INTENSITY, VELOCITY AND MAGNETIC STRUCTURE OF A SUNSPOT REGION .4. PROPERTIES OF A UNIPOLAR SUNSPOT

From an investigation of spectra in a magnetically sensitive (λ 6173, g = 2.5) and insensitive line (λ 5576, g = 0), we derived the following properties for a symmetrical sunspot: (a) The magnetic field strength varies with the distance ρ(ρ ≤ 1) from the sunspot center like H(ρ) = H(0) (1 + ρ2)-1 (b) The zenith angle of the magnetic field varies like 90°ρ. From this and from H(ρ) we find a height gradient of 0.5 gs/km at ρ = 0. (c) The equivalent width and the half width of λ 5576 show an increase in penumbral regions of maximum Evershed flow. Most likely this is due to a combination of inhomogeneities in the Evershed flow and 'microturbulence'. (d) We find the magnetic field strength to be larger in the dark interfilamentary regions of the penumbra. These regions move downwards with respect to the bright filaments and probably have a more horizontal magnetic field. (e) In a weak light bridge and in extensions of bright penumbral filaments into the umbra, we find a decrease of the magnetic field strength, and a more horizontal field direction with respect to the umbral surrounding. li(f) © 1969 D. Reidel Publishing Company.