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Astronomy & Astrophysics manuscript no. 8617lett c ESO 2007 October 4, 2007

Summary: Astronomy & Astrophysics manuscript no. 8617lett c ESO 2007
October 4, 2007
Plasma condensation in coronal loops
E. O'Shea1, D. Banerjee2, and J.G. Doyle1
Armagh Observatory, College Hill, Armagh BT61 9DG, N.Ireland
e-mail: eos@arm.ac.uk
Indian Institute of Astrophysics, II Block, Koramangala, Bangalore 560 034, India
Aims. Using temporal series data from the Coronal Diagnostic Spectrometer (CDS) on SOHO, we seek to investigate plasma conden-
sation through the use of spectroscopic analysis.
Methods. Using a space-time (X-T) type plot we show, for a number of transition region (TR) and coronal lines, the variation of
intensity (radiant flux) with time in an off-limb loop system. Noting a number of pixels where the intensity shows a sharp jump in
value for the TR lines and a corresponding sharp decrease for the coronal lines, we investigate further and plot the intensity and
velocity for these pixels as a function of time. Using standard Fourier techniques, together with a pre-whitening method, we measure
all statistically significant frequencies present in the time series so created.
Results. We find that, for the cooler lines of He I 584 and O V 629 , 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


Source: Armagh Observatory


Collections: Physics