Dissertation projects for the MSc by Research in Astronomy & Astrophysics
Below are some of the MSc(R) projects for this coming year (2013/2014). We will try to keep this list updated, particularly on the lead up to the beginning of the first semester (16th September 2013). However, we encourage prospective MSc(R) students to speak with as many of our academic staff, as early as possible, to find out what we do and to see if there are possible MSc(R) projects available - this list is unlikely to be comprehensive. Note that supervisors and projects should be decided within the first 1-2 weeks of the first semester and they should inform the MSc(R) course director (Dr. Clive Dickinson).
Heating the solar corona: 3D numerical magnetohydrodynamic simulations and 1D modelling of the turbulent dynamo
Supervisor: Prof Philippa BrowningA major unsolved problem in astrophysics is to explain why the solar corona is at a temperature of over a million degrees Kelvin (compared with a surface temperature of about 6000 K). Coronal plasma is believed to be heated by dissipation of stored magnetic energy. Much research concerns modelling the dissipation of magnetic energy through the process of magnetic reconnection. There are two potential projects in this area. One project will involve running numerical simulations using the LARE3D code, which numerically solves the equations of magnetohydrodynamics, and analysing the results. This will build on recent work showing that reconnection can be triggered by the onset of the kink instability in twisted coronal loops, exploring a range of magnetic field configurations and exploring the energy release. The second project will use a simplified analytical model of the effects of turbulent reconnection, building on one-dimensional models widely used for laboratory plasmas in which the turbulence is parameterised as a “dynamo” electric field. These models will be extended to solar coronal loops, requiring some analytical calculations and simple numerical modelling (solution of ordinary differential equations).
High energy particles in solar flares
Supervisor: Prof Philippa BrowningSolar flares are dramatic releases of stored magnetic energy, emitting electromagnetic radiation from radio to hard X-rays or gamma rays. Large numbers of non-thermal ions and electrons are produced, but the origin of these high-energy particles is not understood. A promising theory is that particles are accelerated by the strong electric fields associated with reconnection of the magnetic fieldlines. This can be studied using a "test particle" approach, in which charged particle motion is calculated in electromagnetic fields representative of reconnection. A project is available to use test particle models to study the generation of high energy particles in solar flares - this will involve adapting existing computer codes, as well as some programming and analytical calculations.
Radio Recombination Lines with single dishes
Supervisor: Prof Richard J DavisWe have used Parkes ZOA and HIPASS data at 1.4GHz to study Radio Recombination lines in our Galaxy. This is to study the ionised gas normally detected with Halpha emission to form a template for the Free-Free emission in our Galaxy: so important as a foreground to our CMB measurements, particularly for Planck. However this is not possible for low galactic latitudes due to the dust in our Galaxy. We thus turn to these radio frequencies where the dust is transparent.
We have very good data in the south with Parkes , but need to obtain good data in the north with the Lovell. We need to design a back end correlator system for JBO to enable us to observe the RRL's at JBO. The student will interact with others at JBO and JBCA to cost and design such a system.
HI intensity mapping for the detection of Baryon Acoustic Oscillations
Supervisor: Dr. Clive DickinsonBaryon Acoustic Oscillations (BAOs) are imprinted on matter throughout the Universe. They provide a key cosmological standard ruler, that can be used to measure the expansion of the Universe as a function of redshift and therefore can constrain dark energy models e.g. the equation of state. This is one of the key science drivers for the Square Kilometre Array (SKA) that will be fully operational during the next decade. However, a new technique called "HI intensity mapping" may allow them to be detected at radio wavelengths by mapping the redshifted 21cm HI line on large angular scales. Furthermore, this could be achievable within the next few years, providing complementary information and an independent test of the cosmological model.
We have proposed a single dish experiment, BINGO (BAOs using Integrated Neutral Gas Observations), that has the possibility of detecting BAOs (Battye et al. 2013). We are currently pursuing funding and site locations for the 40m dish required for BINGO. In the meantime, much preparation is required both on the instrumentation side, and on the analysis side. In particular, we need to make detailed simulations of BINGO data, taking into account the bright foregrounds and also instrumental systematic effects that could be problematic. These issues will be critical to the success of the experiment. We are also affiliated with other HI intensity mapping experiments including interferometric arrays that could be the focus of the project depending on progress with both experiments.
