J.; Faurobert, M.; Grec, G.; Vial, J. -C.
2005EAS....14...95A Altcode:
Magnetic fields emerging in the solar atmosphere control the structure,
dynamics and heating of the solar corona. Those fields remain
essentially unattainable with present low corona instrumentation. We
present the most direct way of magnetic field remote measurements
in the internal corona, namely visible and infrared coronal emission
lines magnetometry and we explain why Dome C should be investigated as
a likely outstanding site for such observations. We develop a strategy
towards a large aperture coronal magnetometer at Dome C in the context
of the other main instrumental projects underway for solar physics.
---------------------------------------------------------
Title: Some Considerations about Inferring Coronal Magnetic Fields
and Other Coronal Properties from Coronal Emission Line Polarization
Authors: Arnaud, J.; Habbal, S. R.; Arndt, M.; Woo, R.
2003AGUFMSH42B0506A Altcode:
Ground based studies of Coronal Emission Lines (CEL) linear polarization
had been carried out for the 530.3 nm FeXIV line at Pic du Midi and
for the 1074.7 nm Fe XIII line at Sac Peak in the 1977-1980 period. The
large scale organization of the polarization has clearly revealed the
existence of a large scale structure of the coronal magnetic field. More
recently, the first successful eclipse CEL polarimetric measurements
were made in the 1074.7 nm line during the total solar eclipse of 21
June 2001, confirming earlier results of the predominance of a radial
direction of the coronal magnetic field. A first measurement of the
circular polarization in the 1074.7 nm line has also recently been
performed. Circular polarization gives access to the strength of the
LOS magnetic field while the linear polarization maps the transverse
magnetic field direction. We will use ground based and eclipse 1074.7
nm line polarimetric data to provide examples of the properties (e.g.,
magnetic field, abundances, inhomogeneities) such observations can
help to infer in this 3-D and optically thin medium.
---------------------------------------------------------
Title: The Coronal Magnetic Field, Signatures of Coronal Holes and
Silicon Nanometer Dust Grains
Authors: Habbal, S. R.; Arndt, M. B.; Nayfeh, M.; Arnaud, J.; Woo, R.
2003AGUFMSH41D..04H Altcode:
The near-infrared part of the solar spectrum is where some of the
strongest coronal forbidden lines are formed. Polarized emission in
these lines offers the only tool currently known for the inference
of the direction of the coronal magnetic field. The first successful
observations of the polarized emission from the 1074.7 nm Fe XIII
line were made by Eddy, Lee and Emerson during the eclipse of 1966
in a limited region of the corona. The only subsequent polarimetric
observations in this line were carried out with the coronagraph at Sac
Peak from 1977-1980. We report on the first successful polarimetric
measurements of the 1074.7 nm line in a field of view extending out
to 3.5 solar radii which were made during the total solar eclipse
of 21 June 2001. In addition to confirming earlier results of the
predominance of a radial direction of the coronal magnetic field, these
measurements yielded the first polarimetric signature of coronal holes,
and the signature of nanometer size dust grains in the corona. These
observations suggest the existence of a rich coronal spectrum of narrow
lines in the near-infared produced by the fluorescence of silicon
nanometer dust grains in the inner corona. This work was funded by
NSF grant ATM-0003661 and NASA grant NAG5-10873 to the Smithsonian
Astrophysical Observatory.
---------------------------------------------------------
Title: Center-to-limb variation of scattering polarization in
molecular solar lines: Observations and modeling
Authors: Faurobert, M.; Arnaud, J.
2003A&A...412..555F Altcode:
We present center-to-limb measurements of the scattering polarization
observed in molecular lines of C<SUB>2</SUB> and MgH in the spectral
range between 515.7 and 516.1 nm, together with a radiative transfer
model for the formation of these lines. The observations were performed
in July 2000 with THEMIS inside the south polar limb. We were able
to measure the polarization at distances between 1 arcsec and 50
arcsec from the solar limb. The lines appear as very weak absorption
features in the intensity spectrum but their linear polarization
clearly dominates in the polarization spectrum. We introduce here
a simple radiative transfer model which allows to interpret the
observed center-to-limb variations of both the intensity and linear
polarization. The basic assumption is that molecular lines are
formed higher in the photosphere than the continuous photospheric
radiation. Molecules are thus illuminated by the polarized continuum
photospheric radiation field. We account for a possible Hanle effect
due to weak unresolved magnetic fields but we neglect depolarizing
collisions. The model depends on four parameters which are determined
by fitting both the intensity and polarization in 9 molecular lines of
the observed spectral domain. Making use of the differential Hanle
effect in the different lines of C<SUB>2</SUB> we show that the
C<SUB>2</SUB> lines are affected by the Hanle effect due to a weak
unresolved magnetic field. Its mean strength is on the order of 15
Gauss in the upper photosphere and increases to values on the order of
50 Gauss at larger depths. These results are in good agreement with
those derived previously (Faurobert et al. \cite{Faurobert1}) from
the linear polarization of the SrI 460.7 nm line which was observed
simultaneously. Such a weak field has almost no effect on the MgH lines.
