Our MSc projects are open to students from various Physics & Astronomy MSc tracks, including Astronomy & Astrophysics, Theory and GRAPPA. Students from other MSc programs such as Computer science or Chemistry can potentially also enroll in certain MSc projects, provided that they have sufficient (technical) background. 

If you are interested in a project and want more details, please contact the project advisor(s). For general questions, please contact project coordinator Dr. Alessandra Candian.

List of projects for 2024

Top-down Interstellar carbon chemistry

Advisor: Alessandra Candian

Description:

More than 300 molecules have been detected in space and the large majority are carbon-based. Among them we have molecules like carbon dioxide, methanol,  formamide but also larger Polycyclic Aromatic Hydrocarbon (PAH) molecules and fullerenes (C60). 

The strong UV irradiation coming from stars can dissociate these interstellar molecules providing building blocks to build new ones, initiating the so-called top-down interstellar chemistry. While the standard way to build large molecules from smaller ones (bottom-up interstellar chemistry) is well studied, the top-down chemistry is still largely unexplored.

Recent laboratory work showed for example that irradiating PAH cations of different shapes and sizes with UV leads to the formation of the same hydrocarbons – namely C8H5+ and C7H3+ – and of the carbon rings Cn+ with n=10-15. The reaction pathways leading to these species are unknown and also their IR and UV-vis spectra. These last are fundamental to see if these smaller carbon species might be responsible for the Diffuse Interstellar Bands – the longest standing mystery in astronomical spectroscopy – more than 400 unidentified absorption bands detected in the UV to the near-IR when looking through interstellar clouds.

Within this theme, possible projects available are:

1. Theoretical investigation of the reactions leading to the formation of small hydrocarbons. The formation pathways will be compared to the results from the experiments (collaboration with Pavi Sundararajan, Leiden)

2. Theoretical investigation of the IR and UV-Vis spectrum of Carbon rings and estimate their survivability in the interstellar medium (collaboration with Vince Esposito, NASA AMES). The spectra can be compared to the astronomical spectra of the DIBs and with JWST observations through the PDRs4ALL consortium.

 

Investigating the hydrocarbon chemistry on Titan

Advisor: Alessandra Candian

Description:

Titan, the largest moon of Saturn, is a place like nowhere else in the Solar System. A dense, nitrogen-rich atmosphere, very similar to the one on Earth, is the place where very interesting photochemistry, started by solar photons, forms organic (made of C, H, N and sometimes O), molecules that are the precursors of the haze present in the atmosphere. The haze particles then "rain" on the surface where they are moved by wind to form dunes, lakes, and seas of hydrocarbons.

Understanding the inventory of molecules present in the atmosphere and how this evolves responding to the physical and chemical conditions is of great importance because Titan is one of the best places in the Solar System to look for life.

1. We have experimental IR spectra on proton bombardment of pure phenanthrene (C14H10) ice, phenanthrene:CH3CN mixed ice, and pure CH3 CN ice. Both molecules have been detected in the atmosphere of Titan and are expected to “freeze” at lower altitudes, creating ice clouds. Galactic Cosmic Rays and solar wind can process this ice, leading to new chemistry,  You will analyse the experimental spectra taken over a range of temperatures or over a range of proton fluences and try and identify the physico-chemical evolution of the ‘ices’ and their compositions (e.g. structural changes, chemical reactions, physical properties).

2. You will work with Cassini data to understand and quantify the population of large PAHs on Titan’s higher atmosphere using a database of calculated IR spectra and to figure out the molecular composition of the enigmatic Haystack feature. 

 

Investigating interstellar dust toward the black hole X-ray binary Cygnus X-1
Advisors: Sascha Zeegers (ESTEC), Elisa Costantini (SRON), Nathalie Degenaar

Description:
Interstellar dust plays an essential role in the life cycle of stars and galaxies. Although this dust is well studied, it is not clear how dust survives in the harsh environment of the galactic interstellar medium (ISM). The chemical composition, crystallinity and size distribution of the dust grains are important properties that show us the evolution of these grains as they travel through the ISM. We can study the dust properties by observing dust extinction features in the spectra of stars that are used as a background light. X-ray binaries are particularly suitable to study dust properties. The soft X-ray band provides specific spectral features of dust that reveal the lattice structure, chemical composition and grain size. In this project you will study the spectrum of the blackhole X-ray binary Cygnus X-1. New and detailed observations of the Chandra X-ray observatory will make it possible to investigate the dust particles along the line of sight in great detail. You will compare the spectra with  a database containing laboratory spectra of interstellar dust analogues to unravel the dust properties.

 

Spectroscopic Investigations of Gaia Candidate Exoplanet Targets

Advisor: Gudmundur Stefansson

Description:

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. 

In this project, you will work with a combination of spectroscopic data and other supporting datasets to understand these intriguing systems better with the potential to help detect some of the first exoplanets detected by Gaia. Knowledge of python and MCMC methods for this project would be beneficial.

 

Insights into the Obliquities of Warm Neptunes 

Advisor: Gudmundur Stefansson

Description:

The present architectures of planets can yield insights into how they form and evolve. Stellar obliquity—the angle between the stellar rotation axis and the planet orbital axis—is a key observable of planetary architectures, and has been shown to be a powerful probe of planet formation histories. If we see that a system is on a highly inclined orbit then the question immediately arises: What caused the system to be on a misaligned orbit? There are a few theoretical mechanisms that can cause misalignments (e.g., planet-planet scattering, Lidov-Kozai interactions), while other mechanisms would tend to form ‘well-aligned’ planetary systems (e.g., smooth formation in a disk, close-in planets subject to tidal realignment processes etc.).

The most efficient way that we have of measuring stellar obliquities is through leveraging high resolution in-transit spectroscopic observations of the so-called ‘Rossiter-McLaughlin Effect’, the effect that causes measurable distortions in the stellar lines that occur as a planet crosses in front of a rotating stellar disk. Many such observations have been done for Hot Jupiter systems showing a broad range of obliquities. However, Hot Jupiters are a relatively infrequent outcome of planet formation, with smaller planets much more frequently seen. However, due to their smaller sizes much fewer obliquity measurements exist of such planets, and it is unclear if they should follow the same obliquity distribution as seen for Hot Jupiters.

In this project you will analyze already obtained state-of-the-art high-resolution spectra of 1-2 Rossiter McLaughlin effects of nearby warm Neptune planets obtained with the NEID spectrograph on the WIYN 3.5m Telescope and/or the Maroon-X spectrograph on the 8m Gemini-N telescope. Initial results suggest that they are well-aligned with the spin-axis of their host star. A component of the effort is to help develop and test a ‘Reloded RM Effect’ pipeline—a recently published method that is showing great promise for characterizing the obliquities of small planets. Knowledge of python, and MCMC methods for this project will be beneficial.

 

Winds of change: Illustrious cannibal neutron stars revisited in X-rays 

Advisors: Nathalie Degenaar, Elisa Costantini (SRON), Maria Diaz Trigo (ESO)

Description:

Hercules X-1 and Cygnus X-2 are two bright X-ray sources that contain neutron stars that swallow gas from an accompanying star. Both of these so-called X-ray binaries have been discovered decades ago and studied extensively with many X-ray satellites. However, much remains to be discovered about the table manners of these cosmic cannibals. In this project, you will perform the first detailed high X-ray resolution study of these neutron stars using unpublished X-ray spectral data obtained with ESA’s XMM-Newton satellite. This is expected to shed new light on the trajectory and geometry of the gas flow in these illustrious X-ray binaries. 

 

Winds of change: The UV edition 

Advisor: Nathalie Degenaar

Description:

Hercules X-1 and Cygnus X-2 are two bright X-ray sources that contain neutron stars that swallow gas from an accompanying star. Both of these so-called X-ray binaries have been discovered decades ago and studied extensively with many X-ray satellites. However, much remains to be discovered about the table manners of these cosmic cannibals. In this project, you will perform the first detailed UV analysis of these neutron stars using unpublished data obtained with NASA’s Hubble Space Telescope. This is expected to shed new light on the trajectory and geometry of the gas flow in these illustrious X-ray binaries. 

 

Scrutinizing an X-ray puzzle

Advisor: Nathalie Degenaar

Description:

Neutron stars in X-ray binaries spend long stretches (years) of time in quiescence, during which they must be accreting little or no matter. Apart from thermal X-ray radiation produced by the hot glowing neutron star, often a more energetic X-ray emission component is detected too, but its origin remains unknown. Is it coming from a residual accretion stream or is it produced by the magnetic field of the neutron star? In this project, you will analyse X-ray data from the Chandra and XMM-Newton satellites of a large sample of quiescent neutron star X-ray binaries to scrutinize this long-standing puzzle.

