Hot subluminous stars (or subdwarfs) are low-mass stars that are less luminous than massive main-sequence stars of a similar temperature. They are all evolved stars, most being about 0.5M with helium-burning cores. We seek to explain their origin and to study the physics of their interiors.
Chris Winter and Simon Jeffery worked towards completing a scheme for the automatic spectral classification and parameterization of hot subdwarfs. These build on the classification scheme developed previously by Drilling and Jeffery. David Morgan extracted spectra of 3500sdB stars and blue horizontal-branch stars from the Sloan Digital Sky survey, which will be analyzed using these techniques.
Amir Ahmad and Simon Jeffery made follow-up observations of the unique helium-rich hot subdwarf binary PG1544+488 with the William Herschel Telescope. These demonstrated the orbital period to be almost precisely 12 hours -- making it a difficult target for single-site observations. They also continued their photometric survey of southern helium-rich subdwarfs from the South African Astronomical Observatory, discovering a multi-periodic pulsator with periods in the 1100-3000s range.
Simon Jeffery has embarked on a project to construct theoretical models for subluminous B stars. During six weeks at the Institute of Astronomy in Cambridge, he reinstated his stellar evolution code, introducing contemporary opacities. Further work will allow it to be used for modelling horizontal-branch stars, including the subluminous B stars. These models will be tested using the pulsational properties obtained in campaigns such as that described in Section 3.1.