Fundamental parameters of subgiant stars in detached eclipsing binary systems

Abstract

Detailed studies of stars in long-period, detached eclipsing binary systems remain one of the best ways to test stellar evolutionary models. With so many detections of planets outside of the solar system, research has turned to the characterisation of these planets, which requires a good understanding of the planet host star. For the majority of single stars, determinations of mass and age must come from stellar evolutionary models. For the planet's characterisation to be correct, the stellar evolutionary models need to be correct, and uncertainties from any free parameters must be understood and calibrated.
This thesis looks at determining fundamental parameters (mass, radius, temperature, composition) for four newly discovered detached eclipsing binary systems, each with a subgiant component, to calibrate the stellar evolutionary models. AI Phe, another such system, commonly used for this purpose, has also been studied and has updated parameters. A combination of high-precision ground-based photometry and UVES spectra has enabled the masses to be measured to a typical precision of 0.35% and the radii to 1.4%. Effective temperatures have been found for three of the new systems and AI Phe, while a metallicity has been found for two systems. Calculated distances are found to be in excellent agreement with those provided in the first data release from the Gaia mission.
These parameters act as constraints in fitting GARSTEC stellar evolutionary models, to show how it is possible to start constraining the free parameters in these models. Here, the initial helium abundance and mixing length have been explored, but more detailed models are required to fully explore correlations between the two parameters. These systems provide benchmark systems in a region of the Hertzsprung-Russell diagram that was previously empty, and highlight the need for further calibration work in preparation for upcoming space missions such as PLATO.