HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS FROM SDSS/SEGUE. I. ATMOSPHERIC PARAMETERS AND CHEMICAL COMPOSITIONS

By Wak Aoki, Timothy C. Beers, Y. S. Lee, Satoshi Honda, Hiroko Ito, M. Takada-Hidai, A. Frebel, T. Suda, M. Fujimoto, Daniela Carollo and 1 more. 2012

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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.

Subfields: Astronomy and Astrophysics, Education, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b0090999052aec57e3e0ed234bf79005fbe6f434

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Citations in the corpus

Near-Field Cosmology with Extremely Metal-Poor Stars (2015, background): “Two examples of this are Barklem et al. (2005) and Aoki et al. (2013).”
A SEARCH FOR STARS OF VERY LOW METAL ABUNDANCE. VI. DETAILED ABUNDANCES OF 313 METAL-POOR STARS (2014, background): “Detailed chemical followup of large numbers of stars from the SDSS and SEGUE have been performed by Aoki et al. (2008, 2013), Caffau et al. (2011), and Bonifacio et al. (2012).”
CARBON-ENHANCED METAL-POOR STARS IN SDSS/SEGUE. I. CARBON ABUNDANCE ESTIMATION AND FREQUENCY OF CEMP STARS (2013, methodology): “However, as Aoki et al. (2013) illustrated, there remains the difficulty of identifying CEMP stars in this temperature regime due to the low resolution of the SDSS/SEGUE spectra, such that the CHGband can only be detected for stars with higher carbon abundances.”
The PASTEL catalogue: 2016 version (2016, background): “For instance, the highresolution spectroscopic study of extremely metal-poor stars by Aoki et al. (2013) has been entirely included even if a fraction of the spectra have a S/N lower than our limit owing to the very high interest of the targets.”
The Pristine survey - I. Mining the Galaxy for the most metal-poor stars (2017, methodology): “We have sought for stars studied in high-resolution at the lowmetallicity end by cross-correlating with the studies of Aoki et al. (2013) and Cohen et al. (2013).”
Binarity in carbon-enhanced metal-poor stars (2014, methodology): “In addition to this sample, we targeted four new extremely metal-poor targets with CEMP-no-like abundance patterns, as published in Aoki et al. (2013).”