The Magnetic Configuration of a δ-Spot

摘要

Sunspots, which harbor both magnetic polarities within one penumbra, are called δ-spots. They are often associated with flares. Nevertheless, there are only very few detailed observations of the spatially resolved magnetic field configuration. We present an investigation performed with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope in Tenerife. We observed a sunspot with a main umbra and several additional umbral cores, one of them with opposite magnetic polarity (the δ- umbra). The δ-spot is divided into two parts by a line along which central emissions of the spectral line Ca II 854.2 nm appear. The Evershed flow comming from the main umbra ends at this line. In deep photospheric layers, we find an almost vertical magnetic field for the δ-umbra, and the magnetic field decreases rapidly with height, faster than in the main umbra. The horizontal magnetic field in the direction connecting main and δ-umbra is rather smooth, but in one location next to a bright penumbral feature at some distance to the δ-umbra, we encounter a change of the magnetic azimuth by 90° from one pixel to the next. Near the δ-umbra, but just outside, we encounter a blue-shift of the spectral line profiles which we interpret as Evershed flow away from the δ-umbra. Significant electric current densities are observed at the dividing line of the spot and inside the δ-umbra.