Na-O anticorrelation and horizontal branches. IV. Detection of He-rich and He-poor stellar populations in the globular cluster NGC 6218
Journal article published in 2007 by
E. Carretta,
A. Bragaglia,
R. G. Gratton,
G. Catanzaro,
F. Leone,
E. Sabbi,
S. Cassisi 
,
R. Claudi,
F. D'Antona,
P. François,
G. James,
G. Piotto
,
R. Claudi,
F. D'Antona,
P. François,
G. James,
G. Piotto
