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

Sensitivity of the GOLF signal to combined solar velocity and intensity variations

R.K. Ulrich ¹, R.A. García ², J.-M. Robillot ³, S. Turck-Chièze ², L. Bertello ¹, J. Charra ⁴, H. Dzitko ², A.H. Gabriel ⁴ and T. Roca Cortés <sup>5

1</sup> Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1562, USA
² Service d'Astrophysique, DSM/DAPNIA, CE Saclay, 91191 Gif-sur-Yvette, France
³ Observatoire de l'Université Bordeaux I, B.P. 89, 33270 Floirac, France
⁴ Institut d'Astrophysique Spatiale, CNRS/Université Paris XI, 91405 Orsay, France
⁵ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain

Received 10 May 1999 / Accepted 26 July 2000

Abstract

The GOLF instrument provides a stable and continuous measurement of the intensity of spatially integrated sunlight in one wing of the sodium D lines. Because the detected radiation results from atomic scattering, the GOLF signal can be traced to an atomic reference wavelength. The planned operations were to involve a form of relative photometry through the use of measurements on both the blue and red wings of the solar D lines of neutral sodium. However, due to the occasional malfunction of the polarization subsystem a "one wing photometric mode" operational alternative has been selected in order to ensure achievement of a 100 duty cycle. In this case, the signal observed consists of two photometric measurements at only one wing of each line of the sodium doublet separated by picometers (pm). The sodium cell system in GOLF combines photons scattered at three different wavelengths: one at D₁ and two at D₂. This paper developes a formalism to describe this system in terms of the solar spectral line profiles. A method of converting the one wing data to an effective velocity scale is presented. The method is applied to the nearly continuous 804 day sequence received from the GOLF instrument prior to the loss of telecommunications with SOHO on 24-June-1998. The resulting time sequence is part of the GOLF archive and can be made available to investigators. This publication describes some properties of this time series.

Key words: Sun: atmosphere Sun: oscillations

Send offprint requests to: R.K. Ulrich (ulrich@astro.ucla.edu)

This article contains no SIMBAD objects.

Contents

• 1. Introduction
  • 1.1. General background
  • 1.2. Velocity versus intensity
  • 1.3. Interaction of the instrument and solar line radiation
• 2. Scattering strengths
• 3. Determination of the magnetic modulation from two-wing observations
• 4. Corrections to the photomultiplier outputs
• 5. Conversion of the raw signal to a velocity scale
  • 5.1. General considerations
  • 5.2. Use of the magnetic modulation
  • 5.3. Correction for the working point wavelength variation due to sun-spacecraft velocity changes
• 6. Velocities and detrending
• 7. Results
  • 7.1. Power spectra
  • 7.2. Amplitude in the 5-minute band
• 8. Conclusions
• Acknowledgements
• Appendices
  • A: derivation of the solar line intensity as a function of
• References

© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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