We present a comprehensive study of X-ray emission by, and wind properties of, massive magnetic early B-type stars. Dedicated XMM–Newton observations were obtained for three early-type B-type stars, ξ1 CMa, V2052 Oph and ζ Cas, with recently discovered magnetic fields. We report the first detection of X-ray emission from V2052 Oph and ζ Cas. The latter is one the softest X-ray sources among the early-type stars, while the former is one of the X-ray faintest. The observations show that the X-ray spectra of our programme stars are quite soft with the bulk of X-ray emitting material having a temperature of about 1 MK. We compile the complete sample of early B-type stars with detected magnetic fields to date and existing X-ray measurements, in order to study whether the X-ray emission can be used as a general proxy for stellar magnetism. We find that the X-ray properties of early massive B-type magnetic stars are diverse, and that hard and strong X-ray emission does not necessarily correlate with the presence of a magnetic field, corroborating similar conclusions reached earlier for the classical chemically peculiar magnetic Bp–Ap stars. We analyse the ultraviolet (UV) spectra of five non-supergiant B stars with magnetic fields (τ Sco, β Cep, ξ1 CMa, V2052 Oph and ζ Cas) by means of non-local thermodynamic equilibrium (non-LTE) iron-blanketed model atmospheres. The latter are calculated with the Potsdam Wolf–Rayet (PoWR) code, which treats the photosphere as well as the wind, and also accounts for X-rays. With the exception of τ Sco, this is the first analysis of these stars by means of stellar wind models. Our models accurately fit the stellar photospheric spectra in the optical and the UV. The parameters of X-ray emission, temperature and flux are included in the model in accordance with observations. We confirm the earlier findings that the filling factors of X-ray emitting material are very high. Our analysis reveals that the magnetic early-type B stars studied here have weak winds with velocities not significantly exceeding vesc. The mass-loss rates inferred from the analysis of UV lines are significantly lower than predicted by hydrodynamically consistent models. We find that, although the X-rays strongly affect the ionization structure of the wind, this effect is not sufficient in reducing the total radiative acceleration. When the X-rays are accounted for at the intensity and temperatures observed, there is still sufficient radiative acceleration to drive a stronger mass-loss than we empirically infer from the UV spectral lines.

The consequences of structured flows continue to be a pressing topic in relating spectral data to physical processes occurring in massive star winds. In a preceding paper, our group reported on hydrodynamic simulations of hypersonic flow past a rigid spherical clump to explore the structure of bow shocks that can form around wind clumps. Here we report on profiles of emission lines that arise from such bow shock morphologies. To compute emission line profiles, we adopt a two-component flow structure of wind and clumps using two “beta” velocity laws. While individual bow shocks tend to generate double-horned emission line profiles, a group of bow shocks can lead to line profiles with a range of shapes with blueshifted peak emission that depends on the degree of X-ray photoabsorption by the interclump wind medium, the number of clump structures in the flow, and the radial distribution of the clumps. Using the two beta law prescription, the theoretical emission measure and temperature distribution throughout the wind can be derived. The emission measure tends to be power law, and the temperature distribution is broad in terms of wind velocity. Although restricted to the case of adiabatic cooling, our models highlight the influence of bow shock effects for hot plasma temperature and emission measure distributions in stellar winds and their impact on X-ray line profile shapes. Previous models have focused on geometrical considerations of the clumps and their distribution in the wind. Our results represent the first time that the temperature distribution of wind clump structures are explicitly and self-consistently accounted for in modeling X-ray line profile shapes for massive stars.

