TY - JOUR
T1 - More pieces of the puzzle
T2 - Chemistry and substructures in the galactic thick disk
AU - Helmi, Amina
AU - Williams, Mary
AU - Freeman, K. C.
AU - Bland-Hawthorn, J.
AU - De Silva, G.
PY - 2014/8
Y1 - 2014/8
N2 - We present a study of the chemical abundances of solar neighborhood
stars associated with dynamical structures in the Milky Way's (thick)
disk. These stars were identified as an overdensity in the eccentricity
range 0.3 <epsilon <0.5 in the Copenhagen-Geneva Survey by Helmi
et al. We find that stars with these dynamical characteristics do not
constitute a homogeneous population. A relatively sharp transition in
dynamical and chemical properties appears to occur at a metallicity of
[Fe/H] ~ –0.4. Stars with [Fe/H] > –0.4 have mostly lower
eccentricities, smaller vertical velocity dispersions, are
α-enhanced, and define a rather narrow sequence in [α/Fe]
versus [Fe/H], clearly distinct from that of the thin disk. Stars with
[Fe/H] <–0.4 have a range of eccentricities, are hotter
vertically, and depict a larger spread in [α/Fe]. We also found
tentative evidence of a substructure possibly associated with the
disruption of a metal-rich star cluster. The differences between these
populations of stars is also present in, e.g., [Zn/Fe], [Ni/Fe], and
[SmII/Fe], suggesting a real physical distinction.
AB - We present a study of the chemical abundances of solar neighborhood
stars associated with dynamical structures in the Milky Way's (thick)
disk. These stars were identified as an overdensity in the eccentricity
range 0.3 <epsilon <0.5 in the Copenhagen-Geneva Survey by Helmi
et al. We find that stars with these dynamical characteristics do not
constitute a homogeneous population. A relatively sharp transition in
dynamical and chemical properties appears to occur at a metallicity of
[Fe/H] ~ –0.4. Stars with [Fe/H] > –0.4 have mostly lower
eccentricities, smaller vertical velocity dispersions, are
α-enhanced, and define a rather narrow sequence in [α/Fe]
versus [Fe/H], clearly distinct from that of the thin disk. Stars with
[Fe/H] <–0.4 have a range of eccentricities, are hotter
vertically, and depict a larger spread in [α/Fe]. We also found
tentative evidence of a substructure possibly associated with the
disruption of a metal-rich star cluster. The differences between these
populations of stars is also present in, e.g., [Zn/Fe], [Ni/Fe], and
[SmII/Fe], suggesting a real physical distinction.
KW - Galaxy: disk
KW - Galaxy: formation
KW - stars: abundances
U2 - 10.1088/0004-637X/791/2/135
DO - 10.1088/0004-637X/791/2/135
M3 - Article
VL - 791
SP - 135
JO - The Astrophysical Journal
JF - The Astrophysical Journal
SN - 0004-637X
ER -