Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006a%26a...456..689t&link_type=abstract
Astronomy and Astrophysics, Volume 456, Issue 2, September III 2006, pp.689-695
Astronomy and Astrophysics
Astrophysics
18
Sun: Chromosphere, Sun: Oscillations, Sun: Sunspots
Scientific paper
Context: .Umbral flashes (UFs) and running penumbral (RP) waves are believed to be closely related oscillatory phenomena of sunspots. Aims: .We investigate the association of UFs and RP waves to see whether the latter are a visual pattern created by a common source with UFs or a trans-sunspot wave driven by UFs. Methods: .Simultaneous, two-dimensional, dual-line observations in Ca II 8542 Å and Hα 6563 Å, obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph mounted on the German VTT at Teide Observatory on Tenerife, are used for this study. High-cadence 8 s Doppler velocity images, spectrograms, and spectral-analysis results are used to study the characteristics and the relationship of UFs and RP waves. Results: .Several UFs were observed that seem to fill the whole umbra. Doppler velocity variations with time indicate a shock behaviour for UFs, as well as for umbral and RP waves and a smooth continuous propagation of the latter from the umbra through the umbra-penumbra boundary out to the edge of the penumbra. Furthermore, the spectral analysis shows a decreasing oscillatory frequency as we move from the umbra outwards and a jump at the umbra-penumbra boundary that could possibly reflect, apart from a change in physical conditions, a drastic change of the magnetic field inclination with respect to the vertical. Conclusions: .The results do not permit us to convincingly support one scenario over the other (i.e. visual pattern vs. trans-sunspot wave) for RP waves; however, they do provide important constraints for future models of sunspot oscillations and RP waves.
Mein Nicole
Mein Pierre
Tsiropoula Georgia
Tziotziou Kostas
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