Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...298..260r&link_type=abstract
Astronomy and Astrophysics, v.298, p.260
Astronomy and Astrophysics
Astrophysics
85
Sun: Sunspots, Sun: Photosphere, Sun: Magnetic Fields
Scientific paper
We report on analysis of sunspot observations carried out with a narrow band (20mA) filter and present evidence that the Evershed effect is confined to thin loop-like structures which are elevated above the continuum height over most parts of the penumbra. The vertical extent of these loop structures is limited to approximately one photospheric scale height. The footpoints of these loop structures become visible in the velocity maps representing the deep photosphere and their sizes are <=0.5". The position of Evershed velocity filaments are well correlated with dark filaments seen in intensity maps, provided intensity and velocity signals compared originate from the same height in the photosphere. The continuum intensity and the velocity derived from the core shift of lines formed in the low photosphere show a significant correlation. However, no significant correlation is found between the continuum intensity and the velocity derived from the core shift of spectral lines of medium strength (FeI 5576 A) formed in the upper photosphere. The line profiles measured in Evershed velocity filaments show enhanced equivalent width and enhanced full-width-at-half-maximum (FWHM), indicating that a significant amount of microturbulence is present. We observe systematic differences in the inclination angle of the magnetic field vector between dark and bright filaments. Dark filaments are nearly horizontal while in bright filaments the field vector is more vertical with respect to the solar surface. The magnetic field strength shows little variation between dark and bright filaments. In penumbral grains, we observe a small upward motion on the order 100-200m/s. The line profile in bright penumbral structures is nearly symmetric, in contrast to the strongly asymmetric profile found in dark filaments.
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