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

• Published in: Monthly notices of the Royal Astronomical Society Vol. 349; no. 3; pp. 821 - 832
• Main Authors: Lynn, B. B., Keenan, F. P., Dufton, P. L., Saffer, R. A., Rolleston, W. R. J., Smoker, J. V.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 11-04-2004; Blackwell Science
• Subjects: Galaxy: halo; stars: abundances; stars: AGB and post-AGB; stars: atmospheres; stars: early-type; stars: kinematics; stars: atmospheres; Galaxy: halo; stars: AGB and post-AGB; stars: early-type; stars: kinematics; stars: abundances; Galactic halos; Spectroscopy; B stars; Abundance; Galactic disks; Distances; Silicon stars; Young stars; Peculiar stars; Theoretical model; Positions; Asymptotic giant branch; Spectroscopical observation; Age; Proper motion
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2004.07493.x

High-resolution (R≈ 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 ≤BPG≤ 14.6, corresponding to an approximate distance limit for main-sequence B-type objects of 5 ≤d≤ 40 kpc. Three stars are found to be apparently normal, young stars, based on their positions on the (Teff, 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.