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PhD Application Information
Applications are invited for a 3.5 year postgraduate research studentship(s) tenable at Armagh Observatory & Planetarium from Oct 2021. Armagh Observatory, located in Northern Ireland, UK, is an astrophysical research institute founded in 1789. It has 8 staff astronomers, 4 post-doctoral fellows, 8 PhD students and several visiting astronomers. Research interests include Solar Physics, Solar-System Science, Stellar, Galactic and Extra-galactic Astrophysics.
Candidates must have, or expect to obtain, at least an upper second class honours degree or equivalent, in an appropriate discipline (e.g. Physics, Mathematics, Astronomy or Astrophysics). Successful candidates will enroll at an appropriate university and carry out a research programme at the Armagh Observatory & Planetarium. Applications are encouraged from candidates of any nationality although eligibility may depend on funding source. The successful applicant(s) would receive a grant based on the United Kingdom Science and Technology Facilities Council rate (2020/21: 15,285 per annum). In addition, we would fully fund the university fees.
To ensure prospective candidates receive full consideration, a completed application form and references should be received on or before the 27th November 2020.
First selection will take place shortly after this deadline with subsequent selections thereafter until all positions have been filled.
The application form, CV and other supporting documents should be sent to Human Resources (firstname.lastname@example.org).
If potential applicants have questions they can be sent to the administrator or the potential supervisor for the project which are listed on our website.
Time Domain Astrophysics
Supervisor: Dr Gavin Ramsay
As one famous astronomer once said, if you monitor the brightness of a star with sufficient precision for a sufficiently long time, every star is 'variable'. I have been studying variable stars for many years and use the brightness information to investigate the properties of accretion discs around compact binary systems; how flare originate on low mass stars; how frequent are flares from solar-type stars; search for activity cycles on stars and identify new explosive 'transient' sources from survey data.
A number of potential science projects are available but are expected to partly use data from the Gravitational-wave Optical Transient Observer (GOTO). This survey is an international project which Armagh is a founder partner and aims to detect the optical counterpart of gravitational wave events detected by the Advanced Ligo and Virgo detectors. Other projects could use data from the TESS satellite which is currently surveying the entire sky and providing a unique opportunity to study stellar variability.
These projects would suit someone interested in observational astronomy and ideally someone with experience of computing. languages. It is expected there would be opportunities for travelling to La Palma, Australia or South Africa to help commission new GOTO nodes or help make detailed observations of objects discovered in these surveys.
For further information contact: email@example.com
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 firstname.lastname@example.org
Unravelling the Late Stages of Stellar Evolution
Supervisor: Simon Jeffery
Starting out like our sun, stars 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. The stellar evolution story is not simple; there are many pathways a star can take. If a star loses all its hydrogen and then starts to burn helium, it will become a hot helium-rich subdwarf, a blue star but fainter than the massive hydrogen burning O and B stars.
There are many types of helium star; in Armagh we are exploring how they are connected in order to discover precisely how these unusual stars end their lives.
The student undertaking this project will join the SALT survey of helium-rich subdwarfs. This is a spectroscopic survey using the 11m Southern African Large Telescope to analyse the surface properties and chemical compositions of up to 300 stars. We also intend to explore the Galactic distribution and orbits of these stars using data from the Gaia space astrometry mission and which of these starts are light variable and why using data from the Transiting Exoplanet Survey Satellite (TESS).
The student may work on ensemble studies of the entire sample, and hence develop skills in data science for astronomy, or on focused studies of some of the extraordinary individual stars we are discovering, developing skills in stellar atmospheres and/or pulsations. In either case, enthusiasm for both programming and astrophysics will be desirable.
For further information contact email@example.com.
Supermassive Black Holes with Molecular Gas
Supervisor: Marc Sarzi
For further information contact firstname.lastname@example.org
The Heaviest Stars and Black Holes in the Universe
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 the mass the first stellar generations lose 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 email@example.com
What happens to asteroids in resonances?
Supervisor: Dr Apostolos “Tolis” Christou
The AOP solar system group is carrying out frontline astronomical research in the origin and evolution of the solar system and its small bodies. Highlights include: the discovery that the tenuous atmosphere of Mercury is modulated by impacts with debris from periodic comet Encke (Christou, Killen et al, GRL, 2015); using the distant moons of the giant planets to time key events in early solar system evolution (Li and Christou, Astron. J., 2017); and constraining the production and loss of Mars Trojan asteroids by collisions and radiation forces (Christou et al, Icarus, 2017; Icarus, 2020). Our research is grant-aided by the UK Science and Technology Facilities Council (STFC).
Work done by our group (Christou, Icarus, 2013; Borisov et al, MNRAS, 2017; Christou et al, Icarus, 2020) shows that the Yarkovsky effect causes significant orbit changes or even escape for asteroids in the 1:1 resonance with Mars - the so-called Trojans - while the physical bodies themselves break apart due to YORP spin-up, creating clusters of resonant asteroids. Outcomes of YORP-induced disruption are observed elsewhere, as orbital clusters of Main Belt asteroids (Pravec et al, 2010) and the active shedding of material (eg (6478) Gault, Hui, M-T et al, MNRAS Lett., 2019) while correlations between asteroid orbits and sizes point to size-dependent orbit evolution (Bolin et al, Icarus, 2017; Dermott, Christou et al, Nature Astronomy, 2018).
