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Astron. Astrophys. 364, 816-828 (2000)


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Simulation of resonance scattering helioseismometer signals from spatially resolved images: Application to the GOLF instrument on SOHO

R.K. Ulrich 1, P. Boumier 2, J.-M. Robillot 3, R.A. García 4, T. Roca Cortés 5 and C.J. Henney 6

1 UCLA, Department of Physics & Astronomy, Los Angeles, CA 90095-1562, USA
2 Institut d'Astrophysique Spatiale, Orsay, France
3 Observatoire de l'Université de Bordeaux I, Bordeaux, Floirac, France
4 Service d'Astrophyique, C.E.A., Saclay, France
5 Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
6 National Solar Observatory, 950 North Cherry Avenue, Tucson, AZ 85726-6732, USA

Received 10 May 2000 / Accepted 8 September 2000

Abstract

A step in the analysis of the data from the GOLF (Global Oscillations at Low Frequency) instrument on SOHO (SOlar and Heliospheric Observatory, an ESA/NASA Mission) involves the calculation of the sensitivity of the GOLF signal to the velocity at each point on the solar surface. A successful model of this sort will permit the intercomparison of data from the spatially resolved MDI (Michelson Doppler Imager) instrument to the integrated sunlight GOLF signal. This paper presents a formalism and data adequate for the calculation of the required sensitivity functions. An important complication in the treatment of the GOLF data is the need to include both the sodium D1 and D2 lines. The latter is subject to contamination by telluric absorption and is difficult to observe from ground-based systems. This paper presents some telluric corrected data for the D2 line. The uniform displacement of the solar surface is an important special case which is observed directly by GOLF. The comparison of the appropriate integral of the sensitivity function derived from the ground-based profiles to that derived from GOLF data shows that the model can successfully reproduce important properties of the GOLF instrument function. A formalism and some data are presented which allow the calculation of the sensitivity of the GOLF instrument to magnetic effects. At present this approach takes a form in which the full magnetic effect is approximated by the magnetic effect on the sodium D1 line alone.

Key words: Sun: atmosphere – Sun: oscillations

Send offprint requests to: R.K. Ulrich

Correspondence to: ulrich@astro.ucla.edu

© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001

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