Adaptive optics development at the German solar telescopes

Berkefeld, Thomas; Soltau, D.; Schmidt, Dirk; Lühe, O. von der

doi:10.1364/ao.49.00g155

Cited by 43 publications

(29 citation statements)

References 12 publications

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“…The field-of-view (FOV) of the instrument is 77.1 × 58.2 (688 × 520 pixels after 2×2-pixel binning) with an image scale of 0.112 pixel −1 . All data were taken under good seeing conditions (Fried-parameter r 0 > 15 cm for most of the time) with real-time image correction provided by the Kiepenheuer Adaptive Optics System (KAOS, von der Lühe et al 2003;Berkefeld et al 2010).…”

Section: Observationsmentioning

confidence: 99%

High-resolution imaging spectroscopy of two micro-pores and an arch filament system in a small emerging-flux region

Manrique

González

Denker

2017

A&A

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Context. Emerging flux regions mark the first stage in the accumulation of magnetic flux eventually leading to pores, sunspots, and (complex) active regions. These flux regions are highly dynamic, show a variety of fine structure, and in many cases live only for a short time (less than a day) before dissolving quickly into the ubiquitous quiet-Sun magnetic field. Aims. The purpose of this investigation is to characterize the temporal evolution of a minute emerging flux region, the associated photospheric and chromospheric flow fields, and the properties of the accompanying arch filament system. We aim to explore flux emergence and decay processes and investigate if they scale with structure size and magnetic flux contents. Methods. This study is based on imaging spectroscopy with the Göttingen Fabry-Pérot Interferometer at the Vacuum Tower Telescope, Observatorio del Teide, Tenerife, Spain on 2008 August 7. Photospheric horizontal proper motions were measured with Local Correlation Tracking using broadband images restored with multi-object multi-frame blind deconvolution. Cloud model (CM) inversions of line scans in the strong chromospheric absorption Hα λ656.28 nm line yielded CM parameters (Doppler velocity, Doppler width, optical thickness, and source function), which describe the cool plasma contained in the arch filament system. Results. The high-resolution observations cover the decay and convergence of two micro-pores with diameters of less than one arcsecond and provide decay rates for intensity and area. The photospheric horizontal flow speed is suppressed near the two micro-pores indicating that the magnetic field is already sufficiently strong to affect the convective energy transport. The micro-pores are accompanied by a small arch filament system as seen in Hα, where small-scale loops connect two regions with Hα line-core brightenings containing an emerging flux region with opposite polarities. The Doppler width, optical thickness, and source function reach the largest values near the Hα line-core brightenings. The chromospheric velocity of the cloud material is predominantly directed downwards near the footpoints of the loops with velocities of up to 12 km s −1 , whereas loop tops show upward motions of about 3 km s −1 . Some of the loops exhibit signs of twisting motions along the loop axis. Conclusions. Micro-pores are the smallest magnetic field concentrations leaving a photometric signature in the photosphere. In the observed case, they are accompanied by a miniature arch filament system indicative of newly emerging flux in the form of Ω-loops. Flux emergence and decay take place on a time-scale of about two days, whereas the photometric decay of the micro-pores is much more rapid (a few hours), which is consistent with the incipient submergence of Ω-loops. Considering lifetime and evolution timescales, impact on the surrounding photospheric proper motions, and flow speed of the chromospheric plasma at the loop tops and footpoints, the results are representative for the smallest emergin...

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Section: Observationsmentioning

confidence: 99%

High-resolution imaging spectroscopy of two micro-pores and an arch filament system in a small emerging-flux region

Manrique

González

Denker

2017

A&A

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“…Table 2. The parameter values for GREGOR and EST are taken from Berkefeld et al [7,21]. The values for NST were determined from profiles of the atmospheric turbulence [22].…”

Section: Resultsmentioning

confidence: 99%

Layer-oriented adaptive optics for solar telescopes

Kellerer¹

2012

Appl. Opt.

