Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...276..227f&link_type=abstract
Astronomy and Astrophysics, Vol. 276, p. 227 (1993)
Astronomy and Astrophysics
Astrophysics
4
Sun: Sunspots, Atmospheric Effects, Sun: Oscillations
Scientific paper
Oscillations in sunspots near the solar limb were observed by measuring the variation of their geometric distance to a reference point (the limb) on time series of spectrograms. Observations carried out with this recently introduced technique are quite sensitive to seeing variations. Therefore we present a simple model to estimate the influence of seeing effects on the observations quantitatively. It turns out, that under poor seeing conditions the seeing-induced variations of the spot's position are of the same order of magnitude as the expected displacements due to oscillations. The strong influence of the seeing is clearly demonstrated for a series, which was obtained at the Capri station under unfavourable seeing conditions, in the frequency range where solar oscillations are expected.
A second sunspot was observed simultaneously under good seeing conditions in Hα, Hβ, the nearby Fe I 4860 Å line and in the continuum with the VTT equipment on Tenerife. As a result we find evidence for unusual non-photo spheric umbral oscillations in the range of 0.7±0.5 mHz and 3.5±0.5 mHz.
Federspiel Martin
Mattig Wolfgang
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