---------------------------------------------------------
Title: On the Detection of the Signature of Silicon Nanoparticle
Dust Grains in Coronal Holes
Authors: Habbal, Shadia Rifai; Arndt, Martina Belz; Nayfeh, Munir
H.; Arnaud, Jean; Johnson, Judd; Hegwer, Steve; Woo, Richard; Ene,
Alexandru; Habbal, Feras
2003ApJ...592L..87H Altcode:
We report on polarization measurements in the Fe XIII line at 1074.7
nm made during the total solar eclipse of 2001 June 21, which yielded
the first signature of interplanetary dust in the inner corona. In
the first-ever images at this wavelength, the signature of dust
appears as a tangentially polarized emission in the radial extension
of the low-temperature and low-density coronal holes as opposed to
a predominantly radial polarization direction in the rest of the
corona. The observed emission and polarization are attributed to
fluorescence from silicon nanoparticle dust grains in the inner corona.
---------------------------------------------------------
Title: The 2001 June 21 Eclipse Polarimetric Observations of the Fe
XIII 1074.7 nm Emission Line
Authors: Habbal, S. R.; Arndt, M. B.; Nayfeh, M. H.; Arnaud, J.;
Johnson, J.; Hegwer, S.; Ene, A.
2003SPD....34.0409H Altcode: 2003BAAS...35..812H
Polarimetric measurements of the coronal forbidden lines have been
recognized for quite some time as a diagnostic tool for inferring the
direction of the coronal magnetic field. Following the first successful
measurements by Eddy et al. (1973) during the total solar eclipse
of 1966, an observing campaign using the coronagraph at Sacramento
Peak Observatory was pursued between 1977-1980 (Arnaud and Newkirk,
1987). All these measurements yielded the surprising result that the
direction of polarization implied a predominantly radial coronal
magnetic field. We report on the polarization measurements of the
Fe XIII 1074.7nm line, the strongest of the coronal forbidden lines,
which were obtained during the total solar eclipse of 2001 June 21 from
Zambia. In addition to confirming the earlier results of a predominantly
radial field, the signature of nano-size interplanetary dust in
the inner corona, most likely in the form of silicon nanoparticles,
appeared for the first time in these measurements. The signature of
these particles also coincides with the radial expansion of coronal
holes outwards from the Sun, a signature that has never appeared in
any measurement before. <P />Support for this work was provided by
NSF grant ATM-0003661 and NASA grant NAG5-10873
---------------------------------------------------------
Title: The determination of the coronal magnetic field
Authors: Arnaud, J.
2003EAS.....9..209A Altcode:
Measurements of magnetic fields in the solar corona are needed to
improve our understanding of structures, dynamics and heating of the
corona and of the acceleration of the fast and slow modes of the solar
wind expending into the heliosphere. However, those measurements are
very difficult and still very scarce. I revue the main methods proposed
to access the direction and the strength of the coronal magnetic field
and discuss what seem the main avenues to improve its determination
in the future.
---------------------------------------------------------
Title: Molecular lines observations with THEMIS
Authors: Arnaud, J.; Faurobert, M.; Raouafi, N. -E.; Solanki, S. K.
2003sf2a.conf..111A Altcode: 2003sf2a.confE..39A
Lines of molecules like MgH, C2, TiO, ... represent powerful tools
for the study of the solar atmosphere. Their observations on the
Sun can also help to constrain the polarizability and Lande factors
calculations which are much more complex than for atomic lines. We will
present THEMIS polarimetric observations of these lines to illustrate
some aspects of their use for solar physics.
---------------------------------------------------------
Title: On the Coexistence of a Radial and Non-radial Component of
the Coronal Magnetic Field
Authors: Habbal, S. R.; Woo, R.; Arndt, M.; Arnaud, J.
2003ASPC..307..446H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetism and Activity of the Sun and Stars
Authors: Arnaud, J.; Meunier, N.
2003EAS.....9.....A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Second Solar Spectrum Observations at THEMIS
Authors: Faurobert, M.; Arnaud, J.
2003ASPC..307..431F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Scattering polarization of molecular emission lines in the
quiet solar chromosphere
Authors: Faurobert, M.; Arnaud, J.
2002A&A...382L..17F Altcode:
We present scattering polarization measurements performed with THEMIS
in July 2000 near the south polar limb. The low level of scattered
light at THEMIS, which is the only large solar telescope to include
a superpolished primary mirror, allows, in good seeing conditions,
to observe the emission spectrum of the low chromosphere above
the limb. These are, as far as we know, the first high spectral
resolution observations of the intensity and the first measurements
of the polarization of C<SUB>2</SUB> and MgH molecular lines in
emission above the limb. Molecules are present in a thin layer in
the region of the temperature minimum between the photosphere and
the chromosphere. We present a very simple model for the formation
of the polarized lines and we relate the observed polarization
rates to the so-called intrinsic line polarizability coefficients
W<SUB>2</SUB>. Those quantities may be derived from quantum mechanical
computations involving the solution of the Schrödinger equation for
the molecular potential. Solar observations provide a direct way of
checking these heavy computations and contribute to the improvement
of our knowledge in molecular physics. Nine C<SUB>2</SUB> molecular
transitions and two MgH transitions are present in our spectral window;
we find that for the C<SUB>2</SUB> transitions, the polarizability
is between 0.13 and 0.26 and that it takes higher values, namely 0.41
and 0.46, for the two MgH transitions.
---------------------------------------------------------
Title: Polarimetric Imaging of The Solar Corona During The 21 June
2001 Total Solar Eclipse
Authors: Habbal, S. R.; Arnaud, J.; Arndt, M.; Ene, A.; Esser, R.;
Faurobert, M.; Hale, J.; Hegwer, S.; Johnson, J.; Woo, R.
