Martijn Oei at Leiden Observatory

Recently, our team has discovered Alcyoneus, a radio galaxy of at least 5 Mpc long. In projection, this is the largest structure made by a galaxy known so far! Our work is already peer-reviewed and accepted, and will soon be published by Astronomy & Astrophysics.

High-resolution versions (16.8 MB) can be found here:

• Infrared: blue | Radio: orange
• Infrared: brown | Radio: orange
• Infrared: brown | Radio: blue

Wavefront sensing: Towards a polarization-induced dOTF wavefront sensor

Summary: Sensing wavefront aberrations induced by Earth’s atmosphere is a pivotal part of adaptive optics systems. In this project, we simulate and build a prototype of a new type of wavefront sensor (WFS) using the differential Optical Transfer Function (dOTF) technique. The expected advantage of the dOTF WFS approach over other methods is its low cost and relative simplicity.

When: 2014

Supervisor: Associate Professor Matthew Kenworthy

Research group: Instrumentation, Leiden Observatory, Leiden University

Asteroseismology: Modelling Beta Pictoris' pulsations to weigh its giant planet

Summary: The radial velocity (RV) method is one of the most successful approaches applied so far to detect exoplanets. Rapidly rotating and asteroseismologically active stars prove to be more challenging targets for this method, as the stellar spectral line profiles become not only broadened but also asymmetrically perturbed in a time-dependent fashion. In this project, we aim to attenuate the effect of noise caused by stellar pulsations on RV data in order to improve the accuracy by which planets can be found. As a case study, we examine data of Beta Pictoris, which is known to be orbited by a giant planet that has hitherto escaped RV detection.

When: 2015 - 2016

Supervisor: Professor Ignas Snellen

Research group: Exoplanets, Leiden Observatory, Leiden University

The mean spectral line shape is best analysed with the spectral cross correlation function (CCF). A spectral CCF is made by cross correlating a measured spectrum with some template spectrum. For the Beta Pictoris CCFs, a fixed template spectrum was used. The time evolution of the spectral CCF during one night of observations can be seen in the movie below.

Website under construction.

It is apparent that the spectral CCF has ripples going over it. These are due to stellar pulsations. A big sample of simulated spectral CCFs was created for various modes of pulsation. The movie below shows both the measured CCFs of one night and the corresponding best fitting simulated CCFs.

In the video below, we see a simulation of the effect that a patch of stellar material moving in the radial direction has on the spectral CCF. The velocity of the spot with respect to the surface is much smaller than the equatorial rotational velocity, so that the apparent motion of the blob is due to stellar rotation only.

In the video below, we see a simulation of the effect that a patch of stellar material moving in the azimuthal direction has on the spectral CCF. The velocity of the spot with respect to the surface is much smaller than the equatorial rotational velocity, so that the apparent motion of the blob is due to stellar rotation only.

In the video below, we see a simulation of the effect that a sinusoidal oscillation in the radial direction has on the spectral CCF. 16 waves run over the stellar surface, which have a velocity amplitude of 2 kilometers per second.

In the video below, we see a simulation of the effect that a sinusoidal oscillation in the azimuthal direction has on the spectral CCF. 16 waves run over the stellar surface, which have a velocity amplitude of 2 kilometers per second.

In the video below, we see a simulation of the effect that a superposition of sinusoidal oscillations in the radial and azimuthal direction has on the spectral CCF. The model is made sufficiently general that any orientation of the stellar rotation axis with respect to the line of sight can be simulated.

Radio Astronomy: Wide-bandwidth ionospheric calibration of low-frequency radio data & probing radio galaxy alignments in the cosmic web

Summary: 400MUGS (400 MHz Upgraded GMRT Survey) is an upcoming radio survey of the northern (and possibly, at a later stage, southern) sky that will be conducted with the uGMRT (upgraded Giant Metrewave Radio Telescope) near Pune, India. This effort will lead to a state-of-the-art reference atlas that is unprecedented in terms of sensitivity and resolution in the mid-to-low frequency range (300 - 500 MHz) of the radio spectrum. The 400MUGS database will thus strengthen the science of near-future telescopes and surveys like Pan-STARRS, JWST, eROSITA, LIGO / VIRGO and LSST. Also, on itself, 400MUGS will drive forward a wealth of science cases including, but not limited to, the study of AGNs and their contingent alignment with large scale structure, polarimetric detection of magnetism in galaxies and extragalactic environments, and the characterization of hitherto unknown transients, high-redshift radio galaxies and pulsars.

In this project, I work on improving the advanced data pipeline that will be used for 400MUGS, which is polarization-enabled and has features to mitigate the effects of ionospheric turbulence. Also, I act as a Principal Investigator (PI) for the acquisition of uGMRT data to test this pipeline.

When: 2016 - 2017

Supervisors: Professor Huub Röttgering, postdoc Huib Intema and postdoc Francesco de Gasperin

Research group: Radio Astronomy, Leiden Observatory, Leiden University

Each year, student association De Leidsche Flesch (DLF) sets up numerous social and educational activities for Leiden University bachelor's and master's students in physics, astronomy, mathematics and computer science.

Together with 6 others, I organized DLF's biennial interdisciplinary natural sciences symposium. The day was centered around the theme of Time and featured, inter alios, prominent American physics educator David J. Griffiths. The promotional poster shown on the right is my creation.

Click on it to read the titles of the talks given!

Philosophy

About halfway along in high school, I got fascinated by the Big Questions of Life, the Universe, and Everything. This interest arose from a maturing admiration of and curiousity towards Nature on the one hand, and engaging philosophy lessons on the other. During this first exploration of the world of critical thought, I found the fields of epistemology, philosophy of science, logic, and metaphysics to be most appealing.

Scientific answers

As many prominent thinkers have noted, the natural sciences are increasingly capable to provide conditional answers to some of philosophy's greatest problems. From ignorant speculation around the campfire, our species has progressed to coming excitingly close to knowing the answer to the questions 'Does life exist elsewhere in the Universe?', 'Is the fate of the world pre-determined by the Laws of Nature?' and 'What are the fundamental constituents of matter?', among others. It is important to emphasise that science has already provided humanity with far-reaching philosophical insights. It has clarified the relation between Man and animal, eroding the credibility of the tempting view of absolute human supremacy, thereby building the case for a more emphatic attitude towards non-human sentient beings. It has also shown, inter alia, that planet Earth is not at the centre of the Universe, both spatially and temporally, casting great shadows over the standard creationist narrative of exempli gratia the Abrahamic religions.

Astrophysics

It was the realisation that science has thoroughly invaded the lands of philosophy that drove me to the decision to study physics, the discipline that was, after all, originally known as natural philosophy. Modern physics is inextricably connected to astronomy, which I therefore decided to study too. Nowadays, for instance, Einstein's general relativity and theories of particle physics like the Standard Model are subjected to rigorous cosmological tests. It would be madness not to join the ranks of science and help build our understanding of the dark, unexplored skies above us during these exciting times!