Free Access
Issue
A&A
Volume 541, May 2012
Article Number A108
Number of page(s) 11
Section The Sun
DOI https://doi.org/10.1051/0004-6361/201118275
Published online 10 May 2012

Online material

Appendix A: Analysis of the fine structure of the H-Lyα filament through FFT of perpendicular cuts

thumbnail Fig. A.1

Square of the modulus of the FFT as a function of spatial frequency (converted in spatial scale) limited to the high spatial frequencies for cuts in the filament. a) Subcut 5 of cut area 5. b) Average of cuts of the area 1.

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thumbnail Fig. A.2

Square of the modulus of the FFT as a function of spatial frequency (converted in spatial scale) for a cut in the quiet Sun at X = 3000 of Fig. 4. a) Full power spectrum obtained for the cut. b) Zoom on the high frequencies.

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As mentioned in Sects. 4.1 and 4.3.1, we analysed ten consecutive cuts made at the five positions shown in Fig. 7. We used the usual method of subtracting the average values and of tapering at both ends to avoid unwanted high frequencies. We show in Figs. A.1a and b the square of the modulus of the FFT as a function of spatial frequency (converted in spatial scale) limited to the high- frequency region. Figure A.1a is an example of an individual cut (in region 5) showing power at the 0.4 arcsec scale. We performed a power spectrum estimation through reducing the spectral analysis bandwidth. Between 0.24 and 2 arcsec, our peak at 0.38 arcsec is above 2.5 times the standard deviation, providing a confidence level higher than 95%. We also show an average power spectrum of area 1 (Fig. A.1b) where it is difficult to find power at 0.4 arcsec but where the 2 arcsec scale can definitely be identified. (Other cuts show some power around 1 arcsec.) Finally, for the sake of comparison, we show in Fig. A.2 the FFT square power of a vertical cut in the quiet Sun image performed at X = 3000 (Fig. 4). Figure A.2a displays the full power spectrum where one can distinguish power at about 30 − 35 arcsec, typical of the supergranulation. The zoom performed into the high-frequency region (Fig. A.2b) does not show any power below 4 arcsec.


© ESO, 2012

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