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Astron. Astrophys. 360, 1157-1162 (2000)

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1. Introduction

To understand the granular dynamics of the Sun, thus much of the dynamics of late type stars, observations with high spatial resolution are needed. During the last decades, observations have become available from high quality solar telescopes at excellent sites and with sophisticated post-focus instrumentation. A wealth of granular fine structure has become visible. Space allows only to mention few works: Collados et al. (1996) used the Vacuum Tower Telescope (VTT) at the Observatorio del Teide/Tenerife with a correlation tracker in its scanning mode to obtain two-dimensional (2D) spectroscopic information at high spatial and spectral resolution. They could produce maps in narrow wavelength bands to show the intensity and velocity fluctuations at various heights of the photosphere. Likewise, Nesis et al. (1997, 1999, and further references therein) exploited the VTT's high spatial and spectral resolution slit spectrograph to investigate the problem of turbulence generated by granular motions. Espagnet et al. (1993, 1995) obtained high quality data from the multi-channel subtractive double-pass (MSDP) spectrograph at the Pic du Midi solar telescope. They studied the height dependence of intensity and velocity fluctuations from various wavelength positions in the Na D2 line. A recent review on the solar granulation and its dynamics was presented by Muller (1999) who also references the results from the excellent data obtained with the Swedish solar telescope on San Miguel de la Palma.

The present contribution deals with the continuation of our efforts to reach highest possible spatial resolution from speckle methods combined with 2D spectroscopy by means of a wavelength scanning Fabry-Perot interferometer (FPI) (Krieg et al. 1999, henceforth Paper I). We shall present below an analysis of granular velocities - and their relation to the granular intensity pattern - in a 2D field of view obtained with image restoration techniques.

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© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000