Plasma Condensation in coronal loops

Using temporal series data from the Coronal Diagnostic Spectrometer (CDS) on SOHO, we have detected plasma condensation within coronal loops through the use of spectroscopic analysis

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We find that, for the cooler lines of He I 584 A and O V 629 A there are sharp increases in intensity, accompanied by large blueshifted velocities. In the case of O V there is a substantial rebound to redshifted velocities when the strong brightening fades. The sharp increase in intensity and blueshifted velocity in the cooler lines is accompanied by a corresponding decrease in the intensity of the coronal lines (Mg X 624 A Fe XVI 360 A Si XII 520 A, but with no corresponding change in their velocity values implying an evacuation of plasma. From the Fourier analysis, evidence is found for possible 1st and 2nd harmonics in the He I and O V lines, indicative of standing waves in loops.

We conclude that we are seeing the first spectroscopic evidence of plasma condensation taking place in coronal loops. This work has been published in Astronomy and Astrophysics letters (A&A 475, L25-L28 (2007)

( E. O'Shea, D. Banerjee, J. G. Doyle)