Evershed effect observed in various solar photospheric lines. I - Dependence of the velocity distribution across the penumbra on the equivalent width
Abstract
The spatial variations of the Evershed effect across a sunspot penumbra is investigated using 88 photospheric lines. It is found that the position where the Evershed velocity reaches a maximum varies systematically with the equivalent width of the absorption line; the stronger lines show the maximum velocity at a more outward position of the penumbra. As a result, the dependence of the Evershed velocity on the equivalent width gets weak at the outer edge of the penumbra, where the degree of the line asymmetry is also reduced. To interpret the variations of the Evershed effect across the penumbra, LTE calculations of line profiles are performed based on some inhomogeneous penumbral models. The observed change of the dependence of velocities on the equivalent widths can be well explained by assuming that the material flow occurs in dense filaments elevated in the photo sphere, while the density, therefore the opacity, of the flow channel decreases towards the outer edge of the penumbra. On the other hand, it is difficult to explain the observed characteristics by the model that the Evershed flow is confined in the deep layer and sinks down under the photo sphere at the outer border of the penumbra.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- 1987
- Bibcode:
- 1987PASJ...39..329I
- Keywords:
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- Gas Dynamics;
- Line Spectra;
- Penumbras;
- Solar Spectra;
- Spatial Distribution;
- Sunspots;
- Absorption Spectra;
- Photosphere;
- Spectral Line Width;
- Stellar Models;
- Velocity Distribution;
- Solar Physics