The projects

Searching for transient and variable radio sources in “Big Data”

Supervisor: Antonia Rowlinson
Contact: b.a.rowlinson@uva.nl

Since ancient times, astronomers have been interested in the changing astronomical sky. Variability studies initially started in optical, finding sources like supernovae and variable stars. As new facilities came online, astronomers were able to extend their studies to multiple wavelengths – from gamma-ray to radio. We now know that our Universe is highly dynamic and the sources we observe enable us to probe fundamental physics.

We have now entered the information age, where multi-wavelength facilities are able to obtain vast amounts of data. It is no longer feasible for us to manually search images for variability. Various teams have been developing pipelines and filtering strategies to manage this big data.

In this project, we will use a large radio image dataset, containing many snapshot images, and process them through our LOFAR Transient’s Pipeline. We will create a single python script combining the latest state-of-the-art search strategies to filter the large database of source light curves. We will then quantify transient and variable behaviour in the field and further analyse transient candidates to determine their progenitors.

Knowledge of Python would be very useful. 

GPU-accelerated magnetohydrodynamics

Supervisor: Phillipp Moesta
Contact: p.moesta@uva.nl

This project will involve porting and profiling individual computation kernels for our GPU-GRMHD code GRHydro-X. GRHydro-X is a dynamical-spacetime general-relativistic magnetohydrodynamics code for simulation binary neutron-star mergers and supernova explosions. The project is flexible and can be focused on performance testing and optimization of existing modules of the code for specific GPU architectures or developing new physics modules (e.g. neutrinos, equation of state, magnetic fields). The former will give the student experience working with state-of-the-art GPU systems and gain insights into modern GPU programming while the latter also involves algorithm development for computational physics in astrophysical magnetohydrodynamic simulations.

Characterisation of the small hydrocarbon  C₈H₅⁺ as potential carrier of the Diffuse Interstellar Bands

Supervisor: Alessandra Candian
Contact: a.candian2@uva.nl

The Diffuse Interstellar Bands (DIBs) are one of the longest standing mysteries in astronomical spectroscopy. Detected for the first time in 1922, they are more than 400 unidentified absorption bands detected in the UV to the near-IR when looking through interstellar clouds. They are believed to come from the electronic excitation of molecules. The fact that they are seen in our Galaxy (and even outside) and how many there are tells us that they are due to very abundant molecules.

4 DIBs have been identified as due to the buckminsterfullerene cation, C₆₀⁺ , the largest molecule ever detected in space. Researchers have been trying to link some of the DIBs to other abundant interstellar molecules, such as Polycyclic Aromatic Hydrocarbons  (PAHs). Recent experiments have studied the destruction of PAHs by UV photons. They all end up producing C₈H₅⁺ and C₇H₃⁺ molecules. While the C₇H₃⁺ molecule has already been studied in detail, that is not the case for C₈H₅⁺

In this project, you will investigate what shapes the hydrocarbon C₈H₅⁺ can take and how their electronic spectrum would look like. To do so, you will perform Quantum Chemistry calculations and eventually you will compare the electronic spectra with that of the DIBs.

For more info: https://iopscience.iop.org/article/10.1088/1742-6596/728/6/062005/pdf

Oxygenated PAHs in space?

Supervisor: Alessandra Candian
Contact: a.candian2@uva.nl

Polycyclic Aromatic Hydrocarbons (PAHs) are a class of molecules of great importance for the interstellar medium. They are detected through their infrared bands (the AIBs) in the spectra of many different astronomical environments (planetary nebulae, star-forming regions, protoplanetary disks, the interstellar medium). The JWST telescope, launched in 2022, is collecting high-resolution infrared spectra that are revolutionising our understanding of the lifecycle of PAHs in the ISM. In particular, we are seeing that PAHs can contain also Oxygen atoms. Oxygen-containing PAHs have not been investigated in detail, because we do not how to create them in lab. In this situation computational methods can be very valuable

In this project, you will investigate the properties of Oxygen-containing PAHs: you can choose to compute their vibrational spectrum using Quantum Chemistry techniques or study their photon-driven dissociation, using molecular dynamics simulations.