The student will become a member of the BINGO team and cosmology group at Manchester. Depending on your interest, and background, you will work with the BINGO team to develop simulation tools, component separation and analysis techniques, and may be involved in the design and testing of instrumentation for BINGO (e.g. testing of receivers, programming of digital backends etc.). An important aspect will be dealing with foreground contamination from our Galaxy and extragalactic radio sources.
Radio mapping of the sky using single dish data
Supervisor: Dr. Clive DickinsonSensitive mapping of extended diffuse emission, over a large region of sky, is notoriously difficult with single radio dishes. Firstly, total-power receivers are not stable over long time scales, resulting in large scale variations of power. Secondly, the atmosphere itself fluctuates in terms of the radiated power producing similarly large variations in power. This limits the maps that can be produced, which are traditionally limited in size and often filtered, leaving only compact sources. This is important for projects such as the One-Centimetre Receiver Array (OCRA), which is currently operated on the Torun 32-m telescope in Poland.
This project will investigate mapping techniques to allow single dishes to recover large-scale emission in the presence of large-scale correlated noise. One example is a Fourier-transform based technique by Emerson, Klein & Haslam (1979), but has only been exploited a few times in recent years. Simulations will be made to quantify how well this technique can be used for modern instruments, for a variety of targets and frequencies. Other algorithms (e.g. Maximum Entropy Method, or direct inversion) may be investigated. We will obtain test data from the OCRA instrument from Torun in Poland to test the algorithm and assess its performance.
31 GHz mapping of Galactic objects using the Cosmic Background Imager
Supervisor: Dr. Clive DickinsonOur Galaxy, the milkyway, contains a variety of phenomenon that emit radio waves e.g. synchrotron radiation from supernova remnants and free-free emission from warm ionised gas around hot stars. At high radio frequencies (>~10 GHz), a new component has been discovered, that is associated with dust, and dominates over a narrow range of frequencies from about 10 to 60 GHz. This "anomalous microwave emission" is now thought to be due to electric dipole radiation from small spinning dust grains, but there is still not much detailed information about this new component. At these frequencies, it is particularly important to understand the various emission mechanisms since they must be removed from ultra-sensitive observations of the cosmic microwave background (CMB), which is typically much weaker.
This project will use data taken with the Cosmic Background Imager (CBI). The CBI was a 13 element close-packed interferometer, located in the Atacama desert in Chile. Although its primary aim was to map the CMB (it the first instrument to detect the so-called "damping tail" of the CMB on scales of ~10 arcmin) it also observed a number of Galactic sources at frequencies of 26-36 GHz, some of which have led to publications in astronomy journals. A number of datasets have still yet to be analysed, including high resolution observations of the Rho Ophiuchi molecular cloud, a sample of supernova remnants, Galactic scans among others. You will reduce and calibrate the CBI data for one or more of these targets, learning how radio interferometry works and how to make a deconvolved (CLEANed) map of the source. You will then interpret the images produced, comparing them with multi-frequency data available on the web - including low frequency radio data and infrared data from the IRAS satellite.
E-Merlin studies of gravitational lensing
Supervisor: Dr. Neal JacksonGravitational lenses are systems in which a background object is multiply imaged by the action of the gravitational field of a foreground galaxy. They are important because they can give us indications of mass distributions in distant objects, independent of the light that they emit. Studies of radio gravitational lenses are interesting because they can, as well as mapping the structure associated with the normal lensed images of the background source, also see the central image which forms very close to the line of sight to the lensing galaxy. This image carries information about the central part of the lensing galaxy potential, in the region close to the central black hole and stellar cusp. The image is likely to be very faint, and has evaded detection in all but one case so far. However, with the new generation of instruments, which are about ten times more sensitive than hitherto, we should be able to detect such central images if they exist. The major such instruments are the EVLA and e-MERLIN, based at Jodrell Bank. A large legacy programme for e-MERLIN has been awarded in order to study radio-loud gravitational lens systems.
