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We use 9.5-yr of BiSON Sun-as-a-star data to search for dependence of solar-cycle parameter changes on the angular degree, l, of the data. The nature of the Sun-as-a-star observations is such that for changes measured at fixed frequency, or for changes averaged across the same range in frequency, any l dependence present carries information on the latitudinal distribution of the agent (i.e., the activity) responsible for those changes. We split the 9.5-yr timeseries into contiguous 108-d pieces, and determine mean changes in the damping of, power in, and energy supplied to the modes through the solar cycle. We also apply a careful correction to account for the deleterious effects of the ground-based BiSON window function on the results. From our full analysis we obtain a marginally significant result for the damping parameter, where the mean change is found to be weakest at l=0. The other parameters show hints of some dependence in l. Our main conclusion is that the mean fractional solar-cycle change in the l=0 damping rates is approximately 50 % smaller than was previously assumed. It had been common practice to use an average over all low-l modes; our downward revision of the radial-mode value has implications for comparisons with models of the global solar cycle changes, which are usually based on a spherically symmetric geometry., Comment: 8 pages, 3 figures, 2 tables; Submitted to A&A

We present results of fitting the 50-day time series of photometry of alpha Cen A taken by the WIRE satellite in 1999. Both power spectrum and autocovariance function (ACF) fitting techniques were used in an attempt to determine mode frequencies, rotational splittings, lifetimes and amplitudes of low-l p-modes. In all, using both techniques, we managed to fit 18 modes (seven l = 0, eight l = 1 and three l = 2) with frequencies determined to within 1 - 2 micro-Hz. These estimates are shown to be 0.6 +/- 0.3 micro-Hz lower, on average, than the frequencies determined from two other more recent studies (Bouchy & Carrier, 2002; Bedding et al. 2004) which used data gathered about 19 months after the WIRE observations. This could be indicative of an activity cycle, although due to the large uncertainty, more data would be needed to confirm this. Over a range of 1700 to 2650 micro-Hz we were also able to use the ACF fitting to determine an average lifetime of 3.9 +/- 1.4 days, and an average rotational splitting of 0.54 +/- 0.22 micro-Hz, which is the first ever reliable estimate of this parameter. In contrast to the ACF, the power spectrum fitting was shown to return significantly biased results for these parameters., Comment: 11 pages, 10 figures (some figures are made up from multiple ps files of which there are 17 in total)

We report on results from the first solar Fitting at Low-Angular degree Group (solar FLAG) hare-and-hounds exercise. The group is concerned with the development of methods for extracting the parameters of low-l solar p mode data (`peak bagging'), collected by Sun-as-a-star observations. Accurate and precise estimation of the fundamental parameters of the p modes is a vital pre-requisite of all subsequent studies. Nine members of the FLAG (the `hounds') fitted an artificial 3456-d dataset. The dataset was made by the `hare' (WJC) to simulate full-disc Doppler velocity observations of the Sun. The rotational frequency splittings of the l=1, 2 and 3 modes were the first parameter estimates chosen for scrutiny. Significant differences were uncovered at l=2 and 3 between the fitted splittings of the hounds. Evidence is presented that suggests this unwanted bias had its origins in several effects. The most important came from the different way in which the hounds modeled the visibility ratio of the different rotationally split components. Our results suggest that accurate modelling of the ratios is vital to avoid the introduction of significant bias in the estimated splittings. This is of importance not only for studies of the Sun, but also of the solar analogues that will targets for asteroseismic campaigns.

The fine-structure spacing $d_{\ell}(n) = \nu_{\ell,n} - \nu_{\ell+2,n-1}$ for low-degree solar p modes of angular degree $\ell$ and radial order n, is sensitive to conditions in the deep radiative interior of the Sun. Here, we present fine-structure spacings derived from the analysis of nearly five years of helioseismological data collected between 1991 July and 1996 February by the Birmingham Solar-Oscillations Network (BiSON). These data cover $9 \le n \le 28$ for $d_{0}(n)$, and $11 \le n \le 27$ for $d_{1}(n)$. The measured spacings are much more precise, and cover a greater range, than earlier measurements from BiSON data (Elsworth et al. 1990a). The predicted fine-structure spacings for a ``standard'' solar model are clearly excluded by the BiSON data (at $\approx 10\sigma$); models that include helium and heavy element settling provide a much better match to the observed spacings (see also Elsworth et al. 1995). Since the inclusion of core settling in solar models will tend to slightly increase the predicted neutrino flux, the BiSON fine-structure data appear to reinforce previous conclusions, i.e., an astrophysical solution to the solar neutrino problem seems unlikely., Comment: 14 pages, LaTex 2e, 1 figure (2 encapsulated .PS files); ApJ Letters, in press

Observations of the Sun with the LOWL instrument provide a homogeneous set of solar p-mode frequencies from low to intermediate degree which allows one to determine the structure of much of the solar interior avoiding systematic errors that are introduced when different data sets are combined, i.e., principally the effects of solar cycle changes on the frequencies. Unfortunately, the LOWL data set contains very few of the lowest-degree modes, which are essential for determining reliably the structure of the solar core - in addition, these lowest-degree data have fairly large associated uncertainties. However, observations made by the Birmingham Solar-Oscillations Network (BiSON) in integrated sunlight provide high-accuracy measurements of a large number of low-degree modes. In this paper we demonstrate that the low-degree mode set of the LOWL data can be successfully combined with the more accurate BiSON data, provided the observations are contemporaneous for those frequencies where the solar-cycle-induced effects are important. We show that this leads to a factor-of-two decrease in the error on the inferred sound speed in the solar core. We find that the solar sound speed is higher than in solar models for r < 0.2Rsun. The density of the solar core is, however, lower than that in solar models., Comment: Plain TeX, using MN.tex, v. 1.6. 10 pages, 10 figures. Submitted to Mon. Not. R. astr. Soc