The mean angular diameter of δ Cephei measured by optical long-baseline interferometry.

Long baseline interferometric observations of Cep at the "Grand Interferometre a deux Telescopes" give the rst measurement of its mean angular diameter. Combined with the mean linear radius deduced from spectroscopic data, the mean angular diameter gives an improved distance determination for Cep.Sizepulsationsaremarginallydetectedandthemeasured amplitude is consistent with the theoretical predictions.