The SB9 catalogue: status, comparison with non-single stars from Gaia DR3, and evolution to SBX

The Ninth Catalogue of Spectroscopic Binary Orbits (SB9) is a comprehensive compilation of spectroscopic binaries (SBs) with orbital parameters sourced from the literature, comprising approximately 4000 systems with about 2800 single-lined and 1200 double-lined binaries. This work presents the latest status of the SB9 catalogue after over two decades of development since its online inception in 2004. In particular, we expose the statistical properties of SBs in terms of orbital period distributions and eccentricity─period diagrams per spectral type and evolutionary stage. We perform a careful cross-match with the Gaia Data Release 3 (DR3) to update astrometric parameters and compare with the Gaia DR3 non-single star (NSS) catalogue. Our cross-matching approach uses positional separations, magnitudes, and proper-motion back-propagation to identify counterparts. The final SB9 version updated by D. Pourbaix (2021-03-02) includes 4003 SB systems, some in higher order multiples: 152 in triples, 71 in quadruples, and 14 in higher order systems. Among these 4003 SB, 3976 have matching Gaia DR3 identifiers, while 21 are too bright and six too faint for Gaia detection. 10 red SB9 systems with periods larger than 1180 d (including a spectroscopic triple) have been spatially resolved by Gaia DR3. We identify a common sample of 827 SB9 binaries cross-matched with Gaia NSS, among which 655 are considered as reliable, based on relative period and absolute eccentricity differences not exceeding 10 per cent. The limited overlap (21 per cent of SB9) is primarily due to selection cuts in NSS SB1 analysis, brightness limits, temporal baselines, and partial orbital solutions in the Gaia NSS catalogue. This study highlights the strengths and limitations of both catalogues and establishes a clean benchmark sample for future binary star research. Our work marks the transition of SB9 into SBX, The eXtended Catalogue of Spectroscopic Binary Orbits⋆, featuring a modern relational data base, improved web interface, and Virtual Observatory access standards, aiming to enhance accessibility, data quality, and analysis capabilities for the binary and multiple star community.