F. A. Iglesias

High-resolution, high-sensitivity, ground-based solar spectropolarimetry with a new fast imaging polarimeter

Context. Remote sensing of weak and small-scale solar magnetic fields is of utmost relevance when attempting to respond to a number of important open questions in solar physics. This requires the acquisition of spectropolarimetric data with high spatial resolution (~10 -1 arcsec) and low noise (10 -3 to 10 -5 of the continuum intensity). The main limitations to obtain these measurements from the ground, are the degradation of the image resolution produced by atmospheric seeing and the seeing-induced crosstalk (SIC). Aims. We introduce the prototype of the Fast Solar Polarimeter (FSP), a new ground-based, high-cadence polarimeter that tackles the above-mentioned limitations by producing data that are optimally suited for the application of post-facto image restoration, and by operating at a modulation frequency of 100 Hz to reduce SIC. Methods. We describe the instrument in depth, including the fast pnCCD camera employed, the achromatic modulator package, the main calibration steps, the effects of the modulation frequency on the levels of seeing-induced spurious signals, and the effect of the camera properties on the image restoration quality. Results. The pnCCD camera reaches 400 fps while keeping a high duty cycle (98.6%) and very low noise (4.94 e − rms). The modulator is optimized to have high (>80%) total polarimetric efficiency in the visible spectral range. This allows FSP to acquire 100 photon-noise-limited, full-Stokes measurements per second. We found that the seeing induced signals that are present in narrow-band, non-modulated, quiet-sun measurements are (a) lower than the noise (7 × 10 -5 ) after integrating 7.66 min, (b) lower than the noise (2.3 × 10 -4 ) after integrating 1.16 min and (c) slightly above the noise (4 × 10 -3 ) after restoring case (b) by means of a multi-object multi-frame blind deconvolution. In addition, we demonstrate that by using only narrow-band images (with low S/N of 13.9) of an active region, we can obtain one complete set of high-quality restored measurements about every 2xa0s.

Smear correction of highly variable, frame-transfer CCD images with application to polarimetry.

Image smear, produced by the shutterless operation of frame-transfer CCD detectors, can be detrimental for many imaging applications. Existing algorithms used to numerically remove smear do not contemplate cases where intensity levels change considerably between consecutive frame exposures. In this report, we reformulate the smearing model to include specific variations of the sensor illumination. The corresponding desmearing expression and its noise properties are also presented and demonstrated in the context of fast imaging polarimetry.

Detection of spatially structured scattering polarization of Sr I 4607.3 A with the Fast Solar Polarimeter

Scattering polarization in the Sr I 4607.3 AA line observed with high resolution is an important diagnostic of the Suns atmosphere and magnetism at small spatial scales. At present, spatially resolved observations of this diagnostic are rare and have not been reported as close to the disk center as for

Fast Solar Polarimeter: Description and First Results

mu=0.6

GRISPlus am GREGOR: was ist das, und wozu braucht man das?

. Our aim is to measure the scattering polarization in the Sr I line at

Spatially resolved Stokes measurements in the Sr I (4607.3 Å) line with FSP at VTT/TESOS

mu=0.6

GRIS+ - Instrument Setup and First Data

and to identify the spatial fluctuations with a statistical approach. Using the Fast Solar Polarimeter (FSP) mounted on the TESOS filtergraph at the German Vacuum Tower Telescope (VTT) in Tenerife, Spain, we measured both the spatially resolved full Stokes parameters of the Sr I line at

Fast dual-beam spectropolarimetry - first results on scattering polarization measurements with FSP II at the DST

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Fast Solar Polarimeter: Prototype Characterization and First Results

and the center-to-limb variation of the spatially averaged Stokes parameters. nWe find that the center-to-limb variation of the scattering polarization in the Sr I line measured with FSP is consistent with previous measurements. A statistical analysis of Stokes

Image restoration with a grating spectro-polarimeter at the SST and plans for GREGOR/GRIS

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