We obtained X-ray XMM-Newton observations of the open cluster Berkeley 87 and the massive star-forming region (SFR) ON 2. In addition, archival infrared Spitzer Space Telescope observations were used to study the morphology of ON 2, to uncover young stellar objects, and to investigate their relationship with the X-ray sources. It is likely that the SFR ON 2 and Berkeley 87 are at the same distance, 1.23 kpc, and hence are associated. The XMM-Newton observations detected X-rays from massive stars in Berkeley 87 as well as diffuse emission from the SFR ON 2. The two patches of diffuse X-ray emission are encompassed in the shell-like H II region GAL 75.84+0.40 in the northern part of ON 2 and in the ON 2S region in the southern part of ON 2. The diffuse emission from GAL 75.84+0.40 suffers an absorption column equivalent to AV ≈ 28 mag. Its spectrum can be fitted either with a thermal plasma model at T ≳ 30 MK or by an absorbed power-law model with γ ≈ −2.6. The X-ray luminosity of GAL 75.84+0.40 is LX ≈ 6 × 1031 erg s−1. The diffuse emission from ON 2S is adjacent to the ultra-compact H II (UCH II) region Cygnus 2N, but does not coincide with it or with any other known UCH II region. It has a luminosity of LX ≈ 4 × 1031 erg s−1. The spectrum can be fitted with an absorbed power-law model with γ ≈ −1.4. We adopt the view of Turner & Forbes that the SFR ON 2 is physically associated with the massive star cluster Berkeley 87 hosting the WO-type star WR 142. We discuss different explanations for the apparently diffuse X-ray emission in these SFRs. These include synchrotron radiation, invoked by the co-existence of strongly shocked stellar winds and turbulent magnetic fields in the star-forming complex, cluster wind emission, or an unresolved population of discrete sources.

We present a comprehensive study of X-ray emission and wind properties of magnetic early B-type stars. We compile the complete sample of early B-type stars with detected magnetic fields to date and existing X-ray measurements, in order to study whether the X-ray emission can be used as a general proxy for stellar magnetism. For the first time we analyze the UV spectra of B stars with magnetic fields by means of non-LTE iron-blanketed stellar atmosphere model that account for the X-rays at the intensity and temperatures observed. The mass-loss rates inferred from the analysis of UV lines are significantly lower than predicted by hydrodynamically consistent models. We find that the X-ray properties of early B-type magnetic stars are diverse, and that hard and strong X-ray emission does not necessarily correlate with the presence of a magnetic field.

L’étoile Wolf-Rayet WR 46 est connue pour sa variabilité complexe sur des échelles de temps relativement courtes de quelques heures et sur des échelles de temps plus longues de plusieurs mois. Des décalages périodiques mais intermittents en vitesse radiale ont déjà été observés dans ses raies d’émission optiques. Plusieurs périodes photométriques ont aussi été mesurées dans le passé. Des pulsations non-radiales, une modulation liée à la rotation rapide, ou encore la présence d’un compagnon de faible masse dont la présence reste à confirmer ont été proposées pour expliquer le comportement de l’étoile sur des échelles de temps de quelques heures. Dans un effort pour dévoiler sa vraie nature, nous avons observé WR 46 avec le satellite FUSE sur plusieurs cycles de variabilité à court terme. Nous avons trouvé des variations sur une échelle de temps d’environ 7,5 heures dans le continu ultraviolet lointain, dans l’aile bleue de la composante d’absorption du profil P Cygni du doublet de O vi 1032, 1038, ainsi que dans la composante d’absorption du profil P Cygni de S vi 933, 944. Nous avons également récupéré des données archivées de cette étoile obtenues avec le satellite XMM-Newton. La courbe de lumière en rayons X montre des variations sur une échelle de temps similaire aux courbes de lumière du continu ultraviolet et ultraviolet lointain, et le spectre rayons X de WR 46 est très mou avec un pic d’émission à des énergies plus faibles que 1 keV. Nous discutons des différentes contraintes sur la nature de la variabilité de cette étoile que ces nouvelles observations aident à poser. Parmi les scénarios suggérés, nous concluons que celui des pulsations non-radiales est le plus probable, bien que nous soyons encore loin d’une compréhension détaillée de WR 46. / The Wolf-Rayet star WR 46 is known to exhibit a very complex variability pattern on relatively short timescales of a few hours and also on longer timescales of months. Periodic but intermittent radial velocity shifts of optical lines as well as multiple photometric periods have been found in the past. Nonradial pulsations, rapid rotational modulation or the presence of a yet-to-be-confirmed low-mass companion have been proposed to explain the short-term behaviour. In an effort to unveil its true nature, we observed WR 46 with FUSE over several short-term variability cycles. We found significant variations on a timescale of about 7.5 hours in the FUV continuum, in the blue edge of the absorption trough of the O vi 1032, 1038 doublet P Cygni profile, and in the S vi 933, 944 P Cygni absorption profile. We also retrieved archival XMM-Newton data of this star. We found the X-ray light-curve to show variations on a timescale similar to the UV and FUV continuum light-curves, and the X-ray spectrum of WR 46 to be very soft with a peak below 1 keV. We discuss the different constraints on the nature of the variability that these new observations help to establish. Among the suggested scenarios, we conclude that non-radial pulsations is the most likely, although we are far from a complete picture.

