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Title:
Ca II 8542 Å sunspot oscillations observed with THEMIS
Authors:
Tziotziou, K.; Tsiropoula, G.; Mein, P.
Affiliation:
AA(Observatoire de Paris, Section de Meudon, DASOP, 92195 Meudon Principal Cedex, France ), AB(National Observatory of Athens, Institute for Space Applications and Remote Sensing, 15236 Palea Penteli, Greece ), AC(Observatoire de Paris, Section de Meudon, DASOP, 92195 Meudon Principal Cedex, France )
Publication:
Astronomy and Astrophysics, v.381, p.279-289 (2002) (A&A Homepage)
Publication Date:
01/2002
Origin:
A&A
Astronomy Keywords:
SUN: CHROMOSPHERE, SUN: OSCILLATIONS, SUN: SUNSPOTS
DOI:
10.1051/0004-6361:20011419
Bibliographic Code:
2002A&A...381..279T

Abstract

Oscillations in the umbra and the penumbra of an isolated sunspot located near the solar disk centre were investigated. The observations were obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph operating in the Ca Ii 8542 Å line and installed at the focus of THEMIS (Tenerife). From the MSDP data, two-dimensional intensity and Doppler shift images were computed at different wavelengths within the line. Intensity and Doppler shift oscillations in the umbra and the penumbra of the sunspot showing up as umbral flashes and penumbral waves were analyzed using a 23 min time series with a cadence of 46 s. The Ca Ii umbral flash intensity profile shows an emission core in its blue wing. We investigate the relation between umbral flashes and running penumbral waves by a power spectrum analysis which shows a 6 mHz frequency for the standing umbral oscillations (flashes) which are observed only on the upper half part of the umbra. The running penumbral waves propagate with an average phase velocity of 16 km s-1 and their frequency is constant in the penumbra and equal to 3 mHz. Although the time slice images suggest that umbral flashes and running penumbral waves are probably due to the same resonator, the power analysis shows no direct relationship between the two phenomena. Based on observations made with the THEMIS telescope operated on the island of Tenerife by CNRS-CNR in the Spanish Observatorio del Teide of the Instituto de Astrof{ísica de Canarias.
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