Binaries in the Hipparcos data: Keep digging, I. Search for binaries without `a priori' knowledge of their orbital elements: Application to barium stars

This work makes use of Hipparcos data to test the algorithms of (i) binary detection and (ii) orbital-parameters determination, which could possibly be used in the GAIA pipeline. The first item is addressed in this paper, whereas the second one is addressed in a companion paper by Pourbaix, Jancart, & Jorissen (2004, this volume). Here we test the ability of the algorithm to detect binaries from scratch, i.e., from the astrometric data without any a priori knowledge of the orbital elements. The Hipparcos Intermediate Astrometric Data of a complete sample of 163 barium stars (supposed to be all members of binary systems from theoretical considerations) are used as a test bench. When \varpi > 5 mas and P < 4000 d, the binary detection rate is close to 100%, but it falls to 22% when considering the whole sample, because many barium stars have small parallaxes or very long periods.