PhD Recruitment in Sun, Stars and Exoplanets

A mere thirty years after the first discovered exoplanet, we now know over 6000 known exoplanets. These come in a wonderful variety and exoplanet demographics studies have transformed our view of planet formation and evolution. Yet, we are still to find a true Earth twin or exoplanetary systems resembling the Solar System. Finding and characterising planets like Earth are hindered by variable signals from the star itself. Especially in radial velocity data, essential to measure a planet's mass, these signals are often larger than the planet signals. With Dr Annelies Mortier, projects are possible related to the detection or mass characterisation of small planets, star-planet connections, stellar variability mitigation techniques, or Sun-as-a-star studies. The project will make use of data from high-stability high-resolution spectrographs, such as HARPS-N or HARPS3 (including their Solar telescopes), and can often be complemented by space photometry from TESS or CHEOPS.

Circumbinary exoplanets orbit around both stars at once, like Tatooine in Star Wars. Such planets are rare, but important to better understand the processes behind planet formation and orbital evolution. The project is about collecting data and analysing it in search for circumbinary planets. At Birmingham we search for such signals using radial-velocities, and the transit method, which means we also regularly visit observatories outside the United Kingdom and as remote as the Atacama Desert and the Antarctic Plateau. During the PhD we also anticipate to detect new circumbinary exoplanets using the astrometric method, thanks to ESA’s mission, Gaia.

Finding out whether biology has arisen elsewhere in the Universe has likely been a question as old as humanity itself. At Birmingham we are leading on answering that question thanks to our participation in the only set of telescopes currently able to identify new habitable rocky planets whose atmosphere can then be probed for evidence of biological processes. We use the SPECULOOS network of telescopes across the world to do this work as well as a telescope located in Antarctica called ASTEP. We also analyse data obtained by NASA’s TESS satellite to complement our analyses. SPECULOOS and ASTEP also spend time to confirm long period gas-giants, an essential population to understand the context of planet formation.

Exoplanets span a diverse range of conditions, from ultra-hot Jupiters to lava worlds. The atmospheres of these planets provide an exceptional window into their properties, and can reveal the atmospheric compositions, formation histories and even interior properties of these exciting worlds. The James Webb Space Telescope (JWST) has already begun to provide a wealth of atmospheric observations in its first two years of science operations. However, new modelling efforts are needed to fully interpret these datasets. In this PhD project, the researcher will use atmospheric modelling techniques to explore the properties of exoplanet atmospheres and interpret atmospheric observations.

Understanding what drives stellar activity cycles has wide significance, including how stars influence their local environments including any planets they may host, with obvious implications for exoplanet habitability and placing our own solar system in a wider context. Asteroseismology, the study of stars by observation of their natural oscillations, provides a sensitive diagnostic of stellar cycles and the sub-surface changes that drive stellar variability. This project will make use of asteroseismic data from the NASA Kepler and TESS Missions, as well as new asteroseismic data that will be collected by the upcoming European Space Agency (ESA) PLATO Mission, to seismically track stellar cycles, and “pulses” of activity due to large active regions or nests, in bright solar-type stars; and to hence make inferences about the nature of the surface activity on such stars, as a function of stellar type and age. The project will also make use of helioseismology (solar oscillations) data from Sun-as-a-star observations made by the Birmingham Solar-Oscillations Network (BiSON), to help develop and test the methods applied to other stars.

Bayesian Hierarchical Modelling of Stellar Populations for Exoplanet Host Characterisation - Dr Guy Davies

Precise knowledge of stellar properties is the cornerstone of exoplanet science. Every measurement of an exoplanet’s radius, mass, and age depends critically on our understanding of its host star. Yet, many stellar and planetary parameters remain systematically uncertain due to limitations in stellar modelling and data interpretation.

This PhD project will develop Bayesian Hierarchical Models (BHMs) to infer the fundamental parameters of large stellar populations and their hosted planets in a statistically self-consistent way. By jointly modelling ensembles of stars and incorporating high-quality asteroseismic, spectroscopic, and photometric data, the student will produce revised stellar and planetary parameters that directly feed into next-generation exoplanet demographic studies.