The Ultra--Metal-poor, Neutron-Capture--rich Giant Star CS 22892-052

Sneden, Christopher; McWilliam, Andrew; Preston, George W.; Cowan, J. J.; Burris, Debra L.; Armosky, B. J.

doi:10.1086/177656

Cited by 477 publications

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“…Unfortunately, the isotopic concentration of Ba in metal-poor stars is largely unknown. The '' total '' isotopic abundances of Sneden et al (1996;their Table 3), which rely upon the data of Käppeler, Beer, & Wisshak (1989), were used to estimate the relative strength of the components of the Ba ii blends.…”

Section: Atomic Line Datamentioning

confidence: 99%

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: Atomic Line Datamentioning

confidence: 99%

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Stephens

Boesgaard

2002

The Astronomical Journal

146

182

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“…Accordingly, our sample was selected to include stars that fall into one of several categories: (1) very metal-poor stars that were previously known to exhibit extremely large enhancements of their r-process elements (CS 22892À052 and CS 31082À001: Sneden et al 1996;Cayrel et al 2001); (2) bright metal-poor stars that were studied by previous authors (e.g., McWilliam et al 1995a;Burris et al 2000) and shown to be moderately r-process-element-rich; and (3) candidate very metal-poor giants discovered in the course of the HK survey of Beers and colleagues (Beers et al 1992; Note.- Table 3 is also available in machine-readable form in the electronic edition of the Astrophysical Journal Supplement. a Identification of objects is given in Table 1.…”

Section: Selection Of Targetsmentioning

confidence: 99%

Spectroscopic Studies of Extremely Metal‐Poor Stars with the Subaru High Dispersion Spectrograph. I. Observational Data

Honda

Aoki

Ando

et al. 2004

ASTROPHYS J SUPPL S

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We have obtained high-resolution (R ' 50; 000 or 90,000), high-quality (S= N k 100) spectra of 22 very metalpoor stars ([Fe/H P À 2:5) with the High Dispersion Spectrograph fabricated for the 8.2 m Subaru Telescope. The spectra cover the wavelength range from 3500 to 5100 8; equivalent widths are measured for isolated lines of numerous elemental species, including the -elements, the iron-peak elements, and the light and heavy neutron-capture elements. Errors in the measurements and comparisons with previous studies are discussed. These data will be used to perform detailed abundance analyses in the following papers of this series. Radial velocities are also reported and are compared with previous studies. At least one moderately r-process-enhanced metal-poor star, HD 186478, exhibits evidence of a small-amplitude radial velocity variation, confirming the binary status noted previously. During the course of this initial program, we have discovered a new moderately r-process-enhanced, very metal-poor star, CS 30306À132 ([Fe/H ¼ À2:4; [Eu/Fe ¼ þ0:85), which is discussed in detail in the companion paper.

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“…Table 8 is only available in electronic form at http://www.aanda.org enhanced in r-process elements (i.e., stars having [Eu/Fe] > +1.0 and [Ba/Eu] < 0; hereafter r-II stars, following , for which the measurement of Th and Eu abundances was possible, and whose stellar matter presumably has experienced only a single nucleosynthesis event. The Th/Eu chronometer has been used for determining the age of, e.g., the progenitor of the r-II star CS 22892−052 (Sneden et al 1996;Cowan et al 1997Cowan et al , 1999Sneden et al 2003). Uranium was first detected in a very metal-poor star, CS 31082−001, by Cayrel et al (2001).…”

Section: Introductionmentioning

confidence: 99%

The Hamburg/ESO R-process enhanced star survey (HERES)

Hayek

Wiesendahl

Christlieb

et al. 2009

A&A

109

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AstrophysicsThe Hamburg/ESO R-process enhanced star survey (HERES) The analysis is based on high-quality VLT/UVES spectra and MARCS model atmospheres. We detect lines of 15 heavy elements in the spectrum of CS 29491−069, and 18 in HE 1219−0312; in both cases including the Th II 4019 Å line. The heavy-element abundance patterns of these two stars are mostly well-matched to scaled solar residual abundances not formed by the s-process. We also compare the observed pattern with recent high-entropy wind (HEW) calculations, which assume core-collapse supernovae of massive stars as the astrophysical environment for the r-process, and find good agreement for most lanthanides. The abundance ratios of the lighter elements strontium, yttrium, and zirconium, which are presumably not formed by the main r-process, are reproduced well by the model. Radioactive dating for CS 29491−069 with the observed thorium and rare-earth element abundance pairs results in an average age of 9.5 Gyr, when based on solar r-process residuals, and 17.6 Gyr, when using HEW model predictions. Chronometry seems to fail in the case of HE 1219−0312, resulting in a negative age due to its high thorium abundance. HE 1219−0312 could therefore exhibit an overabundance of the heaviest elements, which is sometimes called an "actinide boost".IV

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The Ultra--Metal-poor, Neutron-Capture--rich Giant Star CS 22892-052

Cited by 477 publications

References 0 publications

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Spectroscopic Studies of Extremely Metal‐Poor Stars with the Subaru High Dispersion Spectrograph. I. Observational Data

The Hamburg/ESO R-process enhanced star survey (HERES)

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