Intensity oscillations in a sunspot plume

Abstract

Observations of a sunspot plume (a compact feature, bright in the transition region line of O V 629.7 Angstroms at 2.2 x 10(5) K), seen above a sunspot in the active region AR8249, have been made with a 15-second time resolution with the Coronal Diagnostic Spectrometer on SOHO. Intensity of the O V 629.7 Angstroms line in the sunspot plume oscillates with an amplitude of up to ten percent and periods of 167 and 182 seconds. The same oscillations are also seen in the Ne IV 543.9 Angstroms, Ne V 572.4 Angstroms and Ne VI 562.8 Angstroms lines (1.7-4x 10(5) K) but with a lower signal-to-noise ratio. Inspection of data for several other sunspots shows that all sunspot plumes show the intensity oscillations of the O V 629.7 Angstroms line and other transition region lines in the 1.7-4x 10(5) K temperature range.