High resolution 2D-spectroscopy of granular dynamics

¹ Universitäts-Sternwarte, Geismarlandstraße 11, 37083 Göttingen, Germany
² Institut für Geophysik, Astrophysik und Meteorologie, Universitätsplatz 5, 8010 Graz, Austria

Corresponding author: J. Hirzberger, jhirzbe@uni-sw.gwdg.de

Received: 16 August 2000
Accepted: 4 December 2000

Abstract

Spectroscopic data with high spatial resolution are used to study the granular dynamics of the Sun. The observations were obtained with the "Göttingen"two-dimensional (2D) Fabry-Perot interferometer in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. Time sequences of spectral scans across the non-magnetic Fei 5576 Åline were taken from disc center. The 2D spectroscopic images were reconstructed with speckle methods, from which a spatial resolution of 0 fraction of arcsecond4-0 fraction of arcsecond5 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 fraction of arcsecond5, 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.