Marino, Anna; Villanova, S; Milone, Antonino; Piotto, G; Lind, Karin; Geisler, D; Stetson, Peter B
The horizontal branch (HB) morphology of globular clusters (GCs) is mainly governed by metallicity. The second parameter problem, well known since the 1960s, states that metallicity alone is not enough to describe the observed HB morphology of many GCs. Despite many efforts to resolve this issue, the second parameter phenomenon still remains without a satisfactory explanation. We have analyzed blue-HB, red-HB, and RR-Lyrae stars in the GC M4 and studied their Fe, Na, and O abundances. Our goal...[Show more]
Items in Open Research are protected by copyright, with all rights reserved, unless otherwise indicated.