No description available.

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Realistic star cluster simulations that dynamically evolve embedded star clusters require an accurate treatment of the stars, gas and their interaction. We present and validate a novel technique which creates an initial gas density distribution based on observational gas column density data. We consider two approaches to this technique where the first is based on randomly sampling from the original gas density distribution and the second assigns one particle to represent the gas in each observed image pixel. To create a three-dimensional distribution, we consider two estimates of cloud depth where one is a constant value and the second involves variable depths calculated using image processing techniques based on density features seen in the plane of the sky. We apply these methods to evolve the Carina region using initial stellar positions derived from the MYSTiX catalogue and gas data from the Herschel Hi-GAL survey. We evolve the stars using an N-body code and the gas using a smoothed-particle hydrodynamics code which are coupled through the AMUSE framework. We analyzed our results using dendrograms to describe the gas distribution over time and the DBSCAN clustering algorithm to track the clustering of stars over time. We model the gas using an adiabatic ideal gas equation of state and find that increasing the initial gas velocity dispersion prevents gas from accumulating and therefore could hinder future star formation. We also find that the stars, initially in subclusters spatially (not necessarily bound), tend to merge together to form one large cluster regardless of the initial conditions of the gas. It is only after the subclusters have merged that the initial conditions of the gas start to have a noticeable effect on the structure of the star cluster. Of the two approaches to our novel technique, the second approach leads to more accurate and realistic results. The second approach also has a significant effect on the stars as the subclusters merge together approximately 1 Myr earlier compared to the first approach. Therefore the choice of initial gas conditions affects the dynamical evolution of star cluster systems and being able to incorporate observational gas data leads to the increasingly accurate dynamical evolution of such systems. / Thesis / Master of Science (MSc)

No description available.

No description available.

Located in the Large Magellanic Cloud, R136 is a rare example of a nearby young and dense massive star cluster in which individual stars can be resolved. Often suggested as a globular cluster in formation, its study is of great interest and promises to provide insights into the early dynamical evolution of massive star clusters. This is crucial to understand more extreme and distant starburst clusters, which contribute to a significant fraction of all current star formation in the Local Universe, in particular in interacting galaxies. The majority of this thesis is based on multi-epoch spectroscopic observations in and around R136 obtained as part of the VLT-FLAMES Tarantula Survey (VFTS), an ambitious programme which targeted nearly 1 000 massive stars in the intricate 30 Doradus star-forming region. The motivations and observing strategy of this survey, designed to address key questions about the evolution of massive stars and clusters, are first introduced. The data reduction procedures applied to VFTS data are described, with an emphasis on the tasks accomplished in the context of this thesis. The VFTS data are first used to perform a detailed kinematic study of R136, determine its dynamical state, and evaluate the importance of gas expulsion in the early evolution of massive star clusters. Orbital motions of binary stars are found to dominate the line- of-sight velocity dispersion of the cluster, illustrating the risk of interpreting velocity dispersion measurements for unresolved extragalactic young massive clusters. However, once the detected binaries are rejected and the contribution of undetected binaries is accounted for through Monte Carlo simulations, the true velocity dispersion of the cluster is found to be low and consistent with it being in virial equilibrium. This suggests that gas expulsion has not had a dramatic effect on the early dynamical evolution of R136. Using the velocity measurements of R136 as a test case, a maximum likelihood method that fits the velocity dispersion of a cluster from a single epoch of radial velocity data is then tested. The method must be applied with care given the high binary fraction of massive stars and the large uncertainties in their binary orbital parameter distributions, but for typical velocity dispersions of young massive clusters (& 4 kms−1), it is shown that the velocity dispersion can be measured with an accuracy of 40% or better. This offers an efficient way of constraining the dynamics of these systems. The radial velocity measurements of apparently single stars in R136 are also used to investigate the internal rotation of the cluster, a potentially important but largely unexplored characteristic of young clusters. Evidence is found, at the 95% confidence level, for rotation of the cluster as a whole. A simple maximum likelihood method is presented to fit rotation curves to the data, from which a typical rotational velocity of 3 kms−1 is found. When compared to the low velocity dispersion of R136, this suggests that star clusters may form with as much as 20% of their kinetic energy in rotation. Finally, a smaller-scale survey of massive stars in the Wing of the Small Magellanic Cloud is introduced. As an example of the particularly interesting massive binaries that can be revealed by the synergy between large optical spectroscopic surveys of young clusters and observations at other wavelengths, the discovery of a new Be/X-ray pulsar binary and associated supernova remnant is reported. With a long spin period of over 1 000 seconds and a young age of 104 years constrained by its association with the supernova remnant, the pulsar in this system is quickly emerging as a unique object that challenges our understanding of the spin evolution of accreting neutron stars.

