Impact of observational duty cycle on the measurement of low-ℓ solar p-mode frequencies

We investigate the impact of a multi-site, ground-based observational window function on the extraction of estimates of the frequencies of low-angular-degree (low-l) solar p modes from decade-long datasets. To effect this study we have made use of some approximate to 10 yr of full-disc, "Sun-as-a-star" Doppler velocity data collected by the Birmingham-Solar Oscillations Network (BiSON). A coherent combination of observations made by all six BiSON sites provided the principal time series of data. This set was then modulated by a whole series of different window functions and the resulting sets analyzed. The windows were made from different combinations and numbers of BiSON stations. We find that for the majority of low-l modes the bias in the frequencies given by the effects of the window function is not significant. However, for modes above approximate to3300 muHz, and some l = 2 modes near approximate to2500 muHz, the bias is important when the frequencies are extracted from long datasets.