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Astron. Astrophys. 364, 799-815 (2000)

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8. Conclusions

This paper has developed a method for converting the signal from the GOLF instrument provided in its "one-wing" mode of operation into a quantity having dimensions of a velocity. An important time sequence is used from the "two-wing" period of operations to constrain the amplitude of the magnetic modulation. A formalism is presented to describe the three components of the scattered light and the interaction between their wavelengths and those of the solar absorption lines. The primary result of the method is to provide a sensitivity function [FORMULA] which converts fractional photometric intensity deviations into a velocity. Such a method requires a reference intensity in order to calculate a deviation. We have presented a model of the GOLF signal which permits the retention of deviations having periods up to 45 days. The reference signal can also be obtained by temporally smoothing the photometric intensity and in this case the same sensitivity function continues to be appropriate.

Using the uniform treatment of the instrument for all time scales between 80 seconds and 80 days, we have provided an estimation of the shape of the sun's power spectrum. While uncertainties remain as to the relative importance of intensity and velocity contributions at low frequencies, the break in the power spectrum found at 25 µHz suggests that active region effects should be small in the frequency band between 100 and 1000 µHz. The very small variation found in the rms amplitude of the oscillatory signal as a function of sun-spacecraft shows that the kinetic energy density of the oscillation decreases with altitude. This is a consequence of the evanescent character of the acoustic oscillations in the photospheric layers combined with extra damping.

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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