The project will begin with analysis of some already existing EVLA data on gravitational lens systems, on which preliminary analysis has already been done. The student will then become involved with e-MERLIN during the commissioning phase, and help with the analysis and interpretation of early data from the e-MERLIN lensing legacy programme. Full details of this programme are given on this webpage.
Polarization Calibration of C-BASS
Supervisor: Dr Paddy LeahyThe C-Band All Sky Survey is a major project to map the Galactic and extragalactic synchrotron emission, and particularly its polarization, across the whole sky. It will be used both to help understand the Galaxy's magnetic field, and to correct Cosmic Microwave Background polarization observations for the foreground synchrotron emission. We are using two telescopes, one in Owens Valley, California, and one in the Karoo desert, South Africa. Shake-down observations with the Owens Valley dish have been in progress for the last year and survey observations are expected to start in autumn 2011, and will rapidly lead to maps of large areas of sky (observations will be complete within one year).
To get an accurate measurement of the polarization of the sky, we have to correct for the inevitable artificial polarization imposed by the instrument itself. The aim of this MSc project is to measure the residual instrumental polarization of the Owens Valley system using observations of standard targets such as planets, the Crab Nebula, etc; to implement software to correct for this within the MATLAB data processing pipeline that we are using for the project, and to cross-check the preliminary C-BASS maps with other polarization surveys such as those made by WMAP and the DRAO Penticton survey.GALFACTS
Supervisor: Dr Paddy LeahyThe Galactic ALFA continuum Transit Survey is mapping nearly half the sky at 21 cm wavelength with the giant Arecibo radio telescope. The major focus is on the polarization of the sky emission, which will reveal the structure of the Milky Way Galaxy's magnetic field in unprecedented detail, using several different tracers: polarized synchrotron radiation from relativistic electrons within the Galaxy, Faraday rotation of 100,000 background radio sources (whose polarization vectors are rotated as the radio waves pass through the magnetised interstellar medium), and Faraday rotation of the emission from the Galaxy itself. At present, the survey is about 25% complete.
This MSc project will analyse the existing data to determine the statistical structure of the Galactic polarized synchrotron emission, primarily by measuring the angular power spectrum. This will be compared to predictions from models of magnetic field turbulence, and to the power spectrum on larger scales measured by WMAP and Planck. As well as constraining the physics of the Galactic magnetic field, these results will help set an upper limit to the impact of Galactic synchrotron emission on cosmological analysis of the Cosmic Microwave Background polarization.All-sky map-making with Single Dish Radio Telescopes
Supervisor: Dr Paddy LeahyThere are many projects in progress to map the radio sky at various different frequencies (from 300 MHz to 857 GHz) by scanning the sky with single dish telescopes. Examples include the WMAP and Planck cosmic microwave background satellites, C-BASS, and the GMIMS polarization survey which uses Penticton, Canada, and Parkes in Australia.
In all these surveys we wish to make a map of the sky, which comes down to finding the brightness of the radio emission (in several Stokes parameters) at each pixel in some convenient tiling of the celestial sphere. The problem is that the data is not collected by pointing at each pixel centre, but by scanning the telescope in some pattern with no particular relation to the sky pixelization. Since the telescope sees the sky convolved with its point-spread function (the "beam", as radio astronomers say), this gives full information about the sky provided that gaps between neighbouring measurements are smaller than half the beam width. The simplest way to treat such data is to bin each measurement into the nearest pixel, and this is what all current surveys do. But in many ways this is very sub-optimal and it would be better to interpolate the data onto the sky pixel grid. There are two problems to be solved: (i) computationally efficient interpolation onto the pixelised sphere (all standard interpolation routines work on a flat cartesian grid) and (ii) determination of the optimum interpolation function. The latter depends on the beam shape and also on the scientific purpose intended for the sky map. One example of the latter is to compensate for highly elliptial beams, such as some of those on WMAP and Planck, which otherwise make the sky maps difficult to interpret, especially in polarization.
