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A. Fludra (Rutherford Appleton Laboratory, UK)
Sunspot plumes are compact features, located close to sunspots and bright in the transition region lines emitted between 1.7 \times 105 and 4\times 105~K. Observations of a sunspot plume in the active region AR8249 have been made with the Coronal Diagnostic Spectrometer (CDS) on SOHO with a 15-second time resolution. We report the finding of intensity oscillations of the O~V 629.7 Å\ line in the sunspot plume, with an amplitude up to 10 percent. Fourier analysis gives two periods of 167 and 182 seconds. Oscillations are also seen in the Ne~IV 543.9 Å, Ne~V 572.4 Å\ and Ne~VI 562.8 Å\ lines (1.7-4\times 105~K). Inspection of CDS data for several other sunspots shows that all sunspot plumes show the intensity oscillations of the O~V 629.7 Å\ line and other transition region lines in the 1.7-4\times 105~K temperature range.
This work was supported by the United Kingdom PPARC.
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