Hot subdwarf stars and related stellar objects: modelling and empirical effective temperatures

Abstract

Hot subdwarf stars are of significant importance in astrophysics, serving as unique laboratories for studying the more exotic and less understood late stages of stellar evolution. In this thesis, I present both theoretical and observational work aimed at understanding hot subdwarfs and related stellar objects across a broad mass range. Among these are the enigmatic Blue Large Amplitude Pulsators, a newly discovered class of pulsators. I demonstrate that Shell Helium Burning hot subdwarfs are strong candidates to explain this class, outperforming several other models proposed thus far. Additionally, I present insights from the discovery and characterisation of J0526, a short-period hot subdwarf binary, confirming it as the smallest known non-degenerate star in a detached binary system. I also explore the outcomes of white dwarf mergers, focusing on Helium, CO, and ONe white dwarf mergers, and show that some of these can successfully explain recently observed phenomena, such as the Gaia Q Branch and the exceptionally massive stellar remnant J005311, which exhibits unusual spectral properties. Finally, I present my extension to hot subdwarfs of the Infrared Flux Method, a technique for determining stellar effective temperatures. To achieve this, I incorporate ultraviolet and optical photometry and explore its implications for GALEX photometry.