High-resolution spectroscopy of extremely metal-poor stars from sdss/segue. I. Atmospheric parameters and chemical compositions

Wako Aoki*, Timothy C. Beers, Young Sun Lee, Satoshi Honda, Hiroko Ito, Masahide Takada-Hidai, Anna Frebel, Takuma Suda, Masayuki Y. Fujimoto, Daniela Carollo, Thirupathi Sivarani

*Corresponding author for this work

Research output: Contribution to journalArticle

110 Citations (Scopus)

Abstract

Chemical compositions are determined based on high-resolution spectroscopy for 137 candidate extremely metal-poor (EMP) stars selected from the Sloan Digital Sky Survey (SDSS) and its first stellar extension, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). High-resolution spectra with moderate signal-to-noise (S/N) ratios were obtained with the High Dispersion Spectrograph of the Subaru Telescope. Most of the sample (approximately 80%) are main-sequence turnoff stars, including dwarfs and subgiants. Four cool main-sequence stars, the most metal-deficient such stars known, are included in the remaining sample. Good agreement is found between effective temperatures estimated by the SEGUE stellar parameter pipeline, based on the SDSS/SEGUE medium-resolution spectra, and those estimated from the broadband (V - K) 0 and (g - r)0 colors. Our abundance measurements reveal that 70 stars in our sample have [Fe/H] < -3, adding a significant number of EMP stars to the currently known sample. Our analyses determine the abundances of eight elements (C, Na, Mg, Ca, Ti, Cr, Sr, and Ba) in addition to Fe. The fraction of carbon-enhanced metal-poor stars ([C/Fe] > +0.7) among the 25 giants in our sample is as high as 36%, while only a lower limit on the fraction (9%) is estimated for turnoff stars. This paper is the first of a series of papers based on these observational results. The following papers in this series will discuss the higher-resolution and higher-S/N observations of a subset of this sample, the metallicity distribution function, binarity, and correlations between the chemical composition and kinematics of extremely metal-poor stars.

Original languageEnglish
Article number13
Pages (from-to)1-22
Number of pages22
JournalAstronomical Journal
Volume145
Issue number1
DOIs
Publication statusPublished - Jan 2013

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