Spot sizes on Sun-like stars

Abstract

The total area coverage by starspots is of interest for a variety of reasons, but direct techniques only provide estimates of this important quantity. Sunspot areas exhibit a lognormal size distribution irrespective of the phase of the activity cycle, implying that most sunspots are small. Here we explore the consequences if starspot areas were similarly distributed. The solar data allow for an increase in the fraction of larger sunspots with increasing activity. Taking this difference between the size distribution at sunspot maximum and minimum, we extrapolate to higher activity levels, assuming different dependences of the parameters of the lognormal distribution on total spot coverage. We find that, even for very heavily spotted (hypothetical) stars, a large fraction of the spots are smaller than the current resolution limit of Doppler images and hence might be missed on traditional Doppler maps.