 

Neutron star anatomy 

Advisors: Rudy Wijnands and Nathalie Degenaar

Description:

Unraveling what neutron stars look like on the inside offers the exciting opportunity to learn how matter behaves under extreme physical conditions that cannot be reproduced in terrestrial laboratories. This can be achieved by studying how neutron stars cool down after they have been heated by swallowing gas from a companion star. In this project, you will measure such cooling trajectories of different neutron stars by analysing new X-ray data obtained with the Chandra and XMM-Newton satellites. Comparison with theoretical simulations then provides very valuable insight into the structure and composition of the crust, as well as the nuclear reactions that occur inside neutron stars. 

 

The variable UV sky 

Advisor: Rudy Wijnands 

Description:

The sky is very variable at all electromagnetic wavelengths and has been intensively studied at these wavelengths. 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 (launched in 2004). 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 up to 2 MSc students that can use this pipeline to search for such types of objects in newly acquired UVOT data and/or study the long-term available UV light curves using the archival data.

Project 1: The student will use archival data to make long term UV light curves of transient or strongly variable sources. The main targets to be probed in this project will be AGN,  Be/X-ray binaries, or Mira variables. The first two types of sources will be used to probe the extreme environments (i.e., accretion) around black holes or neutron stars; the last source type will be used to probe stellar structure and evolution. All source types have not been extensively studied in the UV. Together with the student the exact source type will be selected depending on the interest of the student. In case the student has a particular interest in a source type not listed here, I am open to discuss this and maybe the project can focus on this type. 

Project 2: The student will use the realtime UVOT data to search for transient sources and, when found, study them in detail. It cannot be predicted what types of sources will be found (and therefore in which science direction exactly the project will go) but the most commonly found sources are a host of variable stars, accreting white dwarfs, and AGN. So it is expected that the project will evolve in the direction of one of these source types, all of which have not yet been extensively studied in the UV. 

 

Observational project with the Anton Pannekoek Observatory

Advisors: Rudy Wijnands and Rasjied Sloot

Description:

A project might be offered to a student who is interested in hands-on observing using the equipment available at the Anton Pannekoek Observatorium on the roof of the astronomical institute. Please contact us if you are interested in such an observing project. 

 

Winds from supermassive black holes

Advisor: Elisa Costantini (SRON)

Description:

This project will investigate the complex nature of outflowing winds from a bright supermassive black hole, by means of high resolution X-ray spectroscopy. The student will learn about data analysis and modeling of the primary radiation of the accretion disk around the black hole as well as the chemical and physical characteristics of the photoionized gas. Multi-phase outflows are important in the so-called feedback process, as winds influence the growth of the host galaxy. Moreover, this source will be one of the first targets observed by the to-be-launched XRISM satellite. Therefore the potential publication out of this project will inform future XRISM studies.  

 

Mapping the cold interstellar medium

Advisor: Elisa Costantini (SRON)

Description:

Interstellar dust particles constitute the building blocks of  planetary systems and rocky planets like our own. The initial conditions for a system formation are therefore very important in understanding its fate. X-rays are a powerful tool to study a large variety of interstellar environments, from diffuse media to molecular clouds. This project is multidisciplinary. On one side the student will study and simulate astronomical data, especially of future, high-performing X-ray satellites. On the solid state physics side, the student will analyze high resolution data collected at the Soleil-LUCIA synchrotron beamline.

 

Implement the effects of porosity in DustPy

Advisor: Carsten Dominik

Description:

DustPy is an amazing code to compute dust coagulation globally in a disk. It was written by Sebastian Stammler and Til Birnstil, and I used it recently with a colleague in a paper about the bouncing barrier. The code is extremely flexible.  However, variable (size and time-dependant) porosity during growth has not yet been implemented. This project is to explore this possibility and construct the first such models.

Prerequisite:  You are an excellent Python programmer and are able to use numpy arrays to its fullest.  At least, you need to be a fast learner on these subjects.

 

Build a continuum model for extremely porous particles for compression simulations

Advisor: Carsten Dominik

Description:

Compressing fluffy dust aggregates to compact pebbles is one of the last poorly understood step in planet formation. In this project, we will try to build a continuum model (compressibility, tensile strength) from first principles, so that it can be used in numerical simulations using continuum mechanics. There have been some attempts in the literature, I want to understand these better, improve them, extend them to the extremely porous materials that form first on planet-forming disks.  If we have time, we will also apply this model to compute the compression curves.

Prerequisite: Physical insight, joy with trying new ideas and approaches, fun with an open-ended project.

 

Build simple interfaces to ADDA and T-Matrix to make computing opacities accessible to the astronomical community

Advisor: Carsten Dominik

Description:

Computing opacities for dust particles in astronomical context is a key ingredient in linking any system containing dust to observations in a meaningful way.  In the past, this was an art that had to be re-invented by everyone working on dust.  During COVID lockdowns, I wrote a new tool, called optool, that can be run with a single command from the command line. Over the past 3 year, this code has taken off and is now used by many astronomers.