2002EGSGA..27.6098H Altcode:
We report on the first successful simultaneous eclipse measurements
of the inten- sity and polarization brightness of the K-Corona and the
near-infrared Fe XIII 1074.7 nm emission line. Those observations were
obtained during the total solar eclipse of 21 June 2001. The technique
used for those observations will be presented. Coronal emission lines
polarization measurements are the only tools to date that can yield
the direction of the coronal magnetic field.
---------------------------------------------------------
Title: Polarized Intensity Measurements of the Corona during the 21
June 2001 Total Solar Eclipse
Authors: Habbal, S. R.; Arnaud, J.; Johnson, J.; Hegwer, S.; Ene, A.;
Hale, J.; Esser, R.; Arndt, M.; Kohl, J. L.; Daw, A.; Faurobert, M.;
Woo, R.; Habbal, F.; Havasy, R.; Alford, J. N.
2001AGUFMSH11C0716H Altcode:
We report on the first successful simultaneous polarimetric measurements
of the brightness of the Thompson-scattered white light and intensity
of the near-infrared Fe XIII 10747 Å line, the strongest of the
coronal iron forbidden lines. These observations which extended out
to 3 R<SUB>s</SUB> in the corona were obtained during the total solar
eclipse of 21 June 2001. The novel technique used to acquire these
measurements will be presented. Polarized intensity measurements of the
resonantly scattered component of coronal emission lines are the only
tools to date that can yield the direction of the coronal magnetic
field. Through these simultaneous measurements, we show how the
direction of the coronal magnetic field can be placed in the context
of coronal density structures. We also discuss the implications of
these simultaneous measurements for the source of the solar wind.
---------------------------------------------------------
Title: Investigation of weak solar magnetic fields. New observational
results for the SrI 460.7 nm linear polarization and radiative
transfer modeling
Authors: Faurobert, M.; Arnaud, J.; Vigneau, J.; Frisch, H.
2001A&A...378..627F Altcode:
Scattering polarization measurements were obtained with THEMIS in July
2000, close to the solar south Pole and to the east Equator and in
a period of maximum solar activity. Using the THEMIS multi-lines
spectro-polarimetric mode (MTR), we observed simultaneously
four spectral domains containing the 460.7 nm Sr i line, several
molecular lines around 515.9 nm and the Na i D<SUB>1</SUB> and Na i
D<SUB>2</SUB> lines. This allows us to scan different altitudes in the
solar atmosphere at the same time and provides us with a large set
of constraints to study the behaviour of the magnetic field. This
paper is devoted to the Sr i line which exhibits quite a strong
linear polarization peak outside active regions. A detailed radiative
transfer modeling is performed in order to interpret the observed
center-to-limb variations of the line intensity and polarization. It
was shown previously (Faurobert-Scholl \cite{Faurobert-Scholl1})
that this line, which is sensitive to the Hanle effect, can be used
as a diagnostic tool for the presence of weak turbulent magnetic
fields in the solar photosphere outside active regions. The line
polarization rates that we measured in July 2000 are 25% lower
than what has been reported previously, for observations near the
minimum, or in the increasing phase, of the activity cycle (Stenflo
et al. \cite{Stenflo1}). They are in agreement with other observations
performed with a different observational set-up in August 2000 (Bommier
& Molodij \cite{Bommier4}). We show that they are consistent with
the presence of a weak turbulent magnetic field with an average strength
between 20 G and 30 G in the upper solar photosphere. This is about
twice the value which was derived from previous observations. This
result raises the possiblity of a long-term variation of the turbulent
photospheric magnetic field with the activity cycle.
---------------------------------------------------------
Title: On the Predominance of the Radial Component of the Magnetic
Field in the Solar Corona
Authors: Habbal, Shadia Rifai; Woo, Richard; Arnaud, Jean
2001ApJ...558..852H Altcode:
Polarimetric measurements of the corona out to 2 R<SUB>solar</SUB>
in the Fe XIII 10747 Å line, the strongest of the iron forbidden
lines, are placed for the first time in the context of spatially
resolved images of coronal density structures. These measurements,
which are the only tool currently available to yield the direction
of the magnetic field, date to 1980, the only year when they were
available with polarized brightness images of the corona. Through this
comparison, the observed predominance of the radial component of the
coronal magnetic field, discovered over three decades ago from eclipse
observations and established systematically by Arnaud, is shown to point
to the coexistence of two magnetic field components in the corona:
a nonradial field associated with the large-scale structures known
as streamers and a more pervasive radial magnetic field. This finding
suggests that these two components are the coronal counterparts of the
strong- and weak-field components recently observed in the quiet-Sun
photospheric field and supported by recent theoretical investigations
of the solar dynamo.
---------------------------------------------------------
Title: On the Coexistence of a Radial Magnetic Field with the Large
Scale Field in the Solar Corona
Authors: Habbal, S. R.; Woo, R.; Arnaud, J.
2001AGUSM..SH22E06H Altcode:
Polarimetric measurements of the corona out to 2 R<SUB>s</SUB> in the
Fe XIII 10747 A line, the strongest of the iron forbidden lines, are
placed for the first time in the context of spatially resolved images
of coronal density structures. These measurements, which are the only
tool currently available to yield the direction of the magnetic field,
date to 1980, the only year when they were available with polarized
brightness images of the corona. Through this comparison, the observed
predominance of the radial component of the coronal magnetic field,
discovered over three decades ago from eclipse observations, and
established systematically by Arnaud (1982), is shown to point to
the existence of two components of the coronal magnetic field: a
non-radial component associated with the large scale structures known
as streamers, and the second, more dominant one, a pervasive radial
magnetic field. The coexistence of these two components provides new
information for the distribution of open and closed magnetic flux in
the solar corona.
