The purpose of this dissertation is to prepare and present a critical edition of Carl Nielsen's Quintet for Winds, Op. 43, a major work in the woodwind quintet repertoire. Written for the Copenhagen Wind Quintet in 1922, it is also considered a pivotal composition in Nielsen's artistic output. This treatise offers a brief biography of Carl Nielsen, documents the history and significance of the Quintet for Winds, Op. 43, and presents a critical edition that will enable more accurate performances of this important composition.

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Circular polarization from the Zeeman effect is difficult to detect whenever the ratio of the magnetic field strength to the linewidth is small, as might be expected in the winds of hot stars. However, globally structured fields, such as radially swept fields, do present a characteristically complex Zeeman signature that can be distinguished from noise even when small, because of its telltale features that are antisymmetric about the line. If the emission lines are skewed blueward, a signature of photospheric occultation of the redshifted hemisphere, we find that occultation will also reduce the detectability of the Zeeman effect on the red side of the line, further limiting our ability to detect weak magnetic fields in hypersonic winds. Hence, as instrumental precision improves sufficiently, symmetric emission lines will present advantages over lines skewed blueward by occultation, when seeking a Zeeman signal.

We use a 3D Monte Carlo radiative transfer code to study the polarimetric and photometric variability from stationary corotating interaction regions (CIR) in the wind of massive stars. Our CIRs are approximated by Archimedean spirals of higher (or lower) density formed in a spherical wind originating from the star and we also made allowance for a bright Gaussian spot at the base of the CIR. Comparing results from our code to previous analytical calculations in the optically thin case, we find differences which we attribute mainly to a better estimation of the total unpolarized flux reaching the observer. In the optically thick case, the differences with the analytical calculations are much larger, as multiple scattering introduces additional complexities including occultation effects. The addition of a Gaussian spot does not alter the shape of the polarization curve significantly but does create a small excess in polarization. On the other hand, the effect can be larger on the light curve and can become dominant over the resulting CIR, depending on the spot parameters and density of the wind.

Recombination line profile shapes are derived for ionized spherical stellar winds at radio wavelengths. It is assumed that the wind is optically thick owing to free-free opacity. Emission lines of arbitrary optical depth are obtained assuming that the free-free photosphere forms in the outer, constant expansion portion of the wind. Previous works have derived analytic results for isothermal winds when the line and continuum source functions are equal. Here, semi-analytic results are derived for unequal source functions to reveal that line shapes can be asymmetric about line center. A parameter study is presented and applications discussed.

We present new, contemporaneous Hubble Space Telescope STIS and XMM-Newton observations of the O7 III(n)((f)) star ξ Per. We supplement the new data with archival IUE spectra, to analyze the variability of the wind lines and X-ray flux of ξ Per. The variable wind of this star is known to have a 2.086-day periodicity. We use a simple, heuristic spot model that fits the low-velocity (near-surface) IUE wind line variability very well, to demonstrate that the low-velocity absorption in the new STIS spectra of N iv λ1718 and Si iv λ1402 vary with the same 2.086-day period. It is remarkable that the period and amplitude of the STIS data agree with those of the IUE spectra obtained 22 yr earlier. We also show that the time variability of the new XMM-Newton fluxes is also consistent with the 2.086-day period. Thus, our new, multiwavelength coordinated observations demonstrate that the mechanism that causes the UV wind line variability is also responsible for a significant fraction of the X-rays in single O stars. The sequence of events for the multiwavelength light-curve minima is Si iv λ1402, N iv λ1718, and X-ray flux, each separated by a phase of about 0.06 relative to the 2.086-day period. Analysis of the X-ray fluxes shows that they become softer as they weaken. This is contrary to expectations if the variability is caused by periodic excess absorption. Furthermore, the high-resolution X-ray spectra suggest that the individual emission lines at maximum are more strongly blueshifted. If we interpret the low-velocity wind line light curves in terms of our model, it implies that there are two bright regions, i.e., regions with less absorption, separated by 180°, on the surface of the star. We note that the presence and persistence of two spots separated by 180° suggest that a weak dipole magnetic field is responsible for the variability of the UV wind line absorption and X-ray flux in ξ Per.

