Interferometric Observations of the Mira Star o Ceti with the VLTI/VINCI Instrument in the Near-Infrared

We present K-band commissioning observations of the Mira star prototype o Cet obtained at the ESO Very Large Telescope Interferometer (VLTI) with the VINCI instrument and two siderostats mounted to the VLTI stations EO and GO, forming an unprojected baseline length of 16 m. Rosseland angular radii were derived from the measured visibilities by fitting theoretical visibility functions obtained from center-to-limb intensity variations (CLVs) of different Mira star models, and the phase dependence of the visibility function and the apparent diameter have been investigated. Comparison of the derived Rosseland radii, effective temperatures, and the shape of the observed visibility functions with model predictions suggests that o Cet is a fundamental mode pulsator.