Computer Science – Sound
Scientific paper
Jan 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004iaus..219..717w&link_type=abstract
Stars as suns : activity, evolution and planets, Proceedings of the 219th symposium of the International Astronomical Union held
Computer Science
Sound
3
Scientific paper
We give an extensive overview of Doppler shift oscillations in hot active region loops obtained with SUMER. The oscillations are detected in loops observed 50-100 arcsec off the limb of the Sun in ultraviolet lines Fe XIX and Fe XXI. We measure physical parameters of 54 Doppler shift oscillations in 27 flare-like events and give geometric parameters of the associated hot loops when soft X-ray images are available. The oscillations have periods in the range 7-31 min with decay times 5.5-37.3 min and show an initial large Doppler shift pulse with peak velocities up to 200 km/s. Unlike TRACE oscillations they are mostly not triggered by large flares and may recur 2-3 times within a couple of hours. We have found various lines of evidence to support an interpretation of these oscillations in terms of slow magnetoacoustic standing waves in hot loops: (1) the intensity fluctuation lags the Doppler shifts by 1/4 period; (2) the phase speeds derived from observed periods and loop lengths roughly agree with the sound speed; (3) the dissipation time scales with period in accordance with the expectations of slow waves. We will also discuss the excitation and damping mechanisms of these oscillations.
Huang Guang Li
Wu Haibin
Xu Fanrong
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