The influence of image reconstruction on two-dimensional spectrograms of the solar photosphere
Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany e-mail: [kasia;wolfgang]@kis.uni-freiburg.de
2 National Solar Observatory/Sacramento Peak Observatory, PO Box 62, Sunspot, NM 88349-0062, USA e-mail: email@example.com
Accepted: 28 March 2006
Aims.We present a spectral analysis of small-scale structures in the solar photosphere and investigate the influence of the speckle deconvolution technique on the line profiles.
Methods. A short sequence of two-dimensional spectra is used, taken with the Telecentric Etalon Solar Spectrometer (TESOS) at the German Vacuum Tower Telescope on Tenerife. We observed two small pores surrounded by disturbed and by regular granulation in the non-magnetic neutral Iron line at 557.6 nm. In a first step, a speckle reconstruction is computed by applying an extended Knox-Thompson algorithm to the broad-band data. In a second step, the individual narrow-band filtergrams are deconvolved utilizing the information gained in the first step. We then perform a spectral analysis of the 2D spectra and compare the results obtained with the raw and the restored data.
Results.Important spectral quantities, e.g. line position, line depression and line asymmetry are largely unchanged by the image reconstruction process. We derive the line asymmetry and the line-of-sight flow for granules and intergranular lanes and also for an isolated G-band bright point and find important differences between quiet and magnetically disturbed granulation: the granule centers in the quiet region show a strong asymmetry with significant blue shift (300 m/s) toward deeper layers, while the velocity in the disturbed area show virtually no height dependence. For the intergranular lanes the situation is reversed: no height dependence in the quiet area, significant red-shift toward deeper layers in the disturbed part. An isolated G-band bright point does not show any line-of-sight motion relative to its immediate surroundings. The map of LOS velocities derived from line-wing shifts shows a significant downflow around one of the pores measured in deep layers of the photosphere.
Conclusions.In most cases we do not find any artefacts in the reconstructed line profiles that would compromise their usage for quantitative spectroscopy.
Key words: Sun: photosphere / techniques: spectroscopic / Sun: granulation
© ESO, 2006