Thesis (M. Sc.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. [167]-170). Also available via the World Wide Web.

This paper presents calculations for forbidden emission-line profile shapes arising from colliding wind binaries. The main application is for systems involving a Wolf–Rayet (WR) star and an OB star companion. The WR wind is assumed to dominate the forbidden line emission. The colliding wind interaction is treated as an Archimedean spiral with an inner boundary. Under the assumptions of the model, the major findings are as follows. (i) The redistribution of the WR wind as a result of the wind collision is not flux conservative but typically produces an excess of line emission; however, this excess is modest at around the 10 per cent level. (ii) Deviations from a flat-toped profile shape for a spherical wind are greatest for viewing inclinations that are more nearly face-on to the orbital plane. At intermediate viewing inclinations, profiles display only mild deviations from a flat-toped shape. (iii) The profile shape can be used to constrain the colliding wind bow shock opening angle. (iv) Structure in the line profile tends to be suppressed in binaries of shorter periods. (v) Obtaining data for multiple forbidden lines is important since different lines probe different characteristic radial scales. Our models are discussed in relation to Infrared Space Observatory data for WR 147 and γ Vel (WR 11). The lines for WR 147 are probably not accurate enough to draw firm conclusions. For γ Vel, individual line morphologies are broadly reproducible but not simultaneously so for the claimed wind and orbital parameters. Overall, the effort demonstrates how lines that are sensitive to the large-scale wind can help to deduce binary system properties and provide new tests of numerical simulations.

Theoretical investigation of the dynamics of adiabatic quantum mechanics in two different, highly polar systems has been made. The systems were chosen for their fundamental scientific interest, as they represent atoms and molecules with exaggerated properties, as well as ease of experimental study as such highly polar systems are easier to manipulate using readily-available electric fields. A model two-level system is used to derive one approach for maximizing the probability of adiabatic passage through an avoided crossing and this is compared with the classic Landau-Zener result, and the commonly encountered spin-flip problem of a particle with spin located in a rotating magnetic field. This approach is applied to the avoided crossing between the n = 13, n1 − n2 = 11 (dipole moment of 532 D) and the n = 14, n1 − n2 = −12 (dipole moment of -657 D) highly polar Stark states of the lithium atom at 447 kV/m. Ion-pair formation from two neutral lithium atoms, one in the 2s ground state and the other in an excited state, is also investigated. The cross section σ(v) for free ion-pairs is calculated for the initial colliding pairs of atomic states located below the ion-pair threshold. Li(2s) + Li(3d) is seen to possess the largest cross section (σ(v0) = 569.2 a.u.) at its threshold velocity. The implications of this for bound ion-pair, i.e. heavy Rydberg system, production are briefly discussed. Furthermore, experimental progress towards the production of these atomic and molecular systems from a beam of lithium is presented. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-12-09 16:49:41.184

