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See detailAstrophysical Concepts, seconde édition -- Martin Harwit
Manfroid, Jean ULg

in Ciel et Terre (1989), 105

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See detailAstrophysical parameters and multiplicity of massive stars: a mathematical approach
Mahy, Laurent ULg

Doctoral thesis (2011)

Often quoted for their crucial role in the ecology of galaxies, massive stars remain mysterious. The exact process leading to their formation, their stability or their stellar winds are so many questions ... [more ▼]

Often quoted for their crucial role in the ecology of galaxies, massive stars remain mysterious. The exact process leading to their formation, their stability or their stellar winds are so many questions which are still unanswered. Since the lifetime of these objects is too short to allow them to move far away from their birth places, the large majority of massive stars are located in young open clusters or in OB associations. The observations of massive stars in these locations thus provide with promising information on their formation mechanisms. One of the most interesting properties, in this context, is their multiplicity. Indeed, the proportion of multiple systems, the values of orbital periods, of eccentricities, or of mass ratios are parameters directly linked to the formation mechanism and to the dynamical interactions occurring during the earliest stages of their existence. Moreover, constraining this multiplicity with a sufficient accuracy allows to obtain a better determination of the nature and physical parameters of massive stars. The present work is devoted to the study of the O star populations located in the young open cluster NGC2244 and in the surrounding Mon OB2 association as well as in several OB associations of the Cygnus complex. We establish not only the multiplicity of about thirty stars but also their fundamental parameters such as their masses or their N content. However, the complexity of observed spectra of multiple systems makes these objects difficult to investigate. Their analysis thus requires the development and the utilization of mathematical tools such as the "disentangling" which allows to separate the spectra of the components from the observed ones or such as the Doppler tomography which aims at mapping the wind interactions seen in some binary systems. The first part of this dissertation is dedicated to the development and to the characterization of these mathematical methods whilst the second part focuses on the study of populations of massive stars. We refine the orbital and physical parameters of systems already known as multiple. In this context, the analysis of the two components of LZ Cep system reveals modified abundances for the secondary star, confirming a mass transfer from the secondary towards to primary. We also detect for the first time a third star in the HD150136 system. This object, composed of an O3, an O5.5 and an O6.5, constitutes a new test to apply these mathematical methods and thus to better constrain the physical properties of the system as well as those of each component. Moreover, we find, in the population of NGC2244, of Mon OB2 and of the Cygnus OB associations, six new binary systems and derive the orbital solutions for five of them. These results show that NGC2244 hosts only one long-period binary and none with a short period whilst four short-period and no long-period systems are detected in the Cygnus complex. This obvious lack of short-period system in NGC2244 contrasts with the O star populations in other young open clusters such as NGC6231 or IC 2944. Besides the multiplicity, the fundamental parameters such as the N content also allows us to, notably, adapt the so-called Hunter-diagram to galactic O stars. Moreover, we have obtained photometric data for six O-type stars in NGC2244 and Mon OB2 with the CoRoT satellite. These data of unprecedented quality allow us to detect the presence, in the O star light curves, of red noise which is supposed to originate from either the sub-surface convection zone, the granulation or an onset of clumping in the winds of the stars. We also highlight the existence of non-radial pulsations in the light curve of Plaskett’s Star as well as a hot spot located between the two components of that system. In addition, numerous frequencies, extracted from the CoRoT light curves, reveal, for some of the observed stars, solar-like oscillations or beta Cephei-like pulsations. This analysis thus gives a first observational constraint on the bright end of the massive star instability strip. [less ▲]

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See detailAstrophysical research in France in 1940-1942.
Swings, Polydore ULg

in Astrophysical Journal (1944), 99

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See detailAstrophysical studies of extrasolar planetary systems using infrared interferometric techniques
Absil, Olivier ULg

Doctoral thesis (2006)

The study of extrasolar planetary systems has thrived during the last two decades, stimulated by the discovery of circumstellar dust and extrasolar planets around main sequence stars. However, direct ... [more ▼]

The study of extrasolar planetary systems has thrived during the last two decades, stimulated by the discovery of circumstellar dust and extrasolar planets around main sequence stars. However, direct imaging of planetary systems has been possible in only very special cases so far due to the huge contrast and to the small angular separation between stars and their environments. Even for these favourable cases, the inner regions where terrestrial planets are expected to be forming and where life could develop have not been investigated yet due to the lack of appropriate tools. Infrared interferometry is a very promising technique in this context, as it provides the required angular resolution to separate the emissions from the star and its immediate neighbourhood. The present work aims at developing the high dynamic range capabilities of interferometric techniques for the characterisation of planetary systems. As a first step, we demonstrate that current interferometric facilities have the potential of detecting dust in the first few astronomical units of massive debris disks around nearby stars. Our observations of Vega with the FLUOR near-infrared beam combiner at the CHARA Array reveal the presence of warm dust responsible for a K-band flux 78 times fainter than the stellar photospheric emission. In order to extend the imaging of planetary systems to fainter disks and to giant extrasolar planets, we investigate in a second step the performance of future ground-based nulling interferometers, taking into account atmospheric eff ects in a realistic way. Our simulations show that a nulling instrument installed at the ESO Very Large Telescope Interferometer would detect circumstellar features as faint as a few 10^-4 of the stellar flux. Finally, the third part of this work focuses on the implementation of nulling interferometry on future space-borne missions, the goal being to characterise extrasolar planets with sizes down to that of the Earth. [less ▲]

