HB morphology and the Second Parameter Effect: Faint Stars in a big game
We schematically review some of the main steps in the study of the Horizontal Branch Morphology in Galactic Globular Clusters. Since the first realization of the existence of the so-called Second Parameter Problem (2nd-P) up to now, one could perhaps see a sort of circular path. Actually, many candidate 2nd-P's were proposed during the early '70s, age has been the top-scored 2nd-P during the late '80s, and we are now back to even more candidates, including also possible intriguing combinations of some of them.
astro-ph↗