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Astron. Astrophys. 347, 69-76 (1999)

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Early-type stars in the Galactic halo from the Palomar-Green Survey *

II: A sample of distant, apparently young Population I stars

W.R.J. Rolleston 1, N.C. Hambly 2, F.P. Keenan 1, P.L. Dufton 1 and R.A. Saffer 3

1 Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, Northern Ireland, UK (R.Rolleston@qub.ac.uk)
2 Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, Scotland (N.Hambly@roe.ac.uk)
3 Department of Astronomy and Astrophysics, Villanova University, 800 Lancaster Avenue, PA 19085, USA (saffer@ast.vill.edu)

Received 8 December 1998 / Accepted 17 February 1999

Abstract

We present échelle (R[FORMULA]40 000) spectroscopic observations for a sample of apparently normal, high Galactic latitude, early-type stars drawn from the Palomar-Green Survey. The metal-line spectra show evidence for rotational velocity broadening with values of [FORMULA] km s-1. 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.

Key words: stars: abundances – stars: atmospheres – stars: early-type – stars: kinematics

* Tables 4 and 5 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) (ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/347/69 ) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/347/69

Send offprint requests to: W.R.J. Rolleston

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© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999
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