Bakis, V.Budding, E.Erdem, A.Bakis, H.Demircan, O.Hadrava, P.2025-01-272025-01-2720060035-8711https://doi.org/10.1111/j.1365-2966.2006.10619.xhttps://hdl.handle.net/20.500.12428/22562New spectroscopy of the classical Algol system delta Lib, combined with high-quality optical and infrared photometry, provides the basis for a good understanding of the close binary system's main parameters. Detailed analysis of the photometry reveals the significant role of a third light source, pointing to the existence of a companion to the eclipsing system of mass similar to 1 M-circle dot. We review the methodology of applying high-accuracy positional information, available from the Hipparcos Intermediate Astrometric Data archive, to stars that may have such companions. Analysis of the astrometry of delta Lib also points to a third star similar to the one already identified by Worek from radial-velocity data, although with slightly revised parameters. O-C data do not contradict this, but their general precision (while confirming the close pair's Algol status) fails to allow a decision on the third orbit parameters: Worek's or revised ones. Taking the photometry, spectroscopy and astrometry together, however, the existence of a third star of comparable mass to the Sun, as a relatively close companion to the eclipsing binary (similar to 4 au), is confirmed.eninfo:eu-repo/semantics/openAccessbinaries : closestars : individual : delta LibArticle37041935194510.1111/j.1365-2966.2006.10619.xQ1WOS:0002395173000342-s2.0-33746858098Q1