Thesis (Ph. D.)--Michigan State University. Dept. of Physics and Astronomy, 2008. / Title from PDF t.p. (viewed on July 22, 2009) Includes bibliographical references (leaves 170-174). Also issued in print.

Massive OB stars are very influential objects in the ecology of galaxies like our own. Current catalogues of Galactic OB stars are heavily biased towards bright (g < 13) objects, only typically including fainter objects when found in prominent star clusters (Garmany et al., 1982; Reed, 2003; Maíz-Apellániz et al., 2004). Exploitation of the VST Photometric Hα Survey (VPHAS+) allows us to build a robust catalogue of photometrically-selected OB stars across the entire Southern Galactic plane, both within clusters and in the field, down to ~20th magnitude in g. For the first time, a complete accounting of the OB star runaway phenomenon becomes possible. Along with making the primary selection using VPHAS+ colours, I have performed Markov-Chain Monte Carlo fitting of the spectral energy distributions of the selected stars by combining VPHAS+ u, g, r, i with published J, H, K photometry. This gives rough constraints on effective temperature and distance, whilst delivering much more precise reddening parameters A0 and RV - allowing us to build a much richer picture of how extinction and extinction laws vary across the Galactic Plane. My thesis begins with a description of the method of photometric selection of OB star candidates and its validation across a 2 square degree field including the well- known young massive star cluster Westerlund 2 (Mohr-Smith et al., 2015)1. Following on from this I present spectroscopy with AAOmega of 283 candidates identified by our method, which confirms that ~ 94% of the sample are the expected O and early B stars. I then develop this method further and apply it to a Galactic Plane strip of 42 square-degrees that runs from the Carina Arm tangent region to the much studied massive cluster in NGC 3603. A new aspect I attend to in this expansion of method is tightening up the uniform photometric calibration of the data, paying particular attention to the always-challenging u band. This leads to a new and reliable catalogue of 5915 OB stars. As well as increasing the numbers of identified massive stars in this large region of the sky by nearly an order of magnitude, a more complete picture of massive star formation in the Carina Arm has emerged. I have found a broad over-density of O stars around the highly luminous cluster NGC 3603 and have uncovered two new candidate OB clusters/associations. I have also paired up the ionization sources of a number of HII regions catalogued by the RMS survey. It is also shown that the OB star scale- height can serve as a roughly standard ruler, leading to the result that the OB star layer shows the onset of warping at RG ~ 10kpc. My results confirm that this entire region requires a non-standard (3.5 < RV < 4.0) reddening law for distances greater than ~2kpc. The methods developed in this study are ready to roll out across the rest of the VPHAS+ footprint that has been observed to date. This extension will take in a strip ~ ±2 degrees across the entire Southern Galactic mid-plane (a sky area of over 700 square degrees), within which we expect to find the majority of massive OB stars. This will result in the largest catalogue of Galactic OB stars to date.

Nous étudions la migration radiale des étoiles, et testons son impact sur l’évolution chimique de la Voie Lactée. Pour cela nous utilisons une simulation N-corps+SPH (Gadget-3) de galaxie fortement barrée, afin d’étudier la migration radiale induite par la barre. Nous examinons un nouveau mécanisme de migration radiale: une fraction des étoiles piégées à la corotation de la barre, se déplacent avec le rayon de corotation lorsque celui-ci va vers l’extérieur (quand la vitesse de rotation de la barre diminue, du fait de son évolution séculaire). Nous montrons que ce mécanisme affecte principalement les régions externes du disque, à condition que la corotation atteigne ces régions. Nous montrons également que ce mécanisme n’a pas d’effets dans la Voie Lactée, car les estimations observationnelles des caractéristiques de la barre, indiquent que la corotation est loin des zones externes. Nous analysons également la migration radiale dans cette simulation, afin de construire un modèle empirique de diffusion stellaire dans le disque, et nous incluons ce modèle dans un code semi-analytique d’évolution chimique de galaxie. Nous testons la validité de cette approche en vérifiant que les galaxies simulées N-corps+SPH et semi-analytique ont des propriétés morphologiques et chimiques similaires. Nous appliquons ensuite notre modèle à la Voie Lactée, en adaptant les paramètres du modèle. Puis, nous comparons les résultats obtenus avec un grand nombre d’observations concernant le voisinage solaire (relation âge-métallicité, distribution de métallicité, relation a/Fe vs Fe/H et la bimodalité disque mince - disque épais) , et les gradients radiaux d’abondance. / We study the radial migration of stars, and test its impact on the chemical evolution of the Milky Way. For this we use a simulation-body + SPH (Gadget-3) strongly barred galaxy to study the radial migration induced by the bar. We examine a new mechanism of radial migration: a fraction of stars trapped at corotation with the bar, move with the corotation radius when it goes outwards (when the rotational speed of the bar decreases, because of its secular evolution). We show that this mechanism affects mainly the outer regions of the disc, provided that the corotation reaches these regions. We also show that the mechanism has no effects in the Milky Way, as the observational estimates of the characteristics of the bar indicates that the corotation is not in the outer regions. We also analyze the radial migration in this simulation to construct an empirical model of diffusion in the stellar disk, and we include this model in a semi-analytic code of chemical evolution of galaxy. We test the validity of this approach by ensuring that the galaxies simulated with N-body + SPH and semi-analytic have similar morphological and chemical properties. We then apply our model to the Milky Way, by adapting the model parameters. Then, we compare the results obtained with a large number of observations on the solar neighborhood (age-metallicity relation, metallicity distribution, relationship O/Fe vs. Fe/H and bimodality thin disk - thick disk), and radial gradients of abundances.

