The solar core: New low-l p-mode fine-spacing results from BiSON

The fine-structure spacing d(l)(n) = n(l,n) - n(1+2,n-1) for low-degree solar p modes of angular degree l 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 5 years of helioseismological data collected between 1991 July and 1996 February by the Birmingham Solar Oscillations Network (BiSON). These data cover 9 less than or equal to n less than or equal to 28 for d(0)(n), and 11 less than or equal to n less than or equal to 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 approximate to 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 increase slightly 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.