One of the most important puzzles in modern astrophysics is the nature of dark matter. Stellar streams, formed by tidal stripping of the stars from globular clusters or dwarf galaxies, behave as a... Show moreOne of the most important puzzles in modern astrophysics is the nature of dark matter. Stellar streams, formed by tidal stripping of the stars from globular clusters or dwarf galaxies, behave as a group of test particles allowing us to measure the Milky Way’s dark matter content and, therefore, offering us a key to understanding its nature. Open clusters, loosely bound groups of stars that move through the Galaxy together, are, in contrast, an important driver of stellar evolution research. This Thesis presents our studies of these Galactic substructures and the conclusions we can draw on the larger Universe and physics based on these local observations. In chapters 2 - 4, we apply a novel method to map the Milky Way’s dark matter content using stellar streams, taking care to understand the various possible contributors to the systematics. Chapter 5 is dedicated to the study of the Hyades open cluster. Show less
The high velocity tail of the total velocity distribution of stars provides essential insight into fundamental properties of the Galaxy. Hypervelocity stars (HVSs), travelling on unbound orbits... Show moreThe high velocity tail of the total velocity distribution of stars provides essential insight into fundamental properties of the Galaxy. Hypervelocity stars (HVSs), travelling on unbound orbits coming from the Galactic Centre, are powerful tracers of the underlying Galactic gravitational potential, and can shed light on the stellar population in the proximity of our massive black hole. Runaway stars, ejected from the stellar disk, provide information on binary evolution and stellar clusters' dynamical processes. The advent of the data from the European Space Agency satellite Gaia has revolutionized our knowledge on high velocity stars. In my PhD thesis entitled "Hunting for the fastest stars in the Milky Way" I present my work on searching for the fastest stars in the Milky Way. I start by presenting our modelling work on predicting the HVS population expected to be contained in the Gaia catalogue. Then I illustrate the data mining techniques built and implemented to find these rare objects in the first and second data release of Gaia. Finally, I conclude discussing how HVSs can be used to constrain the Galactic dark matter halo and the binary population in the Galactic Centre. Show less
For centuries astronomers studied the Universe by collecting light. Nowadays, we are living in times of great technological advancements, which allow us to explore our Universe in a new way -... Show moreFor centuries astronomers studied the Universe by collecting light. Nowadays, we are living in times of great technological advancements, which allow us to explore our Universe in a new way - though gravitational wave radiation. There are many gravitational wave sources in our own Galaxy, the Milky Way. For example, white dwarf stars in tight binary systems spinning around each other in less than 1 hour. LISA is a future ESA mission, that will detect a large variety of gravitational wave sources including Galactic double white dwarfs. Although quite faint, double white dwarfs can also be seen by optical telescopes. Thus, astronomers call them “multi-messenger” sources. This means that we can collect information from them using more than one messenger: electromagnetic waves, messengers of the electromagnetic field, and gravitational waves, messengers of the gravitational field. This thesis proposes to use gravitational wave signals from Galactic double white dwarfs to study the Milky Way and its neighbourhood. In particular, it explores how by collecting many electromagnetic and gravitational wave signals from thousands to millions of binary double white dwarfs spread all across our Galaxy, we can perform multi-messenger Galactic Astronomy and learn about the structure and history of the Milky Way. Show less
In this thesis we present research on the stellar halo of our Galaxy. In particular we focus on measuring the shape and profile of the stellar halo through photometric techniques and main sequence... Show moreIn this thesis we present research on the stellar halo of our Galaxy. In particular we focus on measuring the shape and profile of the stellar halo through photometric techniques and main sequence turnoff point star counts. We also present a cross-correlation algorithm that can detect stellar overdensities in the halo (streams or satellites) in Colour Magnitude Diagrams with only two photometric filters and no control field. We use this algorithm to characterize different streams and the vicinity of Globular clusters in search for associated stellar populations. Finally we also search for new substructure in the Kilo Degree Survey fields of Data Releases 1 and 2 and find signatures of the major substructures known in the halo. Show less
Schnitzeler, Dominic Hubertus Franciscus Maria 2008
In this thesis I use the novel technique of Rotation Measure synthesis (RMS) to study the Galactic interstellar medium. With RMS we can study Faraday rotation and synchrotron emission along the... Show moreIn this thesis I use the novel technique of Rotation Measure synthesis (RMS) to study the Galactic interstellar medium. With RMS we can study Faraday rotation and synchrotron emission along the line of sight. I apply RMS to 4 data sets that we obtained with the WSRT. With RMS we can separate the signal of a polarized extragalactic source from the signal from our own Milky Way. Depending on the viewing direction in the Milky Way, the rotation measures of extragalactic sources and diffuse emission (dis)agree. We supplement our observations with MHD simulations of the Galactic ISM, to better understand how we can interpret the observed features as structure in the Galactic ISM and the Galactic magnetic field. Finally, we combined our results with literature values on pulsars, extragalactic sources, and the diffuse emission. We found a way to calculate the electron-density weighted line-of-sight magnetic field strength from the RM and DM that we can either measure or model for these sources. With all this information we determined that the large-scale magnetic field in the second Galactic quadrant shows much more structure than what the currently best available model can predict. Show less
