Étude des étoiles de la branche horizontale extrême par l'astérosismologie

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Maximum mass of neutron stars

We determine the structure of neutron stars within a Brueckner-Hartree-Fock approach based on realistic nucleon-nucleon, nucleon-hyperon, and hyperon-hyperon interactions. Our results indicate rather low maximum masses below 1.4 solar masses. This feature is insensitive to the nucleonic part of the EOS due to a strong compensation mechanism caused by the appearance of hyperons and represents thus strong evidence for the presence of nonbaryonic "quark" matter in the interior of heavy stars.

On the use of rotational splitting asymmetries to probe the internal rotation profile of stars: Application to beta Cephei stars

Rotationally-split modes can provide valuable information about the internal rotation profile of stars. This has been used for years to infer the internal rotation behavior of the Sun. The present work discusses the potential additional information that rotationally splitting asymmetries may provide when studying the internal rotation profile of stars. We present here some preliminary results of a method, currently under development, which intends: 1) to understand the variation of the rotational splitting asymmetries in terms of physical processes acting on the angular momentum distribution in the stellar interior, and 2) how this information can be used to better constrain the internal rotation profile of the stars. The accomplishment of these two objectives should allow us to better use asteroseismology as a test-bench of the different theories describing the angular momentum distribution and evolution in the stellar interiors. (C) 2010 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim

A possible stellar metallic enhancement in post-T Tauri stars by a planetesimal bombardment

The photospheres of stars hosting planets have larger metallicity than stars lacking planets. This could be the result of a metallic star contamination produced by the bombarding of hydrogen-deficient solid bodies. In the present work we study the possibility of an earlier metal enrichment of the photospheres by means of impacting planetesimals during the first 20-30 Myr. Here we explore this contamination process by simulating the interactions of an inward migrating planet with a disc of planetesimal interior to its orbit. The results show the percentage of planetesimals that fall on the star. We identified the dependence of the planet's eccentricity (e(p)) and time-scale of migration (tau) on the rate of infalling planetesimals. For very fast migrations (tau= 10(2) and 10(3) yr) there is no capture in mean motion resonances, independently of the value of e(p). Then, due to the planet's migration the planetesimals suffer close approaches with the planet and more than 80 per cent of them are ejected from the system. For slow migrations (tau= 10(5)and 10(6) yr) the percentage of collisions with the planet decreases with the increase of the planet's eccentricity. For e(p) = 0 and 0.1 most of the planetesimals were captured in the 2:1 resonance and more than 65 per cent of them collided with the star. Whereas migration of a Jupiter mass planet to very short pericentric distances requires unrealistic high disc masses, these requirements are much smaller for smaller migrating planets. Our simulations for a slowly migrating 0.1 M-Jupiter planet, even demanding a possible primitive disc three times more massive than a primitive solar nebula, produces maximum [Fe/H] enrichments of the order of 0.18 dex. These calculations open possibilities to explain hot Jupiter exoplanet metallicities.

On neutron stars in ƒ (R) theories: Small radii, large masses and large energy emitted in a merger

In the context of ƒ (R) gravity theories, we show that the apparent mass of a neutron star as seen from an observer at infinity is numerically calculable but requires careful matching, first at the star’s edge, between interior and exterior solutions, none of them being totally Schwarzschild-like but presenting instead small oscillations of the curvature scalar R; and second at large radii, where the Newtonian potential is used to identify the mass of the neutron star. We find that for the same equation of state, this mass definition is always larger than its general relativistic counterpart. We exemplify this with quadratic R^2 and Hu-Sawicki-like modifications of the standard General Relativity action. Therefore, the finding of two-solar mass neutron stars basically imposes no constraint on stable ƒ (R) theories. However, star radii are in general smaller than in General Relativity, which can give an observational handle on such classes of models at the astrophysical level. Both larger masses and smaller matter radii are due to much of the apparent effective energy residing in the outer metric for scalar-tensor theories. Finally, because the ƒ (R) neutron star masses can be much larger than General Relativity counterparts, the total energy available for radiating gravitational waves could be of order several solar masses, and thus a merger of these stars constitutes an interesting wave source.

Relentless patterns the immersive interior

What happens when patterns become all pervasive? When pattern contagiously corrupts and saturates adjacent objects, artefacts and surfaces; blurring internal and external environment and dissolving any single point of perspective or static conception of space. Mark Taylor ruminates on the possibilities of relentless patterning in interior space in both a historic and a contemporary context.

A phenomenological study of contemplative experiences : implications for interior design

