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Issue A&A
Volume 481, Number 1, April I 2008
Science with Hinode
Page(s) L1 - L4
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20079042
Published online 25 January 2008



A&A 481, L1-L4 (2008)
DOI: 10.1051/0004-6361:20079042

Letter

Properties of high-degree oscillation modes of the Sun observed with Hinode/SOT

U. Mitra-Kraev1, A.G. Kosovichev2, and T. Sekii3

1  University of Sheffield, Department of Applied Mathematics, Hicks Building, Sheffield S3 7RH, UK
    e-mail: U.MitraKraev@sheffield.ac.uk
2  W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
3  National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan

(Received 9 November 2007 / Accepted 6 January 2008)

Abstract
Aims.With the Solar Optical Telescope on Hinode, we investigate the basic properties of high-degree solar oscillations observed at two levels in the solar atmosphere, in the G-band (formed in the photosphere) and in the $\ion{Ca}{ii}$ H line (chromospheric emission).
Methods.We analyzed the data by calculating the individual power spectra as well as the cross-spectral properties, i.e., coherence and phase shift. The observational properties are compared with a simple theoretical model, which includes the effects of correlated noise.
Results.The results reveal significant frequency shifts between the $\ion{Ca}{ii}$ H and G-band spectra, in particular above the acoustic cut-off frequency for pseudo-modes. The cross-spectrum phase shows peaks associated with the acoustic oscillation (p-mode) lines, and begins to increase with frequency around the acoustic cut-off. However, we find no phase shift for the (surface gravity wave) f-mode. The observed properties for the p-modes are qualitatively reproduced in a simple model with a correlated background if the correlated noise level in the $\ion{Ca}{ii}$ H data is higher than in the G-band data. These results suggest that multi-wavelength observations of solar oscillations, in combination with the traditional intensity-velocity observations, may help to determine the level of the correlated background noise and to determine the type of wave excitation sources on the Sun.


Key words: Sun: atmosphere -- Sun: granulation -- Sun: helioseismology -- Sun: oscillations



© ESO 2008


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