For more info: https://arxiv.org/abs/1908.05918

Magnetic Mountains

Supervisor: Oliver Porth
Contact: o.j.g.porth@uva.nl

Some of the brightest galactic X-ray sources are the so-called X-ray binaries.  Here the energetic radiation is emitted by heated gas which revolves around and falls towards a compact object (a black hole or a neutron star).  In contrast to black holes, neutron stars have a hard surface and roughly 50% of the observed radiation is thought to be released when matter crashes into the stellar surface.  There are many open questions about how matter lands and spreads over the star and answering them is key to understanding how the different classes of neutron stars evolve in our universe.

One aspect of this problem is the formation of magnetically supported mountains on the stellar surfaces.  In essence, as matter falls onto the star, it cannot expand sideways due to the strong magnetic field (ionized gas cannot cross field lines) and it piles up as a mountain.  The expected mountain heights are <~100 m and they will eventually collapse when the magnetic support fails.  The properties of the mountains (how high, how massive) are not only interesting for the X-ray emission from the surface, the mountain on the rapidly rotating star could also be an important gravitational wave source.  
In this project, you will simulate what happens when matter rains down to the stellar surface.  When does the mountain collapse?  What is the maximum height you can support?  How does this depend on the properties of the matter?  Does it depend on where on the surface you grow the mountain?  
This project is a great start into numerical simulations using (magneto-) hydrodynamics and for getting a flavor of front line questions in theoretical astrophysics.  

Modeling exoplanet atmospheres

Supervisor: Antonija Oklopčić
Contact: a.oklopcic@uva.nl

Spectroscopic observations of transiting exoplanets allow us to study the properties of their atmospheres, such as the temperature, chemical composition, and dynamics (i.e. winds and outflows). My group specializes in using exoplanet spectroscopy to investigate how exoplanets lose their atmospheres through planetary outflows. A spectral line of helium at the wavelength around 1 micron, which is one of the strongest atmospheric features observable in exoplanets, has been particularly useful for these studies. However, it has only been observed while exoplanets are transiting in front of the host star. The goal of this project is to investigate whether it can be observed during secondary eclipses, i.e. while the planet is passing behind the star. This project will involve using publicly available python-based tools to create atmospheric models of exoplanets and use them to make predictions of spectroscopic observations with large ground-based telescopes or the James Webb Space Telescope.

Visualizing GRMHD simulations

Supervisor: Oliver Porth
Contact: o.j.g.porth@uva.nl

To learn more about the nature of strongly curved spacetime and ultra-dense nuclear matter, my group performs simulations of how gas and magnetic fields behave in the vicinity of black holes and neutron stars (see e.g. www.bhac.science).  As the size of the simulations increases, visualizing and getting the most physics out of 3D simulation data is increasingly difficult as the data can reach hundreds of GB per simulation snapshot.  Furthermore, since we can only see the 2D images on the screen, interacting with 3D data on a computer is hard and often time-consuming.  
In this project you will develop a python-based 3D visualization package that we started recently in our community to make this easier.  We have so far created a prototype which demonstrates the feasibility and provides a starting point for the project.  Besides adding features to the package (e.g. 3D-isocontours, volume-renderings, slices, performance optimization), you will get in touch with the physics of the simulations themselves.  This is a great way to learn about how black holes accrete matter, how magnetohydrodynamic turbulence works and how and when magnetic fields power high-energy cosmic flares.  

Exploring accretion black hole’s disk winds with X-ray spectroscopy

Supervisor: Elisa Costantini
Contact: E.Costantini@sron.nl

Active galaxies (AGN) host a supermassive black hole, whose accretion and ejection activity is not yet fully understood. The AGN ejects winds at several hundreds of km per second which may escape the system and influence the growth and evolution of the host galaxy. 

In this project the student will study the high-resolution X-ray spectrum of the bright AGN Mrk279 using the data of the NASA satellite Chandra. This system is known to eject a muliti-component fast wind. In this project the student will learn about AGN and their importance in the universe and will get familiar with high-resolution spectroscopy.