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with the permission of OSA. The paper can be found at the following URL on the OSA website:http://dx.doi.org/10.1364/AO.51.005743. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. First multiconjugate adaptive-optical (MCAO) systems are currently being installed on solar telescopes. The aim of these systems is to increase the corrected field of view with respect to conventional adaptive optics. However, this first generation is based on a star-oriented approach, and it is then difficult to increase the size of the field of view beyond 60-80 arc sec in diameter. We propose to implement the layeroriented approach in solar MCAO systems by use of wide-field Shack-Hartmann wavefront sensors conjugated to the strongest turbulent layers. The wavefront distortions are averaged over a wide field: the signal from distant turbulence is attenuated and the tomographic reconstruction is thus done optically. The system consists of independent correction loops, which only need to account for local turbulence: the subapertures can be enlarged and the correction frequency reduced. Most importantly, a star-oriented MCAO system becomes more complex with increasing field size, while the layer-oriented approach benefits from larger fields and will therefore be an attractive solution for the future generation of solar MCAO systems.

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“…The good and stable seeing conditions during the observation and the Kiepenheuer-Institut Adaptive Optics System (von der Lühe et al 2003;Berkefeld et al 2010) provided a spatial resolution of about 1 . We combined the Tenerife Infrared Polarimeter (TIP II; Martínez Pillet et al 1999;Collados et al 2007) attached to the Echelle spectrograph, the POlarimetric LIttrow Spectrograph (POLIS; Schmidt et al 2003;Beck et al 2005b), and two additional channels to record the intensity spectra of the Ca ii IR line via the Echelle Beck et al 2007or Kucera et al 2008 for a similar combination using TIP and TESOS).…”

Section: Observationsmentioning

confidence: 99%

Multiwavelength spectropolarimetric observations of an Ellerman bomb

Rezaei

Beck

2015

A&A

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Context. Ellerman bombs (EBs) are enhanced emission in the wings of the Hα line in the solar spectrum. Aims. We study the structure of an EB in the photosphere and chromosphere.Methods. We analyze simultaneous observations of four chromospheric lines (Hα, Ca ii H, Ca ii IR 854 nm, and He i 1083 nm) as well as two photospheric lines (Fe i 630 and Si i 1082.7 nm) along with high-cadence 160 and 170 nm ultraviolet (UV) continuum filtergrams. Full Stokes data from the Helioseismic and Magnetic Imager (HMI) are used to trace the temporal evolution of the magnetic structure.Results. We identify the EB by excess emission in the wings of the Hα line, a brightening in the UV continuum, and large emission peaks in the core of the two Ca ii lines. The EB shows a blueshift in all chromospheric lines, while no shifts are observed in the photospheric lines. The blueshift in the chromospheric layer causes very asymmetric emission peaks in the Ca ii H line. The photospheric Si i spectral line shows a shallower line depth at the location of the EB. The UV continuum maps show that the EB was substantially brighter than its surroundings for about 30 min. The continuum contrast of the EB from 170 nm to 1080 nm shows a power-law dependency on the wavelength. The temperature enhancement amounts to 130 K in the low photosphere and 400 K at the temperature minimum level. This temperature excess is also seen in an LTE inversion of the Ca ii spectra. The total thermal and radiative energy content of the EB is about 10 20 J and 10 18 J in the photosphere and chromosphere, respectively. The HMI data hints at a photospheric magnetic flux cancellation as the driver of the EB. Conclusions. Ellerman bombs release the energy in a height range of several pressure scale heights around the temperature minimum such that they affect both the photosphere and the lower chromosphere.

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Adaptive optics development at the German solar telescopes

Cited by 43 publications

References 12 publications

High-resolution imaging spectroscopy of two micro-pores and an arch filament system in a small emerging-flux region

High-resolution imaging spectroscopy of two micro-pores and an arch filament system in a small emerging-flux region

Layer-oriented adaptive optics for solar telescopes

Multiwavelength spectropolarimetric observations of an Ellerman bomb

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