I want to add two new methods to this code, to be able to compute opacities for compact but irregular particles, like we expect pebbles to be.

 

Project 4: Protecting volatile materials during meteorite fall for delivery to planet

Advisors: Carsten Dominik and Alessandra Candian

Description:

Delivery of volatile materials to a planet through asteroid and comet impacts is an important theme in planet formation and seeding interesting chemistry to a planet.  In this project, we will look at the heating of objects falling through an atmosphere onto a planet. We will study the question under what circumstances volatile material embedded inside the object can be preserved during this fall and “safe;y” delivered to the planetary surface.

 

Project 5: Oumuamua as an extreme low-density object

Advisor: Carsten Dominik

Description:

Omuamua was the first interstellar object discovered in the solar system.  It looks like an asteroid or comet from another solar system.  However, something weird happened.  On its way away from the Sun, it was slightly accelerated, without showing gas ejections one might expect from comets.  One, rather strange, possibility was that this could be an EXTREMELY porous object, with internal densities of 10^(-5).  In this project I want to explore this possibility.

 

Reconstructing the evolutionary history of high-mass X-ray binaries by identifying their parent cluster using Gaia DR3

Advisor: Lex Kaper

Description:

High-mass X-ray binaries (HMXBs) consist of a massive star orbited by a compact X-ray source, a neutron star or a black hole. The compact star is the remnant of the originally most massive star in the system that exploded in a supernova (and/or gamma-ray burst). Due to a phase of mass transfer, the secondary star (now an OB star) gained mass and has become the most massive star in the system. When during the supernova less than half of the total mass of the system is lost, the system can remain bound and will move through interstellar space with high, supersonic velocity. With Gaia it is possible to measure the space velocity very accurately, and to reconstruct the path of the HMXB. In some cases it turns out to be possible to identify the parent star cluster of the massive binary system. The age of the cluster then sets a constraint on the progenitor mass of the compact star, allowing us to reconstruct its evolutionary history. 

 

Hunting for transients in commensal surveys with LOFAR

Advisors: Antonia Rowlinson and Ralph Wijers

Description:

We have been conducting a transient survey in the LOFAR survey of the Northern Sky. To date we have only studied ~6% of the Northern Sky and have already detected a new exciting long period Galactic transient. A special subtraction imaging and candidate filtering strategy to find new transient sources has been developed and is ready for application to more data (de Ruiter et al. 2023). 70% of the LOFAR sky survey is now observed and we want to automatically search these data for more long period Galactic transients. This project will tackle this big data challenge by applying the current strategies to these new data, develop new filtering strategies as required (including the possibility of applying machine learning techniques) and study new transient sources found in these data.

 

Super-fast imaging of LOFAR data for real-time transient hunts

Advisors: Antonia Rowlinson and Jason Hessels

Description:

To date, image plane transients found in LOFAR observations are found weeks to months after the observation took place. This significantly hinders obtaining multi-wavelength follow-up observations that are vital in determining the progenitor of the transient and characterising its properties. Instead, we want to be able to find the brightest transient sources, particularly the long period Galactic transients,  in near real-time. In the coming 2 years, LOFAR is undergoing a significant upgrade and will also have the data streamed in real-time to the EuroFlash cluster (PI: Jason Hessels). This project will test, develop and implement a very fast imaging strategy on the EuroFlash cluster that bypasses the very time consuming calibration steps. We will use existing observations of the LOFAR long period Galactic source and simulated data to test the strategy. Machine learning techniques may be required to filter between transient sources and imaging artifacts.

 

Deciphering the local environments of repeating fast radio burst sources using scintillation

Advisors: Jason Hessels and Ziggy Pleunis

Description:

