Abstract
Spectroscopic data with high spatial resolution are used to study the granular dynamics of the Sun. The observations were obtained with the “Gottingen” two-dimensional (2D) Fabry-Perot interferometer in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. Time sequences of spectral scans across the nonmagnetic Fe i 5576 A line were taken from disc center. The 2D spectroscopic images were reconstructed with speckle methods, from which a spatial resolution of 0. ′′4–0. ′′5 was achieved. A power and coherence analysis of intensity and velocity maps from different photospheric heights has been carried out. The coherence between intensity and velocity fluctuations stays high for structural scales >0. ′′5, which underlines the high spatial resolution of the data. Furthermore, the vertical flow field and its time evolution within exploding granules have been analyzed. We find fast downflows in the dark centers of exploding granules with velocities up to 1.2 km s−1. Additionally, we estimated the flow velocities of so-called “dark dots”. We discuss indications that these structures represent a new type of downflow within the centers of bright granules.
Highlights
Until a decade ago two principal observational techniques existed for analyzing the fine structure of the solar atmosphere: two-dimensional (2D) imaging on the one side and spectroscopy with slit spectrographs on the other side
Spectroscopic data with high spatial resolution are used to study the granular dynamics of the Sun
Hirzberger et al.: High resolution 2D-spectroscopy of granular dynamics demonstrate the advantages of combining two-dimensional spectroscopic observations with efficient image reconstruction techniques
Summary
Until a decade ago two principal observational techniques existed for analyzing the fine structure of the solar atmosphere: two-dimensional (2D) imaging on the one side and spectroscopy with slit spectrographs on the other side. Pure high resolution imaging by, e.g., Roudier & Muller (1987), Title et al (1989), Hirzberger et al (1997, 1999a) have revealed significant differences in the geometrical and brightness structure and the temporal evolution of small and large granules, i.e. large gran-. From these observational studies of solar granulation it has been concluded that the granular dynamics is highly non-linear and that the convective flows are highly turbulent. J. Hirzberger et al.: High resolution 2D-spectroscopy of granular dynamics demonstrate the advantages of combining two-dimensional spectroscopic observations with efficient image reconstruction techniques. This allows us to measure dynamic properties from images as well as spectroscopic parameters in the solar photosphere down to scales close to the resolution limit of present solar telescopes
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