A Spectroscopic Survey of Field Red Horizontal-branch Stars

• Published in: The Astronomical journal Vol. 155; no. 6; pp. 240 - 264
• Main Authors: Af ar, Melike, Bozkurt, Zeynep, Topcu, Gamze Böcek, Casetti-Dinescu, Dana I., Sneden, Christopher, ehitog̅lu, Gizem
• Format: Journal Article
• Language: English
• Published: Madison The American Astronomical Society 01.06.2018; IOP Publishing
• Subjects: Abundance; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATMOSPHERES; Chemical composition; Effective temperatures; ELEMENT ABUNDANCE; GRAVITATION; Horizontal branch stars; Iron; METALLICITY; Organic chemistry; Polls & surveys; PROPER MOTION; RESOLUTION; SIGNAL-TO-NOISE RATIO; SPACE; SPECTRA; Spectrographs; STAR EVOLUTION; STARS; stars: abundances; stars: atmospheres; stars: evolution; stars: horizontal-branch; Stellar kinematics; SURFACES; TELESCOPES
• ISSN: 0004-6256; 1538-3881; 1538-3881
• DOI: 10.3847/1538-3881/aabe86

A metallicity, chemical composition, and kinematic survey has been conducted for a sample of 340 candidate field red horizontal-branch (RHB) stars. Spectra with high resolution and high signal-to-noise ratio were gathered with the McDonald Observatory 2.7 m Tull and the Hobby-Eberly Telescope echelle spectrographs, and were used to determine effective temperatures, surface gravities, microturbulent velocities, [Fe/H] metallicities, and abundance ratios [X/Fe] for seven and Fe-group species. The derived temperatures and gravities confirm that at least half of the candidates are true RHB stars, with (average) parameters Teff ∼ 5000 K and log g ∼ 2.5. From the abundances alone, the thin and thick Galactic populations are apparent in our sample. Space motions for 90% of the program stars were computed from Hipparcos and Gaia parallaxes and proper motions. Correlations between chemical compositions and Galactic kinematics clearly indicate the existence of both thin-disk and thick-disk RHB stars.