Two-dimensional spectroscopy of sunspots. I. Intensity, velocity, and velocity power maps of a sunspot.

Details Two-dimensional spectroscopy of sunspots. I. Intensity, velocity, and velocity power maps of a sunspot. Two-dimensional spectroscopy of sunspots. I. Intensity, velocity, and velocity power maps of a sunspot.

Nov 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...315..603b&link_type=abstract

Astronomy and Astrophysics, v.315, p.603-609

Astronomy and Astrophysics

Astrophysics

30

Sunspots, Sun: Granulation, Oscillations

Scientific paper

A time series of two-dimensional spectra of a sunspot at θ=~45° has been obtained with a spectrometer based on a Fabry-Perot interferometer. From our observations in the FeI line at 709.04nm we find that the gas plasma in the vicinity of the sunspot (the moat) has a velocity of about 500m/s directed outwards. Nevertheless, the Evershed flow shows a sharp decrease by about 1000m/s at the outer boundary of the visible penumbra. The mean white-light image averaged over 1^h^52^m^ still shows radial structures in the penumbra, indicating their long lifetime. Spatial variations of the velocities and continuum intensities have correlation coefficients of +0.66 for the centre-side penumbra and -0.57 for the limb-side one. The correlation coefficients increase to +/-0.75 for the line-centre intensities. This correlation confirms that the Evershed effect is related to the dark filaments. Outside the spot, the long-time average images of the continuum and the line-centre intensities show a chain of bright dots with a size of about one arcsec and intensities up to 4.5% higher than their surroundings. These dots are related to the outer boundary of the velocity field in the moat. In the five-minute range, velocity power spectra show a decrease in the umbra and in the penumbra, but no dependence on the radial structure. In the range between eight and twenty minutes, power is present in the centre-side penumbra; it resembles that of granular areas, but it has a radial structure. In the umbra or the limb-side penumbra, the power values are much lower.

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