---------------------------------------------------------
Title: Scattering Induced Polarization and Hanle Effect Observations
with THEMIS
Authors: Arnaud, J.; Faurobert, M.; Vigneau, J.; Paletou, F.
2001ASPC..248...93A Altcode: 2001mfah.conf...93A
No abstract at ADS
---------------------------------------------------------
Title: Scattering Polarization Measurements with THÉMIS
Authors: Arnaud, J.; Vigneau, J.; Faurobert, M.; Paletou, F.
2001ASPC..236..151A Altcode: 2001aspt.conf..151A
No abstract at ADS
---------------------------------------------------------
Title: First observational campaign at the THEMIS: image quality
and seeing
Authors: Arnaud, J.; Briand, C.; Ceppatelli, G.
1998NewAR..42..499A Altcode:
The THEMIS and its instrumentation are described. The well known diurnal
seeing pattern is confirmed by the seeing measurements taken to date.
---------------------------------------------------------
Title: The Solar Telescope THEMIS
Authors: Arnaud, J.; Mein, P.; Rayrole, J.
1998ESASP.417..213A Altcode: 1998cesh.conf..213A
No abstract at ADS
---------------------------------------------------------
Title: THEMIS: Télescope Héliographique pour l'Étude du Magnétisme
et des Instabilités Solaires.
Authors: Arnaud, J.; Briand, C.; Rayrole, J.
1996JAF....53....5A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Near-Infrared Emission-Line and Continuum Observations from
the 1991 Eclipse
Authors: Penn, M. J.; Arnaud, J.; Mickey, D. L.; Labonte, B. J.
1994ApJ...436..368P Altcode:
We report observations made during the 1991 July 11 total solar eclipse
from the University of Hawaii 61 cm south telescope on the summit of
Mauna Kea, Hawaii. The eclipse observations entail CCD imaging of a
coronal region on the southeast limb of the Sun using four wavelength
channels isolated with narrowband interference filters. We obtain two
long exposure images in each channel including the continuum (lambda
= 10690 A), the two near-infrared (Fe XIII) emission lines (lambda =
10747, 10798 A), and the He I line (lambda = 10830 A). We calibrate the
images to the center-of-disk solar intensity. The (Fe XIII) images are
the first coronal images published from these emission lines. We find
significant structural differences between the line and continuum images
implying large temperature gradients in our small field of view. We
compute the line ratio of the two (Fe XIII) emission lines (R) and find
that the ratio is within the limits 1.2 greater than or = R greater
than or = 15.0. We examine the motion seen in the prominence structure
and find transverse velocities of up to about 30 km/s. Finally we see
no cold coronal emission to a limit of 2 x 10<SUP>-7</SUP> solar BETA.
---------------------------------------------------------
Title: Coronal electron density measurements using the near-ir
[Fe XIII] emission lines
Authors: Penn, M. J.; Kuhn, J. R.; Arnaud, J.; Mickey, D. L.; Labonte,
B. J.
1994SSRv...70..185P Altcode:
Observations made during the 1991 total solar eclipse and recent
observations from NSO/Sac Peak are discussed. The ground-based density
measurements will be complimentary to SOHO observations, particularly
SOHO electron density measurements.
---------------------------------------------------------
Title: Coronal Electron Density Measurements from the Total Solar
Eclipse of 11 July 1991
Authors: Penn, M. J.; Arnaud, J.; Mickey, D. L.; Labonte, B. J.
1993BAAS...25.1210P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: ESO key programme, gravitational lensing: quasars and radio
galaxies; a status report
Authors: Surdej, J.; Angonin, M. C.; Arnaud, J.; Bauer, T.; Borgeest,
U.; Hainaut, O.; Hammer, F.; Hutsemekers, D.; Le Fevre, O.; Nottale,
L.; Magain, P.; Meylan, G.; Remy, M.; Shaver, P.; Smette, A.; Swings,
J. P.; van Drom, E.; Veron-Cetty, M.; Veron, P.
1992daec.conf...97S Altcode:
The scientific background and objectives of our ESO Key Programme are
first recalled. A brief account of our research activities (observing
runs at ESO and elsewhere, meetings, etc.) is then given. Preliminary
scientific results are presented concerning 1) our observational
database for highly luminous quasars and distant powerful radiogalaxies;
2) speckle observations of highly luminous quasars; 3) the photometric
monitoring and 4) detailed studies of several known gravitational
lenses; 5) optical observations of 3C and 4C radio galaxies and 6)
of the well known Einstein ring MG 1131+0456.
---------------------------------------------------------
Title: General properties of the polarization of the Fe XIV 5303 Å
coronal emission line.
Authors: Arnaud, Jean
1992ESASP.348..285A Altcode: 1992cscl.work..285A
The intensity and linear polarization of coronal emission lines
contain information on coronal electron density and magnetic field
direction. The author summarizes several average properties of the
Fe XIV 5303 Å line from measurements performed using the Pic du Midi
monochromatic coronameter. The mean direction of the polarization is
found to be radial while the average polarization rate is consistant
with models taking into account the depolarization produced by density
inhomogeneities and actual fluctuations in magnetic field direction. The
observed large scale organisation of the polarization clearly reveals
the existence of the large scale structure of the coronal magnetic
field.