This MSc project will produce and test an interpolation map-maker using the high-level IDL language, which will function as a prototype for an advanced map-maker for the Planck and C-BASS projects.
The chemistry of giant stars
Supervisor: Dr. Iain McDonald, Prof. Albert ZijlstraTwinkle twinkle, little stars. We don't wonder what you are, because we have measured your spectra. We can determine the abundance of various different elements in stars by measuring the strengths of the absorption lines in their spectra. This project involves measuring lines in the spectra of around 100 stars in a globular cluster, taken with the Very Large Telescope. These are very old stars which formed shortly after the Big Bang. Measuring their composition tells us about how these clusters formed, and about the very first stars that came before them. Previous experience with Linux would be helpful. The student should be prepared to make themselves available for a week during the first semester (subject to taught courses) for a visit by our collaborator, Christian Johnson (UCLA), with whom we will work closely on this project.
The Orbital Parameters of Radio Emitting X-ray Transients
Supervisors: Dr Tim O'Brien & Prof Ralph Spencer (Emeritus)X-ray binaries are close binary star systems in which one star transfers matter to the other. The donor star is typically a main-sequence star (although some are more evolved) whilst the accretor is a more compact object, usually a neutron star or black hole. The release of gravitational potential energy in the accretion process causes the systems to be bright in the X-rays. Some of these systems show outbursts in which the X-ray brightness changes rapidly - these are known as X-ray binary transients. These systems also show radio emission, in many cases in the form of jets. The mechanism which drives these outbursts and variability is still not well understood. This project aims to explore the relationship between the radio/X-ray variability and the orbital parameters. For example, we might expect that binaries with circular orbits would have steadier accretion than those with eccentric orbits and hence might exhibit less variability. The project would involve collecting data on orbital periods etc, where known, and comparing these with known radio and X-ray properties. Observational data will be gathered largely from the published literature although archives, such as from the VLA, could also be mined where data are incomplete. Ways of appropriately characterising 'variability' would need to be investigated - so there are also signal processing aspects of the project.
Observation and modelling of nova explosions
Supervisor: Dr T.J. O'BrienNovae are interacting binary stars in which a white dwarf accretes matter from a companion star. A thermonuclear explosion on the surface of the white dwarf ejects the matter, causing a significant brightening across the spectrum from radio waves to gamma rays. Our group and international collaborators are involved with monitoring nova outbursts using a range of telescopes and interpreting the observations in terms of hydrodynamic models of the explosion. A number of projects are possible in this area, including reduction and analysis of radio observations (including from e-MERLIN), hydrodynamic simulations of shocks and modelling of X-ray emission. Outstanding questions relate to the geometry of the ejecta and the ultimate fate of the white dwarf, in particular whether some of these systems eventually end as supernova explosions.
Direct detection of very high frequency gravitational waves
Supervisor: Prof. Lucio PiccirilloGraviton to photon conversion is possible in the presence of a strong static magnetic field (inverse Gertsenshtein effect). The photon generated will be coherent with the original graviton. We are interested in exploring the theoretical and technical issues related to the direct detection of gravitons in the GHz to optical frequencies. The potential sources of such high frequency gravitons are at a moment very speculative: Kalutza-Klein 5D gravity and/or the inflationary period in the big bang. A prototype detector has been in operation for several months collecting useful data.
The student will be involved in the data analysis and simulations as well as in the continuation of the design studies for a more sensitive detector.
A miniature dilution refrigerator for astrophysical applications
Supervisor: Prof. Lucio PiccirilloBolometers are the preferred detectors of astrophysical radiation in the mm/sub-mm and far infrared. When operating in low background, bolometers need to be cooled to extremely low temperatures 300 mK to 30 mK. Below 100 mK the preferred cooling technology is based on the dilution cooling of mixture of He-3/He-4. Our group is world leading in the development of miniature dilution systems that can be operated in small cryostats suitable for operations at the focal plane of telescopes.