The stellar winds of hot stars have an important impact on both stellar and galactic evolution, yet their structure and internal processes are not fully understood in detail. One of the best nearby laboratories for studying such massive stellar winds is the O4I(n)fp star ζ Pup. After briefly discussing existing X-ray observations from Chandra and XMM, we present a simulation of X-ray emission line profile measurements for the upcoming 840 kilosecond Chandra HETGS observation. This simulation indicates that the increased S/N of this new observation will allow several major steps forward in the understanding of massive stellar winds. By measuring X-ray emission line strengths and profiles, we should be able to differentiate between various stellar wind models and map the entire wind structure in temperature and density. This legacy X-ray spectrum of ζ Pup will be a useful benchmark for future X-ray missions.

Dans l’Univers, on observe des galaxies lointaines ne formant plus d’étoiles, mais les astrophysiciens n’ont pas encore identifié avec certitude les phénomènes physiques à l’origine de leur “mort”. Pour apporter des éléments de réponse, je me suis penchée sur l’étude de phénomènes qui pourraient y jouer un rôle : les processus de rétroaction des étoiles et des trous noirs supermassifs actifs, la formation stellaire, et les vents galactiques. Le Chapitre 1 présente toutes les notions nécessaires à la compréhension du problème : les caractéristiques des galaxies typiques de l’Univers proche et lointain ; les vents galactiques ; la mort des galaxies; les trous noirs supermassifs actifs (noyaux actifs de galaxies, AGN) et les étoiles ; et leur rétroaction. Dans le Chapitre 2, je présente les techniques numériques utilisées : le code de simulations astrophysiques RAMSES et le code de transfert radiatif Cloudy, que j’ai utilisé pour développer une méthode de calcul de l’état d’ionisation d’une galaxie, détaillée au Chapitre 3. Le Chapitre 4 étudie le couplage entre les trous noirs actifs et les étoiles, avec le projet POGO, Origines Physiques des Vents Galactiques. Durant cette thèse, j’ai montré que les trous noirs actifs n’étaient pas en mesure de tuer subitement leur hôte, même en prenant en compte la rétroaction des étoiles, et que leur couplage peut réduire ou renforcer les vents dans les galaxies en fonction de leur masse. Le Chapitre 5 fait un état de l’art du domaine avant et pendant mon doctorat, reprend les conclusions de cette thèse et donne quelques perspectives, notamment en ce qui concerne le rôle additionnel des rayons cosmiques dans la mort des galaxies / In the Universe, we observe galaxies forming no, or almost no, stars anymore, but astrophysicists do not know yet what physical mechanisms cause their “death”. To give clues to solve the problem, I studied feedback processes from stars and active supermassive black holes, star formation and galactic outflows. Chapter 1 presents all the notions to understand the problem: the characteristics of typical galaxies in the local and distant Universe, galactic outflows, galaxy death, active supermassive black holes, stars, and their feedback processes. In Chapter 2, I describe the numerical techniques I used: the simulation code RAMSES, and the radiative transfer code Cloudy, which I used to develop a computation method to get the ionization state of an entire galaxy. This method is presented in Chapter 3. Chapter 4 studies the coupling between the feedback processes of active supermassive black holes and stars, with the POGO project, Physical Origins of Galactic Outflows. During this thesis, I showed that typical active supermassive black hole cannot suddenly kill their host, even when stellar feedback processes are accounted for, and that their coupling either reduces or enhances the mass outflow rate depending on the mass of the host. In Chapter 5, I give a state-of-the-art about active supermassive black holes before and during my thesis, sum up the conclusions of the work, and give perspectives to enlarge the scope of the study, especially regarding the additional role of cosmic rays in the death of galaxies

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 1999. / Includes bibliographical references (leaves 235-243). / A detailed examination of the development of a deep convection event observed in the Greenland Sea in 1988-89 is carried out through a combination of modeling, scale estimates, and data analysis. We develop a prognostic one-dimensional mixed layer model which is coupled to a thermodynamic ice model. Our model contains a representation of the lowest order boundary layer dynamics and adjustable coupling strengths between the mixed layer, ice, and atmosphere. We find that the model evolution is not very sensitive to the strength of the coupling between the ice and the mixed layer sufficiently far away from the limits of zero and infinite coupling; we interpret this result in physical terms. Further, we derive an analytical expression which provides a scale estimate of the rate of salinification of the mixed layer during the ice-covered preconditioning period as a function of the rate of ice advection. / by Jay Alan Austin. / Ph.D.

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Bibliography: leaves 104-107. / by Bruce B. Parker / M.S.