Star formation & stellar evolution with binaries and interferometry

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Most stars are not born in isolation, but as part of binary star systems. One of the big open question concerns how such binaries form and what causes the diversity that is observed in their orbital characteristics. For instance, some binaries are on very close-in orbits that can also be tilted with respect to the stellar rotation axes. These companions cannot have been born at their observed location but must have formed at much wider separation and been transported onto their tilted, close-in orbits afterwards. The goal of this project is to use the CHARA telescope array in order to resolve binaries and to study the orbital configuration and fundamental parameters of hundreds of systems. Besides the orbits, our approach allows us also to measure precision masses & ages of the stars in these systems as well as the alignment between the orbital axis and the stellar rotation axes. The associated survey will provide fundamental new insights on the star formation process and also have a strong impact in the field of stellar evolution.For these studies we will use the CHARA/MIRC-X instrument that has been built as part of a collaboration between the University of Exeter and the University of Michigan, as well as complementary observations with VLTI/GRAVITY. These facilities combine the light from telescopes separated hundreds of meters apart, which enables measurements with extreme precision.In this PhD project, Yi Lu will work on selecting the most promising sources from public catalogues, validate the proposed method, confront the data with theory predictions, and publish first results. He will join our growing & internationally oriented interferometry team and collaborate with the Exeter theory experts and collaborators abroad.