Stellar adiabatic mass loss model and applications

Roche-lobe overflow and common envelope evolution are very important in binary evolution, which is believed to be the main evolutionary channel to hot subdwarf stars. The details of these processes are difficult to model, but adiabatic expansion provides an excellent approximation to the structure of a donor star undergoing dynamical time scale mass transfer. We can use this model to study the responses of stars of various masses and evolutionary stages as potential donor stars, with the urgent goal of obtaining more accurate stability criteria for dynamical mass transfer in binary population synthesis studies. As examples, we describe here several models with the initial masses equal to 1 Msun and 10 Msun, and identify potential limitations to the use of our results for giant-branch stars.Comment: 7 pages, 5 figures,Accepted for publication in AP&SS, Special issue Hot Sub-dwarf Stars, in Han Z., Jeffery S., Podsiadlowski Ph. ed

Tidal friction in close-in satellites and exoplanets. The Darwin theory re-visited

This report is a review of Darwin's classical theory of bodily tides in which we present the analytical expressions for the orbital and rotational evolution of the bodies and for the energy dissipation rates due to their tidal interaction. General formulas are given which do not depend on any assumption linking the tidal lags to the frequencies of the corresponding tidal waves (except that equal frequency harmonics are assumed to span equal lags). Emphasis is given to the cases of companions having reached one of the two possible final states: (1) the super-synchronous stationary rotation resulting from the vanishing of the average tidal torque; (2) the capture into a 1:1 spin-orbit resonance (true synchronization). In these cases, the energy dissipation is controlled by the tidal harmonic with period equal to the orbital period (instead of the semi-diurnal tide) and the singularity due to the vanishing of the geometric phase lag does not exist. It is also shown that the true synchronization with non-zero eccentricity is only possible if an extra torque exists opposite to the tidal torque. The theory is developed assuming that this additional torque is produced by an equatorial permanent asymmetry in the companion. The results are model-dependent and the theory is developed only to the second degree in eccentricity and inclination (obliquity). It can easily be extended to higher orders, but formal accuracy will not be a real improvement as long as the physics of the processes leading to tidal lags is not better known.Comment: 30 pages, 7 figures, corrected typo

Thresholds for adding degraded tropical forest to the conservation estate

Logged and disturbed forests are often viewed as degraded and depauperate environments compared with primary forest. However, they are dynamic ecosystems1 that provide refugia for large amounts of biodiversity2,3, so we cannot afford to underestimate their conservation value4. Here we present empirically defined thresholds for categorizing the conservation value of logged forests, using one of the most comprehensive assessments of taxon responses to habitat degradation in any tropical forest environment. We analysed the impact of logging intensity on the individual occurrence patterns of 1,681 taxa belonging to 86 taxonomic orders and 126 functional groups in Sabah, Malaysia. Our results demonstrate the existence of two conservation-relevant thresholds. First, lightly logged forests (68%) of their biomass removed, and these are likely to require more expensive measures to recover their biodiversity value. Overall, our data confirm that primary forests are irreplaceable5, but they also reinforce the message that logged forests retain considerable conservation value that should not be overlooked

Orthopyroxene to talc transformation

Mineralogical transformations that occur during the weathering of rocks are complex processes involving both physical and chemical changes. Although it may be difficult to relate the primary minerals to the secondary phases of the weathering process, there is evidence that certain transformations occur topotaxially. The clinopyroxene, hedenbergite, alters to montronite, an iron-rich montmorillonite mineral, topotaxially; the transformation has been modelled by a crystallographic shear of 1/2[101] on (100) of the pyroxene. This shear mechanism converts the chain silicate into a sheet structure. A similar process may be postulated for several other pyroxene alterations. The commonly observed orthopyroxene to talc transformation has been studied in detail using electron microscopy, electron microprobe, optical microscopy and x-ray diffraction.The process has been studied in an interaction zone that develops between unaltered orthopyroxene and talc layers formed along grain boundaries and within cracks. The growth of the interaction zone occurs by the migration of the interface into the unaltered orthopyroxene-Fig. 1.</jats:p

Silicate alteration mechanisms

Transmission electron microscopy shows that mineral alteration mechanisms are at least partly controlled by the structure of the altering mineral. Silicates of Fe and Mg with extended sequences of metal-oxygen octahedra change to trioctahedral layer-silicates showing a preferred orientation to the original mineral. Olivine, pyroxene, and biotite conform to this scheme, their alteration products inherit much of their structure. By contrast, framework silicates (which have tetrahedral Al) contribute little of their structure directly to clay-minerals, and alter via an amorphous phase to dioctahedral layer silicates.La microscopie électronique à transmission montre que les mécanismes d'altération des minéraux sont contrôlés, du moins jusqu'à un certain degré, par la structure du minéral qui subit l'altération. Les silicates de Fe et Mg avec des séquences étendues d'octaèdres à métaux et oxygène se changent en silicate phylliteux triocta-édriques,qui montrent une orientation préférentielle par rapport au minéral originel L'olivine, le pyroxene et la biotite se conforment à ce système ; les produits issus de leur altération héritent d'une grande partie de leur structure. Par contraste, les fedspaths et minéraux associés (qui contiennent de l'Ai tétraédrique) ne contri¬ buent que très peu par leur structure aux minéraux argileux, et s'altèrent à travers une phase amorphe pour devenir des silicates phylliteux dioctaédriques .Eggleton R.A, Smith K. L. Silicate alteration mechanisms. In: Pétrologie des altérations et des sols. Vol. I : Pétrologie expérimentale. Colloque international du CNRS, Paris 4-7 juillet 1983. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1983. pp. 45-53. (Sciences Géologiques. Mémoire, 71

Silicate alteration mechanisms

Transmission electron microscopy shows that mineral alteration mechanisms are at least partly controlled by the structure of the altering mineral. Silicates of Fe and Mg with extended sequences of metal-oxygen octahedra change to trioctahedral layer-silicates showing a preferred orientation to the original mineral. Olivine, pyroxene, and biotite conform to this scheme, their alteration products inherit much of their structure. By contrast, framework silicates (which have tetrahedral Al) contribute little of their structure directly to clay-minerals, and alter via an amorphous phase to dioctahedral layer silicates.La microscopie électronique à transmission montre que les mécanismes d'altération des minéraux sont contrôlés, du moins jusqu'à un certain degré, par la structure du minéral qui subit l'altération. Les silicates de Fe et Mg avec des séquences étendues d'octaèdres à métaux et oxygène se changent en silicate phylliteux triocta-édriques,qui montrent une orientation préférentielle par rapport au minéral originel L'olivine, le pyroxene et la biotite se conforment à ce système ; les produits issus de leur altération héritent d'une grande partie de leur structure. Par contraste, les fedspaths et minéraux associés (qui contiennent de l'Ai tétraédrique) ne contri¬ buent que très peu par leur structure aux minéraux argileux, et s'altèrent à travers une phase amorphe pour devenir des silicates phylliteux dioctaédriques .Eggleton R.A, Smith K. L. Silicate alteration mechanisms. In: Pétrologie des altérations et des sols. Vol. I : Pétrologie expérimentale. Colloque international du CNRS, Paris 4-7 juillet 1983. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1983. pp. 45-53. (Sciences Géologiques. Mémoire, 71