Global Oscillations at Low Frequency from the SOHO mission (GOLF)

The GOLF experiment on the SOHO mission aims to study the internal structure of the sun by measuring the spectrum of global oscillations in the frequency range 10−7 to 10−2 Hz. Bothp andg mode oscillations will be investigated, with the emphasis on the low order long period waves which penetrate the solar core. The instrument employs an extension to space of the proven ground-based technique for measuring the mean line-of-sight velocity of the viewed solar surface. By avoiding the atmospheric disturbances experienced from the ground, and choosing a non-eclipsing orbit, GOLF aims to improve the instrumental sensitivity limit by an order of magnitude to 1 mm s−1 over 20 days for frequencies higher than 2.10−4 Hz. A sodium vapour resonance cell is used in a longitudinal magnetic field to sample the two wings of the solar absorption line. The addition of a small modulating field component enables the slope of the wings to be measured. This provides not only an internal calibration of the instrument sensitivity, but also offers a further possibility to recognise, and correct for, the solar background signal produced by the effects of solar magnetically active regions. The use of an additional rotating polariser enables measurement of the mean solar line-of-sight magnetic field, as a secondary objective.

[1]  T. Brown,et al.  p-mode frequency variation in relation to global solar activity , 1993 .

[2]  E. Fossat,et al.  Solar oscillations: full disk observations from the geographic South Pole , 1980, Nature.

[3]  A. J. Miller,et al.  Developing a stratospheric climatology from NMC analyses , 1984 .

[4]  Kenneth G. Libbrecht,et al.  Solar p-mode phenomenology , 1988 .

[5]  J. Kuhn,et al.  Short-term changes in solar oscillation frequencies and solar activity , 1991 .

[6]  A. Claverie,et al.  Solar structure from global studies of the 5-minute oscillation , 1979, Nature.

[7]  P. Delache,et al.  Time Correlation between Solar Structural Parameters: p-Mode Frequencies, Radius, and Neutrino Flux , 1993 .

[8]  P. Pallé,et al.  Variations of the Low l Solar Acoustic Spectrum Correlated with the Activity Cycle , 1990 .

[9]  P. Pallé,et al.  Solar cycle induced variations of the low l solar acoustic spectrum , 1989 .

[10]  P. Pallé,et al.  The search for solar gravity modes , 1991 .

[11]  Y. Elsworth,et al.  Variation of low-order acoustic solar oscillations over the solar cycle , 1990, Nature.

[12]  D. Vignaud,et al.  The solar interior , 1993 .

[13]  P. Pallé,et al.  Variation of the Frequencies of Very Low L p-Modes , 1994 .

[14]  P. Boumier,et al.  Golf: A resonance spectrometer for the observation of solar oscillations I) Numerical model of the sodium cell response , 1993 .

[15]  J. Harvey,et al.  Observations of solar oscillations of low and intermediate degree , 1983, Nature.