Three open clusters containing Cepheids: NGC 6649, NGC 6664, and Berkeley 55 J. Alonso-Santiago, I. Negueruela, A. Marco, H. M. Tabernero and N. Castro A&A, 644 (2020) A136 Published online: 11 December 2020 DOI: 10.1051/0004-6361/202038495