Atmospheric haze, which builds up over South Africa including our study areas, Cape Town and the Mpumalanga Highveld under calm weather conditions, causes public concern. The scope of this study was to determine the concentration and composition of atmospheric aerosol at Khayelitsha (an urban site in the Western Cape) and Ferrobank (an industrial site in Witbank, Mpumalanga). Particulate matter was collected in Khayelitsha from 18 May 2007 to 20 July 2007 (i.e. 20 samples) using a Partisol-plus sampler and a Tapered Element Oscillating Microbalance (TEOM) sampler. Sampling took place at Ferrobank from 07 February 2008 to 11 March 2008 (6 samples) using a Partisol-plus sampler and an E-sampler. The gravimetric mass of each exposed sample was determined from pre- and post-sampling weighing. The elemental composition of the particulate matter was determined for 16 elements at Khayelitsha using Proton Induced X-ray Emission (PIXE). The concentration of the elements Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, As, Br, Sn, and Pb was determined by analysing the PIXE spectra obtained. In similar manner, the elemental composition of the particulate matter was determined for 15 elements at Ferrobank (Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, As, Br and Pb). The average aerosol mass concentrations for different days at the Khayelitsha site were found to vary between 8.5 μg/m3 and 124.38 μg/m3. At the Khayelitsha site on three occasions during the sampling campaign the average aerosol mass concentrations exceeded the current South African air quality standard of 75 μg/m3 over 24 h. At the Ferrobank site, there are no single days that exceeded the limit of the South African air quality standard during the sampling campaign. Enrichment factors for each element of the particles sampled with an aerodynamic diameter of less than 10 μm (PM10) samples have been calculated in order to identify their possible sources. The analysis yielded five potential sources of PM10 : soil dust, sea salt, gasoline emissions, domestic wood and coal combustion. Interestingly, enrichment factor values for the Khayelitsha samples show that sea salt constitutes a major source of emissions, while Ferrobank samples, the source apportionment by unique ratios (SPUR) indicate soil dust and coal emission are the major sources of pollution. The source apportionment at Khayelitsha shows that sea salt and biomass burning are major source of air pollution.

O presente estudo foi desenvolvido para caracterizar a área de influência dos corredores de tráfego, através do monitoramento da concentração de elementos-traço em cascas de árvores. Amostras (n = 98) de cascas de árvores de diversas espécies foram coletadas em cinco parques urbanos da cidade de São Paulo. Para controle, foram coletadas cascas de árvores numa zona rural de Embu-Guaçu, longe de tráfego ou de indústrias. As concentrações de Ba, Co, Cr, Cu, Fe, Ca, Pb, S e Zn foram determinadas nas amostras de cascas de árvores por espectrometria de fluorescência de raios-X. Amostras coletadas nos parques urbanos apresentaram níveis mais elevados de elementos-traço em comparação com as da região controle. Elementos relacionados a atividades antropogênicas exibiram maiores concentrações nas amostras coletads na periferia dos parques, diminuindo gradativamente para os seus centros. Áreas próximas a grandes avenidas ou próximas a semáforos e cruzamentos apresentaram maiores concentrações de elementos nas cascas. Em conclusão, o estudo mostrou que medidas de acúmulo de elementos traço em cascas de árvore, associadas a métodos geoestatísticos, podem auxiliar a determinação das zonas de maior influência da poluição veicular no cenário urbano / The present study was designed to characterize the area of influence of high traffic corridors by monitoring trace element concentrations on tree barks. Samples (n=98) of tree barks were collected from several tree species in five urban parks of the city of São Paulo. For controlling purposes, we collected tree barks in a rural area of Embu-Guaçu which is far from traffic or industries. Concentrations of Ba, Co, Cr, Cu, Fe, Ca, Pb, S and Zn were determined in these barks by X-ray fluorescence spectrometry. Samples from urban parks exhibited higher levels of trace elements in comparison with those from control region. Elements related to anthropogenic activities exhibited higher concentrations in tree barks at the periphery of the parks, decreasing when moving towards their centers. Areas facing the busy streets or those close to traffic lights or traffic junctions presented higher concentrations of elements in barks. In conclusion, the present study showed that measures of trace elements accumulation in tree barks within geostatistical methods can indicate areas of strong influence of vehicular pollution in the urban scene

