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
This paper sets out to reconstruct Pannekoek’s understanding of scientific socialism in order to reconnect Pannekoek’s political and astronomical work. It does so through a close reading of... Show moreThis paper sets out to reconstruct Pannekoek’s understanding of scientific socialism in order to reconnect Pannekoek’s political and astronomical work. It does so through a close reading of Pannekoek’s early socialist essays, where he repeatedly referred to socialism’s scientific character, explaining it in various ways. From this reading, three different but closely related conceptions of scientific socialism can be abstracted. For Pannekoek, socialism was scientific in that it embraced modern science, in that it supposedly uncovered the laws of societal development, and in that it foretold the advent of socialism. The paper shows how, for Pannekoek, socialism was the only ideology with a true interest in scientific research and findings. This line of reasoning allowed Pannekoek to connect his astronomical and socialist persona. Show less
This thesis is about the study of hydrocarbons via infrared spectroscopy. Hydrocarbons play an important role in the chemistry of a variety of astronomical environments from the diffuse... Show moreThis thesis is about the study of hydrocarbons via infrared spectroscopy. Hydrocarbons play an important role in the chemistry of a variety of astronomical environments from the diffuse interstellar medium to dense hydrocarbon atmospheres of solar system bodies (e.g., planetary atmospheres of Jupiter and Saturn’s moon Titan) and exoplanets. For most astronomical objects, the determination of chemical abundances, and consequently an understanding of the chemical evolution relies upon the observation of molecular spectra. However, to date astronomical models need to make assumptions, because not all of the molecules expected have been observed. This is due, in part, to a lack of accurate spectral data, which is needed for unambiguous identification. Using a combination of high-resolution infrared experiments and/or high level ab initio calculations of vibration frequencies and ground state spectroscopic constants, the infrared spectral data of HC2H, HC4H, HC6H, HC8H, C3H4, c-C3H3+ and Dn-PAHs (polycyclic aromatic hydrocarbons, PAH) are studied and presented, in order to fill in some of the missing spectral data. Show less
This thesis presents a study of how science can most effectively be used to engage and educate the global public and specifically describes the role of astronomy in doing this. Astronomy has a... Show moreThis thesis presents a study of how science can most effectively be used to engage and educate the global public and specifically describes the role of astronomy in doing this. Astronomy has a special place in the field of science education and public engagement with science. It has great appeal for large sections of the public for several reasons. We shall use astronomy as a case study to consider the effect and impact of transnational collaborations with innovative approaches and centralised coordination in science education and public outreach. The thesis is based on eight years of designing, implementing and evaluating transnational collaborative programmes in astronomy education and public outreach, from the perspective of the practitioner. We shall also show that large global science EPO projects can result in sustainable outcomes that outlive the projects themselves and analyse the various aspects of global science communication project that are necessary for their success. Show less
The primary focus of this thesis is the formation of low-mass protostars, specifically the earliest deeply embedded phase, when material from the collapsing envelope is still accreted onto the... Show moreThe primary focus of this thesis is the formation of low-mass protostars, specifically the earliest deeply embedded phase, when material from the collapsing envelope is still accreted onto the growing young star. Rotational transitions of CO and O2 data are obtained by the Herschel Space Observatory key projects, WISH and HOP, together with ground-based observations from APEX and the JCMT. We have found that CO and its isotopologs have different line profiles tracing different materials in the protostellar regions. Our new high-J rotational transitons of CO is key to characterize the warmer parts of the protostellar envelope and quantify feedback of the protostars on their surroundings in terms of shocks, ultraviolet (UV) heating, photodissociation, and outflow dispersal. Radiative transfer modeling was performed to determine the CO abundance structure in the envelope, showing evidence for significant freeze-out in the coldest regions in the parts of the envelope where the temperature exceeds 25 K. A tentative detection of O2 is reported toward the source position of a protostar, which originates from the surrounding cloud. These kind of detailed studies of the physical and chemical structure of low-mass protostars are important for a complete understanding of the evolution of young stellar objects (YSOs). Show less
Star formation occurs when a dense cloud of interstellar gas and dust gravitationally collapses. Rotation during this collapse leads naturally to the formation of a flattened circumstellar disk... Show moreStar formation occurs when a dense cloud of interstellar gas and dust gravitationally collapses. Rotation during this collapse leads naturally to the formation of a flattened circumstellar disk around the forming star. These disks are additionally known as protoplanetary disks because the orbiting circumstellar dust and cold gas represent the building blocks for planets. How long this material survives and how it evolves in this time will determine the propensity for (and the diversity of) planetary systems. This thesis is split into three parts that analyze different aspects of disk evolution and the circumstellar environment. In part one, we use observations at millimeter wavelengths to probe (and then model and compare) the dust and gas properties around low-mass Sun-like stars. We conclude that high-resolution spatial and spectral imaging of optically thinner molecular lines will provide the most robust description of the disk structure and evolution using future instrumentation. During these routine observations, we report recurring millimeter flares resulting in part two. We attribute this phenomenon to synchrotron emission from relativistic electrons trapped in the (colliding) magnetospheres of a young binary system. Finally, we present a microgravity experiment to probe the collisional growth mechanism for the first steps of planet formation. Show less
In this thesis we use the very large telescope interferometer in order to observe dust residing in the nuclei of active galaxies. We compare our observations with the commonly accepted unified... Show moreIn this thesis we use the very large telescope interferometer in order to observe dust residing in the nuclei of active galaxies. We compare our observations with the commonly accepted unified model for active galaxies Show less
Starburst galaxies undergo a phase of vigorous star formation. In these galaxies, gas is turned into stars at such a high rate, that the reservoir of available gas is quickly emptied. Numerous... Show moreStarburst galaxies undergo a phase of vigorous star formation. In these galaxies, gas is turned into stars at such a high rate, that the reservoir of available gas is quickly emptied. Numerous massive, bright star clusters are created from the giant molecular clouds. They form an ideal laboratory for the study of rapid star formation. In this thesis, a detailed study of active star-forming regions in the starburst galaxies NGC 4038/4039 and M83 is presented. Sincethe stars are hidden from view by large quantities of dust, we observe them at infrared wavelengths. We address the properties of the newly formed star clusters and the surrounding interstellar matter. Show less
The main goal of the PhD research described is to gain insight in the dynamical structure and evolution of galaxies, globular clusters and other stellar systems. For nearby stellar systems,... Show moreThe main goal of the PhD research described is to gain insight in the dynamical structure and evolution of galaxies, globular clusters and other stellar systems. For nearby stellar systems, realistic axisymmetric and triaxial dynamical models are constructed that fit their photometric and (two-dimensional) spectroscopic observations in detail. For early-type galaxies at higher redshift, the Fundamental Plane is used to investigate the evolution of their mass-to-light ratios. The connection of the results from both approaches allows a better understanding of the formation history of these stellar systems. Show less