---------------------------------------------------------
Title: Foreground Galaxies Superposed on Quasars UM 675 and 0453-423:
The Nature of Absorbers at z <SUP>~</SUP> 0.75
Authors: Thompson, D.; Smith, J.; Djorgovski, S.; Arnaud, J.; Weir, N.
1991BAAS...23Q1340T Altcode: 1991BAAS...23.1340T
No abstract at ADS
---------------------------------------------------------
Title: Initial Light Curve of Q2237+0305
Authors: Corrigan, R. T.; Irwin, M. J.; Arnaud, J.; Fahlman, G. G.;
Fletcher, J. M.; Hewett, P. C.; Hewitt, J. N.; Le Fevre, O.; McClure,
R.; Pritchet, C. J.; Schneider, D. P.; Turner, E. L.; Webster, R. L.;
Yee, H. K. C.
1991AJ....102...34C Altcode:
We present CCD photometry for the gravitationally lensed quasar
system 2237+0305, in optical passbands from B through R, taken over
a time period of more than 3 yr. These data provide new information
about the probable microlensing event reported in Irwin et al. [AJ,
98, 1989 (1989)]; the rise time of this feature is approximately 26
days. Four additional independent brightness changes in the quasar
images are detected.
---------------------------------------------------------
Title: A Measurement of Isoplanetism With the High-Resolution Camera
at T Canada-France-Hawaii Telescope
Authors: McClure, Robert D.; Arnaud, Jean; Fletcher, J. Murray; Nieto,
Jean-Luc; Racine, Rene
1991PASP..103..570M Altcode:
A long-exposure CCD frame has been obtained with image quality of
0.26"-0.34" (FWHM) using the DAO/CFHT image-stabilizing camera at
the prime focus of the Canada-France-Hawaii Telescope. The entrance
aperture was stopped down to 1.2m and, at this aperture size, the
effect of imperfect isoplanatism is seen by comparing images of stars
of varying distances from the guide star. The deterioration of the
image quality is seen to occur faster along the direction toward the
guide star, thus elongating the images, as expected from theoretical
considerations. A centrally peaked "Bismark" profile is found to best
fit the shape of the stabilized point-spread function. It is pointed
out that new image-analysis tools will be required to fully exploit
astronomical data obtained with adaptive optics systems.
---------------------------------------------------------
Title: The shape of central regions in elliptical galaxies.
Authors: Nieto, J. -L.; Bender, R.; Arnaud, J.; Surma, P.
1991A&A...244L..25N Altcode:
Isophote analysis of high-resolution CCD images of a large sample of 75
early-type, mostly elliptical, galaxies shows that at least 1/3 (= 25)
of these objects harbors central bodies that appear separate from the
rest of the galaxy, and whose sizes range between 2 and 10 arcsec; 15
of these 25 central substructures show clearly `pointed' isophotes, and
all objects known to have decoupled core kinematics show a photometric
substructure coinciding in radius with the kinematic substructure. About
60% of `resolved' (r_c,app_/σ*=f>5), ~40% of intermediate (5 >
f > 3) and ~20% of `unresolved' (f < 3) galaxies contain such
separate substructures. The percentage of such phenomena is higher
in galaxies with boxy and irregular isophotal shapes (~55%) than in
those having disky isophotes (~28%). These numbers suggest that a
large fraction of elliptical galaxies, if not all, should be found
to contain separate entities in their central regions if investigated
with sufficient spatial resolution. The separate entities may be formed
in merger events, as it is likely for galaxies with counter-rotating
or otherwise kinematically decoupled cores; however, from the large
variety of early-type galaxies showing this type of phenomenon,
internal mass transfer cannot be excluded. Several arguments suggest
that these central substructures are predominantly disks.
---------------------------------------------------------
Title: The optical counterpart of the X-ray binary in the globular
cluster NGC 6712.
Authors: Nieto, J. -L.; Auriere, M.; Sebag, J.; Arnaud, J.; Lelievre,
G.; Blazit, A.; Foy, R.; Bonaldo, S.; Thouvenot, E.
1990A&A...239..155N Altcode:
Results are presented on R and B high-resolution imaging of the field
of the X-ray source in the globular cluster NGC 6712, carried out with
the Sub-Pupil Imager and the Photon-Counting Detector CP40. The images
reveal the presence of two new stars of 21st magnitude in the B band,
namely S and Z, which are 0.3 arcsec apart and are located within less
than 0.25 arcsec of the U bright object in the field. The B images
also show that the Z star is highly variable, by more than 1 mag. It
is suggested that star Z is a strong candidate for being the optical
counterpart of the X-ray/radio source and, thus, should be also the
U object.
---------------------------------------------------------
Title: The core of the elliptical galaxy NGC 7052.
Authors: Nieto, J. L.; McClure, R.; Fletcher, J. M.; Arnaud, J.;
Bacon, R.; Bender, R.; Comte, G.; Poulain, P.
