Solar core rotation from low-degree BiSON* p-mode splittings: 1981-95

Abstract

In this paper, we present an analysis of the rotational splittings of low-degree solar p modes, as measured in full-disc helioseismological data collected by the Birmingham Solar-Oscillations Network (BiSON) between 1981 and 1995. These data provide coverage over solar activity cycles 21 and 22. Rotationally split multiplets were fitted in two 4-month and seven 8-month frequency spectra with a technique that minimizes a maximum-likelihood function consistent with chi(2) 2-d.o.f. statistics. The fitted modes used in the analysis map the range 1 less than or equal to l less than or equal to 3 and 2.0 less than or equal to v less than or equal to 3.1 mHz. The lower limit to the analysed frequency range was determined by the poorer quality of the pre-1990 data; the upper, very conservative, cut-off was imposed in order to avoid using data where the linewidths of the modes begin to increase substantially above 1 mu Hz.