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Astron. Astrophys. 336, 743-752 (1998)

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1. Introduction

Oscillations in the solar photosphere and chromosphere had already been postulated about 50 years ago (Schwarzschild 1948), but it was not until the beginning of the 1960s (Leighton et al. 1962) that the first observational proof of their existence followed. Despite many successful attempts from theory and observation to further clarify their origin and the nature of the waves involved (e.g. Ulrich (1970) and Deubner (1975)), the oscillatory behaviour of the solar atmosphere still defies a fully satisfactory explanation. The persistent question of the heating of the solar chromosphere and corona also keeps calling for further efforts in this field.

No final answers to the challenge outlined above can be given here, but this paper contributes new observational results to this end. Some unexpected findings from two-dimensional observations obtained with high spatial resolution in the Na D2 line offer new aspects which will have to be considered in the ongoing discussion about chromospheric oscillations.

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© European Southern Observatory (ESO) 1998

Online publication: July 20, 1998