1990A&A...235L..17N Altcode:
CFHT observation with the High-Resolution Camera (HR Cam) of the
central region of the boxy radio galaxy NGC 7052 in the R band reach
the resolution of FWHM = 0.33" (or σ* = 0.14"). This allows us to
trace the structure of the dust previously detected in the central
region of this galaxy. The dust is confined in an extremely sharp lane
seen almost edge-on, ~0.3" away from the central and located along the
projected major axis of the galaxy. The transverse size of the lane
has a FWHM of 0.40", and thus is not resolved by the observations. The
angle with the radio axis is found to be 50 deg. Tracing very accurately
the dust absorption profile allows us to estimate the (small) amount
of absorption at the center, and to derive core properties reliably
corrected for dust absorption. We thus find an apparent core radius,
r_c,app_ = 1.10", and a central surface brightness, μ_app_ = 15.48. The
high r_c,app_/σ* ratio of ~7 implies only modest seeing corrections
of about 10% for these quantities. The mass of the dust is found to
be 10^4^ M_sun_.
---------------------------------------------------------
Title: High-resolution imaging using pupil segmentation.
Authors: Sebag, J.; Arnaud, J.; Lelièvre, G.; Nieto, J. L.; Le
Coarer, E.
1990JOSAA...7.1237S Altcode: 1990JOSA....7.1237S; 1990OSAJ....7.1237S
Recentering and selecting short-exposure images result significant
improvements in spatial resolution compared with that for classical
long-exposure images. A maximum gain in resolution of the order of
3 is possible. A pupil-segmentation experiment has been performed
at the Cassegrain focus of the Canada-France-Hawaii telescope. A
photon-counting camera records short-exposure images. The software
processing is made after acquisition of the data. Recentering is made
by cross correlation of the short-exposure images with a long-exposure
image of a star or a contrasted object. The authors present results
obtained on the gravitational lens Q2237+030.
---------------------------------------------------------
Title: Deep Photometry of Cl.2244-02 in U Colour with an
Electronographic Camera
Authors: Wlérick, G.; Vanderriest, C.; Hammer, F.; Lelièvre, G.;
Horville, D.; Renard, L.; Arnaud, J.; Gouiffes, C.
1990LNP...360..295W Altcode: 1990grle.work..295W
U-color observations of the cluster of galaxies 2244 - 02 are
described with respect to the confirmation and identification of
three faint and/or hidden images predicted by gravitational lens
models. The observations are consistent with current models which
describe the two detectable faint additional images from a distant
spiral galaxy. Deeper U-images and resolution in the radial direction
are suggested as methods for improving the model and therefore the
reconstruction of the shape of the source galaxy.
---------------------------------------------------------
Title: U 1850-08
Authors: Nieto, J. -L.; Auriere, M.; Thouvenot, E.; Sebag, J.;
Lelievre, G.; Foy, R.; Arnaud, J.; Blazit, A.
1990IAUC.4944....1N Altcode: 1990IAUC.4944....0N
J.-L. Nieto, M. Auriere and E. Thouvenot, Observatoire Midi-Pyrenees;
J. Sebag, G. Lelievre and R. Foy, Observatoire de Paris; J. Arnaud,
Canada-France-Hawaii Telescope (CFHT); and A. Blazit, Observatoire de
la Cote d'Azur, report: "On 1988 Sept. 13 we obtained one R and two B
high-resolution (FWHM about 0".4-0".6) images of the field of the x-ray
source 4U 1850-08 in the globular cluster NGC 6712 with the Sub-Pupil
Imaging technique at CFHT. The analysis reveals two new stars (S and
Z; B about 21), 0".3 apart and located 0".6-0".7 arcsec southwest
of X (B about 20), the star proposed by Cudworth (1988, A.J. 96,
105) as the optical counterpart of the x-ray source. S and Z are
therefore between X and KC 62 and as close as star X to the position
of the faint radio source of Machin et al. (IAUC 4818). Clearly, the
U object pointed out by Bailyn et al. (1988, Ap.J. 331, 303), whose
centroid is 0".5 southwest of star X (Bailyn 1990, CfA Preprint 3002,
in agreement with our independent CCD U images), is a blend of stars X,
S and Z on these low-resolution (FWHM about 1".3) images. Star Z is
detected on only one B image, implying strong variability (by about 1
mag). It is therefore a good candidate for the optical counterpart of
the x-ray/radio source, if this star and its variability are confirmed
(we fail to find any technical reason suggesting a spurious effect). If
not, the possible blueness of star S (in B-R) and the blending revealed
by the U images would make S the most likely candidate.
---------------------------------------------------------
Title: Profiles of a Key Programme: Gravitational Lensing
Authors: Surdej, J.; Arnaud, J.; Borgeest, U.; Djorgovski, S.;
Fleischmann, F.; Hammer, F.; Hutsemekers, D.; Kayser, R.; Le Fevre,
O.; Nottale, L.; Magain, P.; Meylan, G.; Refsdal, S.; Remy, M.;
Shaver, P.; Smette, A.; Swings, J. P.; Vanderriest, C.; van Drom,
E.; Véron-Cetty, M.; Véron, P.; Weigelt, G.
1989Msngr..55....8S Altcode: 1989Mgr....55....8S
Prior to Professor van der Laan's enquiry, in the March 1988 issue
of the Messenger, on the general interest among astronomers from the
European community to possibly participate in Key Programmes (KPs)
at the European 80uthern Observatory, at least three distinct groups
(including more than half of the above authors) were already involved
in the study of "gravitational lensing" effects (see box on pages
10-11). Observations were being performed with the help of various
telescopes on La 8illa as weil as at other observatories (VLA, CFHT,
Palomar, Kitt Peak, etc.).
