Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2009-04-29
Astrophys.J.697:L63-L67,2009
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
Accepted by ApJL
Scientific paper
10.1088/0004-637X/697/1/L63
As part of a program to measure abundance ratios in stars beyond 15 kpc from the Galactic center, we have discovered a metal-poor star in the outer halo with a unique chemical signature. We originally identified it in the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey as a distant metal-poor star. We obtained a follow-up spectrum using the Echellette Spectrograph and Imager (ESI) at the Keck 2 telescope, and measure [Fe/H] =-3.17, [Mg/Fe] =-0.10 and [Ca/Fe] =+1.11. This is one of the largest over-abundances of Ca measured in any star to date; the extremely low value of [Mg/Ca]=-1.21 is entirely unique. To have found such an unusual star in our small sample of 27 targets suggests that there may be previously unobserved classes of stars yet to be found in situ in the Galactic halo.
Allende Prieto Carlos
Beers Timothy C.
Bolte Michael
Johnson Jennifer A.
Lai David K.
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