Propagating Slow Sausage Waves in a Sunspot Observed by the New Vacuum Solar Telescope

Abstract

A sunspot is an ideal waveguide for a variety of magnetohydrodynamic waves, which carry a significant amount of energy to the upper atmosphere and could be used as a tool to probe magnetic and thermal structure of a sunspot. In this study, we used the New Vacuum Solar Telescope and took high-resolution image sequences simultaneously in both TiO (7058$\pm$10 Å) and H${}_{\alpha }$ (6562$\pm$2.5 Å) bandpasses. We extracted the area and total emission intensity variations of sunspot umbra and analyzed the signals with synchrosqueezing transform. We found that the area and emission intensity varied with both three and five minute periodicity. Moreover, the area and intensity oscillated in phase with each other, this fact hold in both TiO and H${}_{\alpha }$ data. We interpret this oscillatory signal as propagating slow sausage wave. The propagation speed is estimated at about 8 km$\cdot$s${}^{-1}$. We infer that this sunspot's umbra could have temperature as low as 2800--3500 K.

8 pages, 6 figures,1 table

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Cited by in corpus (6)

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• Diagnosing a Solar Flaring Core with Bidirectional Quasi-Periodic Fast Propagating Magnetoacoustic Waves
• Application of a magnetic-field-induced transition in Fe X to solar and stellar coronal magnetic field measurements
• Doppler shift oscillations of a sunspot detected by CYRA and IRIS
• Very long-periodic pulsations detected simultaneously in a white-light flare and sunspot penumbra
• Solar observation with the Fourier transform spectrometer I : Preliminary results of the visible and near-infrared solar spectrum