Abundances of halo early-type stars

The metal-line spectra show evidence for rotational velocity broadening with values of vsini<=300km/s. In conjunction with Kurucz model atmospheres, we derive stellar photospheric abundances that are consistent with a Population I chemical composition; differential abundances with respect to Galactic disk Population I stars indicate no abundance differences outside the estimated errors.

From a comparison of the derived atmospheric parameters with recent theoretical evolutionary models, we derive distance and age estimates for individual stars. Using kinematical considerations, we conclude that all these objects are `runaway' stars, formed in the Galactic disk and subsequently ejected, possibly by supernovae explosions or dynamical interactions.