The Astrophysical Journal
Volume 672
Number 1
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Judith G. Cohen et al. 2008 ApJ 672 320 doi:10.1086/523638
New Extremely Metal-Poor Stars in the Galactic Halo*
FREE ISSUEJudith G. Cohen1, Norbert Christlieb2, Andrew McWilliam3, Stephen Shectman3, Ian Thompson3, Jorge Melendez1,4, Lutz Wisotzki5 and Dieter Reimers6
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We present a detailed abundance analysis based on high-resolution and high signal-to-noise spectra of eight extremely metal-poor (EMP) stars with [ Fe/H ] 
− 3.5 dex, four of which are new. Only stars with 4900 K < Teff < 5650 K are included. Two stars of the eight are outliers in each of several abundance ratios. The most metal-poor star in this sample, HE 1424–0241, has [ Fe/H ] ~ − 4 dex and is thus among the most metal-poor stars known in the Galaxy. It has highly anomalous abundance ratios unlike those of any other known EMP giant, with very low Si, Ca, and Ti relative to Fe, and enhanced Mn and Co, again relative to Fe. Only (low) upper limits for C and N can be derived from the nondetection of the CH and NH molecular bands. HE 0132-2429, another sample star, has excesses of N and Sc with respect to Fe. The strong outliers in abundance ratios among the Fe-peak elements in these C-normal stars, not found at somewhat higher metallicities ([ Fe/H ] ~ − 3 dex), are definitely real. They suggest that at such low metallicities we are beginning to see the anticipated and long sought stochastic effects of individual supernova events contributing to the Fe-peak material within a single star. With spectra reaching well into the near-UV we are able to probe the behavior of copper abundances in such extreme EMP stars. A detailed comparison of the results of the analysis procedures adopted by our 0Z project compared to those of the First Stars VLT Large Project finds a systematic difference for [ Fe/H ] of ~0.3 dex, our values always being higher.
− 3.5 dex, four of which are new. Only stars with 4900 K < Teff < 5650 K are included. Two stars of the eight are outliers in each of several abundance ratios. The most metal-poor star in this sample, HE 1424–0241, has [ Fe/H ] ~ − 4 dex and is thus among the most metal-poor stars known in the Galaxy. It has highly anomalous abundance ratios unlike those of any other known EMP giant, with very low Si, Ca, and Ti relative to Fe, and enhanced Mn and Co, again relative to Fe. Only (low) upper limits for C and N can be derived from the nondetection of the CH and NH molecular bands. HE 0132-2429, another sample star, has excesses of N and Sc with respect to Fe. The strong outliers in abundance ratios among the Fe-peak elements in these C-normal stars, not found at somewhat higher metallicities ([ Fe/H ] ~ − 3 dex), are definitely real. They suggest that at such low metallicities we are beginning to see the anticipated and long sought stochastic effects of individual supernova events contributing to the Fe-peak material within a single star. With spectra reaching well into the near-UV we are able to probe the behavior of copper abundances in such extreme EMP stars. A detailed comparison of the results of the analysis procedures adopted by our 0Z project compared to those of the First Stars VLT Large Project finds a systematic difference for [ Fe/H ] of ~0.3 dex, our values always being higher.
- Footnote
- Subject headings
nuclear reactions, nucleosynthesis, abundances; stars: abundances; supernovae: general
- Dates
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Issue 1 (2008 January 1)
Received 2007 July 6, accepted for publication 2007 August 30
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New Extremely Metal-Poor Stars in the Galactic Halo
Judith G. Cohen et al. 2008 ApJ 672 320
-
Snapshot Metallicity Estimate of Resolved Stellar Systems Through Lick Fe5270 Diagnostic
A. Buzzoni et al 2009 ApJ 703 L127
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Formation of z~6 Quasars from Hierarchical Galaxy Mergers
Yuexing Li et al. 2007 ApJ 665 187
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The Cosmic Energy Inventory
Masataka Fukugita and P. J. E. Peebles 2004 ApJ 616 643
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