Abundance anomalies in pre-main-sequence stars: Stellar evolution models with mass loss

The effects of atomic diffusion on internal and surface abundances of A and F pre-main-sequence stars with mass loss are studied in order to determine at what age the effects materialize, as well as to further understand the processes at play in HAeBe and young ApBp stars. Self-consistent stellar evolution models of 1.5 to 2.8Msun with atomic diffusion (including radiative accelerations) for all species within the OPAL opacity database were computed and compared to observations of HAeBe stars. Atomic diffusion in the presence of weak mass loss can explain the observed abundance anomalies of pre-main-sequence stars, as well as the presence of binary systems with metal rich primaries and chemically normal secondaries such as V380 Ori and HD72106. This is in contrast to turbulence models which do not allow for abundance anomalies to develop on the pre-main-sequence. The age at which anomalies can appear depends on stellar mass. For A and F stars, the effects of atomic diffusion can modify both the internal and surface abundances before the onset of the MS. The appearance of important surface abundance anomalies on the pre-main-sequence does not require mass loss, though the mass loss rate affects their amplitude. Observational tests are suggested to decipher the effects of mass loss from those of turbulent mixing. If abundance anomalies are confirmed in pre-main-sequence stars they would severely limit the role of turbulence in these stars.Comment: 9 pages, 6 figures, accepeted for publicatio

Temporalité et espace du récit dans les romans de Tony Hillerman

An american writer born and bred among seminole indians, tony hillerman, by reviving the "ethnological mystery novel" genre, acknowledges his main influence : arthur upfield. Hillerman\u27s novels feature two navajo policemen who investigate murders committed on the huge indian reservation. His choice of the scene of the crime and of native officers enables him to explore the complex relationships between two worlds : the first, the spiritual and timeless world of the navajos, rooted in the wisdom of the ancestors, and the second, the world of the white man, trapped within human time, which drives towards the pursuit of material possessions and social advancement. Breaking with the urban tradition and the temporal and thematic structures of the mystery genre, hillerman opens the doors to a navajo perception of the universe. The narration is imbued with this perception through the concept of space, which is present in the descriptions -which invite to a journey through time. The narrative structure itself translates this interference, weaving temporal arrangements characteristic of the navajo oral traditions. Thus, the mythology, controlling both time and space, transforms the mystery novel into an initiatory quest for identity which brings the two investigators into contact with their sacred time in order to restore a navajo harmony