Abundances in metal-rich stars

Feltzing, Sofia; Gustafsson, B.

doi:10.1051/aas:1998400

Cited by 168 publications

(275 citation statements)

References 18 publications

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“…Since most of the stars in this study fall below the magnitude threshold of the Hipparcos mission, one must rely on an alternate method for estimating log g. Results from Gratton et al (1997) with Hipparcos-based gravities also suggest that there are few significant effects due to non-LTE (NLTE) processes that influence the behavior of neutral and ionized Fe lines. However, NLTE analyses of Fe line formation suggest that NLTE processes may affect neutral Fe lines in metal-poor stars (Fuhrmann 1998;Feltzing & Gustafsson 1998;Thévenin & Idiart 1999). Until further research corroborates these initial findings, we assume that the LTE ionization balance gravities are reasonable.…”

Section: Surface Gravitymentioning

confidence: 82%

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Stephens

Boesgaard

2002

The Astronomical Journal

146

182

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There are stars in the halo of the Galaxy whose orbital properties are distinctly different from the majority of the halo population. One suggestion to account for these kinematically peculiar stars is that they have been gravitationally subsumed by the Milky Way through the breakup of nearby dwarf galaxies. One test of this hypothesis lies in determining the chemical composition of the deviant halo stars relative to that of normal ('' native '') halo field stars. The possibly accreted stars are predicted to have different chemical enrichments due to a slower rate of star formation in nearby low-mass spheroidal or irregular galaxies. We have obtained echelle spectra of metal-poor halo dwarfs with unusual orbital properties: from the outer halo, from the '' high '' halo, and on retrograde orbits. Our spectra are at high spectral resolution (35,000-48,000) and high signal-to-noise ratios (median value 140), primarily from the Keck I 10 m telescope with HIRES (53 stars), but also from the echelle spectrometer of the KPNO Mayall 4 m Telescope (three stars). The spectra cover a large spectral range: $4000-6800 Å . The strengths of approximately 9000 lines have been measured to determine the stellar parameters (T eff , log g, [Fe/H], and ) and the abundances of 10 elements, including Na, -fusion products (Mg, Si, Ca, Ti), iron peak elements (Cr, Fe, Ni), and neutron capture elements (Y, Ba). A model atmosphere was computed for each star, which was used to determine the composition under the assumption of LTE. The comparison of the abundances with the kinematic properties revealed no special trends, except that the ratio of the mean of the -fusion elements to Fe is weakly correlated with stellar apogalactica in the sense that the outermost stars have lower ratios of [ /Fe] than those with smaller apogalactica. The hallmark of an accreted halo star is presumed to be a deficiency (compared with normal stars) of the -elements (e.g., O, Mg, Si, Ca, Ti) with respect to Fe, a consequence of sporadic bursts of star formation within the dwarf galaxies. However [Fe/H]. The kinematically peculiar stars in our sample must have had their origins in localized star-forming regions far removed from the Galactic center. They do not carry the chemical signature of an accreted population. It seems clear that the chemical enrichment in our sample comes primarily from Type II supernovae with only a small component from Type Ia supernovae. Our stars would have formed at most $1 Gyr after the beginning of a star formation episode in the remote halo. The general conclusion extracted from these data is that the formation of the nascent Milky Way was not dominated by the late accretion of dwarf galaxies like the ones that currently orbit the Galaxy. However, the assimilation of fragments early in the evolution of the Galaxy is a natural by-product of hierarchical models of structure formation and can explain many properties of the halo population.