Spectroscopic Investigations of Gaia Candidate Exoplanet Targets

Supervisor: Gudmundur Stefansson
Contact: g.k.stefansson@uva.nl

Through its astrometric monitoring of the whole sky, Gaia is revolutionizing our understanding of numerous areas of astrophysics. For exoplanet science, Gaia is expected to detect hundreds if not thousands of exoplanets especially at intermediate orbital distances which have been relatively poorly probed for planets. Recently, the Gaia team released intermediate dataproducts to the astrometric time-series revealing a number of nearby stars that show potential evidence of hosting substellar companions—brown dwarfs or massive planets. Some of these stars are low mass stars, but finding massive planets or brown dwarfs orbiting such stars is particularly interesting, as such companions are known to be intrinsically rare around such stars. We are conducting a program to spectroscopically follow-up all such targets with the Habitable-zone Planet Finder and NASA NEID spectrographs in the Northern hemisphere around nearby low mass stars to confirm if those targets are compatible with the planet or brown dwarf scenario, and to rule out false-positive scenarios such as double-lined binaries. The student will use python and jupyter notebooks and would have opportunities to work on spectroscopic data and other supporting datasets to understand these intriguing systems better. Knowledge of python for this project would be beneficial.

Unveiling the Properties of Radio-Emitting M Stars

Supervisor: Gudmundur Stefansson
Contact: g.k.stefansson@uva.nl

The ongoing LOFAR two meter sky survey has detected a sample of nearby M stars that show evidence of coherent radio emission at low frequencies. This is puzzling, because we do not expect M stars to show such emission. What could be the source? One intriguing scenario is that these M stars could host nearby planets that could be interacting with their host stars generating the radio emission. Another scenario is that these stars host brown dwarfs at long orbital periods that are the true source of the radio emission. This project will seek to help understand this intriguing sample of radio emitting stars through better characterizing the properties of the host stars from available observations. This could include studying photometric observations (e.g., TESS, ZTF) to characterize their flare or rotation rates, and/or analyzing ongoing near-infrared high resolution spectroscopic observations obtained with the Habitable-zone Planet Finder (HPF) spectrograph to characterize their spectral properties. From HPF, we see that at least some of these stars are intriguingly seen in binary or even triple star systems. Opportunities could include helping develop python tools to accurately extract radial velocities in double and triple lined systems. These investigations will help set the stage for planet hunting around this intriguing sample of stars. Knowledge of python for this project would be beneficial.

(Spectro-)Polarimetry at the Anton Pannekoek Observatory

Supervisor: Rasjied Sloot & Stephanie Heikamp
Contact: M.R.Sloot@uva.nl

This Bachelors Project is dedicated to the introduction and development of spectro-polarimetry techniques at the Anton Pannekoek Observatory, with the primary objective of detecting polarimetric signatures in stellar objects. Emphasis will be placed on exploring the fundamental principles of polarimetry and spectroscopy, particularly in the context of observational techniques.

The student undertaking this project will actively participate in practical learning experiences, gaining hands-on exposure to telescope operations, equipment handling, and programming in Python for data analysis. In addition to theoretical knowledge, the project entails observing multiple nights at the observatory, requiring the student to be on stand-by for optimal weather conditions.

The overarching goal is to utilize spectro-polarimetry to measure polarimetric signatures in known (magnetic) stellar objects and subsequently estimate their physical properties.

Trinity tango: exploring mass transfer in triple star systems

Supervisor: Silvia Toonen & Floris Kummer
Contact: S.G.M.Toonen@uva.nl  f.a.kummer@uva.nl

In our universe, stars are often not born alone. They frequently form binary or multiple systems where all stars are gravitationally bound to each other. A particularly fascinating aspect of these multi-star systems is the phenomenon of mass transfer, where one of the stars donates mass to an inner binary. This is a completely novel phenomenon,  and so how the mass transfer affects these systems is still poorly understood. Utilizing a newly developed simulation code, you will investigate the mass transfer of observed triple stars and unravel their final fate. 

