Are Stars with Planets Polluted?

We compare the metallicities of stars with radial velocity planets to the metallicity of a sample of field dwarfs. We confirm recent work indicating that the stars-with-planet sample as a whole is iron rich. However, the lowest mass stars tend to be iron poor, with several having [Fe/H]<-0.2, demonstrating that high metallicity is not required for the formation of short period Jupiter-mass planets. We show that the average [Fe/H] increases with increasing stellar mass (for masses below 1.25 solar masses) in both samples, but that the increase is much more rapid in the stars-with-planet sample. The variation of metallicity with stellar age also differs between the two samples. We examine possible selection effects related to variations in the sensitivity of radial velocity surveys with stellar mass and metallicity, and identify a color cutoff (B-V>0.48) that contributes to but does not explain the mass-metallicity trend in the stars-with-planets sample. We use Monte Carlo models to show that adding an average of 6.5 Earth masses of iron to each star can explain both the mass-metallicity and the age-metallicity relations of the stars-with-planets sample. However, for at least one star, HD 38529, there is good evidence that the bulk metallicity is high. We conclude that the observed metallicities and metallicity trends are the result of the interaction of three effects; accretion of about 6 Earth masses of iron rich material, selection effects, and in some cases, high intrinsic metallicity.Comment: 19 pages 11 figure

Integrated model for the hydro-mechanical effects of vegetation against shallow landslides

Shallow landslides are instability events that lead to dramatic soil mass wasting in sloping areas and are commonly triggered by intense rainfall episodes. Vegetation may reduce the likelihood of slope failure through different hydro-mechanical mechanisms that take place at the soil-plant-atmosphere interface. However, while vegetation’s mechanical contribution has been widely recognized, its hydrological effects have been poorly quantified. In addition, most of the existing models lack a holistic approach, require difficult to measure parameters or are commercially based, making them hardly transferable to land planners and other researchers.In this paper an integrated, robust and reproducible model framework is proposed and evaluated with the aim of assessing the hydro-mechanical effects of different vegetation types on slope stability using easily measureable and quantifiable input parameters. The output shows that the model framework is able to simulate the hydro-mechanical effects of vegetation in a realistic manner and that it can be readily applied to any vegetation, soil and climate types. It also demonstrates that vegetation has positive hydro-mechanical effects against shallow landslides, where plant biomass and evapotranspiration play an important role