We show here evidence for the necessity of an asymmetric form in modelling
the profile of an acoustic mode in the power spectral density. The analysis
was performed on a 805-day series of GOLF data (l=0 to 3). The assumptions
used for the fits are discussed and their consequences quantified, in part
icular for the optimum choice of the fitting spectral window. Values are gi
ven for the bias on the mode parameters (frequency, width, splitting) when
using a Lorentzian fit. The bias depends on the degree l and on the frequen
cy, and when taken into account leads to variations in the mode parameters
with degree more consistent with theoretical expectations.