First stars. I. The extreme r-element rich, iron-poor halo giant CS 31082-001 - Implications for the r-process site(s) and radioactive cosmochronology

By V. Hill, B. Plez, R. Cayrel, Timothy C. Beers, B. Nordström, J. Andersen, M. Spite, F. Spite, B. Barbuy, P. Bonifacio and 3 more. 2002

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We present a high-resolution (R = 75 000, S/N 500) spectroscopic analysis of the bright (V = 11.7), extreme halo giant CS 31082-001 ((Fe/H) = 2.9), obtained in an ESO-VLT Large Programme dedicated to very metal-poor stars. We nd CS 31082-001 to be extremely rich in r-process elements, comparable in this respect only to the similarly metal-poor, but carbon-enriched, giant CS 22892-052. As a result of the extreme overabundance of the heaviest r-process elements, and negligible blending from CH and CN molecular lines, a reliable measurement is obtained of the U II line at 386 nm, for the rst time in a halo star, along with numerous lines of Th II, as well as lines of 25 other r-process elements. Abundance estimates for a total of 43 elements (44 counting Hydrogen) are reported in CS 31082-001, almost half of the entire periodic table. The main atmospheric parameters of CS 31082- 001 are as follows: Te = 4825 50 K, logg =1 :5 0: 3( cgs), (Fe/H) = 2.9 0:1 (in LTE), and microturbulence 1.8 0.2 km s 1 . Carbon and nitrogen are not signicantly enhanced relative to iron. As usual in giant stars, Li is depleted by dilution (log(Li/H) = 0.85). The -elements show the usual enhancements with respect to iron, with (O/Fe) = 0:6 0:2 (from (O I) 6300 A), (Mg/Fe) = 0:45 0:16, (Si/Fe) = 0:24 0:1, and (Ca/Fe) = 0:41 0:08, while (Al/Fe) is near 0.5. The r-process elements show unusual patterns: among the lightest elements (Z 40), Sr and Zr follow the Solar r-element distribution, but Ag is down by 0.8 dex. All elements with 56 Z 72 follow the Solar r-element pattern, reduced by about 1.25 dex. Accordingly, the (r/Fe) enhancement is about +1.7 dex (a factor of 50), very similar to that of CS 22892-052. Pb, in contrast, seems to be below the shifted Solar r-process distribution, possibly indicating an error in the latter, while thorium is more enhanced than the lighter nuclides. In CS 31082-001, log(Th/Eu) is 0:22 0:07, higher than in the Solar System ( 0.46) or in CS 22892-052 ( 0.66). If CS 31082-001 and CS 22892-052 have similar ages, as expected for two extreme halo stars, this implies that the production ratios were dierent by about 0.4 dex for the two objects. Conversely, if the Th/Eu production ratio were universal, an age of 15 Gyr for CS 22892-052 would imply a negative age for CS 31082-001. Thus, while a universal production ratio for the r-process elements seems to hold in the interval 56 Z 72, it breaks down in the actinide region. When available, the U/Th is thus preferable to Th/Eu for radioactive dating, for two reasons: (i) because of its faster decay rate and smaller sensitivity to observational errors, and (ii) because the inital production ratio of the neighboring nuclides 238 Ua nd 232 Th is more robustly predicted than the 151 Eu/ 232 Th ratio. Our current best estimate for the age of CS 31082-001 is 14:0 2: 4G yr. However, the computed actinide production ratios should be veried by observations of daughter elements such as Pb and Bi in the same star, which are independent of the subsequent history of star formation and nucelosynthesis in the Galaxy.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

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Citations in the corpus

HE 1327–2326, an Unevolved Star with [Fe/H] < –5.0. I. A Comprehensive Abundance Analysis (2005, background): “…best estimated from the value observed in the so-called r-II stars, stars with very large enhancements of r-process nuclei with respect to other metals: ½Sr/Ba ¼ 0:41 in CS 22892 052 (Sneden et al. 2003), 0.52 in CS 31082 001 (Hill et al. 2002), and 0.46 in CS 29497 004 (Christlieb et al. 2004b).”
CHEMICAL ABUNDANCES FOR 855 GIANTS IN THE GLOBULAR CLUSTER OMEGA CENTAURI (NGC 5139) (2010, methodology): “The atomic linelist was merged with a molecular CN linelist that was created through a combination of the Kurucz molecular linelist12 and one provided by B. Plez (2007, private communication; see also Hill et al. 2002).”
Nuclear weak-interaction processes in stars (2002, background): “Cayrel et al. (2001) have used their observed 238U/232Th abundance ratio from the star CS31082-001 and the r-process model predictions from (Cowan et al., 1999; Goriely and Clerbaux, 1999) to deduce a value of 12.5± 3.3 Gyr for the age of the star.”
Three-dimensional hydrodynamical simulations of surface convection in red giant stars: impact on spectral line formation and abundance analysis (2007, background): “More recently, the ESO “First Stars” programme (e.g. Hill et al. 2002; Cayrel et al. 2004; Spite et al. 2005) has provided a systematic and homogeneous study of the chemical compositions of a large sample of extremely metal-poor giant as well as dwarf stars ([Fe/H] <∼ −2.5) from the HK survey by…”
First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy (2003, background): “We note that for CS 31082–001 the temperature deduced from (V-R) is higher than the temperature found in Hill et al. (2002), because in the latter paper the transformation V-R vs. temperature had been taken from McWilliam et al. (1995).”
The s process: Nuclear physics, stellar models, and observations (2010, background): “…into the s and r components became also important for the interpretation of abundance patterns of ultra-metal-poor stars (Cowan et al., 2002; Hill et al., 2002; Sneden et al., 2003; Westin et al., 2000), which turned out to agree very well with the scaled solar r component for the elements…”
A Subaru/High Dispersion Spectrograph Study of Lead (Pb) Abundances in Eight s-Process Element-rich, Metal-poor Stars (2002, background): “If this were true, it follows that these four stars show very large excesses of their r-process elements ([Eu/Fe]=1.5∼1.8), similar to CS 31082–001, an extreme r-process-elementenhanced star (Cayrel et al. 2001; Hill et al. 2002).”
Neutron-Capture Elements in the Early Galaxy (2008, methodology): “…of other r-rich stars have confirmed the same scaled Solar-system abundance pattern for elements with Z ≥ 56 (see, e.g., Westin et al. 2000, Cowan et al. 2002, Hill et al. 2002, Johnson 2002, Johnson & Bolte 2002b, Honda et al. 2004, Barklem et al. 2005, Ivans et al. 2006, Frebel et al. 2007).”
NEW RARE EARTH ELEMENT ABUNDANCE DISTRIBUTIONS FOR THE SUN AND FIVE r-PROCESS-RICH VERY METAL-POOR STARS (2009, methodology): “The first and most complete study of this star was published by Hill et al. (2002).”
Solar Chemical Abundances Determined with a CO5BOLD 3D Model Atmosphere (2010, methodology): “Ivarsson et al. (2003) did not study the solar Os abundance, but applied their new log gf values to the analysis of the metal poor giant CS 31082-001, previously analysed by Hill et al. (2002).”
Spectroscopic Studies of Extremely Metal-Poor Stars with the Subaru High Dispersion Spectrograph. II. The r-Process Elements, