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Paper: Interferometric Observations of the Cepheid ζ Geminorum with FLUOR / IOTA
Volume: 194, Working on the Fringe: Optical and IR Interferometry from Ground and Space
Page: 22
Authors: Kervella, P.; Coudé du Foresto, V.; Traub, W. A.; Lacasse, M. G.
Abstract: The classical galactic cepheid zeta Gem has the largest angular diameter of all the northern classical cepheids, making it a very desirable target for interferometric observations. We used the IOTA interferometer and the FLUOR beam combiner to observe this star in late March 1999 over a four nights period. A variation of the angular diameter was detected at the 2 sigma level, allowing us to measure a uniform disk diameter of 2.15 mas +/-0.10 and a pulsation amplitude over the period of 0.38 mas +/-0.20. Based on previous Baade-Wesselink radius estimations of Zeta Gem, our measurements provide a distance of 299 pc +41/-33, in good agreement with the Hipparcos value of 358 pc +149/-81. Very high accuracy (0.5 %) visibility measurements enabled us to derive diameters with 8 % error bars despite a relatively short baseline of 38 m, which hardly resolves the star (mean visibility of 96 %). These observations open new possibilities for distance determination of pulsating stars by combining radial velocity and interferometry measurements. ESO's VLT Interferometer, with 200 m baseline and increased sensitivity will provide angular diameter estimations for hundreds of galactic cepheids at down to 0.1 % precision, and direct distance measurements based on the pulsation amplitude at 1 % precision.
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