HD 115444 – a barium star of extreme Population II

Griffin, Richard; Gustafsson, B.; Vieira, T.

doi:10.1093/mnras/198.3.637

Cited by 33 publications

(19 citation statements)

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“…Abundance studies of halo giant stars HD 115444 (Griffin et al 1982) and HD 122563 (Sneden & Parthasarathy 1983) strengthened the r-process interpretation. Recent studies have demonstrated in excruciating detail the near perfect match between the n-capture abundances of many metal-poor stars and the solar-system r-process-only distribution, especially at the heavy end (Z 56).…”

Section: R-process Starsmentioning

confidence: 84%

Constraints on the Nature of the s- and r-processes

2009

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Abstract. Neutron-capture (Z > 30) elements are detected in many very metal-poor halo stars, and so they must have been manufactured by some of the earliest element donors in our Galaxy's history. The bulk amounts of neutron-capture elements with respect to the iron group vary by several orders of magnitude from star to star at low metallicities. Additionally, abundance distributions among these elements are often strikingly different from that of the solar system. Some stars exhibit abundances that must have been made purely in "rapid" neutron-capture events (the r-process), some in "slow" events (the s-process), and some have hybrid mixes. Here we summarize the major observed categories of the neutron-capture abundances in metal-poor stars, and discuss their implications for early Galactic nucleosynthesis.

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Section: R-process Starsmentioning

confidence: 84%

Constraints on the Nature of the s- and r-processes

2009

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“…The particular version of MOOG that we used includes a proper treatment of continuum scattering (see Sobeck et al 2011 for further details). We refer the reader to Cayrel et al (2004) and Sobeck et al (2011) for a discussion regarding the importance of Raleigh scattering (Griffin et al 1982) at blue wavelengths in metal-poor stars.…”

Section: Stellar Parameters: T Eff Logg ξ T and [Fe/h]mentioning

confidence: 99%

THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ –3.5, ,

Yong

Norris

Bessell

et al. 2012

ApJ

295

232

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We present a homogeneous chemical abundance analysis of 16 elements in 190 metal-poor Galactic halo stars (38 program and 152 literature objects). The sample includes 171 stars with [Fe/H] −2.5, of which 86 are extremely metal poor, [Fe/H] −3.0. Our program stars include 10 new objects with [Fe/H] −3.5. We identify a sample of "normal" metal-poor stars and measure the trends between [X/Fe] and [Fe/H], as well as the dispersion about the mean trend for this sample. Using this mean trend, we identify objects that are chemically peculiar relative to "normal" stars at the same metallicity. These chemically unusual stars include CEMP-no objects, one star with high [Si/Fe], another with high [Ba/Sr], and one with unusually low [X/Fe] for all elements heavier than Na. The Sr and Ba abundances indicate that there may be two nucleosynthetic processes at lowest metallicity that are distinct from the main r-process. Finally, for many elements, we find a significant trend between [X/Fe] versus T eff , which likely reflects non-LTE and/or three-dimensional effects. Such trends demonstrate that care must be exercised when using abundance measurements in metal-poor stars to constrain chemical evolution and/or nucleosynthesis predictions.

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“…The first Extremely Metal Poor (EMP, ) star found to be enriched in n-capture elements was the giant HD 115444 with [Fe/H] ∼ −3 (Griffin et al 1982). Westin et al (2000) found marginal overabundances of Ba and other s-elements relative to iron in this star as compared with the Sun.…”

Section: Introductionmentioning

confidence: 99%

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

Jonsell¹,

Barklem²,

Gustafsson³

et al. 2006

A&A

Self Cite

165

277

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We have derived abundances of 33 elements and upper limits for 6 additional elements for the metal-poor ([Fe/H] = −2.42) turn-off star HE 0338−3945 from high-quality VLT-UVES spectra. The star is heavily enriched, by about a factor of 100 relative to iron and the Sun, in the heavy s-elements (Ba, La, ...). It is also heavily enriched in Eu, which is generally considered an r-element, and in other similar elements. It is less enriched, by about a factor of 10, in the lighter s-elements (Sr, Y and Zr). C is also strongly enhanced and, to a somewhat lesser degree, N and O. These abundance estimates are subject to severe uncertainties due to NLTE and thermal inhomogeneities which are not taken into detailed consideration. However, an interesting result, which is most probably robust in spite of these uncertainties, emerges: the abundances derived for this star are very similar to those of other stars with an overall enhancement of all elements beyond the iron peak. We have defined criteria for this class of stars, r + s stars, and discuss nine different scenarios to explain their origin. None of these explanations is found to be entirely convincing. The most plausible hypotheses involve a binary system in which the primary component goes through its giant branch and asymptotic giant branch phases and produces CNO and s-elements which are dumped onto the observed star. Whether the r-element Eu is produced by supernovae before the star was formed (perhaps triggering the formation of a low-mass binary), by a companion as it explodes as a supernova (possibly triggered by mass transfer), or whether it is possibly produced in a high-neutron-density version of the s-process is still unclear. Several suggestions are made on how to clarify this situation.Key words. stars: population ii -stars: fundamental parameters -stars: abundances -Galaxy: halo -Galaxy: abundances -Galaxy: evolution IntroductionElements with atomic numbers Z > 30 are believed to be almost exclusively synthesized in neutron-capture (n-capture) reactions. In the most metal-poor stars the overall abundance of these elements varies from star to star, by more than a factor of 100 at a given metallicity (McWilliam et al. 1995;Ryan et al. 1996). Also, the different abundance ratios vary, e.g. the Ba/Eu ratio tends to decline with decreasing [Fe/H]

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HD 115444 – a barium star of extreme Population II

Cited by 33 publications

References 0 publications

Constraints on the Nature of the s- and r-processes

Constraints on the Nature of the s- and r-processes

THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ –3.5, ,

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

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