Mean angular diameters, distances, and pulsation modes of the classical Cepheids FF?Aquilae and T?Vulpeculae - CHARA/FLUOR near-infrared interferometric observations

摘要

We report the first angular diameter measurements of two classical Cepheids, FF?Aql and T?Vul, that we obtain using observations with the FLUOR instrument installed at the CHARA interferometric array. We derive average limb-darkened angular diameters of θLD?=?0.878?±?0.013?mas and θLD?=?0.629?±?0.013?mas, respectively, for FF?Aql and T?Vul. Combining these angular diameters with the HST-FGS trigonometric parallaxes leads to linear radii R?=?33.6?±?2.2???R⊙ and R?=?35.6?±?4.4???R⊙, respectively. The comparison with empirical and theoretical period–radius relations leads to the conclusion that these Cepheids are pulsating in their fundamental mode. The knowledge of this pulsation mode is of prime importance to calibrating the period–luminosity relation with a uniform sample of fundamental mode Cepheids.