Periodic Reporting for period 1 - ORBIT-D (Observing Binaries in Transition Discs)
Reporting period: 2023-09-01 to 2025-08-31
Star formation begins when the densest regions in molecular clouds collapse under their own weight forming so called “young stellar objects” (YSOs), i.e. protostars surrounded by a gas and dust disc (known as “protostellar” or “protoplanetary” disc), expected to be the birth place of planets in this newly formed proto-exo-solar systems. The project ORBIT-D (Observing Binaries in Transition Discs) aims to study a special class of these discs that presents a cavity in the disc centre, the so called “transition discs”, that are believed to form due to the presence of an additional planetary/stellar companion to the primary star: i.e. a second protostar or a massive planet. Nevertheless, transition discs in which such a companion was detected are rare, questioning this hypothesis as a mechanism for the formation of such cavities.
In this context, by using analytical, numerical and observational techniques, the project ORBIT-D developed new diagnostics for the indirect detection of binary companions in transition discs, studying and modelling the perturbations that they produce in the disc.
The project produced tools and methods to identify hidden companions, quantify their effects on disc structure, and apply these results to actual astronomical observations. By bridging the gap between theoretical predictions and observational evidence, ORBIT-D contributes to more accurate assessments of disc evolution and planet formation.
The project’s results are particularly relevant for making full use of high-resolution data from modern radio and infrared light telescopes, upcoming facilities such as the Extremely Large Telescope (ELT) and future exo-planet detection missions. ORBIT-D thus addresses both the scientific challenge of understanding complex stellar and planetary systems and the strategic need for effective interpretation of rapidly expanding observational datasets.
In this context, by using analytical, numerical and observational techniques, the project ORBIT-D developed new diagnostics for the indirect detection of binary companions in transition discs, studying and modelling the perturbations that they produce in the disc.
The project produced tools and methods to identify hidden companions, quantify their effects on disc structure, and apply these results to actual astronomical observations. By bridging the gap between theoretical predictions and observational evidence, ORBIT-D contributes to more accurate assessments of disc evolution and planet formation.
The project’s results are particularly relevant for making full use of high-resolution data from modern radio and infrared light telescopes, upcoming facilities such as the Extremely Large Telescope (ELT) and future exo-planet detection missions. ORBIT-D thus addresses both the scientific challenge of understanding complex stellar and planetary systems and the strategic need for effective interpretation of rapidly expanding observational datasets.
ORBIT-D was structured into five work packages (WPs), each addressing a key scientific objective. WP1 developed a statistical framework to estimate the likelihood that a companion carving a disc cavity remains undetected. WP2 produced analytical and numerical models to predict the morphology and kinematics of discs affected by binary companions. WP3, originally aimed at constraining circumbinary disc lifetimes, was postponed due to technical complexity but led to the development of a novel particle “splitting and merging” algorithm, improving the resolution of low-density regions in numerical simulations. WP4 applied the models to real observational data, including radial velocity measurements and proper motion anomalies, providing direct comparisons between theory and observations. WP5 consolidated the project’s software tools into publicly accessible packages on GitHub, enabling the community to analyse circumbinary and transition discs.
Throughout the project, ORBIT-D produced peer-reviewed publications, supervised students, and engaged in international collaborations. High-impact results include methods to quantify companion detectability, models linking disc eccentricity to binary parameters, and novel numerical algorithms for Smoothed Particle Hydrodynamics (SPH) simulations. The project also provided training in observational data reduction and proposal writing.
Throughout the project, ORBIT-D produced peer-reviewed publications, supervised students, and engaged in international collaborations. High-impact results include methods to quantify companion detectability, models linking disc eccentricity to binary parameters, and novel numerical algorithms for Smoothed Particle Hydrodynamics (SPH) simulations. The project also provided training in observational data reduction and proposal writing.
ORBIT-D advanced the state of the art by developing fully integrated methods connecting theoretical, numerical, and observational studies of transition discs. The statistical models for hidden companions, the predictive kinematic and morphological frameworks, and the high-resolution SPH simulation algorithms represent unique contributions to the field. These results provide tools for the broader community to study disc evolution, binary-star interactions, and planet formation with unprecedented accuracy. The work also lays a foundation for extending these methods to other astrophysical systems, such as circumbinary exoplanets and compact object binaries, including black hole mergers. Further uptake will benefit from continued refinement of the software, integration with observational pipelines, and wider dissemination of the simulation datasets.