Symbiotic binaries in the Gaia data – I. Known symbiotics in DR3 and FPR

ABSTRACT Symbiotic stars are long-period interacting binaries composed of an evolved giant and a hot compact companion. Their complex spectra and variability make them both astrophysically valuable and observationally challenging. We investigate how known symbiotic stars are represented in Gaia DR3 and the Focused Product Release (FPR), assess the reliability of these data, and evaluate their usefulness for candidate analysis and searches for new systems. We cross-matched Gaia DR3 and the FPR with confirmed symbiotic stars from the New Online Database of Symbiotic Variables and examined their astrometric, photometric, and spectroscopic data, along with derived products such as astrophysical parameters, orbital solutions, variability properties, and emission-line classifications. Astrometric data reliably constrain the position of symbiotics in the colour–magnitude diagram, aiding searches for new systems, while Renormalized Unit Weight Error is generally not a reliable indicator of their binarity. Most symbiotics are variable in Gaia photometry. Mean and epoch radial velocities, as well as inferred orbital solutions, are broadly consistent with the literature, and we provide the first tentative orbital solutions for two systems. Effective temperatures and metallicities are unreliable due to contamination from nebular continuum and strong emission lines. H $\alpha$ emission is detected in nearly all symbiotics, making it a robust diagnostic. Additionally, resolved companions were identified for two systems, and one previously confirmed symbiotic star was reclassified as non-symbiotic. Gaia DR3 provides a rich dataset for the study of symbiotic binaries. The forthcoming DR4 promises a major leap forward with its longer time baseline, new data products, and epoch data.