Two-dimensional spectroscopy of sunspots

II. Search for propagating waves and drifting velocity filaments in photospheric layers

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: hbalthasar@aip.de
² Kiepenheuer-Institut für Sonnenphysik, Schöneckstr 6, 79104 Freiburg, Germany e-mail: hschleicher@kis.uni-freiburg.de

Received: 13 July 2007
Accepted: 20 November 2007

Abstract

Aims. Running penumbral waves are often reported from observations in chromospheric lines or lines formed in the upper photosphere. In this work we investigate whether they can be detected in a line formed in the mid to lower photosphere.

Methods. We used time series of two-dimensional spectra of an iron line that is insensitive to the magnetic field and that is formed in the lower to mid photosphere.

Results. No running penumbral waves are detected in this line formed in the lower and mid photosphere. In the moat, outward moving velocity features are detected. They are slightly faster than the plasma motions but much slower than running penumbral waves.

Conclusions. Running penumbral waves are a phenomenon occurring in higher layers, i.e. the lower chromosphere and the upper photosphere, but not in the mid photosphere or below. In the moat, we found long-living filamentary velocity features drifting outwards.