Intensity oscillations observed with Hinode near the south pole of the Sun: leakage of low frequency magneto-acoustic waves into the solar corona

• Published in: Astronomy and astrophysics (Berlin) 2008-04, Vol.481 (3), p.L95-L98
• Main Authors: Srivastava, A. K., Kuridze, D., Zaqarashvili, T. V., Dwivedi, B. N.
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; magnetohydrodynamics (MHD); Sun: corona; waves
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20079328

Aims. We study intensity oscillations in the solar chromosphere and corona, above a quiet-Sun magnetic network. Methods. We analyse the time series of He II 256.32 Å, Fe XI 188.23 Å and Fe XII 195.12 Å spectral lines, observed close to the south pole, by the EUV Imaging Spectrometer (EIS), onboard Hinode. We use a standard wavelet tool, to produce power spectra of intensity oscillations above the magnetic network. Results. For all spectral lines, we detect intensity oscillations of period of approximately seven minutes; and for the He II 256.32 Å line only, we detect an intensity oscillation of period of thirteen minutes, with a probability of approximately 96-98%, which provides the most likely signature of magneto-acoustic wave propagation above the network. Conclusions. We propose that field-free cavity areas under bipolar magnetic canopies, in the vicinity of a magnetic network, are likely to serve as resonators for the magneto-acoustic waves. The cavities with photospheric sound-speed, and granular dimensions, can produce waves with observed periods. These waves may propagate upwards in the transition region/corona and cause observed intensity oscillations.