Fast radio bursts (FRBs) are impulses of radio waves that last for only a fraction of a second and that are detectable over extragalactic distances. The origin of FRBs remains elusive, though various types of highly magnetized compact objects, e.g. magnetars, are favoured candidate sources. A small fraction of FRBs has been observed to repeat and the most hyperactive of repeating FRB sources produce up to hundreds of detectable bursts per hour. One key to understanding the origin of FRBs is to study their local environments in detail, which is possible because the FRB signal holds a record of all the burst's interactions with the magnetized plasma it encountered on its way. Free electrons disperse the radio waves and inhomogeneities in the free electron distribution along the way can cause multi-path propagation that lead to scatter-broadening and scintillation of the signal. Magnetic fields furthermore cause Faraday rotation of the polarized light. Especially the lines-of-sight towards repeating FRB sources can be studied in detail as the timeseries of dispersion, scattering and scintillation allow a better decomposition of the structures local to the source and other structures along the way. In this project, the student will use repeating FRB source detections from the CHIME/FRB experiment -- currently the world-leading FRB detection instrument (and potentially data from other radio telescopes as well), and attempt to measure scattering and scintillation in the FRBs. To increase sensitivity to scintillation the student will develop novel techniques for burst stacking. To interpret the results the student will model structures in the interstellar medium. This project will train the student in radio astronomy, transients, the interstellar medium and data analysis techniques.

 

Cleaning radio astronomy data for real-time transient detection

Advisors: Jason Hessels and Daniela Huppenkothen

Description:

Radio telescope data is corrupted by strong `radio frequency interference’ (RFI) that is generated by human technology and activities - e.g., airplane radars, cell phones, and satellite constellations. This presents strong challenges for detecting naturally occurring radio sources in space, and can lead to a high rate of false positive detections of transient signals. Our ability to do ground-breaking science depends directly on how well we can manage RFI. In this project, you will develop machine-learning techniques to catch and filter out RFI from data from the real-time CHORD fast radio burst (FRB) observing system.

 

Space weather report to improve pulsar timing arrays

Advisors: Jason Hessels and Aditya Parthasarathy

Description:

Global Pulsar timing array collaborations opened a new window to the Universe by providing the first compelling evidence of the gravitational wave background signal in 2023. Characterising this signal will help us understand the cosmic population of supermassive black holes and how they evolve in their host galaxies. However, inaccurate models of the interstellar medium bias our measurements of the gravitational wave background. This project will use pulsar observations with the LOFAR radio telescope to better understand our current limitations in modelling the interstellar medium. The student will gain experience in Bayesian statistics, computing and a solid understanding of radio pulsar data sets.

 

Exploring repeating fast radio bursts with the Nançay Radio Telescope

Advisor: Jason Hessels 

Description:

With the Nançay Radio Telescope (south of Orléans, in France) we have an ongoing programme that monitors repeating fast radio burst (FRB) sources at high time resolution (16us). The goal of this project is to help extend the observing capabilities of the project to be able to record raw voltage data and thereby study these FRB sources at orders-of-magnitude higher time and frequency resolution. This is critical both for understanding the origin(s) of these repeating sources as well as their local environments.

 

Decoding black hole X-ray variability

Advisor: Phil Uttley

Description:

Stellar mass accreting black holes in X-ray binaries show rapid X-ray variability on time-scales of seconds to milliseconds, which must originate close to the black hole where the X-rays are produced. We have developed advanced Fourier methods to decode, disentangle and model the variations produced by the different emission components: the accretion disk and corona. In this project you will use these techniques together with state-of-the-art data from X-ray observatories such as NICER and HXMT, to work out the relationship between the regions close to the black hole. By comparing their behaviour with the latest physical models, you will be able to determine the structure of these regions and how they change as the system evolves through an outburst. 

 

Developing the science case for an X-ray interferometer

Advisors: Phil Uttley and Roland den Hartog (SRON)

Description:

We are leading an effort to develop X-ray interferometry for use in space. If successful, we will see gains of at least 3 orders of magnitude in spatial resolution over current instrumentation, which will enable imaging of many energetic astrophysical environments such as the coronae of nearby stars, the accretion disks and winds of X-ray binary systems and be able to resolve pc-scale accreting supermassive black hole binaries from across the visible universe. In this project you will help to develop the science case for an X-ray interferometric mission, by learning to simulate and use interferometric data made from ‘mock images’ of real (and currently unresolved) astronomical X-ray sources, which you will create based on their known physical properties. As part of our team you will also be able to join our group working on the demonstration of X-ray interferometry in the lab at SRON, and incorporate the lessons learned from the lab into your simulations.  

 

Are Active Galactic Nuclei super-sized X-ray binaries? An X-ray timing view

Advisors: Phil Uttley and Daniela Huppenkothen

Description:

The accreting supermassive black holes in Active Galactic Nuclei (AGN) show many similarities with their stellar-mass cousins in X-ray binaries. One interesting connection is in their X-ray variability (‘timing’) properties: AGN show characteristic variability time-scales which scale linearly with black hole mass and can be extrapolated all the way down to the stellar mass systems. However, timing behaviour in X-ray binaries also shows a deep connection to the ‘accretion state’ of the system, which determines whether the black hole is able to power the launching of jets or winds. Long-term X-ray monitoring can be used to test whether AGN show the same states as X-ray binaries, but this test has been difficult in the past because of the computational time needed to model the data. In this project you will use a new, much faster Bayesian time-series analysis method based on Gaussian processes, to robustly compare AGN and X-ray binary timing behaviour and show whether they have even more in common than we think.

