Astron. Astrophys. 333, 362-368 (1998)

1. Introduction

The solar eigenmodes of oscillation appear in the solar background velocity spectrum as Lorentz shaped lines. The position of the lines on the frequency axis is obviously one fundamental datum, and some solar properties can be inferred from the individual or collective study of the other parameters of these lines. Mode frequencies tables are used in the determination of solar internal structure, sound speed velocity or chemical composition, the combination of width and amplitude of the peaks can produce an estimation of the power fed to a mode from the excitation source, the measurement of the separation between split components gives an estimation of the solar internal rotation and the line asymmetry gives the location of the excitation source. As 'collective' properties, the pseudo-equidistance of the successive harmonics' 'big separation', or the 'small separation' of even- or odd- groups, are well known to be excellent tests of solar models. All these studies include an important amount of modelling of the data and optimisation of some cost function (fitting) to extract the desired model parameters from the data (Anderson et al. 1990, Gelly et al. 1997, Appourchaux et al. 1995, Elsworth et al. 1994). We have used such a fitting procedure on the IRIS network data to produce 4 tables of p-modes frequencies with error-bars (Gelly et al., 1997) and we wish to review here the modelling of the power spectrum which enables us to quote statistical error-bars on all the parameters of our fits. A study of the solar p-modes linewidths illustrates the discussion.

Fig. 1a-c. a One realisation of the real part of a group without background noise. b Same after convolution by the true complex window, showing the sidelobes. c Corresponding spectral density after addition of the background noise.

© European Southern Observatory (ESO) 1998

Online publication: April 15, 1998
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