Extremely metal-deficient red giants. I - A new objective-prism, photometric, and radial-velocity survey

Abstract

Results of an extensive objective-prism survey to detect extremely metal-deficient red giants and a subsequent investigation of the photometric and radial velocity properties of the newly discovered stars are presented. The 132 red giants with Fe/H abundance ratios less than or equal to -1.5 discovered in the present objective-prism survey on a 10-deg prism down to B magnitudes of 11.5, and by previous objective-prism and other surveys, are listed, together with results of radial velocity and photometric measurements. Examination of the Stromgren m1 index calibrated against high-resolution spectroscopic determinations of the Fe-H abundance ratio indicates that population III field giants with abundance ratios less than -3 are extremely rare. The Stromgren c1 index is used as an indicator of surface gravity and anomalous CH strengths, resulting in the identification of field red horizontal-branch stars, field asymptotic-branch giants and subgiants. Radial velocities obtained for about half the stars reveal that essentially all of them have halo motions, and that the incidence of spectroscopic binaries is very low.