Photospheric magnetic field and chromospheric emission

We present a statistical analysis of network and internetwork properties in the photosphere and the chromosphere. For the first time we simultaneously observed (a) the four Stokes parameters of the photospheric iron line pair at 630.2 nm and (b) the intensity profile of the Ca H line at 396.8 nm. The vector magnetic field was inferred from the inversion of the iron lines. We aim at an understanding of the coupling between photospheric magnetic field and chromospheric emission. 1 Observations and data reduction We observed a series of 13 maps of a network region and the surrounding quiet Sun at a heliocentric angle of 53, close to the active region NOAA 10675 on September 27, 2004, with POLIS (Schmidt et al. 2003; Beck et al. 2005) at the German VTT in Tenerife. The Kiepenheuer Adaptive Optics System (KAOS) was used to improve spatial resolution to about 1 arcsec (von der Lühe et al. 2003). Using the average profile of each map, we normalized the intensity at the line wing at 396.490 nm to the FTS profile (Stenflo et al. 1984). ¿From the intensity profile of Ca H we define line properties like, e.g., the H-index, which is the integral around the line core from 396.8 nm to 396.9 nm. The separation between network and internetwork is based on (i) the maps of magnetic flux density, (ii) the presence of Stokes-V signals and emission in Ca H. 2 Inversion An inversion was performed for the two iron lines at 630 nm using the SIR code (Ruiz Cobo & del Toro Iniesta 1992). To mimic unresolved magnetic fields, we used a model atmosphere with one magnetic and one field-free component, plus stray light. The inversion yields a magnetic field vector, a line-of-sight velocity, and the magnetic flux per pixel. These quantities are constant along the line of sight. Using the flux density maps, we created a mask to separate network and internetwork regions. 3 Magnetic field distribution The polarization signal in Q(λ), U(λ), and V(λ) is normalized by the local continuum intensity, Ic, for each pixel. The rms noise level of the Stokes parameters in the continuum 2 R. Rezaei et al.: Photospheric magnetic field and chromospheric emission Figure 1. Top to buttom: the continuum intensity close to 630 nm, the H-index, and the magnetic flux density obtained from the inversion. 0.2 0.4 0.6 0.8 1.0 1.2 1.4 B (kG) 0 2 4 6 8 10