We have obtained a Chandra/HETGS spectrum of one of the most massive and luminous stars in the Galaxy: the blue hypergiant Cyg OB2-12 (HIP 101364, spectral type B3 Ia+). This is the first measurement at high resolution of X-ray spectral lines in a blue hypergiant and allows comparison of X-ray properties between massive stars at different but related evolutionary stages: O-type supergiants, luminous blue variables, Wolf-Rayet stars, and blue hypergiants stars. The new data provide a look at how the most massive stars shed mass during their pre-supernova evolution. We find that In Cyg OB2-12 the resolved Si and Mg lines are broadened by about 1000 km/s (FWHM). The lines, however, do not show appreciable centroid shifts (/s), which would be much larger for canonical moderately thick winds (~500 km/s). The He-like Mg XI lines show evidence of photo-excitation, implying a wind origin close to the UV-bright photosphere. The spectrum also indicates relatively high temperature plasma, up to 22 MK (1.9 keV), showing significant continuum and emission lines below 5A (above 2.5 keV). Hence, at first glance, the spectrum resembles neither an O-star thick wind, nor a magnetically confined (narrow-line) plasma. We will present more detailed wind models using both X-ray and UV spectra to constrain fundamental physical parameters of this star.

As WR 6 is a putatively single WN4 star, and is relatively bright (V = 6.9), it is an ideal case for studying the wind mechanisms in these extremely luminous stars. To obtain higher resolution spectra at higher energy (above 1 keV) than previously obtained with the XMM/Newton RGS, we have observed WR 6 with the Chandra High Energy Transmission Grating Spectrometer for 450 ks. We have resolved emission lines of S, Si, Mg, Ne, and Fe, which all show a “fin”-shaped profile, characteristic of a self-absorbed uniformly expanding shell. Steep blue edges gives robust maximal expansion velocities of about 2000 km/s, somewhat larger than the 1700 km/s derived from UV lines. The He-like lines all indicate that X-ray emitting plasmas are far from the photosphere – even at the higher energies where opacity is lowest – as was also the case for the longer wavelength lines observed with XMM-Newton/RGS. Abundances determined from X-ray spectral modeling indicate enhancements consistent with nucleosynthesis. The star was also variable in X-rays and in simultaneous optical photometry obtained with Chandra aspect camera, but not coherently with the optically known period of 3.765 days.

The nature of the edge-on eclipsing binary Epsilon Aurigae remains perplexing, despite notable progress since the recent 2009-2011 eclipse. The binary involves an early F supergiant with a still unknown companion enshrouded in a disk. Although the eclipse geometry produces a significant broad band polarization signature, semiregular pulsations of the F supergiant are also a source of variable polarization, with an amplitude that is commensurate with the effect of the eclipse. This fact makes use of the polarization for studying the disk of the companion far more challenging. In an effort to better understand the pulsation nature of the supergiant, we explore a simple model for the stellar contribution to the polarization signal. The model does reasonably well in characterizing the gross properties of the time-variable polarization.

Co-rotating Interaction Regions (CIRs) are a well-known phenomenon in the solar wind, and is a favored culprit for certain cyclical behavior observed in the spectra of some massive stars. A prime example are the discrete absorption components (DACs) seen in the UV wind lines of many O stars. Here we report on modeling for the variable continuum polarization that could arise from the presence of CIR structures. Considerations are limited to optically thin scattering. Using a core-halo approach for winds that are thick to electron scattering, an application to observed variable polarization of WR6 (EZ CMa; HD 50896) is presented.

Thesis (M. Dev.) -- University of Limpopo, 2005 / Refer to document

Thesis ( M.Dev.) -- University of Limpopo, 2010 / Refer to document

Among the different types of massive stars in advanced evolutionary stages is the enigmatic WN8h type. There are only a few Wolf–Rayet (WR) stars with this spectral type in our Galaxy. It has long been suggested that WN8h-type stars are the products of binary evolution that may harbor neutron stars (NS). One of the most intriguing WN8h stars is the runaway WR 124 surrounded by its magnificent nebula M1-67. We test the presence of an accreting NS companion in WR 124 using ~100 ks long observations by the Chandra X-ray observatory. The hard X-ray emission from WR 124 with a luminosity of L X ~ 1031 erg s−1 is marginally detected. We use the non-local thermodynamic equilibrium stellar atmosphere code PoWR to estimate the WR wind opacity to the X-rays. The wind of a WN8-type star is effectively opaque for X-rays, hence the low X-ray luminosity of WR 124 does not rule out the presence of an embedded compact object. We suggest that, in general, high-opacity WR winds could prevent X-ray detections of embedded NS, and be an explanation for the apparent lack of WR+NS systems.

