Imaging Spectropolarimetry with IBIS. II. On the Fine Structure of G-band Bright Features

We present new results from first observations of the quiet solar photosphere performed through the Interferometric BIdimensional Spectrometer (IBIS) in spectropolarimetric mode. IBIS allowed us to measure the four Stokes parameters in the Fe I 630.15 nm and Fe I 630.25 nm lines with high spatial and spectral resolutions for 53 minutes; the polarimetric sensitivity achieved by the instrument is 3 × 10?3 the continuum intensity level. We focus on the correlation which emerges between the G-band bright feature brightness and magnetic filling factor of ∼103 G (kG) fields derived by inverting the Stokes I and V profiles. In more detail, wepresent the correlation first in a pixel-by-pixel study of a ≃3″ wide bright feature (a small network patch) and then we showthat such a result can be extended to all the bright features found in the data set at any instant of the time sequence. The higher the kilo-Gauss filling factor associated to a feature, the higher the brightness of the feature itself. Filling factors up to ≃35% are obtained for the brightest features. Considering the values of thefilling factors derived from the inversion analysis of spectropolarimetric data and the brightness variation observed in the G-band data we put forward an upper limit for the smallest scale over which magnetic flux concentrations in intergranular lanes produce a G-band brightness enhancement (≃0″.1). Moreover, the brightness saturation observed for feature sizes comparable to the resolution of the observations is compatible with the large G-band bright features being clusters of sub-arcsecond bright points. This conclusion deserves to be confirmed by forthcoming spectropolarimetric observations at higher spatial resolution.