NICER studies of turbulent black hole accretion disks

Supervisor: Phil Uttley
Contact: p.uttley@uva.nl

Accreting stellar-mass black holes in our galaxy allow us to study the behaviour of matter close to the black hole, by studying the X-ray emission from their accretion disks. The disk emission shows rapid and large-amplitude variability, which evolves through the black hole outburst to a more stable state. However the origin of the variability and the reasons for this change are still a mystery. NICER is an X-ray telescope with an unprecedented capability to study the rapid variability of the disk, and you will use NICER data with new analysis techniques to try to understand how the disk turbulence changes and why.  This project involves using Python programming to analyse and model data, so is well-suited to someone with some Python experience.

Searching for Ultra-Fast Radio Bursts

Supervisor: Jason Hessels & Kaustubh Rajwade
Contact: j.w.t.hessels@uva.nl rajwade@astron.nl

Fast radio bursts (FRBs) are short (typically millisecond duration) radio flashes that are cosmological in nature. Their large luminosities and distances make them one of the most energetic and widely seen events in the Universe. Despite their discovery more than a decade ago, the physics of their origins still eludes us. Further breakthroughs in the field depend on expanding the FRB search parameter space. Very recently, this was achieved by the discovery of isolated micro-second FRBs (Snelders et al. 2023), which suggests that there might be a large population of ultra-fast radio bursts (uFRBs) that have been missed by current searches due to the existing biases against them. Discovering uFRBs is extremely important as the minimum duration of an FRB helps us constrain/rule out theoretical models of FRB emission. Furthermore, their incredibly short durations make them excellent probes to accurately measure the most important physical quantities in Cosmology (e.g. Hubble Constant) in a way that complements other existing techniques. To that end, we propose to search high-time-resolution data from the Westerbork Synthesis Radio Telescope (Wb RT-1) and the 100-m Effelsberg telescope on two well-known repeating FRBs to look for isolated uFRBs. Discovering a sample of these events will lead to significant breakthroughs in FRB emission physics. The student will search for these bursts in already existing data using state-of-the-art data processing software. The project will provide significant experience in coding (Python), time-domain data analysis, and machine learning. It will equip the student with a vital skill set that will prove beneficial in domains beyond astronomy as well. 

The eating pattern of the neutron star UW CrB

Supervisor: Nathalie Degenaar
Contact: N.D.Degenaar@uva.nl

Neutron stars and black holes are the collapsed remnants of once massive stars that ended their lives in a supernova explosion. These cosmic cannibals are notorious for their very strong gravitational pull, which allows them to pull gas from their surroundings. The astronomical object called UW CrB contains such a neutron star that devours gas from its unfortunate companion star. Recently, we made a surprising discovery that this neutron star not only swallows gas but also blows gas away in a wind and at present we don’t understand how this happens. In this project, you will use NASA software to analyse several observations of UW CrB, taken with different X-ray satellites. By studying the energy spectrum and variations of the X-ray emission, we hope to better understand the eating patterns of this neutron star and how this can lead to the ejection of gas.

Note: Although I list two possible projects in my group, I can take only 1 student this year. Therefore, depending on interest, only one of these projects will actually be offered.

Charting the properties of black holes and neutron stars in our Galaxy

Supervisor: Nathalie Degenaar
Contact: N.D.Degenaar@uva.nl

Neutron stars and black holes are the collapsed remnants of once massive stars that ended their lives in a supernova explosion. Our Milky Way contains nearly 300 black holes or neutron stars that are known to live in binary star systems wherein they can swallow gas from their companion star. In late 2023, a brand new catalog of these so-called X-ray binaries was published, and this contains a wealth of information for instance about their position in the sky, but also about their brightness at X-ray, optical and infrared wavelengths, their rotation period and much more. In this project, you’ll use this new catalog to chart the origin of the optical and infrared emission, for fist time for such a large source sample. This will be very important to understand different types of behavior and sub-classes. It may also serve as a template to find new X-ray binaries in large surveys with new and future telescopes.

