A retrospective of the GREGOR solar telescope in scientific literature

Denker, C.; Luehe, Oskar von der; Feller, A.; Arlt, K.; Balthasar, H.; Bauer, Svend‐Marian; González, N. Bello; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, Andreas; Granzer, T.; Hahn, T.; Halbgewachs, C.; Heidecke, F.; Hofmann, Axel; Kentischer, T.; Klvaňa, M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, Emil; Puschmann, K. G.; Rendtel, J.; Schmidt, Dirk; Schmidt, Wolfgang; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassméier, K. G.; Volkmer, R.; Waldmann, T.; Wiehr, E.; Wittmann, A.; Woche, M.

doi:10.1002/asna.201211728

Cited by 10 publications

(3 citation statements)

References 17 publications

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“…With the integration of the scanning mechanism in April 2014, the IR spectropolarimeter of the new 1.5 m solar telescope GREGOR (von der Lühe et al 2001;Schmidt et al 2012;Denker et al 2012) has become fully operational. Using the GREGOR Adaptive Optics System (GAOS, Berkefeld et al 2012), we observed the disk passage of several active regions between April and July 2014 (see Table A.2 for a list of the sunspots observed in the IR).…”

Section: Data In the Near-infrared From Grismentioning

confidence: 99%

Magnetic fields of opposite polarity in sunspot penumbrae

Fränz

Collados

Bethge

et al. 2016

A&A

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Context. A significant part of the penumbral magnetic field returns below the surface in the very deep photosphere. For lines in the visible, a large portion of this return field can only be detected indirectly by studying its imprints on strongly asymmetric and three-lobed Stokes V profiles. Infrared lines probe a narrow layer in the very deep photosphere, providing the possibility of directly measuring the orientation of magnetic fields close to the solar surface. Aims. We study the topology of the penumbral magnetic field in the lower photosphere, focusing on regions where it returns below the surface. Methods. We analyzed 71 spectropolarimetric datasets from Hinode and from the GREGOR infrared spectrograph. We inferred the quality and polarimetric accuracy of the infrared data after applying several reduction steps. Techniques of spectral inversion and forward synthesis were used to test the detection algorithm. We compared the morphology and the fractional penumbral area covered by reversed-polarity and three-lobed Stokes V profiles for sunspots at disk center. We determined the amount of reversed-polarity and three-lobed Stokes V profiles in visible and infrared data of sunspots at various heliocentric angles. From the results, we computed center-to-limb variation curves, which were interpreted in the context of existing penumbral models. Results. Observations in visible and near-infrared spectral lines yield a significant difference in the penumbral area covered by magnetic fields of opposite polarity. In the infrared, the number of reversed-polarity Stokes V profiles is smaller by a factor of two than in the visible. For three-lobed Stokes V profiles the numbers differ by up to an order of magnitude.

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Section: Data In the Near-infrared From Grismentioning

confidence: 99%

Magnetic fields of opposite polarity in sunspot penumbrae

Fränz

Collados

Bethge

et al. 2016

A&A

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“…In this article, initial results are presented from the improved High-resolution Fast Imager (HiFI+) at the 1.5-meter GREGOR solar telescope 26 – 28 The imaging system was designed to monitor the solar photosphere and chromosphere with high spatial and temporal resolution in six wavelength bands. The instrument description includes the optical layout, the sCMOS and CMOS camera systems including control computers and software, and data processing and archiving.…”

Section: Introductionmentioning

confidence: 99%

Improved High-resolution Fast Imager

Denker

Verma

Wiśniewska

et al. 2023

J. Astron. Telesc. Instrum. Syst.

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The improved High-resolution Fast Imager (HiFI+) is a multiwavelength imaging filtergraph, which was commissioned at the GREGOR solar telescope at Observatorio del Teide, Izaña, Tenerife, Spain, in March 2022followed by science verification in April 2022, after which it entered routine observations. Three camera control computers with two synchronized sCMOS and CMOS cameras each provide near diffraction-limited imaging at high cadence in six wavelength bands (Ca II H at 396.8 nm, G-band at 430.7 nm, blue continuum at 450.6 nm, narrow-and broad-band Hα at 656.3 nm, and TiO bandhead at 705.8 nm). This unique combination of photospheric and chromospheric images provides "tomographic" access to the dynamic Sun and complements spectropolarimetric observations at the GREGOR telescope. High image acquisition rates of 50 and 100 Hz facilitate image restoration, where time series of restored images have a typical cadence of 6 and 12 s, which is sufficient to resolve the dynamics of the solar photosphere and chromosphere. In principle, all imaging channels can be restored individually using the speckle masking technique or multiframe blind deconvolution (MFBD). However, images recorded strictly simultaneously in the narrow-/broad-band Hα and the G-band/blue continuum channels can be pairwise subjected to multiobject multiframe deconvolution (MOMFBD) expanding the science capabilities of HiFI+. For example, the narrowband (FWHM = 60 nm) Halle Hα Lyot filter isolates the Hα line core, which facilitates matching chromospheric fibrils and filamentary structures to photospheric bright points. Likewise, dividing G-band by blue continuum images enhances small-scale brightenings, which are often related to small-scale magnetic fields so that their evolution can be tracked in time. A detailed description of the improved high-cadence, large-format imaging system is presented and its performance is assessed based on first-light observations.

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“…Imaging spectropolarimetry is nowadays carried out with complex Fabry-Perót interferometers (FPIs). Examples include the Triple Etalon SOlar Spectrometer (TESOS) [1,2] at the Vacuum Tower Telescope (VTT), the Interferometric BIdimensional Spectropolarimeter (IBIS) [3] at the Dunn Solar Telescope (DST), the CRisp Imaging SpectroPolarimeter (CRISP) [4] at the Swedish Tower Telescope (SST), and the GREGOR Fabry-Perót Interferometer (GFPI) [5,6] at the 1.5meter GREGOR solar telescope [7][8][9] located at Observatorio del Teide, Tenerife, Spain. The next generation of FPIs is already on the horizon.…”

Section: Introductionmentioning

confidence: 99%

Measuring the etalon quality of the GREGOR Fabry–Pérot interferometer

Verma

Denker

2020

J. Astron. Telesc. Instrum. Syst.

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Imaging spectropolarimetry is an important observational tool in solar physics because of fast-cadence spectral scans with high-spectral resolution, large field-of-view, and its inherent suitability for post-facto image restoration. Fabry-Pérot etalons are the key optical elements of these instruments. Their optical quality critically defines the instrument's performance. The two etalons of the GREGOR Fabry-Pérot Interferometer (GFPI) were used for more than 10 years, raising questions about the potential deterioration of etalons coatings. We present an assessment of the etalons optical quality, describe the inspection method based on Zernike polynomials, discuss the field dependence of the finesse and its consequences for instrument design, and investigate the impact of the measurement technique to achieve plate parallelism. We find that extended exposure to sunlight affects the etalon coatings, i.e., lowering the peak transmission and leaving an imprint of the pupil of the GREGOR solar telescope on the etalon that is directly exposed to sunlight. The finesse of both etalons, however, remains high so that the impact on imaging spectropolarimetry is negligible.

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A retrospective of the GREGOR solar telescope in scientific literature

Cited by 10 publications

References 17 publications

Magnetic fields of opposite polarity in sunspot penumbrae

Magnetic fields of opposite polarity in sunspot penumbrae

Improved High-resolution Fast Imager

Measuring the etalon quality of the GREGOR Fabry–Pérot interferometer

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