Event Details

The evolution of stars in a binary system and their position in the colour-magnitude diagram can behave in strange ways.Evolutionarily speaking, if the stars in a binary system are far enough apart they will not interact, and their evolution can be described by single star evolution models. However, when they are close enough, they interact, initiating a mass transfer phase that transforms the fate of the stars in the system, and brings their evolution to paths extremely different than the ones they would have as single stars. Even though all binary stars evolve differently, when multicolour photometry is considered, they have one feature in common: their ab-normal behaviour in the colour-magnitude diagram. In this work, we use Hubble Space Telescope multicolour photometry of the globular cluster 47 Tucanae to uncover a population of stars that present a strange behaviour in the colour-magnitude diagram and are likely cluster members. By comparing those stars with evolutionary models and X-ray source catalogues we were able to show that the majority of those stars are likely binary systems that do not have any X-ray source nearby, most formed by a white dwarf and a main sequence star and a small number of possible double degenerate systems. Additionally, we present spectroscopic analysis for two of our stranger stars obtained with the Multi Unit Spectroscopic Explorer instrument, of the European Southern Observatory, indicating high probabilities of them being binary systems.