PhD Programme

Polarimetry of Near Earth Objects - Supervisor: Stefano Bagnulo

Thanks to an international collaboration, Armagh Observatory has access to a 1m telescope located in Calern (France), that can be operated in remote. The telescope is equipped with a multifilter polarimeter that is routinely used for various scientific projects. AOP is offering a studentship to explore the polarimetric properties of Near Earth Objects (NEOs, asteroids that come in close proximity with our planet), and use these data to determine their size and surface structure. The student will be in charge of the observations of NEOs, but will be also expected to contribute to various aspects of the wider observational activity linked to that telescope, like helping with the data reduction and mantaining the archive of the observations. In addition, the student will have the opportunity to use for their work the VLT Survey Telescope (VST). This is a 2.6m telescope located in Cerro Paranal (Chile), that will be equipped with polarimetric optics. The VST will become the only facility in the world capable of deep imaging polarimetry over a field of view as large as 1 deg x 1 deg.  The PhD student will help to develop and test calibration and data-analysis procedures, and obtain data for various objects of the solar system, including NEOs.

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

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 Herschel 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

Searching for stellar activity cycles using multi-wavelength data - Supervisor: Gavin Ramsay

For more than 150 years we’ve known that the Sun has an activity cycle which lasts around a dozen years, over which the number of sunspots and flares decreases from sunspot maximum to minimum. We have also known for several decades that other Solar type stars show activity cycles. By comparing the duration and amplitude of stellar activity cycles of stars of different mass and age we can gain a better understanding of magnetic fields in stars in general.

In the last decade or so hints that activity cycles occur in stars which have masses less than half the Sun’s mass have been revealed. However, this is very difficult because their complex (and red) spectra makes it difficult to get robust radial velocities and also photometric data needs to be well sampled over many years to cover the likely cycle durations.

The next few years will provide many resources with which to search for and better understand activity levels and cycles in stars with a wide range in mass. ESA’s Plato mission is due to be launched in Dec 2026 with first data being released in the Spring or Summer of 2026. This will be obtaining photometric data of ~200,000 stars in a ~2100 square degree patch of sky for at least 2 years. The targets will also have been observed using the TESS for at least some of the last 4 years giving a very recent history of the star’s activity levels. Watson is a member of the Plato Mission Consortium and Ramsay is the ESA Plato Community Scientist and member of the ESA Plato Science Working Team.

Potential projects include searching for activity cycles using photometry but also using archival spectroscopic data. Additional data could come from the GOTO all-sky survey of which Armagh is a partner and NGTS, in which QUB is a Core Institute and Armagh is a participating Institute.  Radio data from Europe, South Africa and Australia and X-ray data from a number of satellites could also be used.

This project would be co-supervised with Chris Watson (QUB).

For further information contact gavin.ramsay@armagh.ac.uk

Time Domain Astrophysics - Supervisor: Gavin Ramsay

Time Domain Astrophysics is the branch of astronomy which utilises the apparent brightness variations of objects on timescales ranging from
less than a second (neutron stars) to minutes (compact binary star systems and pulsating stars) to hours (accreting objects) and months
or years (active galactic nuclei and accreting objects) to probe different physical processes. Other examples include supernovae and
exoplanets orbiting other stars.

Armagh is a founder member of the Gravitational-wave Optical Transient Observer (GOTO) project which has robotic telescopes on La Palma in
the Canary islands and Siding Spring in Australia. The prime goal of this project is to detect the optical counterpart of Gravitational
Wave events detected by Ligo/Virgo/Kagara. These telescopes have sufficiently wide sky coverage that we map the entire visible sky every few days. Armagh is also a member of the BlackGem project which currently has three telescopes in Chile and has the same primary goal as GOTO.

The exact project which any a new PhD student would undertake be open according to their interests and expertise. However, it would be
expected to make use of GOTO and BlackGem data, with additional data potentially coming from the TESS satellite and radio data obtained
from I-LOFAR.

For further information contact gavin.ramsay@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

The heaviest stars and black holes - 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  evolution & fate of the first few stellar generations.

The goal of this computational PhD project is to predict the amount of mass the first stellar generations loose through stellar winds, and to
determine the final masses of these stars as Black Holes.

The predicted black hole masses will be compared to data from gravitational wave observatories.

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

Origin and evolution of solar system small bodies -- Supervisor: Apostolos 'Tolis' Christou

Atomic data and model atmospheres for chemically peculiar hot subdwarfs - Supervisor: Simon Jeffery

Stars provide extreme environments governed by physical conditions which are difficult to reproduce in the laboratory. Such physics can manifest in extremely unusual stars such as the heavy-metal hot subdwarfs. These are low-mass core-helium burning stars in which the surface abundances of exotic chemical elements, such as krypton, zirconium, and lead, appear to be 1000 to 100,000,000 times higher than expected. Are these exotic chemistries due to nucleosynthesis and subsequent dredge-up of neutron-capture elements, or to radiative processes in the outermost layers of the star? How much do excessive abundances modify the structure of the stellar atmosphere ? What clues do their exotic surfaces give regarding the origin of these rare stars? 

In order to answer these questions it is necessary to compute accurate atomic data for chemical species observed in their atmospheres. These data simply do not exist at present. They will be used to build a  self-consistent model atmosphere which accounts for the diffusive migration of chemical species under the competing processes of radiative levitation and gravitational settling. The model atmospheres will show whether particular species can be highly concentrated into thin layers within the atmosphere.  The models can then be used to compute theoretical spectra which, when compared with observations, provide measurements of surface abundance as well as evidence of chemical stratification.    

This PhD project will include the calculation of atomic data for at least one ion observed in heavy-metal subdwarfs. These data will be incorporated into existing model atmosphere codes, and new model atmospheres and synthetic spectra will be computed. The models will then be used to analyze high-quality spectra from the Southern African Large telescope and the Hubble Space Telescope.

This project would be co-supervised by Connor Ballance (QUB) + Kathy Ramsbottom (QUB)

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