Brightness temperature of the spots (in units of 10⁹ K) vs. the deconvolved sky-projected spot area (in AU²). The spot area is defined as A_m = (π/ 4) ab, a and b being the deconvolved FWHM along the major and minor axes, respectively. Circles with crosses indicate the spots with T_mA_m ≥ 300 × 10⁹ K AU². The red dashed line gives the best hyperbolic fit to these points, T_m ∝ 1/A_m. The inset shows an enlargement of the region with T_m ≤ 10¹⁰ K.