---------------------------------------------------------
Title: Interacting Pairs of Elliptical Galaxies
Authors: Davoust, E.; Prugniel, P.; Arnaud, J.
1989woga.conf..348D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Detection of a galaxy near the line of sight toward the
QSO 1209+107.
Authors: Arnaud, J.; Hammer, F.; Jones, J.; Le Fevre, O.
1988A&A...206L...5A Altcode:
Deep imaging of the field of the QSO 1209+107 (z=2.19) are presented
here. We report the detection of an extended source very close to the
QSO line of sight, which seems to be associated with the absorption
line system detected at z_a_=0.63 in the QSO spectrum. This new object,
added to the galaxy at z=0.392 discovered by Cristiani (1987) seven
arcseconds away from the QSO, imply a significant amount of matter along
the line of sight. We show that gravitational lensing may therefore
significantly affect the QSO intrinsic properties.
---------------------------------------------------------
Title: Galaxy near QSO 1209+107
Authors: Arnaud, J.; Hammer, F.; Jones, J.; Le Fevre, O.
1988IAUC.4546....3A Altcode: 1988IAUC.4546....1A; 1988IAUC.4546....0A
J. Arnaud, Canada-France-Hawaii Telescope (CFHT); F. Hammer,
Paris-Meudon Observatory; and J. Jones and O. le Fevre, CFHT,
communicate: "From two R-band CCD frames obtained 1987 June 17 at
the prime focus of the 3.6-m CFHT under very good seeing conditions,
we have discovered a faint galaxy (R = 22.0), only 1".3 from the
line-of-sight of QSO 1209+107 (R = 17.6, z = 2.19). The fainter galaxy
is very likely responsible for the Mg II and Fe II absorption systems
observed at z = 0.64 in the spectrum of the QSO (cf. Young et al. 1982,
Ap.J. Suppl. 48, 455)."
---------------------------------------------------------
Title: High-Resolution Imaging with Segmented Pupils
Authors: Lelievre, G.; Nieto, J. L.; Salmon, D.; Boulesteix, J.;
Arnaud, J.
1988igbo.conf..378L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal emission-line polarization.
Authors: Smartt, Raymond N.; Arnaud, Jean
1988sscd.conf..451S Altcode:
Polarization measurements from two large data sets are discussed. The
first set consists of measurements obtained in the 5303 Å line of
Fe XIV with the Pic du Midi Coronameter, at heights ranging from 1.1
R<SUB>sun</SUB> to 2.0 R<SUB>sun</SUB> from disk center. The second
set consists of similar observations in the 10747 Å line obtained with
the HAO/SPO Coronal Emission-Line Polarimeter, from 1.1 R<SUB>sun</SUB>
to 1.8 R<SUB>sun</SUB>. Both of the polarization vectors are close to
radial with a mean magnitude of 0.016 and 0.12, respectively. Comparison
of these data with NSO/SP coronal images in the 5303 Å line confirms
that the vectors trace out the coronal loop systems in cases where such
systems are well-defined. For both sets of observations, the magnitude
of the measured polarization is much less than that predicted from
simple scattering theory. The discrepancy is discussed in terms of
the various mechanisms and special geometries that can account for it.
---------------------------------------------------------
Title: Polarimetry of Comet p/ Halley - Continuum Versus Molecular
Bands
Authors: Le Borgne, J. F.; Leroy, J. L.; Arnaud, J.
1987A&A...187..526L Altcode:
Measurements of the linear polarization of molecular bands in comets
P/Halley and Hartley-Good are presented. The measured bands are the
C2 Swan (5140 Å), the CN (3880 Å), the C3 (4060 Å) and the OH (3090
Å). The phase angle dependence of the polarization of C2, C3 and CN is
in good agreement with theory. However the polarization of OH is found
5 times smaller than expected. The direction of polarization of C2,
C3 and OH is usually perpendicular to the scattering plane, though
some measurements are parallel to it. For CN half the measures show
significant deviations from the perpendicular to the scattering plane.
---------------------------------------------------------
Title: Mean properties of the polarization of the Fe XIII 10747 A
coronal emission line
Authors: Arnaud, J.; Newkirk, G., Jr.
1987A&A...178..263A Altcode:
Several average properties of the Fe XIII 10,747 A line observed with
a coronal emission-line polarimeter are summarized and compared with
other observations and with theory. The mean polarization direction
is found to be radial, while the average polarization rate is below
that predicted by standard theoretical models by a factor of about
three. This lower value is consistent with models which take into
account the depolarization produced by density inhomogeneities and
actual fluctuation in magnetic-field direction. The observed large-scale
organization of the polarization clearly reveals the existence of the
large-scale structure of the coronal magnetic field.
---------------------------------------------------------
Title: Polarimetry of visible and near-UV molecular bands - Comets
P/Halley and Hartley-Good
Authors: Le Borgne, J. F.; Leroy, J. L.; Arnaud, J.
1987A&A...173..180L Altcode:
Preliminary results are given on new measurements of the polarization
of the violet band of CN (3880 angstroms), the Swan band of C2 (5140
angstroms), and the OH band around 3090 angstroms in comets. The
measurements essentially refer to P/Halley with some additional data
from comet Hartley-Good. The measurements are compared with the
theoretical dependence with phase angle alpha of the fluorescence
polarization of the molecular bands. C2 data are in good agreement
with this dependent while CN data show some significant deviations. C2
data usually show a polarization perpendicular to the scattering
plane. Deviations up to 20 deg are found for the CN band. There is a
possible correlation between the deviations of polarization degree and
angle for CN but no explanation was found for the observed deviations
from the classical fluorescence mechanism for the CN and OH bands.
