# SST CRISP images

During April 2008, the CRisp Imaging SpectroPolarimeter (CRISP) was installed at the SST on La Palma. The tunable filter part of this system is a dual Fabry-Pérot Interferometer (FPI) system, usable from 510 to 860 nm with 0.3-0.9 nm wide pre-filters. It has a compact telecentric optical design with a minimum number of optical surfaces and high overall transmission. Polarization measurements are made by liquid crystal (LC) modulation and a polarizing beam splitter, located close to the final focal plane and feeding two 1k×1k-pixel Sarnoff CCD cameras. MOMFBD image restoration is aided with a third CCD providing broad-band images synchronized with the two narrowband images and recorded through the pre-filter of the FPI system. The optimization of the FPI system is described by Göran Scharmer (2006, A&A 447, 1111), the overall design and details of CRISP will be described in a forthcoming publication and also provided on our web site.

Tomas Hillberg observed two large pores of opposite polarities using CRISP on 22 April 2008. The two CRISP narrowband images shown here (jpeg by clicking on the thumbnails, 1000 km tickmarks; in FITS format below, 0.071 arcsec pixels) are recorded at $-5$ pm from the line core and in the nearby continuum, resp., of the Zeeman-sensitive Fe I line at 630.2 nm. The filter passband is about 6.5 pm at this wavelength. The CRISP tuning sequence used scanned the line in 11 wavelength positions plus one continuum wavelength during < 11 s, while cycling through 4 polarization states. Such data, consisting of a total of 338 images from the broadband camera and 334 polarimetric images each from the two CRISP narrowband cameras, was processed as a single MOMFBD data set by Mats Löfdahl. The restored polarimetric images, each based on 7 exposures, demonstrate impressive spatial resolution at or near the diffraction limit of the telescope (0.16 arcsec at this wavelength) and very high polarimetric sensitivity.

This is presently the most highly resolving solar spectropolarimeter in the world as regards spatial resolution. Polarimetric analysis of the data is under way.

The construction of CRISP was made possible thanks to a grant from the Marianne and Marcus Wallenberg Foundation.

Time-stamp: <2013-04-19 11:02:18 mats>