In this project we want to quantify resonant asteroid orbit and/or spin evolution under non-gravitational forces, applying our findings to different settings, make predictions and interpret observations. Breaking up of resonant or co-orbital asteroids near the Earth’s orbit may form compact orbital clusters (de la Fuente Marcos & de la Fuente Marcos, MNRAS Lett., 2019), contribute to debris structures observed at the orbits of the Earth (Dermott et al, Nature, 1994) or, more recently, Venus (Jones et al, Science, 2013; Pokorny & Kuchner, ApJ, 2019) and give rise to meteor showers. Outside the solar system, any debris co-orbital with close-in exoplanets would evolve significantly and rapidly, giving rise to features that may betray the presence of the planetary body.
The successful applicant will collaborate with Dr Christou in attacking this multi-faceted problem, with the scope and direction of the resulting PhD project depending primarily on the student's individual inclinations. Work methods will include, but are not necessarily limited to, intensive N-body numerical simulations. Some familiarity in the areas of dynamics, statistical methods or numerical analysis will be seen as an advantage.
For further information contact Apostolos.Christou@armagh.ac.uk
Finding Meteor Showers on Other Planets
Supervisor: Dr Apostolos “Tolis” Christou
At certain times of the year, the Earth passes through streams of dust left behind by comets, leading to a natural fireworks display: a meteor shower. One of the best-known is the August Perseids; at the peak of the shower, one can see about 100 meteors per hour on a dark clear night. In what became one of the first successful linkages between a meteor shower and its parent comet, astronomer Giovanni Schiaparelli proposed in 1867 that the Perseid meteors originate from a comet seen just five years previously and now known as 109P/Swift-Tuttle.
The Earth is not the only planet that sweeps up cometary dust in its path. In 2014, long-period comet C/Siding Spring grazed the planet Mars, loading its upper atmosphere with tons of cometary material. The aftermath was recorded by instruments onboard Mars-orbiting probes like NASA’s MAVEN and ESA’s Mars Express.
This project aims to understand how the atmospheres and surfaces of planets can serve as natural area detectors, to find new streams and to test our understanding of streams and showers at the Earth. One project aspect will focus on the stream of comet 2P/Encke that is incident on the planet Mercury.
Comet 2P/Encke has been linked to several strong daytime and nighttime meteor showers at Earth, the so-called Taurid complex. The NASA MESSENGER spacecraft that orbited Mercury between 2011 and 2015 showed seasonal modulation of Ca in the exosphere. The leading candidate mechanism to explain this seasonality in Ca production is meteoroid impact vaporisation (Killen and Hahn, Icarus, 2015), however models of the sporadic meteoroid environment at Mercury have failed to reproduce the full profile of Ca production rate over time. In 2015 we showed that the Ca production is most likely modulated by impacts with Encke debris and placed constraints on the age and size of the stream meteoroids (Christou, Killen et al, Geophysical Research Letters, 2015; see figure from this NASA press release). This model has so far stood the test of time (Pokorny et al, ApJ, 2018) but important questions remain. The ESA-JAXA Bepicolombo mission is currently on its way to Mercury and its arrival in 2025 will provide further opportunities to test the link between Mercury’s exosphere and the Encke meteor stream (Plainaki et al, JGR (Planets), 2017). It is now necessary to construct higher-fidelity models of this stream, to apply to available MESSENGER data on other exospheric species (eg Na) but also to the new datasets expected from BepiColombo.
Project work will include, but may not be limited to, intensive numerical simulations, which has been the state-of-the-art in stream modelling since their successful application to the Leonid meteor storms ~20 yr ago. Some familiarity with techniques of dynamical astronomy will be seen as an advantage.
For further information contact firstname.lastname@example.org
Investigating the outflows of black hole progenitors in different galaxies
Supervisor: Andreas Sander
Classical Wolf-Rayet (WR) stars are a rare, but important class of evolved, helium-burning stars. Their spectra are dominated by huge emission lines, indicating strong outflows. With mass-loss rates that are about ten times higher than those of O supergiants, just a few WR stars are enough to easily outweigh the feedback of a whole population of OB stars. As the last long-lived stage before core collapse, helium-burning WR stars are also tied to our fundamental understanding of heavy black holes. The amount of mass lost by these stars defines the eventual black-hole masses but depends strongly on their metallicity environment and our understanding of their outflow physics and properties.
This PhD project will combine observational and theoretical efforts to reach a quantitative understanding of WR stars and their impact in different environments. To achieve this, the student will analyse WR stars in different galaxies with stellar atmosphere models, gaining first-hand experiences with a new generation of models that directly connect the observed WR spectra with fundamental physical insights. Different treatments for wind physics in the derived model atmospheres will be investigated. By comparing observational data to the derived models, the project will provide an important piece to the decade-lasting puzzle of WR mass loss and how it scales with different environments. The analyses of multiple WR single and binary systems in various galaxies will provide the necessary gauging of theoretical relations to accurately constrain the nature of the heavy black holes discovered in Gravitational Wave events.
For further information contact email@example.com
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.
Rendering from the Mopra molecular cloud survey of the galactic plane. Two axes are position on the sky, the third is the velocity of the gas along the line of site. It provides a proxy for distance. This can be constrained through the use of complementary data sets at other wavelengths to turn this image into a three-dimensional map of the Galaxy.
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.firstname.lastname@example.org
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