Letter to the Editor

Suppression of convection around small magnetic concentrations

¹ Department of Astronomy, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan e-mail: shuji.morinaga@nao.ac.jp
² National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³ Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁴ Nobeyama Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Minamisaku, Nagano 384-1305, Japan

Received: 8 November 2007
Accepted: 16 January 2008

Abstract

Aims. It is well known that convective motions in the photosphere are suppressed by magnetic fields. However, it has been difficult to study the interaction between convection and small magnetic features, such as G-band bright points (GBPs) or pores with polarimetric measurements, because of the available spatial resolution (~1´´). This situation is changed by the advent of the Spectro-Polarimeter (SP) aboard the Hinode satellite, which has 0 3 spatial resolution.

Methods. We analyzed the pore and its surrounding region in NOAA 10940 near the disk center. We obtained the field strength and filling factor through the Milne-Eddington inversion of the Stokes profiles. We also derived the line-of-sight velocity by the shift of the line core. Using these physical parameters, we investigated the physical conditions needed to suppress the convection.

Results. We found that the convection is suppressed, not by the strength of the magnetic field itself, but by high concentration of magnetic flux tubes. We also found that GBPs and pores are distinguished in terms of the filling factor (f); for GBPs and –0.9 for pores.