Near-infrared spectropolarimetry of a δ-spot

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: hbalthasar@aip.de
² National Solar Observatory/Sacramento Peak, PO Box 62, Sunspot NM 88349, USA
³ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Straße 2, 37191 Katlenburg-Lindau, Germany

Received: 10 December 2013
Accepted: 16 January 2014

Abstract

Sunspots harboring umbrae of both magnetic polarities within a common penumbra (δ-spots) are often but not always related to flares. We present first near-infrared observations (Fe i λ1078.3 nm and Si i λ1078.6 nm spectra) obtained with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope in Tenerife on 2012 June 17, which afford accurate and sensitive diagnostics to scrutinize the complex fields along the magnetic neutral line of a δ-spot within active region NOAA 11504. We examined the vector magnetic field, line-of-sight (LOS) velocities, and horizontal proper motions of this rather inactive δ-spot. We find a smooth transition of the magnetic vector field from the main umbra to that of opposite polarity (δ-umbra), but a discontinuity of the horizontal magnetic field at some distance from the δ-umbra on the polarity inversion line. The magnetic field decreases faster with height by a factor of two above the δ-umbra. The latter is surrounded by its own Evershed flow. The Evershed flow coming from the main umbra ends at a line dividing the spot into two parts. This line is marked by the occurrence of central emission in the Ca iiλ854.2 nm line. Along this line, high chromospheric LOS-velocities of both signs appear. We detect a shear flow within the horizontal flux transport velocities parallel to the dividing line.