 

Unravelling enigmatic radio emission from a nearby M dwarf

Advisors: Rob Kavanagh (ASTRON) and Gudmunder Stefansson

Description:

Most exoplanets orbit close-in around M dwarf stars. M dwarfs also possess powerful magnetic fields, multiple orders of magnitude stronger than that of the Sun. Planets orbiting sufficiently close to their host stars can magnetically interact, producing bright emission from both the star and planet. Signatures of such interactions are thought to be especially strong at radio wavelengths. These processes have been established as a viable detection method for planets around M dwarfs, and the LOFAR radio telescope is providing us with the first tentative signs of such interactions. One such recently detected M dwarf is GJ 1151. This detection is particularly interesting, in that the star is known to be very inactive. In parallel to this, recent radial velocity measurements have begun to hint at a massive companion orbiting GJ 1151. In this project, the student will investigate the origin of this enigmatic radio emission from GJ 1151 and how it may relate to the presence of a massive companion. For this, 3D numerical models will be utilised and developed. The results of this work will provide a framework for hunting for planets around M dwarfs through a radio lens.

 

How can gamma-ray bursts happen in constant-density environments?

Advisors: Ralph Wijers and Antonia Rowlinson

Description:

When a long gamma-ray burst explodes at the end of the life of a massive star, we can deduce the density profile of the circumstellar medium from the way the light curve of the GRB afterglow declines. From the behaviour of the light curves, we infer that GRB afterglows appear to be about equally divided between cases where the density is uniform, and where the density declines as 1/r^2, as one would expect from a stellar wind. Simple calculations however show that the uniform case should be occur only rarely, if ever. So what is going on?

In this project you will explore, partly analytically and partly computationally, the interaction between the wind of a massive star and its environment, and see what kinds of conditions are needed to allow uniform circumstellar media to be seen in GRB afterglows. Interest in massive stars and GRBs is helpful, and no particular aptitude for computational work is required.

 

How many flares can you see? Playing hide-and-seek with transients

Advisors: Ralph Wijers and Antonia Rowlinson

Description:

Many transient sources either emit periodic flares of radiation, or a more random pattern of flares, in which for example the wait times between flares have a  poison or log-normal distribution, and the brightness of a flare may depend on the wait time from the previous, or to the next. Our observations of such flaring source are never complete: we can only see it at night, or only during half a satellite orbit, and we will not get to use the source at all times when it is visible. In that non-ideal-state, how much can we derive about the true frequency and pattern of the flares, given observing constraints? And, to reverse the question, what is the ideal observing strategy to derive the true properties of a flaring source of a certain type.

In this project you will explore this problem using Monte Carlo simulations in which we model both the properties of the source and of the observatory. The project is fairly compute- and programming-intensive, so interest in computing is a must, and interest in the physics of high-energy flare source such as Soft Gamma Repeaters and Fast Radio Bursts is helpful.

 

PPM for accretion-powered pulsars  (more astro-oriented)

Advisor: Anna Watts

Description:
Using a technique called Pulse Profile Modelling (PPM), based on relativistic ray-tracing of emission from X-ray pulsars, we are able to infer their mass and radius, and also map the hot X-ray emitting hotspots.  We use mass and radius to learn about the properties of the supranuclear density matter in the neutron star core, while the latter tells us about - for example - the configuration of the star’s magnetic field. This technique has been developed in the first instance for use with NICER data of rotation-powered millisecond X-ray pulsars.

We are now trying to apply PPM to accretion-powered millisecond X-ray pulsars, which tend to spin faster than the NICER sources, enhancing the relativistic effects that we take advantage of.  But this brings a host of new challenges, not least the contribution from the accretion disk. This project will focus on improving our modelling of these sources - looking at issues, for example, like disk emission and obscuration, which are not currently included in our models.

 

Resolution in PPM  (more compute/statistics oriented)

Advisor: Anna Watts

Description:
Using a technique called Pulse Profile Modelling (PPM), based on relativistic ray-tracing of emission from X-ray pulsars, we are able to infer their mass and radius, and also map the hot X-ray emitting hotspots.  We use mass and radius to learn about the properties of the supranuclear density matter in the neutron star core, while the latter tells us about - for example - the configuration of the star’s magnetic field. This technique has been developed in the first instance for use with NICER data of rotation-powered millisecond X-ray pulsars.

