Mass Transfer by Stellar Wind

I review the process of mass transfer in a binary system through a stellar wind, with an emphasis on systems containing a red giant. I show how wind accretion in a binary system is different from the usually assumed Bondi-Hoyle approximation, first as far as the flow's structure is concerned, but most importantly, also for the mass accretion and specific angular momentum loss. This has important implications on the evolution of the orbital parameters. I also discuss the impact of wind accretion, on the chemical pollution and change in spin of the accreting star. The last section deals with observations and covers systems that most likely went through wind mass transfer: barium and related stars, symbiotic stars and central stars of planetary nebulae (CSPN). The most recent observations of cool CSPN progenitors of barium stars, as well as of carbon-rich post-common envelope systems, are providing unique constraints on the mass transfer processes.Comment: Chapter 7, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe

Capturing the trans influence in low-spin d(8) square-planar platinum(II) systems using molecular mechanics

Molecular modeling of coordination complexes continues to present challenges for force field methods. Implicit or explicit treatment of the significant d electron effects is mandatory. Ligand field molecular mechanics is designed for coordination complexes by explicitly including the ligand field stabilization energy (LFSE) and it is applied here to model the trans influence in tetracoordinate Pt-II complexes of general formulas PtX4, PtX3Y, cis-PtX2Y2, and trans-PtX2Y2, where X and Y are OH2, H-, Cl-, Br-, PR3, SH2, NR3, and pyridine. Parameters have been developed within the Merck molecular force field using DFT structures and energies as reference data. Both geometric changes and relative energies are generally well-reproduced although PH3 and H- complexes show deviations. However, for phosphine complexes, replacing PH3 with PMe3 resolves all bar one of these. The LFSE associated with the low-spin d(8) configuration ensures planar coordination and provides an electronic connection between all the ligands, thus enabling a correct description of the trans influence. The parameters developed for NR3 and PR3 with R = H work well for R = Me and Et and, in agreement with experimental and/or DFT structures, display either a tetrahedral distortion or even ligand dissociation

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

Surface velocity observations from satellite tracked drifters made between 1987 and 2008 were used to resolve the surface circulation of the western Coral Sea, west of 158°E, and the Great Barrier Reef (GBR). The mean surface current map depicts well the major circulation patterns of the region, such as the position of the north Vanuatu and north Caledonia jets (NVJ and NCJ) and the western boundary currents. The North Queensland Current (NQC) and the East Australian Current (EAC) are well defined, flowing at speeds greater than 50 cm s−1 to the north, south of 15°S and 19°S, respectively. The NQC/EAC is mainly formed by the NVJ/NCJ flows, respectively. The presence of the Queensland Plateau greatly affects the westward flow, causing a zone of weak and highly variable currents that extends from 15°S to 18°S between the Queensland Plateau and the GBR shelf. Of the 235 drifters that crossed the western Coral Sea, 75 entered the GBR. Analysis of the drifter trajectories inside the GBR reveals the presence of a northwestward circulation at speeds of 22 cm s−1 north of 18°S and 0.5 cm s−1 south of 18°S. Drifter travel times used to evaluate the water residence times within the GBR indicate residence times of a few weeks for most of the lagoon