Influence of a sunspot penumbra on the oscillatory regime of neighboring regions

The spectra of radial-velocity oscillations in the immediate vicinity of a sunspot beyond the observable boundary of the penumbra have been analyzed. The radial velocities were derived using a differential method. The oscillation spectra at two heights (lower photosphere and chromosphere) were compared with reference spectra for the middle penumbra and an unperturbed region obtained using the same method. The oscillatory regime characteristic of the sunspot penumbra extends more than 15″ beyond its observable boundary. It is proposed that deep photospheric layers in the region surrounding the penumbra have physical conditions similar to those observed inside its outer boundary.