Binaries workshop 2025

Rationale

Binary stars serve as fundamental astrophysical laboratories. They are among the few tools available for directly measuring stellar masses and distances, making them essential calibrators for models of stellar evolution. Recently, their significance has expanded to include the explanation of the diverse exotic stellar populations observed in star clusters, as well as insights into the final stages of stellar evolution and the hidden populations of compact objects such as black holes, neutron stars, pulsars, and white dwarfs. The study of binary stars has become increasingly vital in the era of gravitational wave astrophysics, particularly with the observation of black hole and neutron star mergers. Additionally, understanding binary systems is crucial for studying Type Ia supernovae, which serve as reliable standard candles for investigating the relatively distant universe. 

In recent years, the number of known and well-characterized binary stars has surged, largely due to advances in spectroscopic, photometric, astrometric, and astroseismic surveys. Notable examples include Gaia, Kepler, APOGEE, and LAMOST. However, our understanding of binary stars remains significantly incomplete. Despite the critical role of space-based surveys like Gaia in detecting and characterizing binary systems, these efforts face challenges in compiling large stellar samples in dense cluster environments, particularly among the faint stars found in distant globular clusters. Significant progress has been made using integral field instruments such as MUSE at the ESO VLT, demonstrating that coordinated and ambitious observational strategies can yield substantial results. Additionally, alternative methods for identifying potential binary candidates in star clusters have been underexplored. These include extensive machine learning searches on survey catalogs and publicly available spectra, as well as the use of indicators of stellar interaction and chromospheric activity.

On the theoretical front, several new public codes for simulating the evolution of (interacting) binary systems have recently become available. These range from statistical codes designed to simulate entire binary populations, such as SEVN, to detailed stellar evolution codes like MESA. However, these codes still contain significant approximations and simplifications, and their impacts are not yet fully understood. To effectively test and refine models, large observational samples of various well-characterized binary stars are essential. Additionally, fostering a robust community that brings together diverse expertise is necessary for exchanging vital information on unresolved issues, to identify potential solutions, and to lay the foundation for future collaborative opportunities.