The size distribution of magnetic bright points derived from Hinode/SOT observations

¹ IGAM/Institute of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria e-mail: dominik.utz@edu.uni-graz.at
² Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, 8042 Graz, Austria
³ Laboratoire d'Astrophysique de Toulouse et Tarbes, UMR 5572, CNRS et Université Paul Sabatier Toulouse 3, 57 avenue d'Azereix, 65000 Tarbes, France
⁴ Institute of Mathematics, University of Vienna, Nordbergstraße 15, 1090 Wien, Austria

Received: 27 August 2008
Accepted: 14 January 2009

Abstract

Context. Magnetic bright points (MBPs) are small-scale magnetic features in the solar photosphere. They may be a possible source of coronal heating by rapid footpoint motions that cause magnetohydrodynamical waves. The number and size distribution are of vital importance in estimating the small scale-magnetic-field energy.

Aims. The size distribution of MBPs is derived for G-band images acquired by the Hinode/SOT instrument.

Methods. For identification purposes, a new automated segmentation and identification algorithm was developed.

Results. For a sampling of 0.108 arcsec/pixel, we derived a mean diameter of  km for the MBPs. For the full resolved data set with a sampling of 0.054 arcsec/pixel, the size distribution shifted to a mean diameter of  km. The determined diameters are consistent with earlier published values. The shift is most probably due to the different spatial sampling.

Conclusions. We conclude that the smallest magnetic elements in the solar photosphere cannot yet be resolved by G-band observations. The influence of discretisation effects (sampling) has also not yet been investigated sufficiently.