Cepheid distances from infrared long-baseline interferometry^*

I. VINCI/VLTI observations of seven Galactic Cepheids

¹ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
² Département Fresnel, UMR CNRS 6528, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
⁴ LESIA, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France

Corresponding author: P. Kervella, pkervell@eso.org

Received: 19 June 2003
Accepted: 26 November 2003

Abstract

We report the angular diameter measurements of seven classical Cepheids, X Sgr, η Aql, W Sgr, ζ Gem, β Dor, Y Oph and  Car that we have obtained with the VINCI instrument, installed at ESO's VLT Interferometer (VLTI). We also present reprocessed archive data obtained with the FLUOR/IOTA instrument on ζ Gem, in order to improve the phase coverage of our observations. We obtain average limb darkened angular diameter values of  mas,  mas,  mas,  mas,  mas,  mas, and  mas. For four of these stars, η Aql, W Sgr, β Dor, and  Car, we detect the pulsational variation of their angular diameter. This enables us to compute directly their distances, using a modified version of the Baade-Wesselink method:  pc,  pc,  pc,  pc. The stated error bars are statistical in nature. Applying a hybrid method, that makes use of the Gieren et al. ([CITE]) Period-Radius relation to estimate the linear diameters, we obtain the following distances (statistical and systematic error bars are mentioned):  pc,  pc,  pc,  pc,  pc,  pc,  pc.