Plasma condensation in coronal loops

被引：0

作者：

O'Shea, E. ^{[1
]}

Banerjee, D. ^{[2
]}

Doyle, J.G. ^{[1
]}

机构：

[1] Armagh Observatory, College Hill, Armagh BT61 9DG, United Kingdom

[2] Indian Institute of Astrophysics, II Block, Koramangala, Bangalore 560 034, India

来源：

Astronomy and Astrophysics | 2007年 / 475卷 / 02期

关键词：

Aims. Using temporal series data from the Coronal Diagnostic Spectrometer (CDS) on SOHO; we seek to investigate plasma condensation 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 Hel 584 Åand O V 629 Å; 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 × 624 Å; Fe XVI 360 Å; Si XII 520 Å); 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. Conclusions. We conclude that what we are seeing is the first spectroscopic evidence of plasma condensation taking place in coronal loops. © ESO 2007;

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Journal article (JA)

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