Astron. Astrophys. 355, 743-750 (2000)

Analysis of asymmetric p-mode profiles in GOLF data

S. Thiery ¹, P. Boumier ¹, A.H. Gabriel ¹, L. Bertello ², M. Lazrek ³, R.A. García ⁴, G. Grec ⁵, J.M. Robillot ⁶, T. Roca Cortés ⁷, S. Turck-Chièze ⁴ and R.K. Ulrich <sup>2

1</sup> Institut d'Astrophysique Spatiale, Unité mixte CNRS - Université Paris XI, 91405 Orsay, France
² Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1562, USA
³ Centre National de la Recherche, CNCPRST, Rabat, Morocco
⁴ Service d'Astrophysique, DSM/DAPNIA, CE Saclay, 91191 Gif-sur-Yvette, France
⁵ Observatoire de la Côte d'Azur, Lab. Cassini CNRS URA1362, 06304 Nice, France
⁶ Observatoire de l'Université de Bordeaux 1, B.P. 89, 33270 Floirac, France
⁷ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain

Received 10 May 1999 / Accepted 29 November 1999

Abstract

We show here evidence for the necessity of an asymmetric form in modelling the profile of an acoustic mode in the power spectral density. The analysis was performed on a 805-day series of GOLF data (=0 to 3). The assumptions used for the fits are discussed and their consequences quantified, in particular for the optimum choice of the fitting spectral window. Values are given for the bias on the mode parameters (frequency, width, splitting) when using a Lorentzian fit. The bias depends on the degree and on the frequency, and when taken into account leads to variations in the mode parameters with degree more consistent with theoretical expectations.

Key words: methods: data analysis Sun: oscillations Sun: interior

Send offprint requests to: S. Thiery

Correspondence to: thiery@medoc-ias.u-psud.fr

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Contents

• 1. Introduction
• 2. Mode asymmetry
• 3. Fitting the GOLF data
• 4. Evidence of asymmetry as a property of p-modes
  • 4.1. Evidence of an effect
  • 4.2. Solar activity
  • 4.3. Influence of background
  • 4.4. Influence of high modes
• 5. Results
  • 5.1. Choice of the fitting window
  • 5.2. Asymmetry parameter
• 6. Bias introduced when fitting a Lorentzian profile to an asymmetric resonance
  • 6.1. Determination of a bias uncertainty
  • 6.2. Bias on the frequency
  • 6.3. Bias on the linewidth
  • 6.4. Bias on the splitting
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000
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