Title:
Interferometric Observations of the Cepheid ζ Geminorum with FLUOR / IOTA
Authors:
Kervella, P.; Coudé du Foresto, V.; Traub, W. A.; Lacasse, M. G.
Affiliation:
AA(ESO, pkervell@eso.org), AC(Harvard-Smithsonian CfA), AD(Harvard-Smithsonian CfA)
Journal:
Working on the Fringe: Optical and IR Interferometry from Ground and Space. Proceedings from ASP Conference Vol. 194. Edited by Stephen Unwin and Robert Stachnik. ISBN: 1-58381-020-X (1999), p.22
Publication Date:
00/1999
Origin:
ADS
Bibliographic Code:
1999wfoi.conf...22K

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.