Cette recherche, basée sur le vécu de la maladie cancéreuse, chez l’adulte atteint d’une tumeur solide à risque mortel et à fort potentiel traumatique, étudie la pertinence de la notion de pulsion d’emprise dans son articulation à Eros et Thanatos. Elle vise à éclairer un constat clinique : la discordance entre l’évolution satisfaisante de la maladie et le ressenti subjectif péjoratif du malade et, analyser les enjeux psychiques, suivant les discours théorico-cliniques (historique, médical, philosophique, psycho-oncologique, psychanalytique). Une première partie souligne l’évolution médicale, sociétale de cette atteinte, marquée par des représentations mortifères, contrastant avec la scientificité actuelle. La notion de temporalité est étudiée, celles de la maladie cancéreuse et de ses traitements en rapport à celle du sujet. La deuxième partie aborde le champ de l’emprise dans le discours psychanalytique. L’étude clinico-théorique de situations cliniques montre la force de la pulsion d’emprise et ses valeurs contrastées dans le travail psychique du malade, marqué par la prégnance de la représentation de la mort.La troisième partie métapsychologique décrit la conflictualité entre les instances psychiques, le corps et le cancer. L’analyse du pulsionnel et particulièrement de la pulsion anarchiste interroge l’articulation entre la pulsion d’emprise et la pulsion de vie sans oublier le nouage de cette dernière à la pulsion de mort. Le rapport entre le moi-corps et le médium malléable est questionné.L’hypothèse de la valeur de l’emprise est étudiée comme un aménagement nécessaire, temporaire avant l’acceptation par le moi des pertes induites par le cancer. / This research, based on the experience of cancer disease, in adult patients with solid tumors at deadly risk and potential trauma, studies the relevance of the concept of right of way in its drive joint Eros and Thanatos. It aims to inform clinical observation: the discrepancy between the satisfactory evolution of the disease and the subjective feeling pejorative patient and analyze the psychological issues, according to the theoretical and clinical speech (historical, medical, philosophical, psycho-oncology, psychoanalytic). The first part stresses the medical evolution, this social achievement, marked by deadly performances, contrasting with the current scientific. The concept of temporality is studied, those of the cancer disease and its treatment in relation to that of the subject. The second part addresses the influence of the field in the psychoanalytic discourse. Clinical and theoretical study of clinical situations shows the strength of the grip and drive its contrasting values in the psychological work of the patient, marked by the predominance of the representation of death. The third part describes the metapsychological conflict between the psychic instances, the body and cancer. The analysis of the drive and especially the anarchist impulse questioned the link between the drive and grip the life instinct not to mention tying the latter to the death drive. The relationship between bodily and the pliable medium is questioned. The assumption of the value of the grip is studied as a necessary development, temporary before acceptance by me of losses induced by cancer.

Denna uppsats diskuterar den komplexa och undermedvetna process som ger upphov till spontana musikaliska idéer. Förhoppningen med detta arbete är att fungera som underlag för vidare och mer utarbetade teorier kring uppkomsten av spontana musikaliska idéer och hur vi kan kombinera vår intuitiva och diskursiva kunskap i syfte att få mer originella idéer. För att uppnå syfte har fyra musikaliska verk inspirerade av färger skrivits med fokus på det melodiska innehållet. De fyra verken är komponerade utan instrument (Idémedium) och har sedan på gehör programmerats och arrangerats (digitalt) med utgångspunkt i de respektive färgunderlagen. Övningen har sedan utvärderats och diskuterats med utgångspunkt i de idéer om den intuitiva härledningsprocessen som formulerats i samband med arbetet. Produkterna av de fyra musikaliska verken för detta arbete uppvisar tydliga olikheter sinsemellan. Vissa tydligt medvetna associationer går direkt att härleda ur respektive färgunderlag samtidigt som vissa mer svårmotiverade val har gjorts under komponerings- och arrangeringsprocessen. / This study has been formed through a series of thoughts regarding the complex and subconscious process that form spontaneous musical ideas - the process of intuition. The expectations with this essay is to underlay future, and more thorough, theories about the origin of spontaneous ideas and how we can combine our intuitive knowledge and our discursive knowledge in order to get more original ideas. In an attempt to test how spontaneous musical ideas might get affected by the use of a medium for translating ideas (in this case a musical instrument) four songs have been composed without the use of musical instruments. In the process of composing the songs, colours have figured as a source of inspiration in an attempt to “force” the intuitive process to take less direct ways to a source of information based on past experience of music. The argument for this is that a colour is a non-musical stimulus which in contrast to a musical stimulus (something with musical qualities to it) makes it harder for our intuition to take shortcuts to relevant data based on our past experiences of music. The four songs later got lightly arranged with an intuitive approach, which in this case means to ”as little as possible” reflect (discursively) over the choices of instruments and other aspects of the arrangement. This exercise has then been discussed and evaluated with reference to my assumptions about the intuitive process. The result of i this exercise shows four songs that are remarkably different from one another and also some potentially ”unwanted” side effects of the chosen method for testing these ideas.

We utilize a Poisson likelihood in a maximum likelihood statistical analysis to analyze X-ray spectragraphic data. Specifically, we examine four extragalactic supernova remnants (SNR). IKT 5 (SNR 0047-73.5), IKT 25 (SNR 0104-72.3), and DEM S 128 (SNR 0103-72.4) which are designated as Type Ia in the literature due to their spectra and morphology. This is troublesome because of their asymmetry, a trait not usually associated with young Type Ia remnants. We present \emph{Chandra X-ray Observatory} data on these three remnants, and perform a maximum likelihood analysis on their spectra. We find that the X-ray emission is dominated by interactions with the interstellar medium. In spite of this, we find a significant Fe overabundance in all three remnants. Through examination of radio, optical, and infrared data, we conclude that these three remnants are likely not "classical" Type Ia SNR, but may be examples of so-called "prompt" Type Ia SNR. We detect potential point sources that may be members of the progenitor systems of both DEM S 128 and IKT 5, which could suggest a new subclass of prompt Type Ia SNR, Fe-rich CC remnants. In addition, we examine IKT 18. This remnant is positionally coincident with the X-ray point source HD 5980. Due to an outburst in 1994, in which its brightness changed by 3 magnitudes (corrsponding to an increase in luminosity by a factor of 16) HD 5980 was classified as a luminous blue variable star. We examine this point source and the remnant IKT 18 in the X-ray, and find that its non-thermal photon index has decreased from 2002 to 2013, corresponding to a larger proportion of more energetic X-rays, which is unexpected.