The magnetic canopy above light bridges

¹ Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic e-mail: jurcak@asu.cas.cz
² Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain

Received: 4 November 2005
Accepted: 26 January 2006

Abstract

An analysis of high-resolution Stokes observations of two light bridges in active region NOAA 8990 is presented. The observations were recorded with the La Palma Stokes Polarimeter attached to the Swedish Vacuum Solar Telescope. The stratification over the solar atmosphere of different physical parameters is retrieved from these data using the Stokes inversion based on response functions (SIR). Our results confirm previous observations of features such as the decrease in magnetic field strength and the increase in inclination in the light bridges. We also confirm a temperature increase in these structures with respect to the surrounding umbrae. The maps of the magnetic field strength and of the orientation of the magnetic field vector indicate the presence of a canopy structure above the light bridges. We derive the vertical component of electric current density (J_z) from the configuration of the magnetic field. The increased temperature found in the upper layers is studied in the context of the proposed canopy topology and could also explain the recently observed chromospheric heating processes found above light bridges.