Solar p-mode linewidths from recent BiSON helioseismological data

Abstract

We present low-degree solar p-mode linewidths from the analysis of several high-resolution frequency spectra generated from high-quality Doppler velocity data collected - in integrated sunlight - by the Birmingham Solar-Oscillations Network (BiSON) between 1991 July and 1995 July. We have used linewidths, Delta nu, measured in a 32-month frequency spectrum, to test the power-law dependence of the widths at low frequencies. Over the range 1473 less than or equal to nu less than or equal to 1822 mu Hz, we find Delta nu proportional to nu(7.0+/-1.5). If an effort is made to correct for finite observing time systematics, the fitted index increases to 7.3 (and even higher, to 7.8, if a naive, single-bin-width correction is applied). This is somewhat steeper than reported in previous observations of intermediate-degree modes, and is more in line with theoretical calculations which predict Delta nu proportional to nu(8) over this frequency range. If one assumes that the steep dependence reported here persists down to lower frequencies, low-degree-mode coherence (e-folding) times at 800 mu Hz of > 14 yr, and at 300 mu Hz (i.e. near the frequency expected for the fundamental) of > 13 000 yr are implied.