The presence of dark matter is inferred at scales ranging from rotations of galaxies to imprints in the CMB – the Big Bang after-glow. The nature of dark matter is, however, still unknown as no detection other than the gravitational one has been made. This thesis presents two analyses searching for a neutrino signal from dark matter annihilations in the Milky Way. The first analysis searched for an excess of νμ charged current events with directions from the central region of the dark matter halo and, was focused on low energy events, thus probing low dark matter particle masses. Approximately 319 days of data collected with the 79-string configuration of the IceCube detector was used in the analysis. Despite a large deficit in the number of observed events the data were found to be consistent with background and upper limits were set on &lt;σⱴ&gt;. At the time of the analysis these limits were the strongest set by a neutrino experiment below 100 GeV. The second analysis was performed on a data sample originally used in an unfolding analysis of the atmospheric and astrophysical neutrino spectra. The data consisted of contained cascade events above 1 TeV collected with the 79-string configuration and the completed detector in the 86-string configuration during two years of data-taking. The limits set by this analysis were more constraining by up to a factor of 10 compared to previous IceCube analyses, and the most competitive limits are set assuming a Burkert halo profile. These two analyses prompted the development of a signal subtraction likelihood method to address the problem of signal contamination in background estimates based on scrambled data. Additionally a study concerning future extensions of IceCube in the Gen2 project is presented. The cascade reconstruction performance was examined and compared for different proposed detector extensions.

This dissertation presents two chemo-dynamical analyses of metal-poor stars found within the Milky Way. 115 metal-poor candidate stars, including 28 confirmed very metal-poor stars, selected from the narrow-band Pristine photometric survey are presented based on CFHT high-resolution ESPaDOnS spectroscopy. An additional 30 confirmed very metal-poor stars selected from Pristine are examined based on Gemini/GRACES spectroscopy. Chemical abundances are determined for a total of 19 elements (Li, Na, Mg, K, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Y, Zr, Ba, La, Nd, Eu) across these studies, which are combined with Gaia DR2 parallaxes and proper motions to paint a chemically diverse map of ancient stars in the Galaxy. Abundance patterns similar to those seen in "normal" metal-poor Galactic halo stars are found in a majority of the stars studied here, however new discoveries of a handful of chemically unique and kinematically intriguing metal-poor stars are presented. The chemo-dynamics of these novel stellar relics point towards chemical signatures of unique and potentially unstudied stellar yields, in addition to stars with origins in accreted dwarf galaxies and the ancient progenitors of the proto-Milky Way. The success of these relatively small studies heralds the great contributions to Galactic archaeology expected from the next generation of large multi-object spectroscopic surveys. Contained within are two other projects that introduce data products related to Gemini Observatory instruments. A version of the convolutional neural network StarNet, tuned to medium-resolution R~6000 H-band spectra is presented. This model was trained on synthetic stellar spectra containing a range of data augmentation steps to more accurately reflect the observed spectra expected from medium-resolution instruments, like the Gemini-North Near-Infrared Integral Field Spectrometer (NIFS) or GIRMOS. In an era when spectroscopic surveys are capable of collecting spectra for hundreds of thousands of stars, fast and efficient analysis methods are required to maximize scientific impact, and StarNet delivers on these expectations over a range of spectral resolutions. Finally, a python package called Nifty4Gemini, and its associated Pyraf/Python based pipeline for processing NIFS observations is included. Nifty4Gemini reduces NIFS raw data and produces a flux and wavelength calibrated science cube with the full signal-to-noise, ready for science analysis. / Graduate

No description available.

Globular clusters are found in the halos of all types of galaxies, and have been shown to play major roles in the formation of stars and galaxies. The purpose of this thesis is to advance our level of understanding of the dynamical evolution of globular clusters through N-body simulations of clusters with a range of circular, eccentric, and inclined orbits. Theoretical studies have historically assumed that globular clusters experience a static tidal field, however the orbits of globular clusters are all non-circular and the tidal field of most galaxies is not symmetric. Understanding how clusters evolve in realistic potentials allows for them to be used to constrain the formation, merger history, and evolution of a host galaxy and even map out the current size, shape, and strength of a galaxy's gravitational field. We find that dense and compact clusters evolve as if they are in isolation, despite being subject to a non-static tidal field. For larger clusters, tidal shocks and heating inject energy into the cluster and significantly alter its evolution compared to previous studies. We describe how a non-static field alters the mass loss rate and relaxation time of a cluster, and propose methods for calculating a cluster's size and orbit. We then apply our work to clusters in the giant galaxies M87, NGC 1399, and NGC 5128. We consider each cluster population to be a collection of metal poor and metal rich clusters and generate models with a range of orbital distributions. From our models we constrain the orbital anisotropy profile of each galaxy, place constraints on their formation and merger histories, and explore the effects of nearby galaxies on cluster evolution. By advancing studies of globular cluster evolution to include the effects of a non-static tidal field, we have made an important step towards accurately modelling globular clusters from birth to dissolution. Our work opens the door for globular clusters to be used as tools to study galaxy formation, evolution, and structure. Future studies will explore how galaxy formation and growth via the hierarchical merger of smaller galaxies will affect cluster evolution. / Thesis / Doctor of Philosophy (PhD)

No description available.

No description available.

No description available.