A Spectroscopic Survey of Field Red Horizontal-branch Stars


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AFŞAR M. , BOZKURT Z. , TOPCU G. B. , CASETTI-DINESCU D., Sneden C., SEHITOGLU G.

ASTRONOMICAL JOURNAL, vol.155, no.6, 2018 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 155 Issue: 6
  • Publication Date: 2018
  • Doi Number: 10.3847/1538-3881/aabe86
  • Title of Journal : ASTRONOMICAL JOURNAL
  • Keywords: stars: abundances, stars: atmospheres, stars: evolution, stars: horizontal-branch, LARGE-MAGELLANIC-CLOUD, G-DWARF STARS, MAGNITUDE DIAGRAM DATABASE, NEARBY GLOBULAR-CLUSTERS, GALACTIC THICK DISK, LARGE HOMOGENEOUS V, LINE-DEPTH RATIOS, LATE-G GIANTS, STELLAR PARAMETERS, COLOR-MAGNITUDE

Abstract

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 2.7m 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 a and Fe-group species. The derived temperatures and gravities confirm that at least half of the candidates are true RHB stars, with (average) parameters T-eff similar to 5000K and log g similar to 2.5. From the a 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.