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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.
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.
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.
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.
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. Bibcode: 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⊙. 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⊙ 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. Bibcode: 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.
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.
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.
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.
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 Bibcode: 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. Bibcode: 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 Bibcode: 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 - 4r2), 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. Bibcode: 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.

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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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⊙). 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⊙. 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. Bibcode: 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).
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.
Methods: The polarimeter uses Nematic Liquid Crystal (NLC) technology at the primary focus of the refractor, in spectroscopic or imagery mode.
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.
Conclusions: .Some aspects of the spatial variation of the polarization with respect to the granulation pattern require further investigation at higher spatial resolution.

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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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).

The 2004 opportunity was the first observed by electronic equipment. Sets of several images were acquired by widely different instruments, at different wavelengths.

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.

[1] F. Link, Eclipse phenomena in Astronomy, Springer Verlag (Berlin 1969)

[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. Bibcode: 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. Bibcode: 2005SPIE.5901..305V Altcode: Classical externally-occulted coronagraphs are presently limited in their performances by the distance between the external occulter and the front objective. The diffraction fringe from the occulter and the vignetted pupil which degrades the spatial resolution prevent observing the inner corona inside typically 2-2.5 solar radii. Formation flyers open new perspectives and allow to conceive giant, externally-occulted coronagraphs using a two-component space system with the external occulter on one spacecraft and the optical instrument on the other spacecraft at approximately 100 m from the first one. ASPICS (Association de Satellites Pour l'Imagerie Coronographique Solaire) is a mission proposed to CNES in the framework of their demonstration program of formation flyers which is presently under study to exploit this technique for coronal observations. In the baseline concept, ASPICS includes three coronagraphs operating in three spectral domains: the visible continuum (K-corona brightness), the HI Lyman alpha emission line at 121.6 nm, and the HeII emission line at 30.4 nm. Their unvignetted fields of view extend from 1.1 to 3.2 solar radii with a typical spatial resolution of 3 arcsec. In order to connect coronal activity to photospheric events, ASPICS further includes two disk imagers. The first one is devoted to the HI Lyman alpha emission line. The second one is a multi-channel instrument similar to SOHO/EIT and devoted to the HeII (30.4 nm), FeIX/X (17.1 nm) and FeXII (19.5 nm) emission lines. Two concepts of the space system are under consideration: a symmetric configuration where the disk imagers and the external occulter are on one spacecraft and the coronagraphs on the other, an asymmetric configuration where the external occulter is on one spacecraft and the scientific instruments are regrouped on the other one. Title: Coronal Magnetometry Authors: Arnaud, J.; Faurobert, M.; Grec, G.; Vial, J. -C. Bibcode: 2005EAS....14...95A Altcode: Magnetic fields emerging in the solar atmosphere control the structure, dynamics and heating of the solar corona. Those fields remain essentially unattainable with present low corona instrumentation. We present the most direct way of magnetic field remote measurements in the internal corona, namely visible and infrared coronal emission lines magnetometry and we explain why Dome C should be investigated as a likely outstanding site for such observations. We develop a strategy towards a large aperture coronal magnetometer at Dome C in the context of the other main instrumental projects underway for solar physics. Title: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2003A&A...412..555F Altcode: We present center-to-limb measurements of the scattering polarization observed in molecular lines of C2 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 C2 we show that the C2 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 Bibcode: 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. Bibcode: 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.

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. Bibcode: 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. Bibcode: 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. Bibcode: 2003ASPC..307..446H Altcode: No abstract at ADS Title: Magnetism and Activity of the Sun and Stars Authors: Arnaud, J.; Meunier, N. Bibcode: 2003EAS.....9.....A Altcode: No abstract at ADS Title: Second Solar Spectrum Observations at THEMIS Authors: Faurobert, M.; Arnaud, J. Bibcode: 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. Bibcode: 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 C2 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 W2. 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 C2 molecular transitions and two MgH transitions are present in our spectral window; we find that for the C2 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. Bibcode: 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. Bibcode: 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 Rs 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. Bibcode: 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 D1 and Na i D2 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 Bibcode: 2001ApJ...558..852H Altcode: Polarimetric measurements of the corona out to 2 Rsolar 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. Bibcode: 2001AGUSM..SH22E06H Altcode: Polarimetric measurements of the corona out to 2 Rs 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 10-7 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 ~ 0.75 Authors: Thompson, D.; Smith, J.; Djorgovski, S.; Arnaud, J.; Weir, N. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1988igbo.conf..378L Altcode: No abstract at ADS Title: Coronal emission-line polarization. Authors: Smartt, Raymond N.; Arnaud, Jean Bibcode: 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 Rsun to 2.0 Rsun 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 Rsun to 1.8 Rsun. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 C2 Swan band at 5140 Å, the CN 3880 Å band, the C3 4060 Å band and the OH 3090 Å band. The phase angle dependance of the polarization of C2, C3 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 C2, C3 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1984C&T...100..112A Altcode: No abstract at ADS Title: The analysis of Fe XIV 5303 coronal emission-line polarization measurements Authors: Arnaud, J. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1977ROLun..12..137A Altcode: No abstract at ADS Title: Beam and fiber optics Authors: Arnaud, J. A. Bibcode: 1976bfo..book.....A Altcode: No abstract at ADS