>Magister Scientiae - MSc / To study nuclear reactions and nuclear structures, target materials are bombarded with high-energy particles. The target material can either be in a form of a metal film or gas. A target material designed to study certain nuclear reactions or to produce nuclei to study their structure should yield as minimum as possible of competing reactions under ion bombardment. This requires a chemically and isotopically pure target material prepared as a self supporting thin film, or as alternative, prepared on a thin career foil. Additional requirement for lifetime measurement experiments are homogeneity and precise thickness of the target material. Some of the data obtained from the stopping power experiment where targets of 114Cd were used for lifetime measurement are presented. Moreover, a nuclear target should influence the spectroscopic resolution as little as possible. Thus, film thickness must be adjusted to the respective reaction under study while observing the optimum thickness homogeneity.

Le développement des techniques de microscopie 3D offrant une résolution spatiale de l'ordre du micromètre a ouvert un large champ de recherche en biologie cellulaire. Parmi elles, un avantage intéressant de la micro-tomographie par faisceau d'ions est de donner des résultats quantitatifs en termes de concentrations locales d'une manière directe, en utilisant une technique d'émission de rayonnement X (PIXET) combinée à la microscopie ionique en transmission (STIMT). Le traitement des données expérimentales constitue un point délicat. Après une brève introduction aux techniques de reconstruction existantes, nous présentons le principe du code DISRA, le plus complet écrit jusqu'à ce jour, qui nous a servi de base pour ce travail de thèse. Nous avons modifié et étendu le code DISRA en considérant les aspects spécifiques des échantillons biologiques. Un logiciel de traitement de données complet a ainsi été développé, avec une interface utilisateur permettant le contrôle de chaque étape de la reconstruction. Les résultats d'expériences de STIMT et/ou PIXET effectuées au CENBG sur des spécimens de référence et sur des cellules végétales ou humaines isolées sont présentés.

<p>This thesis addresses the electronic structure of vanadium and copper oxides using soft X-ray absorption (SXA) spectroscopy and resonant inelastic X-ray scattering (RIXS) at high brightness synchrotron radiation sources. In RIXS incident photons, tuned to the energy of specific absorption resonances, are inelastically scattered leaving behind a low energy valence excitation in the system studied. Effects of electron localization are reflected by the occurrence of low-energy excitations in form of dd- and charge-transfer excitations that are modelled by cluster calculations. Band-like states are dominating when the intermediate core excited state is delocalized.</p><p>RIXS at V 2p and O 1s resonances has been used to study the electronic structure of the monovalent vanadium oxides VO₂ and V₂O₃, and of the mixed valence compounds, NaV₂O₅ and V₆O₁₃. For NaV₂O₅ and V₆O₁₃ significant contributions from localized low-energy excitations reflect the partly localized character of their valence band electronic structure, whereas VO₂ and V₂O₃ appear mostly as band-like. Effects of carrier doping are addressed for the case of Mo doping into VO₂ and reveal a quasi-rigid band behavior. In the cases of VO₂ and V₆O₁₃ the temperature dependent metal-insulator transition could be monitored by following the spectral evolution of bands originating from V 3d and V 3d - O2p hybridized states. For Na₂V₃O₇ nanotubes it was possible to selectively probe states from the apical and the basal oxygen sites of VO₅ pyramids that constitute these nanotubes. Furthermore, the RIXS technique has been demonstrated to be highly valuable in characterizing the charge transfer processes that accompany lithium insertion into vanadium oxide battery cathodes. Finally, for insulating cuprates RIXS at O 1s, Cu 3p and Cu 3s resonances has been recorded at high-resolution for the detailed investigation of crystal field excitations.</p>