R. Asiain

The Pleiades Moving Group: Substructures and Evolution

We analyse here the spatial and kinematic evolution of the Pleiades moving group substructures found in Asiain et al. (1999). This allows us to investigate both the birthplaces and kinematic ages of these substructures. We also study the possibility that stellar complexes are the progenitors of moving groups. Our main tools are the epicycle theory and the integration of the equations of motion using a realistic gravitational potential of the Galaxy. The disc heating effect is implemented in our algorithm to determine stellar trajectories in order to study the disruption of unbound stellar systems.

Effective temperatures and surface gravities of early type stars

Intermediate band photometry is a powerful tool to determine physical parameters of early type stars. Among others, Moon & Dworetsky (1985) (hereinafter MD) built a grid that relates effective temperatures and surface gravities to Stromgren photometric indices (c o,β) up to 20,000K on the basis of line-blanketed LTE models of stellar atmospheres from Kurucz (1979). Recently, Castelli (1991) (hereinafter Cs) and Napiwotzki et al (1993) (hereinafter NSW) extended this grid to higher temperatures and proposed new interpolations.

Age Determination for Am Stars

From uvby and H β photometry, individual stellar ages for A type stars have been derived using three different evolutionary models. In this paper we evaluate the corrections for metallicity and rotation to be applied to the physical parameters of Am and their influence on the determined ages. A test based on the Hyades open cluster is also presented.