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List of Master Projects

Below is a list of the Masters projects available for 2020. If you are interested in a project and want more details or want to know if other projects are available, please contact the project supervisor. For general questions, please contact project coordinator Prof. Dr. Carsten Dominik (c.dominik@uva.nl)

1.  Seeding planet formation with interstellar objects

Supervisors: Rico Visser, Carsten Dominik
In a recent paper, https://arxiv.org/abs/1903.04451, Susanne Pfalzner and Michele Bannister have made an attempt to estimate if it is possible to seed planet formation in a protoplanetary disk by catching interstellar objects like Oumuamua and using them as seeds for Pebble Accretion.  While this is a fascinating idea, the paper does not do a proper job in modeling if and how efficiently objects can be captured in the protoplanetary disk, and what the role of capturing smaller objects (cm, m, 1km sized) could play.  In this master project, you will get to do a much better job, derive and model the capture properly and get a real answer on whether new planetary systems build on the ejecta from old planetary systems.

2.  Radial distribution and motion of high-temperature material in planet-forming disks

Supervisor: Carsten Dominik
The meteoritic record shows that some high-temperature condensates that formed extremely early in the solar system (CAI’s are the oldest solids in the entire system) are distributed out to the asteroid region and even into the cometary regions of the solar system.  For energetic reasons, CAI very likely must have formed close to the Sun, probably during the early infall and disk formation phase.  In this project we will study the radial spread of such material, to understand when and if such material needs to form and can be moved outward in the disk, even while disk gas is moving inward due to accretion.  The topic is extremely timely, it touches on the key questions of solar system research currently being persued. In this project you will have to dig into the dynamics of particles in a disk.  Good understanding of physics and very good abilities to work with python are key skills you need to bring.

3.  Decoding X-ray variability from black holes with NICER

Supervisors: Phil Uttley, Arkadip Basak
NICER is a state-of-the-art X-ray telescope that has been operating from the International Space Station since 2017. It’s uniquely able to observe the brightest X-ray sources in the sky: accreting black holes in X-ray binary systems, simultaneously measuring both the energy and arrival time (to 40 ns precision!)  of each X-ray photon. This gives us a powerful window to study the rapid variability from the innermost regions of the accretion flow and use it to probe accretion physics and the effects of extreme gravity on the dynamics of the accreting gas. As members of the NICER Science team, we are offering up to two projects with us, to carry out novel analyses on NICER observations of black hole X-ray binaries. In these projects, you will apply new ‘spectral-timing’ techniques that can measure the time delays between variations of the different spectral components (accretion disk and corona/jet-base) and so work out the physical origin of the variability and what it tells us about the regions closest to black holes. The work will be mostly analytical, using existing software and writing your own to extract new information from the data, but you can also branch into theory and physical modelling of any interesting results you discover. You should consider this project if you are interested in high-energy astrophysics/black holes and  programming to develop advanced data analysis techniques.

4. Searching for (near-)ultraviolet transients using MeerLICHT and Swift/UVOT

Supervisors: Rudy Wijnands, David Modiano
The sky is very variable at all electromagnetic wavelengths and has been intensively studied at all time scales. However, one understudied regime is the ultraviolet (UV). This is mostly because the UV is absorbed by the Earth's atmosphere and space-based instrumentation is prohibitively expensive, i.e., instruments with very large field-of-view (FOV). However, space-based UV facilities are available that frequently observe the same part of the sky and the near-UV (NUV) can still be observed using ground-based facilities. During this MSc project, you will search for UV and NUV transients in data obtained with the UV/Optical Telescope (UVOT) aboard the Swift satellite and/or with the ground-based MeerLICHT telescope (located in Sutherland in South Africa). In this project, you will focus on real-time transients, meaning that the discovery of the transients will be done within hours to at most a few days after the data were taken so that follow-up observations (both photometric as well as spectroscopic) can be acquired at times when the transients are still active. These follow-up observations will considerably help us to further study the transients we will discover. The transients we expect to find are flares from active stars and interactive binaries, accretion powered outbursts in compact binaries (harboring white dwarfs, neutron stars, or black holes), and a host of more extreme events like all kinds of different types of supernova explosions.

5. Potential extragalactic flares with AARTFAAC

Supervisors: Ralph Wijers, Mark Kuiack
Using an all-sky radio telescope we find that bright extragalactic sources such as AGN sometimes flare up, for only 10-20s. Usually this flare does not come from the source itself, but is due to plasma near the Earth (e.g., the ionosphere) acting as a magnifying lens. However, there is at least one case where the flare could be due to the AGN itself, and that would be truly remarkable and unprecedented. The evidence for this comes from the delay in the peak of the flare caused by the radio waves travelling through interstellar and intergalactic medium. Can we turn this hint into strong enough evidence, but examining the flares more closely and finding more examples? This is the question we shall ask and answer in this project. You will use hundreds of hours of data to search for the flares, and then study them in detail using models of the electron density in space.

You will work in the radio transients group of Rowlinson and Wijers; skills you will develop is analysis of large data volumes (using mostly python scripts), statistics of rare unusual phenomena, and understanding of radio emission from high-energy sources.

6. Can we see prompt radio emission from gamma-ray bursts?

Supervisors: Ralph Wijers, Deniz Aksulu
There are mechanisms by which the central engine of a gamma-ray burst (GRB) can produce strong coherent emission at radio wavelengths. If we could observe that emission it would teach us a lot, not only about the GRB but also about the intergalactic medium through which the radio signal travels. However, there may be a nearby spoil-sport: the shock caused by the GRB itself can absorb the radio waves right after they are emitted! This likely means that there is a narrow window during which radio waves can get out, and that therefore the time history of radio emission is very telling about the conditions in the GRB. In this project, you will calculate the development of a GRB shock using (somewhat complex) analytical approximations, and use those to find out about which GRBs we can receive radio signals from, and what this will tell us about those GRBs. You will use analytical approximations and possible some numerical integration techniques, and learn about relativistic fluid mechanics and radiation mechanisms. You will work in the radio transients group of Rowlinson and Wijers.

