New constraints on the binary system HD 327083 and its gaseous and dusty environments

Context . Binary systems with circumbinary molecular and dust rings are of great interest because they provide insights into the dynamics and evolution of stellar systems and the chemistry of the surrounding material. Aims . We aim to elucidate the nature of the B[e] binary system HD 327083 and constrain its orbital parameters and evolutionary status as well as the physical properties of its circumstellar and circumbinary envelopes. Methods . We present multi-epoch high-spectral resolution optical and near-infrared observations acquired at various observatories combined with VLTI/MIDI observations and ASAS-3 photometry. The data were analysed to obtain the orbital parameters, study individual members of the system, and derive the properties of the atomic and molecular gas and the dusty components of the complex environment of HD 327083. Results . We improved the orbital solution of HD 327083 and derived a period of P = 107.699 ± 0.005 d. Most optical lines display variations in shape and intensity when folded with the orbital motion. We assigned F6 II-III and B1 spectral types respectively to the cool and hot stellar components. A ring of molecular gas revolves around the system, and its appearance varies with the orbital phase. The MIDI flux distribution shows a silicate band in absorption at 9.7 µm. The interferometric data also indicate that the dust distribution has an elliptical shape, with its inner edge varying with orbital phase between 12.5 AU and 44 AU. Conclusions . We conclude that the B[e] binary system HD 327083 comprises a B-type massive accreting star and an F-type companion filling over 60% of its Roche lobe. The F-type companion is evolving towards the red supergiant stage. The deformed shape of the F-type star causes a broad minimum in the light curve. The hot companion (26 000 K, log g = 3.0) is hidden by a compact disc and shows a bi-polar outflow. The entire binary system presents an O-rich environment. It is surrounded by warm CO and SiO molecular rings, which are enclosed by an elliptical dust structure. All these components were formed by the evolved donor star during its evolution towards the red supergiant phase.