The angular diameter and distance of the Cepheid ζ Geminorum

¹ European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching, Germany
² Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
³ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA

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

Received: 21 September 2000
Accepted: 12 December 2000

Abstract

Cepheids are the primary distance indicators for extragalactic astronomy and therefore are of very high astrophysical interest. Unfortunately, they are rare stars, situated very far from Earth. Though they are supergiants, their typical angular diameter is only a few milliarcseconds, making them very challenging targets even for long-baseline interferometers. We report observations that were obtained in the band (2-2.3 μm), on the Cepheid ζ Geminorum with the FLUOR beam combiner, installed at the IOTA interferometer. The mean uniform disk angular diameter was measured to be 1.64 +0.14 -0.16 mas. Pulsational variations are not detected at a significant statistical level, but future observations with longer baselines should allow a much better estimation of their amplitude. The distance to ζ Gem is evaluated using Baade-Wesselink diameter determinations, giving a distance of 502 ± 88 pc.