---------------------------------------------------------
Title: Polarimetry of molecular bands in Comets P/Halley and
Hartley-Good
Authors: Le Borgne, J. F.; Leroy, J. L.; Arnaud, J.
1986ESASP.250a.571L Altcode: 1986ehc1.conf..571L
Measurements of the linear polarization of molecular bands in comets
P/Halley and Hartley-Good are presented. The measured bands are
the C<SUB>2</SUB> Swan band at 5140 Å, the CN 3880 Å band, the
C<SUB>3</SUB> 4060 Å band and the OH 3090 Å band. The phase angle
dependance of the polarization of C<SUB>2</SUB>, C<SUB>3</SUB> and CN
is in good agreement with theory. However the polarization of OH is
found 5 time smaller than foreseen. The direction of polarization of
C<SUB>2</SUB>, C<SUB>3</SUB> and OH is usually perpendicular to the
scattering plane, though some measurements are parallel to it. For CN
half the measures shows significant deviations from the perpendicular
to the scattering plane.
---------------------------------------------------------
Title: Evidence for intrinsic polarization in the optical radiation
of planetary nebulae.
Authors: Leroy, J. L.; Le Borgne, J. F.; Arnaud, J.
1986A&A...160..171L Altcode:
Linear polarization measurements have been obtained in several regions
of the five planetary nebulae NGC 2392, NGC 3242, NGC 6720, NGC 7009,
and NGC 6572. While the data obtained are in agreement with those of
Hamilton and Liller (1973), the present measurements in various parts
of the nebulae images reveal a nonuniform polarization pattern with
curious features. Intrinsic polarization maps support the suspected
trend of a tangential polarization pattern. Simple computations based
on spherical nebulae models indicate that electron scattering must be
ruled out as a cause because it only accounts for a small part of the
observed polarization; it is suggested that the observed phenomena
result from scattering by dust.
---------------------------------------------------------
Title: Effect of dust on the linear polarization of planetary nebulae.
Authors: Le Borgne, J. F.; Leroy, J. L.; Arnaud, J.
1986CRJS....8...53L Altcode: 1986nepl.conf...53L
The authors have measured the linear polarization in several regions
of 5 PN through various filters ([O III] 5007 Å, continuum around 5500
Å). While the measured [O III] polarization of PN centers is probably
due to interstellar matter, the measurements in various parts of PN
reveal non-uniform polarization patterns, usually tangential. Electron
scattering would only contribute for a small part of the observed
polarization. Assuming the usually accepted dust content of PN,
one still finds insufficient scattering effects, unless one assumes
large-sized (≡0.1 μm), high refractive index particles.
---------------------------------------------------------
Title: Fe XIII 10747 Å and Fe XIV 5303 Å coronal emission lines
polarization.
Authors: Arnaud, J.
1984ESASP.220..115A Altcode: 1984ESPM....4..115A
The polarization direction is found to be mainly radial. The average
polarization rate is below standard theoretical models by a factor about
3. The existence of a large scale pattern of the polarization provides
evidence for the existence of a large scale structure in the coronal
magnetic field. The emission line polarization brightness provides a
new method to study the heterogeneity of the plasma and abundance of
Fe in the corona.
---------------------------------------------------------
Title: Les moissons de l'espace
Authors: Arnaud, J. -F.
1984C&T...100..112A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The analysis of Fe XIV 5303 coronal emission-line polarization
measurements
Authors: Arnaud, J.
1982A&A...116..248A Altcode:
Polarization measurements obtained in September 1978 in the green
coronal line with the Pic-du-Midi coronameter are discussed. As the
K-corona polarization was simultaneously measured values of mean
and local electron density are inferred as minimum values of ion
abundance. Those abundances are insensitive to the unknown density
irregularities along the line of sight. The minimum value of iron
abundance deduced is 7 x 10 to the -5th: it appears to be larger
than recent photospheric abundances. The interest of simultaneous
measurements in the 10747 A line of Fe XIII is emphasized. The problem
of infering the magnetic field direction is discussed.
---------------------------------------------------------
Title: Observed polarization of the Fe XIV 5303 coronal emission line
Authors: Arnaud, J.
1982A&A...112..350A Altcode:
The polarization of the Fe XIV 5303 A line has been observed between
1.1 and 2.0 solar radii from disk center at Pic-du-Midi during
1977-1980. The polarization direction is found to be mainly radial. The
average polarization degree is 1.6%. This low polarization may be due
to a significant contribution of collisional excitation to the radiation
in the denser coronal structures, as well as to magnetic depolarization
when the magnetic field is not in the radial direction. The average
values of polarization and intensity agree well with a strongly (but
realistically) inhomogeneous density model of the corona.
---------------------------------------------------------
Title: Les moissons de l'espace : recherche spatiale et vie
quotidienne
Authors: Arnaud, Jean Francois
1982mers.book.....A Altcode: 1982QB500.A698.....
No abstract at ADS
---------------------------------------------------------
Title: Polarization of the Fe XIV 5303 line measured in the corona
between 1.1 R sun and 1.4 R sun.
Authors: Arnaud, J.
1977ROLun..12..137A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Beam and fiber optics
Authors: Arnaud, J. A.
1976bfo..book.....A Altcode:
No abstract at ADS
