EDP Sciences
Free access
Volume 385, Number 1, April I 2002
Page(s) 264 - 272
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20020081

A&A 385, 264-272 (2002)
DOI: 10.1051/0004-6361:20020081

Weak magnetic flux features on the Sun

B. Hartje and F. Kneer

Universitäts-Sternwarte, Geismarlandstraße 11, 37083 Göttingen, Germany

(Received 16 November 2001 / Accepted 15 January 2002 )

We observed weak magnetic flux in enhanced Ca K network and in its surroundings at various positions on the solar disc ( $\cos\theta=1.0\dots0.1$). The Gregory Coudé Telescope at the Observatorio del Teide on Tenerife was used together with an image scanner and a Stokes V polarimeter. ${1\over2}(I_\lambda\pm V_\lambda)$ spectrograms in the 6302 Å region were taken. A second order flat fielding and smoothing brought the polarimetric sensitivity to a detection limit of 0.001  Ic (with Ic = continuum intensity) for exposure times of 300 ms in pixels corresponding to 0 $\farcs$ $5\times$0 $\farcs$19 ( $\widehat=$ slit width  $\times$ pixel size of detector). We present correlations between continuum intensity, line center intensity, and magnetic flux and discuss Stokes V profiles. The V amplitude asymmetry from areas with strong flux decreases towards the limb, a change of sign is not identified. The magnetic fields are ordered around strong flux centers with decreasing mean field strength outwards from the centers. In the range of $1\times 10^{16}$ Mx to $5\times 10^{16}$ Mx (in one pixel of $5\times 10^{14}$ cm 2) the probability distribution of the magnetic flux is ~ $\vert\Phi\vert^{-q}$ with $q\approx3$, different from a Gaussian distribution. From this we derive tentativily a radial dependence from the flux centers of the form $\Phi(r)\sim1/r$. For the probability distributions a significant center-to-limb variation is not detected. Together with the center-to-limb behaviour of the asymmetries, we interpret this tentatively as an isotropic orientation of the weak magnetic flux elements and of the gas flows. A vertical orientation of the magnetic fields is also compatible with the measurements, though.

Key words: Sun: photosphere -- magnetic fields -- techniques: polarimetric

Offprint request: F. Kneer, kneer@uni-sw.gwdg.de

© ESO 2002