Minimising magnetic activity effects in PLATO observations: insights from the Sun-as-a-star
Recent studies showed that magnetic activity effects in solar-type stars can substantially bias seismic inferences, particularly age estimates, regardless of modelling strategy or surface treatment. We quantified how magnetic activity effects in the Sun-as-a-star are smoothed by temporal averaging by analysing 182.5-, 365-, 730-, and 1460-day time series from the BiSON network and the GOLF instrument. We estimated the activity-induced systematic uncertainty using two metrics and compared results across baselines to evaluate how the observing window shapes activity-induced biases. Solar-cycle signatures persist even in 1460-day windows. The suppression of magnetic activity effects with increasing baseline is non-monotonic: one- and four-year windows reduce biases far more effectively than shorter baselines in most cases, whereas 730-day windows provide only limited improvement over 365-day ones. Improvements arise from enhanced frequency determination (dominant at 365 days) and from increasingly efficient temporal averaging of the activity cycle (dominant at 1460 days). In contrast, 730-day is an intermediate regime: frequency accuracy has already plateaued and the observing window remains too short to smooth out cycle-related variability. On average, we find that magnetic activity effects decrease by 24%, 12%, 30%, and 38% when transitioning from 182.5 to 365 days, 365 to 730 days, 730 to 1460 days, and 365 to 1460 days for frequency-based fits; the corresponding improvements for ratio-based fits are 13%, 14%, 20%, and 31%. These results indicate that a continuous single-field four-year PLATO observing programme would provide the most effective suppression of magnetic-activity biases for solar analogues, whereas a 2+2-year strategy (in two distinct fields) is significantly more sensitive to magnetic effects, with limited gains between 365- and 730-day windows.