When carrying out PPM, we make a lot of choices regarding resolution settings - in our data binning, in our relativistic ray-tracing meshes, and in our statistical sampling.  These choices affect not only how well we can recover parameters, but also the computational cost.  In this project we’ll explore the effects of resolution settings to determine the optimal choices for our studies.

Searching for Magnetar Starquakes in NICER data

Advisor: Daniela Huppenkothen

Description:
Magnetars are among the most extreme objects in the universe. They are neutron stars with extreme magnetic fields, and show short X-ray bursts with energies otherwise only seen from accretion events or stellar explosions. The detection of rare oscillations in a few of their X-ray light curves opened up the potential of neutron star seismology: exploring the interior of the star through these oscillations. However, these oscillations are rare and difficult to find, and require new statistical approaches. In this project, we will look for oscillations in observations taken with the X-ray telescope NICER, using a recently developed technique. This project would be great for someone who is curious about delving deeper into time series analysis and excited about high-energy astrophysics. 

 

Searching for PAHs with machine learning

Advisors: Daniela Huppenkothen and Alessandra Candian

Description:
The key idea is to figure out what we can learn about the structure and composition of Polycyclic Aromatic Hydrocarbon (PAH) and carbonaceous dust in the interstellar medium through the use of machine learning on high-resolution JWST infrared spectra. Machine learning methods are often applied on real data, but they are complicated models that are challenging to interpret. In this project we will explore how much they can tell by carefully calibrating unsupervised machine learning models on simulations first. We will run adversarial attacks on our models: what happens when we give the model data it hasn’t seen before? We will explore methods to build trust in machine learning models. This project would be great for someone who would like to delve deeper into machine learning and astrochemistry. If you’ve ever asked yourself “ok, but how do we know this machine learning system is doing the right thing?”, this project is for you. 

 

Viewing biases in astronomical data through the lens of epidemiology 

Advisor: Daniela Huppenkothen

Description:
It may seem strange at first, but astronomy and epidemiology—the study of how diseases occur in populations and why—are very similar: they are observational sciences, and they have to fight with observational biases: in astronomy, we can often only observe a small subset of a population (of stars, of galaxies, of planets, …) due to observational constraints or limits on our telescopes. These skewed subsets of the true populations can lead us to make very wrong conclusions about the subject we’re studying. Epidemiology has a sophisticated language and set of methods to mitigate those biases. In this project, we will explore if and when and how we can apply these methods to astronomical problems. This is a pretty experimental project, ideal for someone who is curious about interdisciplinary research, and would like to delve pretty deeply into statistical concepts around causal inference. I think it’ll also be really fun! :)

 

Astrophysical jets

Advisor: Sera Markoff

Description:
I prefer not to list pre-defined projects, rather I like to discuss with students and design projects based on their interests and what they want to learn!   In general there are two “sides” to my group: 1)  semi-analytical modelling of MWL spectra of X-ray binaries and AGN, using leptonic and/or hadronic models (with connection to GRAPPA) and state of the art fitting techniques, and 2) numerical modelling using a general relativistic magnetohydrodynamics (GRMHD) code, H-AMR.  The projects can range from running the existing versions of the codes and applying to new data sets, to more code-development oriented projects.  There are also possibilities to try to apply machine learning techniques to improve our ability to model complex sources.   I’m also interested in some “path-finding” projects like looking for the first time at simulated Cherenkov Telescope Array data via the Science Data Challenge and learning how to work with the data and to model VHE sources, perhaps more of interest to GRAPPA track students? 

 

Stripped stars

Advisors: Silvia Toonen and Thomas Kupfer (U. of Hamburg)

Description:
Most stars do not live their lives in isolation, they live in small stellar systems in which they often interact with a companion star. These interactions can completely change the faith of the star; prematurely ending it, prolonging it, and most interestingly it can lead to unique objects that cannot be formed in any other way. In this project we will focus on Subdwarf B stars, aka a ‘stripped’ star - stripped of its hydrogen envelope by the companion. Here we want to investigate their formation and envelope and compare with the recently published a catalog of SdB binaries. This catalog is truly amazing as it is the largest most complete catalog we’ve ever seen. SdB binaries are also known sources of gravitational wave emission, but their prospects have been overlooked so far. With an improved understanding of their formation, we can make accurate predictions for the impact of SdB binaries for GW detectors like LISA. 

