The deenition of the model to t to the observed spectra depends on the physics we are assuming is present in the phenomena we are observing. Here we present the results obtained following the t of several models (described in poster GOLF.II, Roca Cort es et al.). Therefore the effects of asymmetrical line shapes, a common background for all modes, xed relative power in the components of a multiplet and a constant splitting between the components of each multiplet on the resonant frequencies (and their errors) of the modes will be evaluated. Finally, a table of frequencies and splittings will be given.

We present a study of the impact of a ground-based, multi-station window function on estimates of the power and damping of low-l solar p modes extracted from fits to resonant structure in the frequency domain. The window functions come from six-site observations made by the Birmingham Solar-Oscillations Network (BISON) over the 10-yr period beginning 1991 January. Two strategies were adopted. In the first, we used an 800-d time series of continuous observations made by the GOLF instrument on board the ESA/NASA SOHO satellite. These data were modulated by a variety of BISON window functions, with fractional duty cycles ranging from similar to0.4 to similar to0.8, and the resulting series analyzed. In the second we generated artificial 10-yr time series and studied the effect on these of the complete BISON window.

The predominant contribution to the frequency splitting of low-l solar p modes arises from the rotation of the solar interior and this lifts the frequency degeneracy in l to give a symmetric pattern where the observed (synodic) separation between adjacent m (i.e. for \Deltam\=1) is similar to400 nHz. Magnetic fields can also contribute to the splitting, but they do so in such a way as to introduce asymmetries in the arrangement of the components within each multiplet. In disc-integrated data this effect may become apparent when lgreater than or equal to2. Here, we attempt to extract estimates of the frequency asymmetries at l=2 from the analysis of disc-integrated data collected by the ground-based Birmingham Solar Oscillations Network (BiSON) and the GOLF instrument on board the ESA/NASA SOHO satellite. Our analyses demonstrate that we have evidence for there being non-zero asymmetries present (significance approximate to3-4sigma) during an epoch coincident with high levels of surface activity close to the maximum of solar cycle 23. The asymmetries are indistinguishable from zero at minimum levels of activity near the cycle 22/23 boundary. We also compare the observed asymmetries with those calculated from a model that is based upon the recent predictions of Moreno-Insertis & Solanki. While the level of agreement between the two is found to be reasonable, the observations suggest (though with poor constraints placed upon this) that the influence on the mode frequencies of high-latitude activity may not be as strong as in the model.

With over 5 years of GOLF data having some 90% continuity, a new attempt has been made to search for possible solar g modes. Statistical methods are used, based on the minimum of assumptions regarding the solar physics; namely that mode line-widths are small compared with the inverse of the observing time, and that modes are sought in the frequency interval 150 to 400 muHz. A number of simulations are carried out in order to understand the expected behaviour of a system consisting principally of a solar noise continuum overlaid with some weak sharp resonances. The method adopted is based on the FFT analysis of a time series with zero-padding by a factor of 5. One prominent resonance at 284.666 muHz coincides with a previous tentative assignment as one member of an n = 1, l = 1, p-mode multiplet. Components of two multiplets, previously tentatively identified as possible g-mode candidates from the GOLF data in 1998, continue to be found, although their statistical significance is shown to be insufficient, within the present assumption regarding the nature of the signal. An upper limit to the amplitude of any g mode present is calculated using two different statistical approaches, according to either the assumed absence (H0 hypothesis) or the assumed presence (H1 hypothesis) of a signal. The former yields a slightly lower limit of around 6 mm/s.

The predominant contribution to the frequency splitting of low-l solar p modes arises from the rotation of the solar interior and this lifts the frequency degeneracy in to give a symmetric pattern where the observed (synodic) separation between adjacent m (i.e., for \Deltam\ = 1) is similar to400 nHz. Magnetic fields can also contribute to the splitting, but they do so in such a way as to introduce asymmetries in the arrangement of the components within each multiplet. In full-disc data this effect may become apparent when l greater than or equal to 2. Here, we extract estimates of the frequency asymmetry for l = 2, investigate variations over the activity cycle and compare tile results with the near-surface predictions of Dziembowski et al. (2000) which are based upon observations from higher l.

Parallels are drawn between the asymmetric resonance profiles observed in global helioseismology and the Fano theory for autoionisation profiles in atomic spectroscopy. We show that the underlying physics of the interaction of a discrete resonance with a correlated continuum is common to both systems. The approximate formula normally used for fitting to profiles in helioseismology is essentially similar to that developed for atomic spectroscopy by Fano. We propose that the two systems are in reality equivalent. This proposition enables us to understand better which resonances in helioseismology will be correlated with each other and with which solar background "continua". We also question whether the two interacting influences of excitation sources and correlated solar background, are really separate independent processes.

accurate determination of the rotation rate in the inner radiative zone (0.2 < r/R-circle dot < 0.5) of the sum from helioseismic observations requires rotational frequency splittings of exceptional quality. Indeed, only low degree modes are sensitive to the dynamics of the deep interior.Low amid intermediate degree splittings have been estimated from a variety of instruments as well as different data analysis procedures. It is therefore not surprising that these determinations present significant differences.We present a study of the three more common data sets used to infer the solar rotation rate, namely LOWL, GONG and SOI/MDI. Our purpose is to find the common features present in the three sets, in order to build a robust determination of the rotation rate in the solar interior.We also have analyzed the effect of using: rotational splittings estimated by fitting an asymmetric profile rather than a symmetric Lorenzian as a model for the limit spectrum.

