Hinode/EIS observations of propagating low-frequency slow magnetoacoustic waves in fan-like coronal loops

Details Hinode/EIS observations of propagating low-frequency slow magnetoacoustic waves in fan-like coronal loops Hinode/EIS observations of propagating low-frequency slow magnetoacoustic waves in fan-like coronal loops

2009-08-03

arxiv.org/abs/0908.0310v1

Astronomy and Astrophysics, Volume 503, Issue 3, 2009, pp.L25-L28

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

4 pages and 4 figures, with 3 online figures and 1 online table; Astron & Astrophys Letter, in press

Scientific paper

10.1051/0004-6361/200912534

We report the first observation of multiple-periodic propagating disturbances along a fan-like coronal structure simultaneously detected in both intensity and Doppler shift in the Fe XII 195 A line with the EUV Imaging Spectrometer (EIS) onboard Hinode. A new application of coronal seismology is provided based on this observation. We analyzed the EIS sit-and-stare mode observation of oscillations using the running difference and wavelet techniques. Two harmonics with periods of 12 and 25 min are detected. We measured the Doppler shift amplitude of 1-2 km/s, the relative intensity amplitude of 3%-5% and the apparent propagation speed of 100-120 km/s. The amplitude relationship between intensity and Doppler shift oscillations provides convincing evidence that these propagating features are a manifestation of slow magnetoacoustic waves. Detection lengths (over which the waves are visible) of the 25 min wave are about 70-90 Mm, much longer than those of the 5 min wave previously detected by TRACE. This difference may be explained by the dependence of damping length on the wave period for thermal conduction. Based on a linear wave theory, we derive an inclination of the magnetic field to the line-of-sight about 59$\pm$8 deg, a true propagation speed of 128$\pm$25 km/s and a temperature of 0.7$\pm$0.3 MK near the loop's footpoint from our measurements.

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