This research reports on a project concerned with the relationship between the person and the environment in the context of achieving a contemplative or existential state – a state which can be experienced either consciously or subconsciously. The need for such a study originated with the desire to contribute to the design of multicultural spaces which could be used for a range of activities within the public and the personal arena, activities including contemplation, meditation and prayer. The concept of ‘sacred’ is explored in the literature review and in primary interviews with the participants of this study. Given that the word ‘sacred’ is highly value-laden and potentially alienating for some people, it was decided to use the more accessible term ‘contemplative’. The outcomes of the study inform the practice of interior design and architecture which tends currently to neglect the potential for all spaces to be existentially meaningful. Informed by phenomenological methodology, data were collected from a diverse group of people, using photo-elicitation and interviews. The technique of photo-elicitation proved to be highly effective in helping people reveal their everyday lived experience of contemplative spaces. Reflective analysis (Van Manen 2000) was used to explore the data collected. The initial stage of analysis produced three categories of data: varying conceptions of contemplation, aspects of the person involved in the contemplation, and aspects of environment involved in contemplation. From this, it was found that achieving a state of contemplation involves both the person and the environment in a dialectic process of unfolding. The unfolding has various physical, psycho-social, and existential dimensions or qualities which operate sequentially and simultaneously. Two concepts emerged as being central to unfolding: ‘Cleansing’ and ‘Nothingness’. Unfolding is found to comprise the Core; Distinction; Manifestation; Cleansing; Creation; and Sharing. This has a parallel with Mircea Eliade’s (1959) definition of sacred as something that manifests itself as different from the profane. The power of design, re-contextualization through utility and purpose, and the existential engagements between the person and environment are used as a basis for establishing the potential contribution of the study to interior design. In this way, the study makes a contribution to our understanding of how space and its elements inspire, support and sustain person environment interaction – particularly at the existential level – as well as to our understanding of the multi-dimensional and holistic nature of this interaction. In addition, it points to the need for a phenomenological re-conceptualisation of the design/client relationship. In summary, the contributions of this research are: the exploration of contemplative experience as sacred experience; an understanding of the design of space as creating engagement between person and environment; a rationale for the introduction of a phenomenological approach to the relationship between designer and clients; and raising awareness of the spiritual in a holistic approach to design.

Diagramming the interior

Mark Taylor's new essay assesses the impact of the diagram on interior design from the late 19th century to the present. Taylor identifies the pop-cultural discourse of advice writing in both books and magazines as a starting point for his analysis. Drawing on diverse sources, his analysis focuses on texts relating to the dynamics of use and flexibility by Catherine Beecher, Harriet Beecher Stowe, Melusina Fay Peirce, Mary Haweis and Christine Frederick among others. The examples in these texts use the home, domestic housekeeping and kitchens as the sites and practices of intervention through which interior design innovations can be enacted. Taylor's analysis identified the innovations in both the social and the political aspects of space and the critique of static space behind these seemingly amateurish and innocuous texts. Identifying these contributions as early precursors of Modernism's open-plan and flexible, dynamic spaces, Taylor also interprets them with a critical concern for the oppositions and hierarchies that can exist in spatial design, and which are the hallmarks of recent Postmodern, phenomenological approaches to interior design and its theorisations. The progressive and subversive "paradigms for living" implicit in these diagrams can be argued to present a model of greater economic, social and political equality as well as representing a more balanced set of power relations in the home. Progressing through the 20th century to the present, Taylor's analysis shifts byond the dressed body and on to the more intimate rituals of the revealed body to further examine how diagrams of the interior, and the interior as a set of diagrams, are also mediators, sites and grounds for the design of social and sexual intimacy. Through a consideration of the link between design, indentity and intimacy (whether of the invisible, fashioned or sexualised body), the diagrms of interiors are reconfigured as radical and critical tools for an animate, material and emancipatory "redressing" of the balance between the body, identity, sexuality, gender, function, mis(use), aesthetics and the interior.

Rhetoric of landscape architecture and interior design discourses : preparation for cross-disciplinary practice

The rhetoric of the pedagogic discourses of landscape architectural students and interior design students is described as part of a doctoral study undertaken to document practices and orientations prior to cross-disciplinary collaboration. We draw on the theoretical framework of Basil Bernstein, an educational sociologist, and the rhetorical method of Kenneth Burke, a literary dramatist, to study the grammars of ‘landscape’ representation employed within these disciplinary examples. We investigate how prepared final year students are for working in a cross-disciplinary manner. The discursive interactions of their work, as illustrated by four examples of drawn images and written text, are described. Our findings suggest that we need to concern ourselves aspects of our pedagogic discourse that brings uniqueness and value to our disciplines ,as well as that shared discourses between disciplines.

Stars are made of glass : children as capable and creative communicators

This booklet is the third in the Research in Practice Series, designed to complement Belonging, being & becoming: The Early Years Learning Framework for Australia (DEEWR, 2009). It focuses on Learning Outcome 5 of the Early Years Learning Framework (EYLF): Children are effective communicators (DEEWR, 2009).

On location : the imagined private interior in public life

This paper reveals the interior landscapes of selected contemporary Australian films, such as The Caterpillar Wish and Bad Boy Bubby, to develop a number of thematic influences on the manner in which domestic and private lives are constructed through filmic imagination. The research uncovers the conditions that contribute to particular scenographic representations of the humble interiors that act as both backdrop and performer to subtle and often troubled narratives. Such readings are informed by the theoretical works of writer Gertrude Stein, among others, who explore the relationships between the scenographic third dimension and the fourth dimensional performance in the representation of narrative space. A further theoretical thread lies in Giuliana Bruno’s work on the tension between private and public filmic space, which is explored through the public outing of intensely private spaces generated through narratives framed by the specificities of found interiors. Beyond the interrogation of qualities of imagined filmic space is the condition whereby locations, once transformed by the event of movie making are consequently forever revised. These altered conditions subsequently reinvest the lives of those who return to the location with layered narratives of occupation. Situationally, the now reconverted interior performs as contributor to subsequent private inhabitation, even if only as imagined space. The possibility here is that the qualities of the original may be superimposed and recontextualised to invest post-produced interiors with the qualities of the other space as imagined. This reading of film space explores new theoretical design scenarios for imagined and everyday interior landscapes.