PhD Programme

Magnetic Fields of Degenerate Stars - Supervisor: Stefano Bagnulo

White dwarfs (WDs) are the end point of 90% of stellar evolution. 15–20% of such stars possess strong magnetic fields. The fields range over five dex in strength, from below ten kG (one Tesla) up to about 1000 MG. The fields are roughly dipolar, and show no evidence of rapid secular changes. They seem to be “fossil fields”, produced in earlier evolution that evolve slowly by ohmic decay. At present, there is no single firmly established theoretical scenario that explains how prior evolution through the red giant and AGB phases can leave strong surface fossil magnetic fields in a significant fraction of WDs. Possibilities include retaining fields from earlier evolutionary phases, or field generation during binary mergers.

Using various facilities at the Very Large Telescope, at the Canada-France-Hawaii Telescope, and at the William Heschel Telescope, Armagh astronomers are performing a large survey of magnetic WDs in the vicinity of our solar system, with the goal to understand if and how magnetic fields evolve with time, and if they are correlated to other features of the stellar atmospheric chemistry, mass, and age. A PhD project is offered to help to obtain observational constraints that will be used to understand the origin of magnetic fields in WDs.

The student will learn how to use spectro-polarimetric techniques to detected and model stellar magnetic fields. She or he will help with the preparation of proposal for telescope time, with the execution and analysis of the observations, with the search for correlation between magnetic fields and other stellar parameters, and with the modelling of time series of polarised spectra and of surface magnetic field structure of of WDs. The project will be more theoretically or observationally oriented according to the preference and skills of the student.

For further information contact stefano.bagnulo@armagh.ac.uk

The origins of helium stars - Supervisor: Simon Jeffery

Stars like our Sun convert hydrogen to helium, grow to become red giants, exchange mass with companions and ultimately run out of fuel and collapse to become a white dwarf, neutron star or black hole. There are many pathways that stellar evolution can take — some of the most interesting produce exotic “helium stars” where all the surface hydrogen has been burnt, blown, or stripped away. Helium stars are rare, because their lifetimes are short and the evolution pathways are unusual, and  diverse, ranging from cool giants like the R Coronae Borealis variables through to extremely hot white dwarfs.

Armagh astronomers are using the 11m Southern African Large Telescope (SALT) to make the largest multi-epoch survey of early-type helium stars in the Galaxy, including over 200 helium-rich hot subdwarfs and extreme helium stars. We also use data from other large-scale surveys including Gaia, TESS, and LAMOST to provide a full description of stellar properties, distribution and kinematics. The survey is yielding many new and unusual helium stars.  The goal is to explore connections between these discoveries  and hence to identify evolutionary pathways. Key questions include: How fast do helium stars evolve?  What do the surface chemistries of helium stars tell us about their past? Which helium stars forrmed in mergers, which by ingesting their surfaces, and which by stripping? What do pulsations tell us about the interiors of helium stars?

The PhD project will make use of  new and historic observations, as well the latest generation of computational tools for modeling stellar atmospheres, evolution and pulsation.   The project may involve one or more of analysis of the observations, including spectroscopy and pulsations,  focused studies of extraordinary individual stars, and developing and testing new theoretical models for  stellar evolution.

For further information contact simon.jeffery@armagh.ac.uk.

Spectroscopy of The Heaviest Stars - Supervisor: Jorick Vink

Some few hundred million years after the Big Bang the Universe lit-up by the formation of the First Stars, which are thought to have been very massive owing to their pristine chemistry. Despite their key role in setting the stage for the subsequent Cosmic chemistry, we know surprisingly little about the properties of the first few stellar generations.

The goal of this observational/modelling Project is to utilize ongoing and new large-scale spectroscopic surveys (HST ULLYSES, X-Shooting ULLYSES at ESO’s VLT in Chile, and WEAVE on the island of La Palma) to determine the fundamental  stellar properties, constrain the evolution of massive stars, and  assess the final mass before collapsing into a Black Hole.

The project can be be more observational or theoretical depending on the interests and skills of the student.

For further information contact jorick.vink@armagh.ac.uk

Determining the physical conditions of the interstellar medium and the structure of the Milky Way Galaxy - Supervisors: David Eden and Michael Burton

For further information contact  david.eden@armagh.ac.uk

Astrophysical Data Visualisation - Supervisor: Michael Burton & Marc Sarzi

This project aims to apply data visualisation techniques to the investigation of complex, multi-dimensional astrophysical data sets.  It brings together astronomy, statistical analysis and data analytics in one project, with the opportunity to use the immersive environment of the Armagh Planetarium to render visualisations in and experiment with audience engagement.  The project lies at the interface of astrophysics and visual analytics.

Several multi-dimensional data sets are available, in particular to study the structure of both the Milky Way galaxy in detail and of external galaxies for a large number objects. For the Milky Way, we aim to investigate the 3D structure of the Milky Way Galaxy using a new data base on the distribution of the molecular gas in the galactic plane that we have obtained using the Mopra radio telescope in Australia.  Combined with data sets on the distribution of dust, interstellar extinction and stars in the Galaxy this can be used to constrain the distances to the spiral arms where the star forming molecular clouds lie. For external galaxies, we aim to use archival MUSE integral-field spectroscopic data obtained with the European Southern Observatory Very Large Telescope for the distribution and motions of the ionised-gas in order to better understand the processes leading to the formation of stars and therefore the growth of galaxies. Ancillary data may also be used for these objects.

For further information contact  Michael.burton@armagh.ac.uk  

Developing deep all-sky imaging polarimetry with the VST - Supervisor: Stefano Bagnulo

The VLT Survey Telescope (VST), located in Cerro Paranal (Chile), is a 2.6m telescope with a 268-megapixel camera, called OmegaCAM. It will be equipped with polarimetric optics, then re-commissioned, and will produce the first science data whithin the next three years. At this point, the VST will become the only facility in the world capable of deep imaging polarimetry (thanks to its 2.6m mirror) over a field of view as large as 1 deg x 1 deg. AOP is offering a studentship to help to learn how to make the best use of the telescope in polarimetric mode. The PhD student will help to develop and test calibration and data-analysis procedures, and will have an important role in the identification of the observational projects that can maximise the scientific return of this unique facility. Scientific targets will include solar system objects, interstellar medium, and magnetic stars, and any target for which the rapid follow-up capabilities of the telescope may show of crucial importance. In preparation of the science validation of the VST, the student will also use polarimetric data obtained from ESO instruments and telescopes, in particular the FORS instrument of the Very Large Telescope. The student will be supervised at the Armagh Observatory by Dr Stefano Bagnulo in close collaboration with other international teams, mainly in the Netherlands and in Italy.

For further information contact stefano.bagnulo@armagh.ac.uk