Speaker
Description
Circumfacular regions are dark structures surrounding active regions that appear in chromospheric observations, yet their physical properties and role in solar variability remain poorly constrained. Using ChroTel synoptic observations in Hα and Ca II K spanning the maximum of solar cycle 24 to the onset of cycle 25, we derive the photometric and geometric properties of circumfacular regions and compare them with plages, sunspots, and filaments. This study provides the most comprehensive characterization of circumfacular regions to date. We introduce a circumfacular photometric index and show that it is strongly correlated with established solar-activity proxies, with temporal variability primarily driven by changes in area coverage. The strength of these correlations evolves with the global activity level. We discuss the implications of these results for the interpretation of Balmer-line variability in the Sun and solar-like stars.