NORMAL AND OUTLYING POPULATIONS OF THE MILKY WAY STELLAR HALO AT [Fe/H] <–2

From detailed abundance analysis of >100 Hamburg/ESO candidate extremely metal-poor (EMP) stars we find 45 with [Fe/H] < -3.0 dex. We identify a heretofore unidentified group; Ca-deficient stars with sub-solar [Ca/Fe] ratios and the lowest neutron-capture abundances; the Ca-deficient group com...

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Bibliographic Details
Published in:The Astrophysical journal 2013-11, Vol.778 (1), p.1-29
Main Authors: Cohen, Judith G, Christlieb, Norbert, Thompson, Ian, McWilliam, Andrew, Shectman, Stephen, Reimers, Dieter, Wisotzki, Lutz, Kirby, Evan
Format: Article
Language:English
Subjects:
ABUNDANCE
APPROXIMATIONS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Bands
CAPTURE
Capture (nuclear)
CARBON
CARBON STARS
DISTRIBUTION
ELECTROMAGNETIC PULSES
Halos
Iron
METALS
MILKY WAY
NEUTRON REACTIONS
Outliers (statistics)
R PROCESS
RADIAL VELOCITY
S PROCESS
Stars
Strontium
TRITIUM
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Summary:From detailed abundance analysis of >100 Hamburg/ESO candidate extremely metal-poor (EMP) stars we find 45 with [Fe/H] < -3.0 dex. We identify a heretofore unidentified group; Ca-deficient stars with sub-solar [Ca/Fe] ratios and the lowest neutron-capture abundances; the Ca-deficient group comprises ~ 10% of the sample, excluding Carbon stars. Our radial velocity distribution shows that the carbon-enhanced stars with no s-process enhancements, CEMP-no, and which do not show C sub(2) bands are not preferentially binary systems. Ignoring Carbon stars, approximately 15% of our sample are strong ([> or =, slant] 5[sigma]) outliers in one or more elements between Mg and Ni; this rises to ~19% if very strong ([> or =, slant]10[sigma]) outliers for Sr and Ba are included. Examples include: HE0305-0554 with the lowest [Ba/H] known; HE1012-1540 and HE2323-0256, two (non-velocity variable) C-rich stars with very strong [Mg,A1/Fe] enhancements; and HE1226-1149, an extremely r-process rich star.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/778/1/56