Recent studies have established that peaks in solar oscillation power spectra are not Lorentzian in shape but have a distinct asymmetry. Fitting a symmetric Lorentzian profile to the peaks, therefore, produces a shift in frequency of the modes. Accurate determination of low-frequency modes is essential to infer the structure of the solar core by inversion of the mode frequencies. In this paper we investigate how the changes in frequencies of low-degree modes obtained by fitting symmetric and asymmetric peak profiles change the inferred properties of the solar core. We use data obtained by the Global Oscillations at Low Frequencies (GOLF) project on board the SOHO spacecraft. Two different solar models and inversion procedures are used to invert the data in order to determine the sound speed in the solar core. We find that for a given set of modes no significant difference in the inferred sound speed results from taking asymmetry into account when fitting the low-degree modes.

We show here evidence for the necessity of an asym- metric 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 par- ticular 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 ac- count leads to variations in the mode parameters with degree more consistent with theoretical expectations.

During the years 1996 through 1998 the Michelson Doppler Imager (MDI) and the Global Oscillations at Low Frequency (GOLF) experiments on the Solar and Heliospheric Observatory (SOHO) mission have provided unique and nearly uninterrupted sequences of helioseismic observations. This paper describes the analysis carried out on power spectra from 759 days of calibrated disk-averaged velocity signals provided by these two experiments. The period investigated in this work is from 1996 May 25 to 1998 June 22. We report the results of frequency determination of low-degree (l ≤ 3) acoustic modes in the frequency range between 1.4 mHz and 3.7 mHz. Rotational splittings are also measured for nonradial modes up to 3.0 mHz. The power spectrum estimation of the signals is performed using classical Fourier analysis and the line-profile parameters of the modes are determined by means of a maximum likelihood method. All parameters have been estimated using both symmetrical and asymmetrical line profile-fitting formula. The line asymmetry parameter of all modes with frequency higher than 2.0 mHz is systematically negative and independent of l. This result is consistent with the fact that both MDI and GOLF data sets investigated in this paper are predominantly velocity signals, in agreement with previous results. A comparison of the results between the symmetric and asymmetric fits shows that there is a systematic shift in the frequencies for modes above 2.0 mHz. Below this frequency, the line width of the modes is very small and the time base of the data does not provide enough statistics to reveal an asymmetry. In general, the results show that frequency and rotational splitting values obtained from both the MDI and GOLF signals are in excellent agreement, and no significant differences exist between the two data sets within the accuracy of the measurements. Our results are consistent with a uniform rotation of the solar core at the rate of about 435 nHz and show only very small deviations of the core structure from the standard solar model.

An 800 day series of GOLF velocity data, with uniquely high continuity and stability, offers the best ever signal to noise ratio obtained in global Sun observations. Following meticulous efforts to provide reliable calibration, these data have been used for measurements of frequencies, line-widths and power in the p-modes, which are used for inversion to give the internal sound speed, for comparison with theoretical models. A search for g-modes is at present inconclusive, but has yielded two possible candidate frequencies. The analysis available today is regarded as preliminary and more complete methods are currently in hand. With the resumption of routine observations following the SOHO recovery, it is hoped that the data can be considerably extended, enabling changes with the solar cycle to be explored, as well as an extended g-mode search.

Data acquired by GOLF experiment onboard SOHO during approximate to 20 months has been analysed. GOLF is a disk-integrated sunlight experiment therefore biased to observe very low l modes (l less than or equal to 3). However the excellent ratio signal to background (S/B) achieved permits also the detection of some modes with 4 less than or equal to l less than or equal to 6 and those from n greater than or equal to 8 up to the cut-off frequency and even beyond with the pseudomodes signal. Due to the nature of the excitation function of the modes (which we will call noise) the line shapes look "spiky" rising the possibility (the necessity?) to use several methods of analysis of such data: a) FFT spectrum and maximum likelihood fitting technique, b) averaged FFT spectra of subseries and least squares fitting technique, c) HD spectra and least squares fit. Moreover, as a consequence of the characteristics of the spectrum: 1 less than or equal to S/B less than or equal to 10(4), linewidths of 0.1 less than or equal to Gamma less than or equal to 40 mu Hz and the presence of noise, several fit strategies have to be defined in order to fit. appropriately and accurately the mode line shapes. In this poster these methods and fit strategies will be explained and comparative results will be presented.

The GOLF instrument, as its name implies, was designed to optimise the possibility of measuring low frequency oscillations, in the range of the g-modes and the lower p-modes. The high stability of the instrument , combined with a continuity of data close to 100 % has contributed to providing a velocity time series in which the instrumental noise is indeed extremely low. However, in the region of the expected g-modes, global oscillations compete with a quite signiicant solar velocity background, due to the non-global convective movements in the photo-sphere. With now 2 years of high-quality data, the GOLF team is employing several diierent techniques to search for these modes. An identiication of g-mode frequencies would yield a highly sensitive probe for the properties of the core, in contrast to the p-modes for which extremely precise frequencies are required for the inversion. We present here the current status of the g-mode search programme.

The definition of the model to fit to the observed spectra depends on the physics we are assuming is present in the phenomena we are observing. Here we present the results obtained following the fit of several models (described in poster GOLF.II, Roca Cortes et al.). Therefore the effects of asymmetrical line shapes, a common background for all modes, fixed relative power in the components of a multiplet and a constant splitting between the components of each multiplet on the resonant frequencies land their errors) of the modes will be evaluated. Finally, a table of frequencies and splittings will be given.