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See detailAstrophysics and industry
Swings, Polydore ULg

in Leaflet - Astronomical Society of the Pacific (1953), 6(286), 283-290

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See detailAstrophysics, and how to attract young people into Physics
Nazé, Yaël ULg; Stavinschi, Magda; Vanherck, Martine ULg

Book (2005)

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See detailAstrophysics: 1951
Swings, Polydore ULg

in Leaflet - Astronomical Society of the Pacific (1952), 6(273), 178-188

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See detailAstrophysique : le spectre de la comète 1957c (Encke)
Swings, Polydore ULg; Fehrenbach, Charles; Woszczyk, Andrzej

in Publications de l'Observatoire de Haute-Provence (1957), 4(7), 3

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See detailAstrophysique : le spectre de la nébuleuse planétaire NGC 6543 et de son noyau dans le proche infrarouge
Swings, Polydore ULg; Fehrenbach, Charles; Haser, Leo

in Publications de l'Observatoire de Haute-Provence (1957), 3(60), 3

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See detailL'Astrophysique moléculaire
Swings, Polydore ULg

in Astronomie (L') (1956), 70

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See detailAstroPoles : Astronomy from the Polar Plateaus; The astronomy program for the International Polar Year
Burton, M.; et al.; Surdej, Jean ULg et al

Poster (2006, August)

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See detailAstrospheres of young and old stars
Cox, N.; Decin, L.; Marle, A.J. et al

Poster (2013, October)

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See detailLas astucias de la ilusión. El ”caso” Mallarmé
Durand, Pascal ULg

in Sanz Roig, Diana (Ed.) Bourdieu después de Bourdieu (2014)

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See detailAsymmetric Diels-Alder reactions of a nitroso compound derived from D-bornane-10,2-sultam
Gouverneur, Véronique; Dive, Georges ULg; Ghosez, Léon

in Tetrahedron, Asymmetry (1991), 2(12), 1173-1176

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See detailAsymmetric dihydroxylation of C,C double bonds using catalytic amounts of osmium tetroxide, selenides, and air
Krief, A.; Colaux, Catherine ULg

in Pure & Applied Chemistry (2002), 74(1), 107-113

Selenides, selenoxides, osmium tetroxide, and potassium osmate dihydrate are in equilibrium in aqueous tert-butanol containing potassium carbonate. We took advantage of this feature to withdraw the ... [more ▼]

Selenides, selenoxides, osmium tetroxide, and potassium osmate dihydrate are in equilibrium in aqueous tert-butanol containing potassium carbonate. We took advantage of this feature to withdraw the equilibrium in each of the two directions to produce allylalcohols from allylselenides and diols from olefins. The latter reaction performed in the presence of catalytic amounts of Cinchona alkaloids and osmium tetroxide allows the enantioselective dihydroxylation of C,C double bonds. [less ▲]

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See detailAsymmetric facial skin viscoelasticity during climacteric aging.
Pierard, Gérald ULg; Hermanns-Le, Trinh; Gaspard, Ulysse ULg et al

in Clinical, cosmetic and investigational dermatology (2014), 7

BACKGROUND: Climacteric skin aging affects certain biophysical characteristics of facial skin. The purpose of the present study was to assess the symmetric involvement of the cheeks in this stage of the ... [more ▼]

BACKGROUND: Climacteric skin aging affects certain biophysical characteristics of facial skin. The purpose of the present study was to assess the symmetric involvement of the cheeks in this stage of the aging process. METHODS: Skin viscoelasticity was compared on both cheeks in premenopausal and post-menopausal women with indoor occupational activities somewhat limiting the influence of chronic sun exposure. Eighty-four healthy women comprising 36 premenopausal women and 48 early post-menopausal women off hormone replacement therapy were enrolled in two groups. The tensile characteristics of both cheeks were tested and compared in each group. A computerized suction device equipped with a 2 mm diameter hollow probe was used to derive viscoelasticity parameters during a five-cycle procedure of 2 seconds each. Skin unfolding, intrinsic distensibility, biological elasticity, and creep extension were measured. RESULTS: Both biological elasticity and creep extension were asymmetric on the cheeks of the post-menopausal women. In contrast, these differences were more discrete in the premenopausal women. CONCLUSION: Facial skin viscoelasticity appeared to be asymmetric following menopause. The possibility of asymmetry should be taken into account in future studies of the effects of hormone replacement therapy and any antiaging procedure on the face in menopausal women. [less ▲]

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See detailAsymmetric Foreign Exchange Risk Exposure: evidence from U.S. multinationals
Muller, Aline ULg; Verschoor, Willem

in Journal of Empirical Finance (2006), 13

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See detailAsymmetric Optical Second-Harmonic Generation from Chiral G-Shaped Gold Nanostructures
Valev, V. K.; Silhanek, Alejandro ULg; Verellen, N. et al

in Physical Review Letters (2010), 104(12),

We present a new electromagnetic phenomenon-the asymmetric second-harmonic generation from planar chiral structures. The effect consists in distinguishing the handedness of a chiral material by rotating ... [more ▼]

We present a new electromagnetic phenomenon-the asymmetric second-harmonic generation from planar chiral structures. The effect consists in distinguishing the handedness of a chiral material by rotating the sample in an experiment involving solely linearly polarized light. This phenomenon originates in the surface plasmon resonance of chiral gold nanostructures, where homodyne interference of anisotropic and chiral electric and/or magnetic multipoles appears to play an important role. [less ▲]

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