Mean angular diameters, distances and pulsation modes of the classical   Cepheids FF Aql and T Vul - CHARA/FLUOR near-infrared interferometric   observations
  We report the first angular diameter measurements of two classical Cepheids, FF Aql and T Vul, that we have obtained with the FLUOR instrument installed at the CHARA interferometric array. We obtain average limb-darkened angular diameters of \theta_LD = 0.878 +/- 0.013 mas and \theta_LD = 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 Rsol and R = 35.6 +/- 4.4 Rsol, 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 the pulsation mode is of prime importance to calibrate the Period-Luminosity relation with a uniform sample of fundamental mode Cepheids. 
A. Gallenne, P. Kervella, A. M\'erand, and H. McAlister, T. ten   Brummelaar, V. Coud\'e du Foresto, J. Sturmann, L. Sturman...
astro-ph.SR astro-ph.IM