Diffusive foam wetting process in microgravity

We report the experimental study of aqueous foam wetting in microgravity. The liquid fraction $\ell$ along the bubble edges is measured and is found to be a relevant dynamical parameter during the capillary process. The penetration of the liquid in the foam, the foam inflation, and the rigidity loss are shown all to obey strict diffusion processes.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let

Formation of Galactic Systems in Light of the Magnesium Abundance in Field Stars.III.the Halo

We analyze the relations between the relative magnesium abundances, metallicities, and Galactic orbital elements for halo stars. We show that the relative magnesium abundances in protodisk halo stars are virtually independent of metallicity and lie within a fairly narrow range while presumably accreted stars demonstrate a large spread in relative magnesium abundances up to negative [Mg/Fe]. The mean metallicity of magnesium-poor ([Mg/Fe]<0.2 dex) accreted stars has been found to be displaced toward the negative values when passing from stars with low azimuthal velocities to those with high ones at \Delta[Fe/H]=0.5dex. The mean apogalactic radii and inclinations of the orbits also increase while their eccentricities decrease. As a result negative radial and vertical gradients in relative magnesium abundances are observed in the accreted halo in the absence of correlations between the [Mg/Fe] ratios and other orbital elements, while these correlations are found at a high significance level for genetically related Galactic stars. We surmise that as the masses of dwarf galaxies decrease, the maximum SNII masses and hence, the yield of \alpha-elements in them also decrease. In this case, the relation between the [Mg/Fe] ratios and the inclinations and sizes of the orbits of accreted stars is in complete agreement with numerical simulations of dynamical processes during the interaction of galaxies. Thus the behavior of the magnesium abundance in accreted stars suggests that the satellite galaxies are disrupted and lose their stars en masse only after dynamical friction reduces significantly the sizes of their orbits and drags them into the Galactic plane. Less massive satellite galaxies are disrupted even before their orbits change appreciably under tidal forces.Comment: accepted 2006, Astronomy Letters, Vol. 32 No. 8, P.545, 18 pages, 6 figure

Alpha-elements in mildly metal-poor stars

Accurate relative abundances of light elements (C to Ca) have been obtained in a sample of mildly metal-poor stars (Decauwer et al. 2005). Combined with the results of a previous study (Jehin et al. 1999), we find different slopes in the correlations between the different alpha-elements. These results can be explained by postulating that the stars exhibiting lower than average alpha/Fe form in low mass clouds, unable to sustain the formation of very massive stars

Capillary rise in foams under microgravity

peer reviewedThe motion of liquid into a foam under low-gravity conditions is studied both experimentally and theoretically. The foam is confined to two dimensions in a Hele-Shaw cell and the liquid fraction measured by image analysis. The foam imbibition is shown to be a diffusive process. Two models are analysed, corresponding to the limits of rigid and mobile interfaces in the Plateau borders. Liquid fraction profiles are compared to experimental ones. (c) 2004 Elsevier B.V. All rights reserved

Abundance correlations in mildly metal-poor stars. II. Light elements (C to Ca)

Accurate relative abundances have been obtained for carbon, oxygen, sodium, aluminium, silicon, and calcium in a sample of mildly metal-poor stars. This analysis complements a previous study carried out by Jehin et al. ([CITE], A&A, 341, 241), which provided the basis for the EASE scenario. This scenario postulates that field metal-poor stars were born in self-enriched proto-globular cluster clouds. By further investigating the correlations between the different alpha-element abundances, we propose a modified scenario for the formation of intermediate metallicity stars, in which the stars exhibiting lower than average alpha/Fe abundance ratios would form in low mass clouds, unable to sustain the formation of very massive stars (M ⪠30~M_o). Moreover, the carbon-to-iron ratio is found to decrease as one climbs the so-called Population IIb branch, i.e. when the s-element abundance increases. In the framework of the EASE scenario, we interpret this anticorrelation between the carbon and the s-element abundances as a signature of a hot bottom burning process in the metal-poor AGB stars which expelled the matter subsequently accreted by our Population IIb stars. Based on observations collected at the European Southern Observatory, La Silla, Chile (ESO Programmes 56.E-0384, 57.E-0400 and 59.E-0257)