7. What is the famous neutron star X-ray binary SAX J1808.4-3658 doing in quiescence?

This is one example, but look below for other project ideas related to the overarching theme of “multi-wavelength observations of accreting neutron stars and black holes”.

Supervisor: Nathalie Degenaar
Low-mass X-ray binaries (LMXBs) and millisecond radio pulsars (MSRPs) are two different manifestations of neutron stars in binary systems. It is thought that LMXBs evolve into MSRPs once a neutron star is done feasting on its companion star. However, many questions about the connection between these source types remain. The famous neutron star LMXB SAX J1808.4-3658 has long been suggested to switch on as a MSRP during times that it is not accreting from its companion star. However, despite extensive efforts, radio pulsations have never been detected from it. Possibly, there is still matter flowing towards the neutron star during its apparent “off” states, which prevents radio pulsations to switch on, or to be observed.

In this project, you will investigate what happens to SAX J1808 when its accretion appears to switch off, by studying its UV and optical emission. You will use UV imaging data from the Hubble Space Telescope and optical data from the 4-m SOAR telescope located in Chile. Specifically, you will test whether its UV emission can be explained by a cold accretion disk, or whether the UV emission is coming from the surface of the neutron star. The latter could be an exciting alternative explanation that potentially allows us to measure the temperature of this unusually cold neutron star. Such a measurement could have important implications for the physics of ultra-dense matter.

This is an observational project in which you will learn to work with UV and optical imaging data from different ground-based and space-based telescopes. The science topics involved are X-ray binaries, accretion, the evolution of neutron stars in binary systems and the physics of ultra-dense matter.

Apart from this specific project, there are plenty of other opportunities for multi-wavelength observational studies of accreting neutron stars and black holes in my group. If you are interested in a specific topic or a particular wavelength, we can discuss the possibilities for a tailored project. You can also look at my website for some other project ideas!

8.  Title: Coming soon - with a vengeance!

Supervisor:  Anna Watts
Something involving either relativistic pulse profile modelling of NICER data *or* hydrodynamical modelling of exploding oceans. Or even both (in parallel, not in the same project).

9. Beyond the oblique dipole for pulsar magnetospheres

Supervisor: Oliver Porth
Recent X-ray pulse profile modeling of data collected with the NICER satellite has revealed that the magnetosphere of millisecond pulsars might be much more complex than previously thought.  In the pulsar J0030, three to four X-ray emitting hotspots are observed on a single hemisphere which cannot be explained with the standard oblique rotating dipole model.  It is likely that the accretion process which spins up the pulsar to millisecond periods has burried'' the fields, leading to weaker magnetic fields with complex morphology.  Including higher order multipoles could resolve the issue of the hotspots, but the properties of complex magnetospheres such as spin-down rate and radio / X-ray pulse shapes are largely unknown.

Using (general-) relativistic force-free electrodynamics which describes the interaction of strong magnetic fields with a conducting plasma, you will perform simulations (with the BHAC code) of complex magnetospheres inspired by the recent observational data.  Depending on your strengths, the project can branch out in two direction: on the one hand, modeling observational signatures in gamma- X-ray and radio bands will be extremely interesting in particular as more data from NICER is coming in.  Among other outputs, this can inform hotspot models in the modeling pipeline used for NICER data.  On the other hand, the project can shed light on fundamental properties of pulsars: for example, the dependence of spin-down rate on obliqueness and frame dragging is entirely unknown in multipolar force-free magnetospheres. Another subject of interest is the stability of such complex field structures around neutron stars with applications to magnetar flares.

10. Modelling the evolution of magnetic O-type stars

Supervisors: Zsolt Keszthelyi (daily advisor); Alex de Koter (second advisor)
Description:
Surface magnetic fields are routinely detected in stars all across the Hertzsprung Russell diagram, from early to late evolutionary stages. In low-mass stars, the incidence rate of magnetism is 100%, and it is understood that these fields are generated by a dynamo mechanism powered by the convective envelope. In intermediate and high-mass stars, the incidence rate of magnetism is only 7%, and likely it is not a result of an active dynamo mechanism as massive stars possess radiative envelopes.

While the origin of such fossil magnetic fields in massive stars is still unknown (part might be the result of stellar mergers), it has become clear that their presence drastically changes the physical properties of stars, particularly their mass loss and surface rotation. Consequently, the evolution of massive stars is significantly affected by fossil magnetic fields. There are, however, only a handful of known magnetic O-type stars, 11 as of now. Hence a detailed investigation of this sample is very important to enable further progress in the field.

Goals:
The key goal of the project is to find how well current state-of-the-art stellar evolution models can be reconciled with known magnetic O-type stars, whether discrepancies can be identified, and if so, how these discrepancies may be resolved. The project can focus on one specific star or study the sample collectively. The project should establish a clear picture of the uncertainties/limitations in reproducing the evolutionary state of the sample stars and detail which physical assumptions are critical. The candidate will have to collect observational data reported in the literature and compare them to new model calculations, with the final goal to be able to draw relevant conclusions from the comparison.

Numerical tools:
MESA, Python, Linux/OS op. system

Candidate:
The candidate should have a profound interest in stellar evolution and stellar physics and the willingness to learn relevant numerical tools to perform simulations with a state-of-the-art code. The candidate will learn to use the MESA stellar evolution code and be able to compute stellar evolution models.