 

Catalysing LMXBs with stellar triples

Advisor: Silvia Toonen 

Description:
This project is about Low Mass X-ray Binaries; binaries where a neutron star or black hole is accreting material from its Sun-like companion star. These binaries are known to give rise to bright X-ray emission or X-ray outbursts. However, we do not understand the formation of these systems. This problem was first noted in the 1980’s - and it still stands! But recently it was discovered that one well known LMXB has a third companion - it is in fact a triple star system. Given the difficulty with detecting the triple nature of an LMXB, it may indicate that triple evolution is in fact an important part of the solution. Triple evolution is a very new field in astronomy, and in Amsterdam we have and develop one of the few codes that can simulate their evolution. In this project, we will simulate the evolution of stellar triples to try and form LMXBs and determine if triple evolution can solve the LMXB formation problem. 

 

NEBULA-Xplorer: An SRON X-ray timing smallSAT

Advisors: Benjamin Ricketts and Phil Uttley

Description:
SRON Netherlands Institute for Space Research is looking to build an X-ray spectral-timing telescope for the purpose of performing observations of galactic binary objects on time scales from milliseconds to months. Observing binary objects such as black holes and neutron star binaries gives us insight into accretion processes around these objects and information about photon arrival times allows us to probe periodic behavior as well as how these objects evolve on short timescales. To this point, x-ray timing instruments have been highly competitive to observe with and long term continuous observation is impossible. Continuous observation will allow us to capture rapidly developing behavior in these sources as well as collect comprehensive spectral timing datasets of individual objects.

The project is geared towards developing young people’s abilities towards the space industry and as such, the instrument will be built by master’s students. Projects like these are driven by science, so we are looking for a student to contribute to the development of the science case for this satellite. 

In this project, you will be involved in the design process with engineering master’s students at SRON and will be taking legacy data from current instruments (primarily NICER on the ISS) and assessing the impact of instrumental choices on x-ray timing analysis. You will learn about X-ray binary objects as well as get the unique opportunity to help contribute to the development of a X-ray telescope that will hopefully be launched into space and contribute to science!

Physics at the boundary: what really happens between accretion disk and the neutron star surface?

Advisor: Oliver Porth

Description:
Generally it is assumed that when an accretion disk touches a solid neutron star surface, “some process” generates viscosity which leads to the dissipation of kinetic energy accompanied with boundary layer emission.

Recent hydrodynamic simulations suggest a new picture: waves are excited at the boundary and transport energy and angular momentum away, both into the star and into the disk. If this is truly what’s happening, then we have to re-think an important chapter of accretion theory as the energy is not released locally. In this project, we will use general relativistic magnetohydrodynamic simulations to investigate this wave mode; coupling between star and disk. It is particularly interesting to check where the energy will actually be released and how much this mechanism can contribute to heating of the neutron star crust. We also plan to carry out the first  magnetohydrodynamic simulations of this process.
This project looks at fundamental physical processes of importance to many accreting systems and the implications can be far reaching!

 

Machine learning for slow light

Advisors: Oliver Porth and Jordy Davelaar (Princeton)

Description:
To generate models of the emission from compact objects, we frequently raytrace simulations in a post-processing step (see e.g. the simulation library for the EHT).  Since the gas around a black hole moves with a sizable fraction of the speed of light, in principle the emitting matter changes significantly while the photon travels from the source to the observer (this is called the ‘slow light effect’).  However, in practice this is rarely taken into account as it requires to load TBs of simulation data into memory and perform expensive 4D interpolations (three in space, one in time).  This limits our ability to investigate causal relationships between emission components and properly address multi-wavelength source variability (e.g. X-ray reverberation). 
The goal of this project is to use ML techniques to learn the dynamics between coarsely sampled snapshots so that we can cut down on the amount of data we need to store and load. Since neural networks are thought of as universal function estimators, they should be well suited to this type of problem.  We will assess how well neural nets can act as ‘advector’ of the plasma dynamics and ideally couple them to a general relativistic raytracing code.  It’s early days for this kind of work, so much remains to be explored!  

 

The optical variable night sky

Advisor: Jan van Roestel 

Description:
I specialize in stellar evolution and interactions from an observational perspective. I use survey telescopes like the Zwicky Transient Facility (ZTF, youtube) and in the recently inaugurated Dutch MEERlicht/BlackGEM telescopes to study the optical variable night sky. There are multiple projects available with these telescopes; they either involve data mining the telescope data for weird and interesting objects or focus on single objects that were recently discovered and detailed followup observations are available. There is also a possibility to use AI methods to study all this data.