[en] After the IRAS discovery of galaxies with large far-infrared to blue luminosity ratio, it has been proposed that an enhanced star formation could be the origin of the far-infrared emission through dust heating. Whether a simple photometric model is able to account for the FIR and optical properties of IRAS galaxies was investigated. The L sub IR/L sub B ratio, (B-V) color and H sub alpha equivalent width of normal spirals are well reproduced with smooth star formation histories. In the case of starburst galaxies, several theoretical diagrams allow us to estimate the burst strength and extinction. L sub IR/L sub B ratio up to 100 can be rather easily reached, whereas extreme values probably require IMF truncated at the low end

[en] The huge optical brightness of GRB 080319B (the 'Naked Eye Burst') makes this event really challenging for models of the prompt GRB emission. In the framework of the internal shock model, we investigate a scenario where the dominant radiative process is synchrotron emission and the high optical flux is due to the dynamical properties of the relativistic outflow : if the initial Lorentz factor distribution in the jet is highly variable, many internal shocks will form within the outflow at various radii. The most violent shocks will produce the main gamma-ray component while the less violent ones will contribute at lower energy, including the optical range.

[en] A simple photometric model has been developed in order to check whether the large far-infrared activities of some IRAS galaxies could be accounted for by bursts of star formation. Though the presence of active nuclei hidden by dust cannot be excluded, the model is able to reproduce the far-infrared and optical properties of IRAS galaxies, up to the most extreme objects

[en] SN 1987 A has been a peculiar object, mostly by its optical emission rather than by its neutrino signature. Indeed, the Kamioka and IMB detections were in good agreement with the energy release expected from the formation of a neutron star by the core collapse mechanism while the supernova optical rise time, visible and UV color evolution, light curve and progenitor star were unusual. It was rapidly realized that most of these peculiarities could be explained by the fact that the progenitor was a blue supergiant of radius R_* = 40 - 50 solar radius, instead of a red supergiant with R_* ∼ 1000 solar radius. By fitting the light curve, important constraints were obtained on explosion parameters, such as the shock energy or the mass of synthetized ⁵⁶Ni. However, the conditions for which a massive star can explode in the blue supergiant phase are still not well understood due to uncertainties in the models, especially in the treatment of convection and in the mass loss rates

[en] We have calculated models of rigidly rotating B and Be stars. With these models and considering the spectral type change produced by the gravitational darkening effect, we show that there is no Be star in critical rigid rotation. The variation of the angular momentum of B and Be stars during their evolution is briefly discussed

[en] The recent proposal that type I supernovae could be produced by the coalescence of two degenerate dwarfs is discussed in some detail. Such models are free from the problems encountered by the more classical scenario of carbon deflagration following accretion of hydrogen rich material. However, the dynamics of the coalescence and the subsequent evolution of the thick disk which is formed are still very uncertain. Much work will then be needed to clarify these difficulties and confirm the coalescence mechanism

[en] The melting curve of charged bosons and fermions is interpolated between known classical and ground state limits, using a generalized Lindemann criterion; the maximum temperature of stability of the solid is ten times higher than previously estimated. (Auth.)

[en] We use a simple pulse model to investigate the origin of the time lag-luminosity relation (LLR) discovered by Norris et al. (ApJ, 534 (2000) 248). We show that, at least for single pulse bursts which satisfy both the hardness-intensity and the hardness-fluence correlations, the LLR can be simply obtained as a consequence of the Amati relation

[en] In this work we study the effects of the cylindrical differential rotation upon the determination of the V sin i parameter. We show that the width of a line broadened by a cylindrical differential rotation may correspond to two different values of the V sin i parameter

[en] There is observational evidence of the presence of young neutron stars in old binary systems. A likely explanation is that those neutron stars were produced in the collapse of old C+O white dwarfs. Old white dwarfs being cold and at least partially solid, accretion-induced mass growth should finally lead in a number of cases, to their collapse rather than to their explosion. We show in detail how mass accretion on initially solid white dwarfs can leave central solid cores when dynamical instability sets in. We also study the different effects of the existence of such cores on the outcome of the competition between thermonuclear explosion and gravitational collapse