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Astron. Astrophys. 341, 625-633 (1999)

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On the nature of the current GOLF p-mode signal

P.L. Pallé 1, C. Régulo 1, T. Roca Cortés 1, R.A. García 2, A. Jiménez 1, P. Boumier 3, A. Gabriel 3, G. Grec 4, J.M. Robillot 5, S. Turck-Chièze 2, R.K. Ulrich 6 and SOI Team 7

1 Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
2 Service d'Astrophysique, DSM/DAPNIA, CEA Saclay, F-91191 Gif-sur-Yvette, France
3 Institute d'Astrophysique Spatiale, Unité Mixte CNRS, Université Paris XI, F-91405 Orsay, France
4 Département Cassini, URA 1362 du CNRS, Observatoire de la Cóte d'Azur, F-06304 Nice, France
5 Observatoire de l'Université de Bordeaux 1, B.P. 89, F-33270 Floirac, France
6 Astronomy Department, University of California, Los Angeles, USA
7 Stanford University, Stanford, USA

Received 15 May 1998 / Accepted 21 October 1998

Abstract

The GOLF experiment on board SOHO is designed to measure global oscillations of the disk-integrated sunlight with high sensitivity and with long term stability. The GOLF data is thus ideally suited for both the study of the p-mode spectrum and to address the search for gravity modes. Due to their occasional malfunction the project decided to stop the rotating polarizing elements at an optimum place in order to maintain a precise sequence of measurements with the highest possible duty cycle. This action means that subsequently GOLF only measures two monochromatic intensities [FORMULA] and [FORMULA] on the blue wing of the sodium doublet. In this work we investigate the nature of these signals separately and in combinations. Our method is to study the temporal relative phase relations between the low degree ([FORMULA]) p-mode signals derived from data sets obtained from simultaneous observations, both from other SOHO instruments (GOLF and SOI) and from Mark- I, the Tenerife station of the ground-based BiSON network. It is found that these signals are "almost" pure velocity signals. A simple model indicates that a contamination of a pure intensity-like signal of 14% amplitude would fully explain the true nature of the current GOLF signal. Moreover, it is found that the ratios, defined for other instruments (Mark-I, SOI and, by extension BiSON and IRIS), also have exactly the same nature as the GOLF ratio.

Key words: Sun: general – Sun: interior – Sun: oscillations

Send offprint requests to: P.L. Pallé

Correspondence to: plp@ll.iac.es

This article contains no SIMBAD objects.

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© European Southern Observatory (ESO) 1999

Online publication: December 4, 1998
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