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

Journal Article · Tue Jan 01 00:00:00 EST 2013 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/145/1/13· OSTI ID:22089716

Aoki, Wako; Suda, Takuma ^[1]; Beers, Timothy C. ^[2]; Lee, Young Sun ^[3]; Honda, Satoshi ^[4]; Ito, Hiroko ^[5]; Takada-Hidai, Masahide ^[6]; Frebel, Anna ^[7]; Fujimoto, Masayuki Y. ^[8]; Carollo, Daniela ^[9]; Sivarani, Thirupathi ^[10]

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1. National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan)
2. National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)
3. Department of Physics and Astronomy and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States)
4. Kwasan Observatory, Kyoto University, Ohmine-cho Kita Kazan, Yamashin a-ku, Kyoto 607-8471 (Japan)
5. Department of Astronomical Science, School of Physical Sciences, The Graduate University of Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
6. Liberal Arts Education Center, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa 259-1292 (Japan)
7. Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
8. Department of Cosmosciences, Graduate School of Science, Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sapporo 060-0810 (Japan)
9. Department of Physics and Astronomy, Astronomy, Astrophysics, and Astrophotonic Research Center, Macquarie University North Ryde, NSW 2109 (Australia)
10. Indian Institute of Astrophysics, 2nd block Koramangala, Bangalore 560034 (India)

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){sub 0} and (g - r){sub 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.

• OSTI ID: 22089716
• Journal Information: Astronomical Journal (New York, N.Y. Online), Vol. 145, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTRONOMY
ASTROPHYSICS
BARIUM
CARBON
CHEMICAL COMPOSITION
CORRELATIONS
DISTRIBUTION FUNCTIONS
DWARF STARS
ELECTROMAGNETIC PULSES
ELEMENT ABUNDANCE
EMISSION SPECTROSCOPY
GALAXIES
GIANT STARS
IRON
MAGNESIUM
MAIN SEQUENCE STARS
RESOLUTION
TELESCOPES
TITANIUM
TRITIUM