Letter to the Editor

The intensity contrast of solar granulation: comparing Hinode SP results with MHD simulations

¹ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Straße 2, 37191 Katlenburg-Lindau, Germany e-mail: danilovic@mps.mpg.de
² Sterrekundig Instituut, Utrecht University, Postbus 80 000, 3508 TA Utrecht, The Netherlands
³ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Received: 27 March 2008
Accepted: 16 April 2008

Abstract

Context. The contrast of granulation is an important quantity characterizing solar surface convection.

Aims. We compare the intensity contrast at 630 nm, observed using the Spectro-Polarimeter (SP) aboard the Hinode satellite, with the 3D radiative MHD simulations of Vögler & Schüssler (2007, A&A, 465, L43).

Methods. A synthetic image from the simulation is degraded using a theoretical point-spread function of the optical system, and by considering other important effects.

Results. The telescope aperture and the obscuration by the secondary mirror and its attachment spider, reduce the simulated contrast from 14.4% to 8.5%. A slight effective defocus of the instrument brings the simulated contrast down to 7.5%, close to the observed value of 7.0%.

Conclusions. A proper consideration of the effects of the optical system and a slight defocus, lead to sufficient degradation of the synthetic image from the MHD simulation, such that the contrast reaches almost the observed value. The remaining small discrepancy can be ascribed to straylight and slight imperfections of the instrument, which are difficult to model. Hence, Hinode SP data are consistent with a granulation contrast which is predicted by 3D radiation MHD simulations.