Early-type stars in the Galactic halo from the Palomar-Green survey - III. Completion of a magnitude range limited sample

High-resolution (R approximate to 40 000) echelle spectroscopic observations of 13 high-latitude early-type stars are presented. These stars comprise the final part of a complete magnitude range limited sample based on low-resolution spectroscopy of targets drawn from the Palomar-Green survey. The magnitude range under consideration is 13 less than or equal to B-PG less than or equal to 14.6, corresponding to an approximate distance limit for main-sequence B-type objects of 5 less than or equal to d less than or equal to 40 kpc. Three stars are found to be apparently normal, young stars, based on their positions on the (T-eff, log g) diagram, normal abundance patterns and relatively large projected rotational velocities. A further star, PG 1209+263, was found to belong to the chemically peculiar (CP) silicon star class of objects. The remainder are evolved subluminous stars lying on post- horizontal branch (post-HB) tracks, with the exception of PG 2120+062, which appears to be in a post-asymptotic giant branch evolutionary stage. For the young stars in the sample, we have derived distance and age estimates through comparison of the atmospheric parameters with recent theoretical evolutionary models. We discuss formation scenarios by comparing times-of- flight and evolutionary time-scales. It is found that all stars could have formed in the Galactic disc and been ejected from there soon after their birth, with the exception of PG 1209+263. The adopted proper motion is found to be a crucial factor in the kinematical analysis. We also present some number densities for young B-type halo stars, which indicate that they are extremely scarce objects.

Model atmosphere and kinematical analyses of early-type stars from the Edinburgh-Cape Survey

We present high-resolution spectroscopic observations of 21 B- type stars, selected from the Edinburgh-Cape Blue Object Survey. Model atmosphere analyses confirm that 14 of these stars are young, main-sequence B-type objects with Population I chemical compositions. The remaining seven are found to be evolved objects, including subdwarfs, horizontal branch and post-AGB objects. A kinematical analysis shows that all 14 young main-sequence stars could have formed in the disc and subsequently been ejected into the halo. These results are combined with the analysis of a previous subsample of stars taken from the Survey. Of the complete sample, 31 have been found to be young, main-sequence objects, with formation in the disc, and subsequent ejection into the halo, again being found to be a plausible scenario.