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Section: Surface Gravitymentioning

confidence: 82%

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Stephens

Boesgaard

2002

The Astronomical Journal

146

182

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“…Spectral lines for the analysis were selected using the solar line list by Moore et al (1966) as well as various sources from the literature (notably Feltzing & Gustafsson 1998;Stephens 1999;and Nave et al 1994 for Fe ). The lines were then checked for suitability (line strength, blends, etc.)…”

Section: Equivalent Widthsmentioning

confidence: 99%

Elemental abundance trends in the Galactic thin and thick disks as traced by nearby F and G dwarf stars

Bensby

Feltzing

Lundström

2003

A&A

Self Cite

851

119

1,264

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Abstract. Based on spectra from F and G dwarf stars, we present elemental abundance trends in the Galactic thin and thick disks in the metallicity regime −0.8 [Fe/H] +0.4. Our findings can be summarized as follows. 1) Both the thin and the thick disks show smooth and distinct abundance trends that, at sub-solar metallicities, are clearly separated. 2) For the α-elements the thick disk shows signatures of chemical enrichment from SNe type Ia.3) The age of the thick disk sample is in the mean older than the thin disk sample. 4) Kinematically, there exist thick disk stars with super-solar metallicities. Based on these findings, together with other constraints from the literature, we discuss different formation scenarios for the thick disk. We suggest that the currently most likely formation scenario is a violent merger event or a close encounter with a companion galaxy. Based on kinematics the stellar sample was selected to contain stars with high probabilities of belonging either to the thin or to the thick Galactic disk. The total number of stars are 66 of which 21 belong to the thick disk and 45 to the thin disk. The analysis is based on high-resolution spectra with high signal-to-noise (R ∼ 48 000 and S /N 150, respectively) recorded with the FEROS spectrograph on La Silla, Chile. Abundances have been determined for four α-elements (Mg, Si, Ca, and Ti), for four even-nuclei iron peak elements (Cr, Fe, Ni, and Zn), and for the light elements Na and Al, from equivalent width measurements of ∼30 000 spectral lines. An extensive investigation of the atomic parameters, log g f -values in particular, have been performed in order to achieve abundances that are trustworthy. Noteworthy is that we find for Ti good agreement between the abundances from Ti  and Ti . Our solar Ti abundances are in concordance with the standard meteoritic Ti abundance.

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“…However, spectroscopic studies are in general limited to small samples of a few hundred stars at most (e.g. Feltzing & Gustafsson 1998;Bensby et al 2003Bensby et al , 2005Bensby et al , 2007Soubiran et al 2005;Reddy et al 2006;Ramírez et al 2007) and only a few studies have been based on samples as large as 1000 stars (e.g. Gazzano et al 2010;Gazzano 2011;Petigura & Marcy 2011).…”

Section: Introductionmentioning

confidence: 99%

A newα-enhanced super-solar metallicity population

Adibekyan¹,

Santos²,

Sousa³

et al. 2011

A&A

158

214

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We performed a uniform and detailed analysis of 1112 high-resolution spectra of FGK dwarfs obtained with the HARPS spectrograph at the ESO 3.6 m telescope (La Silla, Chile). Most stars have effective temperatures 4700 K ≤ T eff ≤ 6300 K and lie in the metallicity range of −1.39 ≤ [Fe/H] ≤ 0.55. Our main goal is to investigate whether there are any differences between the elemental abundance trends (especially [α/Fe] ratio) for stars of different subpopulations. The equivalent widths of spectral lines are automatically measured from HARPS spectra with the ARES code. The abundances of three α elements are determined using a differential LTE analysis relative to the Sun, with the 2010 revised version of the spectral synthesis code MOOG and a grid of Kurucz ATLAS9 atmospheres. The stars of our sample fall into two populations, clearly separated in terms of The metal-poor high-α stars (thick disk) and metal-rich high-α stars are on average older than chemically defined thin disk stars (low-α stars). The two α-enhanced families have different kinematics and orbital parameters. The metal-rich α-enhanced stars, such as thin disk stars have nearly circular orbits, close to the Galactic plane. We put forward the idea that these stars may have been formed in the inner Galactic disk, but their exact nature still remains to be clarified.

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Abundances in metal-rich stars

Abstract: Abstract. We have derived elemental abundances of O,

Cited by 168 publications

References 18 publications

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Elemental abundance trends in the Galactic thin and thick disks as traced by nearby F and G dwarf stars

A newα-enhanced super-solar metallicity population

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