Dual-line spectral and phase analysis of sunspot oscillations

Abstract

Context. Sunspots exhibit a wide range of oscillatory phenomena within their umbrae and penumbrae. Aims. We investigate the behavior of intensity and Doppler velocity oscillations in the umbra and the penumbra to study sunspot oscillations and their associations.Methods. Simultaneous, high-cadence (8 s), two-dimensional, Ca ii 8542 Å and Hα 6563 Å observations are used. Doppler velocity and intensity variations are studied with a wavelet spectral, phase difference and coherence analysis, both at distinct positions and within the whole umbra and the penumbra. Results. The analysis reveals the presence of several umbral flashes (UFs) that seem to fill the whole umbra. The spectral analysis indicates oscillating elements of size 2.5 to 5 within the umbra with periods around the 3-min band and oscillation periods around the 5-min band within the penumbra. Two remarkable jumps of the oscillation period and the intensity-velocity phase difference are present at both umbra-penumbra and penumbra-superpenumbra boundaries reflecting a drastic change in physical and/or magnetic conditions. The intensity-velocity phase analysis shows a delay of the intensity response to the velocity variations in accordance with the physics of the observed sawtooth velocity behavior. Most of the UFs oscillate incoherently, while the calmest umbral area seems to be associated with velocity spreading from neighboring UFs. The derived incoherency among UFs in conjunction with the existence of coherently oscillating elements within the umbra suggests the presence of umbral areas with slightly different physical and/or magnetic field conditions. Conclusions. The presented analysis provides further important constraints for realistic models and theoretical interpretations describing sunspot oscillations.

Dynamics of the solar atmosphere above a pore with a light bridge

“…At R ∼ 1.5 (the visible umbral boundary), the frequencies higher than 4 mHz essentially disappear from the power spectrum and all the power is shifted towards 2−3 mHz with a second power bulk at frequencies below 1 mHz, where plasma motions dominate. This is similar to the change in frequencies found by Tziotziou et al (2007) at the penumbra-superpenumbra boundary (Fig. 6 of that paper).…”

“…In the Hα line centre the waves appear to propagate beyond the outer edge of the penumbra to the superpenumbra. Distinct morphological parts of the evolved sunspot (umbra, penumbra, superpenumbra) seem to have different seismic properties (Tziotziou et al 2007). The oscillation power spectrum and the running penumbral waves might possibly be used to indicate the presence of a superpenumbra also in the case of pores.…”

Oscillations and Waves in Sunspots

“…As was discussed in Sections 2, 3 and 5, the power of velocity and intensity oscillations is distributed in a complex way across the sunspot umbra, penumbra and the surrounding plage regions (Jain and Haber, 2002;Tziotziou et al, 2007;Nagashima et al, 2007;Mathew, 2008;Jess et al, 2013).…”

Fast imaging spectroscopy with MSDP spectrometers. Vector magnetic maps with THEMIS/MSDP

“…and mode 2 for H α . Thanks to the good seeing of Tenerife, many topics were investigated, either with H α alone, such as the dynamics of arch filament systems (Mein et al 1996) and the non-LTE inversion of prominence profiles (Molowny-Horas et al 1999), or with H α and 854.2 CaII, such as asymmetries of flare profiles (Mein et al 1997) and Fourier analysis of sunspot oscillations (Tziotziou et al 2007).…”

“…But velocity fields and magnetic fields observed at high levels strongly depend on photospheric values, so spectropolarimetry of different wavelength ranges are often required. Time scales smaller than one minute characterize local events such as the triggering of waves across sunspots (Tziotziou et al 2007) or emerging fluxes and Ellerman bombs in active regions (Pariat et al 2007). But short time scales not only concern small-size events.…”