Research Note

Response to “Stray-light correction in 2D spectroscopy” by R. Schlichenmaier and M. Franz

¹ Institute for Solar Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
e-mail: scharmer@astro.su.se
² Stockholm Observatory, Dept. of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
³ Royal Swedish Academy of Sciences, 10405 Stockholm, Sweden

Received: 30 July 2013
Accepted: 8 October 2013

Abstract

We discuss a recent paper by Schlichenmaier & Franz (SF; 2013, A&A, 555, A84), in which the claim is made that the penumbral dark downflows detected for the first time with the Swedish 1-m Solar Telescope (SST) by Scharmer et al. and Joshi et al. could be produced by overcompensation for straylight. We show that the analysis of SF is fundamentally flawed, because it ignores the constraints on the strength of such straylight from 3D convection simulations and on the spatial extent of the straylight point spread function from the measured minimum intensity in the sunspot umbra. Furthermore, we show that the claim made by SF, that the spatial straylight of Hinode is less than 10%, is false. We conclude that the analysis of SF is of no relevance in relation to the straylight compensation method applied to the SST data.