In this thesis we study the interaction of supernova ejecta in the environment of young massive clusters. It has been already shown that winds of massive stars can be thermalized by mutual interactions inside the cluster and drive the strong star cluster wind. The SNe are, as discrete and extremely energetic events, in all ways diferent from the continuous stellar winds. This triggers the question under which parameter and if at all can the SNe ejecta interaction from a smooth star cluster wind. Therefore we at first parametrize the SNe explossions and based on the 3D simulations in FLASH we show for the first time that the convergence of the SNe ejecta interaction to a smooth star cluster wind is controlled by a single parameter ΠSN . The paramater ΠSN estimates the mean number of interacting SN ejecta based on a comparison of supernova rate and crossing time of SN ejecta in a cluster. For high enough values ΠSN > 1 the cluster is able to build up smooth a star cluster wind. This allows us to use a 1D semi-analytic code WINDCALC to calculate the cooling of the hot gas due to dust and estimate under which conditions the SNe-inserted matter is captured. This may explain the origin of so-called anomalous globular clusters. 1

Most star formation in galaxies takes place in embedded clusters, within Giant Molecular Clouds (GMCs). Stars also generally form as part of binary star systems, with almost all massive stars having at least one close companion. Binaries shape the physical properties of older star clusters by setting their central density and ejecting low-mass stars, but also play a role during cluster formation by modifying the mechanical and radiative feedback from massive stars and shedding enriched material in the cluster’s gas reservoir. Conversely, dynamical interactions between stars in dense stellar environments are known to form, modify, and destroy binary systems. In consequence, the populations of binaries observed in the Galactic field and in old stellar clusters are understood to be shaped by a combination of the physics of star formation and subsequent dynamical interactions in embedded clusters, although the relative importance of these processes remains unknown. In this thesis, we implement a prescription for an initial population of binaries in the coupled N-body and radiation hydrodynamics star cluster formation code Torch, and investigate how this initial population is modified in the earliest stages of cluster formation, while gas and stars coexist. As an ansatz for the initial population of binaries, we use the properties of main-sequence binaries in the Galactic field. We first perform a suite of simulations initialized from a 10^4 M⦿ cloud, in which the simulations only differ by their stellar content (i.e. presence or absence of an initial population of binaries, and stochasticity of star formation). We compare the populations of binaries identified 1.2–2 Myr after the onset of star formation and find that an initial population of binaries is needed at all masses to reproduce the multiplicity fraction observed in main-sequence stars. We also show that this initial population is modified in a systematic manner before the effects of feedback from massive stars shape the gas. We further find evidence of both preferential formation and preferential destruction of binaries via dynamical interactions. The net effect of these interactions shifts the distributions of primary masses and semi-major axes to lower values, and the distributions of mass ratios and eccentricities to larger values. In a second time, we perform simulations with different virial parameters and initial turbulent velocity patterns, and find that the trends previously identified are robust to those changes in our initial conditions. We however find that both the virial parameter and the initial turbulent velocity pattern have a strong influence on the star formation rate, and therefore on the rapidity with which the distributions are modified. We conclude that dynamical interactions in embedded clusters are important for shaping the populations of binaries observed in the MilkyWay, thus opening the floor to future investigations of the impact of binaries on star cluster formation. / Thesis / Master of Science (MSc)

Star formation is an inherently multi-scale process, connecting scales from the kiloparsecs of the galactic disk to the single AU scale of a protostar. In the middle of these scales are star clusters and molecular clouds, the structures in which most stars form. The clouds and clusters are connected via the interstellar medium, the gas and dust making up the matter between stars. In the cold phases of this medium rests the first steps of star formation, the formation of molecular gas and networks of filaments. This cold, neutral medium (CNM) hosts a handful of physical mechanisms, all contributing to the structures that feeds star formation. In this thesis work, we present a suite of simulations using the magneto-hydrodynamical code Ramses to investigate the role of turbulence, magnetic fields and cooling on the formation of filaments and clusters in the CNM. Through 9 different models we find that velocity dispersions in the CNM play a significant role in the formation of structure, requiring a balance between turbulence, self gravity and cooling to form filaments. We find magnetic fields, initialized at strengths of 7 muG, affect the formation of filaments, creating higher percentages of star-forming dense gas and lower percentages of molecular gas. Both magnetic fields and velocity dispersion in the gas affect the formation rate of clusters early in the simulation. Our 8 km/s simulations present a good initial condition for star formation that can include multiple scales of the process and recreate accurate clouds and filamentary structure. / Thesis / Master of Science (MSc)

No description available.