Instrument-independent validation of two populations of coronal bright points and their dependence on observational parameters

Abstract

Recent studies have suggested that coronal bright points (CBPs) comprise two statistically distinct populations exhibiting different relationships with the solar activity cycle. However, this conclusion was based on observations from a single instrument and classification using only maximum CBP intensity, leaving it unclear whether the observed bimodality reflects an intrinsic property of CBPs or depends on instrumental characteristics or the choice of observational parameter. We test the robustness of the proposed two-population scenario using four independent long-term datasets obtained with SOHO/EIT (195 Å), SDO/AIA (193 and 211 Å), and Hinode/XRT. Applying an identical automated identification procedure to all datasets, we compare the solar-cycle behaviour of CBPs classified according to six observational parameters describing their local radiative and geometric properties. All four datasets consistently reproduce two CBP populations exhibiting opposite correlations with the solar cycle and distinct latitude–time distributions. Bright CBPs follow Spörer’s law and form a butterfly diagram, whereas dim CBPs are distributed over a much broader range of heliographic latitudes. Robust bimodal separation is preserved by local radiative parameters, namely maximum intensity, mean intensity, and local background intensity. In contrast, projected area, total integrated intensity, and CBP-to-background contrast do not provide comparable discrimination. Together, these results demonstrate that the proposed two-population classification is instrument independent and therefore likely reflects an intrinsic property of coronal bright points. The preferential preservation of the bimodal behaviour by local radiative parameters provides new observational constraints on the physical origin of the two populations.