First results from the ESO VLTI calibrators program

The ESO Very Large Telescope Interferometer (VLTI) is one of the leading interferometric facilities. It is equipped with several 8.2 and 1.8 m telescopes, a large number of baselines up to 200 m, and with several subsystems designed to enable high quality measurements and to improve significantly the limits of sensitivities currently available to long-baseline interferometry. The full scientific potential of the VLTI can be exploited only if a consistent set of good quality calibrators is available. For this, a large number of observations of potential calibrators have been obtained during the commissioning phase of the VLTI. These data are publicly available. We briefly describe the interferometer, the VINCI instrument used for the observations, the data flow from acquisition to processed results, and we present and comment on the volume of observations gathered and scrutinized. The result is a list of 191 calibrator candidates, for which a total of 12 066 observations can be deemed of satisfactory quality. We present a general statistical analysis of this sample, using as a starting point the angular diameters previously available in the literature. We derive the general characteristics of the VLTI transfer function, and its trend with time in the period 2001 through mid-2004. A second paper will be devoted to a detailed investigation of a selected sample, aimed at establishing a VLTI-based homogeneous system of calibrators.