Note: Although I list two possible projects in my group, I can take only 1 student this year. Therefore, depending on interest, only one of these projects will actually be offered.

Investigating Bayesian inference for X-ray spectroscopy of Supernova Remnants

Supervisor: Jacco Vink & Manan Agarwal
Contact: j.vink@uva.nl   m.agarwal@uva.nl

In X-ray spectral analysis it is common practice to fit models by varying the parameters of the spectral components until a certain statistic (like chi^2) is optimized with regard to the observed X-ray spectrum. However, this frequentist approach becomes less reliable and inefficient as the datasets become large or the models have complex parameter spaces with strong degeneracies as in the case of supernova remnants. A Bayesian framework allows for systematic exploration of complex parameter spaces as well as error estimation and model comparison. For this project, the student will simulate X-ray spectra of the supernova remnant, Cas A, which will soon be observed by the new JAXA/NASA X-ray telescope, XRISM, and was observed by NASA’s JWST last year (Milisavljevic et al 2024, Vink et al 2024). The student will perform spectral fitting on these simulated spectra to statistically check the robustness of Bayesian methods (BXA; Buchner et al 2014). The student will learn X-ray spectral analysis and advanced statistical techniques like Markov Chain Monte Carlo, Nesting Sampling, Bayesian Inference, etc. Prior knowledge of Python is recommended. If interested in this topic please contact Jacco Vink ( j.vink@uva) and/or Manan Agarwal (m.agarwal@uva.nl). We can also customize a project if the student as specifics interests in X-ray spectroscopy of supernova remnants.

The ultraviolet variable sky

Supervisor: Rudy Wijnands
Contact: r.a.d.wijnands@uva.nl

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), mostly because UV radiation is nearly completely absorbed by the Earth's atmosphere and space-based instrumentation is prohibitively expensive (i.e., for instruments that have the large field of views, FOV, to make serendipitous sources for UV variables and transients viable). However, small FOV instruments are available: e.g., the UV and optical telescope (UVOT) aboard the Swift satellite. Over the last few years, we have developed an extensive pipeline (in Python) to search newly acquired data as well as archival observations obtained with the UVOT to search for and study a large variety of variable objects (ranging from variable stars to explosions from accreting compact objects) as well as new transients in the UV regime. This project could place at most 2 BSc students that can use this pipeline to search for such types of objects in the UVOT data.

Additional information: 2 BSc students can work on this project but all will work independently on their own data sets although with close collaboration with each other and other group members. The student(s) will have weekly meetings with the supervisors as well as participate in the weekly group meetings.

Software packages used: Knowledge of Python would be very useful.

Surfing the waves in an exploding neutron star ocean

Supervisor: Anna Watts, Yves Kini, Tuomo Salmi
Contact: A.L.Watts@uva.nl  y.kini@uva.nl  t.h.j.salmi@uva.nl

The oceans of accreting neutron stars regularly explode due to unstable thermonuclear burning of hydrogen and helium, giving rise to bright X-ray bursts.  In some cases we see brighter patches form on the burning surface, but what triggers this remains unknown nearly 30 years after they were first observed. One possibility is the formation of global-scale standing waves in the burning ocean. In this project you will develop a mode pattern module for an existing relativistic ray-tracing code, and use it to explore whether the mode hypothesis is consistent with observations. 

Probing mass-loss from low-mass stars via radio observations

Supervisor: Robert Kavanagh
Contact: kavanagh@astron.nl

Low-mass stars like our own Sun lose mass over their lifetime via outflows known as stellar winds. Understanding stellar winds is important, as they can severely impact the atmospheres of orbiting planets. Measurements of stellar winds have only been possible in a handful of cases, hindering our knowledge of how they affect exoplanets. However, radio observations with upcoming telescopes such as DSA-2000 and the Square Kilometre Array (SKA) will likely revolutionise measuring the winds of these stars. In this project, the student will develop and utilise numerical models in Python to both constrain stellar winds from current radio observations, and provide a framework for measuring stellar winds with next-generation telescopes.