Global Oscillations at Low Frequency from the SOHO mission (GOLF) |
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| Authors: | A H Gabriel G Grec J Charra J -M Robillot T Roca Cortés S Turck-Chièze R Bocchia P Boumier M Cantin E Cespédes B Cougrand J Crétolle L Damé M Decaudin P Delache N Denis R Duc H Dzitko E Fossat J -J Fourmond R A García D Gough C Grivel J M Herreros H Lagardère J -P Moalic P L Pallé N Pétrou M Sanchez R Ulrich and H B van der Raay |
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| Institution: | (1) Institut d'Astrophysique Spatiale, CNRS/Université Paris XI, 91405 Orsay, France;(2) Département d'Astrophysique, CNRS URA 709, Université de Nice, 06034 Nice, France;(3) Observatoire de l'Université Bordeaux 1, BP 89, 33270 Floirac, France;(4) Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain;(5) Service d'Astrophysique, DSM/DAPNIA, CE Saclay, 91191 Gif-sur-Yvette, France;(6) Service d'Aéronomie, 91371 Verrières-le Buisson, France;(7) Observatoire de la Côte d'Azur, Lab. Cassini CNRS URA1362, 06304 Nice, France;(8) Dept. of Applied Math. and Theor. Physics, University of Cambridge, England;(9) Astronomy Department, University of California Los Angeles, U.S.A.;(10) Department of Physics, University of Birmingham, England |
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| Abstract: | 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. |
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| Keywords: | sun helioseismology |
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