Formation of granular intensity fluctuations on the Sun

Rodríguez, E. Pérez; Kneer, F.

doi:10.1051/0004-6361:20021239

Cited by 7 publications

(2 citation statements)

References 19 publications

(16 reference statements)

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“…In order to estimate the line formation heights of the two iron lines we computed temperature response functions (RFs) with a code described in Pérez Rodríguez & Kneer (2002). The RFs are shown in Fig.…”

Section: Observationsmentioning

confidence: 99%

On small scale magnetic structures in the solar photosphere

Stangl¹,

Hirzberger²

2005

A&A

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Abstract. The distribution of the magnetic field on the solar surface is as yet unknown in detail, but of considerable importance for solar physics in general. We have observed two different solar regions, one containing a small pore, the other region comprising a network in the light of the Fe  λ6301.5 Å and Fe  λ6302.5 Å lines at the German Vacuum Tower Telescope of the Observatorio del Teide (Tenerife, Spain) with the "Göttingen" Fabry-Pérot Interferometer. By applying image reconstruction techniques to broad-and narrowband filtergrams we obtained continuum images, line core images, as well as line-of-sight velocity and magnetic field maps. We present scatter plots of the line core intensity vs. the Doppler velocity and the vertical component of the magnetic field, which reveal that the line core brightness is not a clear indicator for magnetic fields in the solar atmosphere. Furthermore, we estimate the swaying motion of flux tubes to be mostly smaller than 0. 3 and thus in good agreement with the predictions of theoretical dynamic models. Finally, we show how the choice of the observed solar target influences the results and their interpretation. We claim that generalizations can mislead, and strongly depend on the presence or absence of solar (magnetic) features in the analyzed data.

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Section: Observationsmentioning

confidence: 99%

On small scale magnetic structures in the solar photosphere

Stangl¹,

Hirzberger²

2005

A&A

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“…We have calculated the RF of Line I and III to T perturbations (R T ) and V LOS perturbations (R V LOS ), applying the SIR code (Ruiz Cobo & del Toro Iniesta 1992). We refer also to Sheminova (1998), Gadun et al (1997Gadun et al ( , 1999 and Pérez Rodríguez & Kneer (2002) for other calculations of response functions.…”

Section: Heights Of Formation Of the Spectral Linesmentioning

confidence: 99%

Time series of high resolution photospheric spectra in a quiet region of the sun

Puschmann

Vázquez

Bonet

et al. 2003

A&A

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Abstract.A 50 min time series of one-dimensional slit-spectrograms, taken in quiet sun at disk centre, observed at the German Vacuum Tower Telescope (Observatorio del Teide), was used to study the global and spatial variations of different line parameters. In order to determine the vertical structure of the photosphere two lines with well separated formation heights have been considered. The data have been filtered of p-modes to isolate the pure convective phenomenon. From our studies of global correlation coefficients and coherence and phase shift analyses between the several line parameters, the following results can be reported. The convective velocity pattern preserves structures larger than 1 . 0 up to the highest layers of the photosphere (∼435 km). However, at these layers, in the intensity pattern only structures larger than 2 . 0 are still connected with those at the continuum level although showing inverted brightness contrast. This confirms an inversion of temperature that we have found at a height of ∼140 km. A possible evidence of gravity waves superimposed to the convective motions is derived from the phase shift analysis. We interprete the behaviour of the full width at half maximum and the equivalent width as a function of the distance to the granular borders, as a consequence of enhanced turbulence and/or strong velocity gradients in the intergranular lanes.

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On the continuum intensity distribution of the solar photosphere

Wedemeyer

Voort²

2009

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Context. For many years, there seemed to be significant differences between the continuum intensity distributions derived from observations and simulations of the solar photosphere. Aims. In order to settle the discussion on these apparent discrepancies, we present a detailed comparison between simulations and seeing-free observations that takes into account the crucial influence of instrumental image degradation. Methods. We use a set of images of quiet Sun granulation taken in the blue, green and red continuum bands of the Broadband Filter Imager of the Solar Optical Telescope (SOT) onboard Hinode. The images are deconvolved with point spread functions (PSF) that account for non-ideal contributions due to instrumental stray-light and imperfections. In addition, synthetic intensity images are degraded with the corresponding PSFs. The results are compared with respect to spatial power spectra, intensity histograms, and the centre-to-limb variation of the intensity contrast.Results. The intensity distribution of SOT granulation images is broadest for the blue continuum at disc-centre and narrows towards the limb and for longer wavelengths. The distributions are relatively symmetric close to the limb but exhibit a growing asymmetry towards disc-centre. The intensity contrast, which is connected to the width of the distribution, is found to be (12.8 ± 0.5)%, (8.3 ± 0.4)%, and (6.2 ± 0.2)% at disc-centre for blue, green, and red continuum, respectively. Removing the influence of the PSF unveils much broader intensity distributions with a secondary component that is otherwise only visible as an asymmetry between the darker and brighter than average part of the distribution. The contrast values increase to (26.7 ± 1.3)%, (19.4 ± 1.4)%, and (16.6 ± 0.7)% for blue, green, and red continuum, respectively. The power spectral density of the images exhibits a pronounced peak at spatial scales characteristic for the granulation pattern and a steep decrease towards smaller scales. The observational findings like the absolute values and centre-to-limb variation of the intensity contrast, intensity histograms, and power spectral density are well matched with corresponding synthetic observables from three-dimensional radiation (magneto-)hydrodynamic simulations. Conclusions. We conclude that the intensity contrast of the solar continuum intensity is higher than usually derived from groundbased observations and is well reproduced by modern radiation (magneto-)hydrodynamic models. Properly accounting for image degradation effects is of crucial importance for comparisons between observations and numerical models.

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Formation of granular intensity fluctuations on the Sun

Cited by 7 publications

References 19 publications

On small scale magnetic structures in the solar photosphere

On small scale magnetic structures in the solar photosphere

Time series of high resolution photospheric spectra in a quiet region of the sun

On the continuum intensity distribution of the solar photosphere

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