The student will be heavily involved in the design, realisation and testing of a fully tiltable miniature dilution refrigerator.
Development of a novel passive correlator for the next generation of radio astronomy interferometers.
Supervisor: Prof. Lucio PiccirilloDiffraction of electromagnetic waves limits the angular resolution of radio telescopes. The larger the diameter of the telescope the better the angular resolution. Unfortunately, building larger telescope to achieve better and better resolution is very expensive: it scales roughly with the diameter to the power of 2.8. Radio interferometry allows us to achieve high resolution by combining the amplitude/phase of the electromagnetic waves coming from many small telescope. The combination is achieved by electronic correlators. Correlators are very complex electronic devices: the current limit to the number of antennas that can be correlated is of the order of few tens (the number of signals, or baselines, goes as the square of the number of antennas).
A novel passive correlator will be studied theoretically and especially experimentally. The idea to be tested consists in optically combining the amplitudes of the waves coming from each telescope in an optical "beam combiner". This system can potentially correlate hundreds of telescopes. The student will work with a team that will design, build and test a 3 x 3 quasi optical correlator working at 11 GHz. The prototype will be fielded at the Jodrell Bank Observatory from where observations of some strong radio sources will be performed.
Study fast radio transients with the Lovell Telescope
Supervisor: Dr. Ben StappersRadio Transients provide an opportunity to study some of the most extreme environments in the Universe. It is already well known that neutron stars can give off bursts of emission on timescales as short as nanoseconds, but bright radio bursts are also expected from Gamma-ray bursts, merging neutron stars or blackholes, or perhaps even evaporating black holes. The study of transients in the radio has recently undergone a rapid evolution with the building of new telescopes and significant improvements in computing capabilities. We have recently purchased hardware to undertake a survey for variable and transient radio emission with the Lovell Telescope. We will use this to piggy-back on nearly all observations with the Lovell, to get sufficient observing time to detect rare and interesting events. This project is to help develop the software required to perform these observations and to analyse the data. Once observations are possible the student will analyse the data to look for new, and known sources of transient radio emission with a view to detecting rare, and thus scientifically important events. This project requires someone with a good understanding of computing and software.
Searching for new pulsars with LOFAR
Supervisor: Dr. Ben StappersThe LOW Frequency ARray, LOFAR, is the first of the next generation of radio telescopes to be built. It is located predominantly in the Netherlands but extends over much of Europe. unlike traditional radio telescopes that are based around large parabolic surfaces it uses small dipole-like antennae and combines them using sophisticated software and large computing power. Moreover it works below about 300 MHz, a frequency region previously very poorly studied. We have performed a survey of parts of the Northern sky to search for new radio pulsars. Pulsars are highly magnetised and rapidly rotating neutron stars and are some of the most extreme objects known. They are used for studies as varied as the behaviour of plasma in regions of high magnetic field to searching for gravitational waves. This project is to work on developing new and effective ways to find pulsars and to apply these techniques to our existing and new data sets to try and find new pulsars.
A polarized view on the pulses of radio pulsars
Supervisor: Dr. Patrick WeltevredeRadio pulsars are highly magnetised neutron stars which spin with periods of between a few millisecond and seconds. Each rotation the radio emission, which is beamed along the magnetic poles, sweeps across the Earth and can be detected by very sensitive radio telescopes as a regular sequence of pulses. The rotation of the neutron stars is extremely stable which makes them very accurate clocks allowing tests of the general theory of relativity. However, each of the individual pulses of the observed sequence vary greatly in shape, intensity and polarisation properties. These variations caused by largely unknown physical processes in the magnetosphere of these stars. In some cases these variations happen in a coordinated fashion, which are known as drifting subpulses. We have recently shown that this property seems to be endemic to the overall emission process of pulsars. In this project we want to compare the radio polarisation properties of a large sample of pulsars with their drifting subpulse properties to better determine the physics of the emission process. This process is still a mystery since the discovery of pulsars more than 40 year ago.
