Some TH´EMIS-MTR observations of the second solar spectrum

The aim of the present paper is twofold: first, observations of the scattering polarization spectrum achieved near the solar limb in quiet regions (North Pole) are reported for a series of lines: Sr I 460.7 n m, Na I D1 589.6 nm and D2 589.0 nm, Ba II D1 493.4 nm and D2 455.4 nm, C I 493.2 nm. The TH´EMIS observational and data reduction techniques are briefly described. Second, the depolarizing effect of the hyperfine structure on the scattering polarization of the Na I D2 line is investigated, in view of future observations interpretation. Results of computation show that the depolarization due to the hyperfine splitting is important in Na I D2. The lower-level polarizationeffect is investigated also

Characterizing the Adaptive Optics Off-Axis Point-Spread Function. II. Methods for Use in Laser Guide Star Observations

Most current astronomical adaptive optics (AO) systems rely on the availability of a bright star to measure the distortion of the incoming wavefront. Replacing the guide star with an artificial laser beacon alleviates this dependency on bright stars and therefore increases sky coverage, but it does not eliminate another serious problem for AO observations. This is the issue of PSF variation with time and field position near the guide star. In fact, because a natural guide star is still necessary for correction of the low-order phase error, characterization of laser guide star (LGS) AO PSF spatial variation is more complicated than for a natural guide star alone. We discuss six methods for characterizing LGS AO PSF variation that can potentially improve the determination of the PSF away from the laser spot, that is, off-axis. Calibration images of dense star fields are used to determine the change in PSF variation with field position. This is augmented by AO system telemetry and simple computer simulations to determine a more accurate off-axis PSF. We report on tests of the methods using the laser AO system on the Lick Observatory Shane Telescope. [Abstract truncated.]Comment: 31 pages, 5 figures, accepted by PAS

The European Solar Telescope

The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope, the German Vacuum Tower Telescope and GREGOR, the French Télescope Héliographique pour l'Étude du Magnétisme et des Instabilités Solaires, and the Dutch Open Telescope. With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems

The European Solar Telescope

The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope, the German Vacuum Tower Telescope and GREGOR, the French Télescope Héliographique pour l’Étude du Magnétisme et des Instabilités Solaires, and the Dutch Open Telescope. With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems

Far Infrared Telescope (TIR) Project


We present the Far Infrared Telescope project submitted to the micro satellite programme of CNES and initially combined to a γ ray mission. Millimeter wave emission from MeV-electrons is now well known, and on very few occasions non solar dedicated γ ray detectors have revealed emission from electrons at still higher energies. The combination of two diagnostics: relativistic electrons-synchrotron radiation in the far infrared and Bremsstrahlung at γ ray would probe electrons at energies above 10 MeV with 100 ms time resolution, yielding unique information on the yet unknown high energy cut-off of the electron spectrum, and on the response of the high photosphere to energy input during flares. We emphasize the opportunity to observe solar flares in far infrared bands and to test uncooled detectors at the ground based station dome C in Antarctica.

Some THEMIS-MTR observations of the second solar spectrum (2000 campaign)

We report spectropolarimetric observations with the THEMIS telescope multi-lines operating mode (MTR) during the 2000 observational period from August 27th to September 1st. We measured the resonance polarization at the limb of a series of lines: \ion{Sr}{i} 460.7 nm, \ion{Na}{i} D1 589.6 nm and D2 589.0 nm, \ion{Ba}{ii} D1 493.4 nm and D2 455.4 nm, \ion{C}{i} 493.2 nm. The data analysis method is mainly described in Bommier & Rayrole ([CITE]), and has been completed by using the beam exchange facility as available in 2000 THEMIS, i.e., in a single Stokes parameter. A so-called “generalized beam exchange” technique has been settled on, for the full Stokes vector measurement under this limitation. The observations have been devoted to the measurement of the scattering polarization which is a linear polarization observed near the limb of the Quiet Sun, eventually modified by a weak magnetic field (the so-called Hanle effect). The entrance slit of the spectrograph has been oriented parallel to the tangential direction of the solar limb, and data have been averaged in time and along the spatial direction of the slit in order to increase the polarimetric resolution. Two different cameras have been used to record simultaneously the two polarization states exiting the beam-splitter. The results of our polarization measurements are in good agreement with those given in the second spectrum solar atlas of Gandorfer ([CITE]), based on 1999–2000 observations. Nevertheless, with regard to a quantification of the polarization signal, we found that the signal is systematically smaller than previous results obtained during the 1994–96 observational period and was also observed as decreasing during the 1998 observational period, as if a 11-year cyclic variation of the limb polarization occured. This signal variability obviously requires further observational and interpretative investigations. We noticed other differences to previous results, in particular, the linear polarization shape of the \ion{Na}{i} D1 line that also requires further observational investigation

Quelques observations THÉMIS-MTR du Second Spectre Solaire

National audienc

Performance analysis for T.H.E.M.I.S(*) image stabilizer optical system

Numerical simulations of anisoplanatism effects after compensation by the T.H.E.M.I.S. image stabilizer optical system when observing extended sources are presented. The residual wavefront error after correction is computed using the expansion on the Zernike polynomials to analyze the performances of different adaptive optics systems for solar observations. The long exposure optical tranfer functions are derived to simulate the image quality after correction for extended field of view. We demonstrate the capacity of the image stabilizer system for very large field of view observations with medium image quality while the capacity of high order adaptive optics system is suitable for high image quality observations but to the price of a reduction of the field of view

Large Field-of-View Spectropolarimetric Observations with a Large Aperture Telescope

International audienc

Second Spectrum of Na I D1 Observed with THEMIS

International audienceThe second solar spectrum (spectrum of the linear polarization observed near the solar limb in a quiet region) of Na I D1 has always been found antisymmetrical when observed with THEMIS tep{b12 TB01,b12 BM02}. The same holds also for atlas of tet{b12 Ga00}. On the contrary, tet{b12 SK97} and tet{b12 St00} observed a differently shaped profile, showing a central peak. We investigated in depth our treatment of THEMIS data, in particular looking for possible beam misalignments, by observing other unpolarized lines, but we have failed to put in evidence any misalignment. We discuss these complementary observations. In addition, we present a structure in the V/I profile of Na I D1 and D2, which we have repeatedly observed, and which we suggest be due to the Kemp effect (the alignement-to-orientation transfer that occurs in the transition from the Zeeman effect to the Paschen-Back effect)