Noise filtering in solar speckle masking reconstructions

Boer, Charles R. de

doi:10.1051/aas:1996285

Cited by 49 publications

(27 citation statements)

References 5 publications

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“…The FPI observations were reconstructed with the Göttingen speckle code (de Boer 1996;Janssen 2003;Bello González et al 2007). The Stokes measurements were demodulated to yield the profiles (I λ , Q λ , U λ , V λ ) over the field of view (FOV) as described in Rezaei et al (2012).…”

Section: Observations and Data Analysismentioning

confidence: 99%

Shear and vortex motions in a forming sunspot

González

Kneer²,

Schlichenmaier

2012

A&A

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Aims. We measure proper motions of fine structures in a forming sunspot to infer information about the dynamics of flux emergence at the sub-photospheric level. Methods. The active region NOAA 11024 was observed with the Vacuum Tower Telescope at Observatorio del Teide/Tenerife over several days in July 2009. Here, we concentrate on a two-hour sequence taken on July 4, when the leading spot was at an early stage of its evolution. Speckle reconstructions from Ca ii K images and polarimetric data in Fe i λ6173 allow us to study proper motions of umbral fine structures. Results. We detect three prominent features: (1) A light bridge, divided by a dark lane along its axis, shows proper motions in opposing directions on its sides, with velocities of ∼100-500 m s −1 . The flows are seen in both the Ca ii K and the broadband time sequences. (2) Umbral dots in one umbral region outline a vortex with speeds of up to 550 m s −1 . The direction of the motion of the umbral dots is different from that in the light bridge. (3) At one rim of the umbra, the fine structure of the magnetic field moves horizontally with typical velocities of 250-300 m s −1 , prior to the formation of the penumbra. Conclusions. We report on shear and vortex motions in a forming sunspot and interpret them as tracers of twist relaxation in magnetic flux ropes. We suggest that the forming sunspot contains detached magnetic flux ropes that emerge at the surface with different amounts of twist. As they merge to form a sunspot, they untwist giving rise to the observed shear and vortex motions.

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Section: Observations and Data Analysismentioning

confidence: 99%

Shear and vortex motions in a forming sunspot

González

Kneer²,

Schlichenmaier

2012

A&A

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“…The tip-tilt mirror of the SST assured an effective correction for image motion. Bursts of some dozens of images were reconstructed using the speckle-masking method (Weigelt 1977;Pehlemann & von der Lühe 1989;de Boer 1996). An example is shown in Fig.…”

Section: Two-dimensional Imagingmentioning

confidence: 99%

Solar limb faculae

Hirzberger¹,

Wiehr²

2005

A&A

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Abstract. We observe solar limb faculae at an unprecedented spatial resolution with the new 1 m Swedish Solar Telescope SST on La Palma. Speckle-reconstructed images are used to study 4475 limb facular grains simultaneously in the 430 nm G-band and the 587.5 ± 1.5 continuum up to only 1 from the limb (cos θ = 0.05). No systematic contrast decrease is found even a few arcsec from the solar limb. The facular grains appear to be "projected" on the limb-side neighboring granules; approaching the disc center, the corresponding features occur as inter-granular G-band bright points. Independently, we took spectra with the French-Italian THEMIS telescope on Tenerife and find that the known "line-gap effect" from disc center disappears near the limb. Here, the facular continuum is enhanced whereas the normalized profiles are unchanged with respect to the undisturbed neighborhood.

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“…These are used for image restoration with well established speckle methods (e.g. de Boer et al 1992;de Boer 1996;Wilken et al 1997). The spectral ratio method (von der Lühe 1984) gives estimates of the amplitude correction factors (in Fourier space).…”

Section: Speckle Reconstructionmentioning

confidence: 99%

Speckle spectro-polarimetry of solar magnetic structures

Koschinsky

Kneer

Hirzberger

2001

A&A

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Abstract. We present speckle observations of small-scale magnetic structures on the Sun. They were obtained with the "Göttingen" Fabry-Perot interferometer (FPI) in the Vacuum Tower Telescope at the Observatorio del Teide, Tenerife, from quiet and active regions close to disc center. A Stokes V polarimeter was added to the FPI to measure V profiles in the Fe I 6302.5Å line. The setup allows image reconstruction with speckle methods. The achieved spatial resolution in the magnetograms is 0. 4-0. 5. We describe the observational technique and the data reduction. The results from small-scale magnetic flux elements in a very quiet region, in an active region with pores and abnormal granulation, and in a sunspot with its surroundings are discussed. In the quiet Sun, granular dynamics dominate the time evolution of the magnetic elements. Flux occurs in both bright intergranular points and in dark intergranular spaces. Likewise, with the present spatial resolution, no preference of magnetic flux in abnormal granulation in an active region can be found. Flux occurs in both bright (abnormal) small-scale granules and in the darker spaces in between them. The small sunspot studied has very little magnetic flux in its ambient quiet regions, especially no strong, conspicuous concentrations of returned flux, i.e. of flux with polarity opposite to that in the sunspot.

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Noise filtering in solar speckle masking reconstructions

Cited by 49 publications

References 5 publications

Shear and vortex motions in a forming sunspot

Shear and vortex motions in a forming sunspot

Solar limb faculae

Speckle spectro-polarimetry of solar magnetic structures

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