Hinode/EIS observations of propagating low-frequency slow magnetoacoustic waves in fan-like coronal loops
Abstract
Aims: 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 Å line with the EUV Imaging Spectrometer (EIS) onboard Hinode. A new application of coronal seismology is provided based on this observation.
Methods: We analyzed the EIS sit-and-stare mode observation of oscillations using the running difference and wavelet techniques.
Results: Two harmonics with periods of 12 and 25 min are detected. We measured the Doppler shift amplitude of 1-2 km s-1, the relative intensity amplitude of 3%-5% and the apparent propagation speed of 100-120 km s-1.
Conclusions: 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 ± 8°, a true propagation speed of 128 ± 25 km s-1 and a temperature of 0.7 ± 0.3 MK near the loop's footpoint from our measurements.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 2009
- DOI:
- 10.1051/0004-6361/200912534
- arXiv:
- arXiv:0908.0310
- Bibcode:
- 2009A&A...503L..25W
- Keywords:
-
- Sun: atmosphere;
- Sun: corona;
- Sun: oscillations;
- Sun: UV radiation;
- waves;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Cosmology and Extragalactic Astrophysics
- E-Print:
- 4 pages and 4 figures, with 3 online figures and 1 online table