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, Δv, measured in a 32-month frequency spectrum, to test the power-law dependence of the widths at low frequencies. Over the range 1473 ≤ v ≤ 1822 μ.Hz, we find Δv, ∝v 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 Δv ∝ v8 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 μHz of > 14yr, and at 300 μHz (i.e. near the frequency expected for the fundamental) of > 13 000 yr are implied. © 1997 RAS.