On the binarity of the classical Cepheid X Sagittarii from interferometric observations G. Li Causi, S. Antoniucci, G. Bono, S. Pedicelli, D. Lorenzetti, T. Giannini and B. Nisini A&A, 549 (2013) A64 Published online: 19 December 2012 DOI: 10.1051/0004-6361/201220207