CHEMICAL ABUNDANCES OF THE MILKY WAY THICK DISK AND STELLAR HALO. I. IMPLICATIONS OF [{alpha}/Fe] FOR STAR FORMATION HISTORIES IN THEIR PROGENITORS

Journal Article · Sun Jul 01 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/753/1/64· OSTI ID:22036883

Ishigaki, Miho N; Aoki, Wako ^[1]; Chiba, Masashi ^[2]

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1. National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
2. Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-8578 (Japan)

We present the abundance analysis of 97 nearby metal-poor (-3.3 < [Fe/H] <-0.5) stars having kinematic characteristics of the Milky Way (MW) thick disk and inner and outer stellar halos. The high-resolution, high-signal-to-noise optical spectra for the sample stars have been obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of Fe, Mg, Si, Ca, and Ti have been derived using a one-dimensional LTE abundance analysis code with Kurucz NEWODF model atmospheres. By assigning membership of the sample stars to the thick disk, inner halo, or outer halo components based on their orbital parameters, we examine abundance ratios as a function of [Fe/H] and kinematics for the three subsamples in wide metallicity and orbital parameter ranges. We show that, in the metallicity range of -1.5 < [Fe/H] {<=}-0.5, the thick disk stars show constantly high mean [Mg/Fe] and [Si/Fe] ratios with small scatter. In contrast, the inner and the outer halo stars show lower mean values of these abundance ratios with larger scatter. The [Mg/Fe], [Si/Fe], and [Ca/Fe] for the inner and the outer halo stars also show weak decreasing trends with [Fe/H] in the range [Fe/H] >-2. These results favor the scenarios that the MW thick disk formed through rapid chemical enrichment primarily through Type II supernovae of massive stars, while the stellar halo has formed at least in part via accretion of progenitor stellar systems having been chemically enriched with different timescales.

• OSTI ID: 22036883
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 753; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTRONOMY
ASTROPHYSICS
ELEMENT ABUNDANCE
ENRICHMENT
HYDROGEN
IRON
LTE
MAGNESIUM
MILKY WAY
ONE-DIMENSIONAL CALCULATIONS
RESOLUTION
SILICON
STELLAR ATMOSPHERES
SUPERNOVAE
TITANIUM
VISIBLE SPECTRA