Mean angular diameters, distances, and pulsation modes of the classical Cepheids FF Aquilae and T Vulpeculae

CHARA/FLUOR near-infrared interferometric observations

¹ LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
e-mail: alexandre.gallenne@obspm.fr
² European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Santiago 19, Chile
³ Center for High Angular Resolution Astronomy, Georgia State University, PO Box 3965, Atlanta, Georgia 30302-3965, USA

Received: 23 February 2012
Accepted: 21 March 2012

Abstract

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 θ_LD = 0.878 ± 0.013 mas and θ_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   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.