Les étoiles massives, de type O ou B, sont d'une importance capitale pour le budget énergétique des galaxies et l'enrichissement du milieu interstellaire. Néanmoins, leur formation, contrairement à celle des étoiles de type solaire reste sujet à débats, sinon une énigme. Les toutes premières étapes de la formation des étoiles massives ainsi que la formation de leur nuage parent sont des thèmes qui stimulent une grande activité sur les plans théorique et observationnel depuis une décennie. Il semble maintenant acquis que les étoiles massives naissent dans des cœurs denses massifs, qui se forment au travers de processus dynamiques, tels que les flots de gaz collisionnels. Au cours de ma thèse, j'ai mené une étude approfondie de la formation des cœurs denses et des étoiles massives au sein de la structure hypermassive W43-MM1, localisée à 6~kpc du soleil. Dans un premier temps, j'ai montré une corrélation directe entre l'efficacité à former des étoiles et la densité volumique des nuages moléculaires, en décalage avec un certain nombre d'études précédentes. En effet, la distribution spatiale et de masse des cœurs denses massifs en formation au sein de W43-MM1 suggère que ce filament hypermassif est en phase de flambée de formation d'étoiles, flambée d'autant plus grande que l'on se rapproche de son cœur. J'ai comparé ces résultats observationnels aux modèles numériques et analytiques d'efficacité de formation stellaire les plus récents. Cette confrontation permet non seulement d'apporter de nouvelles contraintes sur la formation des filaments hypermassifs, mais suggère aussi que la compréhension de la formation d'étoiles dans les nuages hypermassifs nécessite une description fine de la structure de ces objets exceptionnels. En second lieu, ayant montré que la formation des étoiles massives est fortement dépendante des propriétés des filaments qui les forment, je me suis naturellement intéressé aux processus de formation de ces filaments, grâce à une étude de leur dynamique globale. Plus précisément, j'ai utilisé un traceur de chocs (la molécule de SiO) pour discerner les chocs dûs aux processus locaux de formation des étoiles (jets et flots bipolaires), des chocs dûs aux processus permettant la formation du nuage. J'ai ainsi pu, via une étude sans précédent alliant observations et modélisation de chocs dans une région formant de nombreuses étoiles, montrer l'existence de chocs à basse vitesse, première signature directe de la formation du nuage moléculaire dans lequel les étoiles massives se forment. Ces résultats constituent une étape importante reliant, via des processus dynamiques, la formation des nuages moléculaires à la formation des étoiles massives. / O and B types stars are of paramount importance in the energy budget of galaxies and play a crucial role enriching the interstellar medium. However, their formation, unlike that of solar-type stars, is still subject to debate, if not an enigma. The earliest stages of massive star formation and the formation of their parent cloud are still crucial astrophysical questions that drew a lot of attention in the community, both from the theoretical and observational perspective, during the last decade. It has been proposed that massive stars are born in massive dense cores that form through very dynamic processes, such as converging flows of gas. During my PhD, I conducted a thorough study of the formation of dense cores and massive stars in the W43-MM1 supermassive structure, located at ~ 6 kpc from the sun. At first, I showed a direct correlation between the star formation efficiency and the volume gas density of molecular clouds, in contrast with scenarii suggested by previous studies. Indeed, the spatial distribution and mass function of the massive dense cores currently forming in W43-MM1 suggests that this supermassive filament is undergoing a star formation burst, increasing as one approaches its center. I compared these observational results with the most recent numerical and analytical models of star formation. This comparison not only provides new constraints on the formation of supermassive filaments, but also suggests that understanding star formation in high density, extreme ridges requires a detailed portrait of the structure of these exceptional objects. Second, having shown that the formation of massive stars depends strongly on the properties of the ridges where they form, I studied the formation processes of these filaments, thanks of the characterization of their global dynamics. Specifically, I used a tracer of shocks (SiO molecule) to disentangle the feedback of local star formation processes (bipolar jets and outflows) from shocks tracing the pristine formation processes of the W43-MM1 cloud. I was able, via an unprecedented study combining observations and modeling of shocks in a starbust region, to show the existence of widespread low velocity shocks, that are the first direct signature of the formation of the massive molecular cloud from which massive stars form.These results are an important step connecting, via dynamical processes, the formation of molecular clouds to the formation of massive stars.

We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada–France–Hawaii Telescope and the Narval spectropolarimeter at the Télescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of −810 ± 150 and +680 ± 190 G, implying a minimum surface dipole polar strength of 2850 ± 500 G. In contrast, we derive an upper limit (3σ) to the primary's surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission – previously interpreted as a consequence of colliding stellar winds – in this context. We conclude that HD 47129 represents a heretofore unique stellar system – a close, massive binary with a rapidly rotating, magnetized component – that will be a rich target for further study.

No description available.

The work consists of two parts. In the first part which is concerned with random walks, we construct the conditional versions of a multidimensional random walk given that it does not leave the Weyl chambers of type C and of type D, respectively, in terms of a Doob h-transform. Furthermore, we prove functional limit theorems for the rescaled random walks. This is an extension of recent work by Eichelsbacher and Koenig who studied the analogous conditioning for the Weyl chamber of type A. Our proof follows recent work by Denisov and Wachtel who used martingale properties and a strong approximation of random walks by Brownian motion. Therefore, we are able to keep minimal moment assumptions. Finally, we present an alternate function that is amenable to an h-transform in the Weyl chamber of type C. In the second part which is concerned with Brownian motion, we examine the non-exit probability of a multidimensional Brownian motion from a growing truncated Weyl chamber. Different regimes are identified according to the growth speed, ranging from polynomial decay over stretched-exponential to exponential decay. Furthermore we derive associated large deviation principles for the empirical measure of the properly rescaled and transformed Brownian motion as the dimension grows to infinity. Our main tool is an explicit eigenvalue expansion for the transition probabilities before exiting the truncated Weyl chamber.

The work consists of two parts. In the first part which is concerned with random walks, we construct the conditional versions of a multidimensional random walk given that it does not leave the Weyl chambers of type C and of type D, respectively, in terms of a Doob h-transform. Furthermore, we prove functional limit theorems for the rescaled random walks. This is an extension of recent work by Eichelsbacher and Koenig who studied the analogous conditioning for the Weyl chamber of type A. Our proof follows recent work by Denisov and Wachtel who used martingale properties and a strong approximation of random walks by Brownian motion. Therefore, we are able to keep minimal moment assumptions. Finally, we present an alternate function that is amenable to an h-transform in the Weyl chamber of type C. In the second part which is concerned with Brownian motion, we examine the non-exit probability of a multidimensional Brownian motion from a growing truncated Weyl chamber. Different regimes are identified according to the growth speed, ranging from polynomial decay over stretched-exponential to exponential decay. Furthermore we derive associated large deviation principles for the empirical measure of the properly rescaled and transformed Brownian motion as the dimension grows to infinity. Our main tool is an explicit eigenvalue expansion for the transition probabilities before exiting the truncated Weyl chamber.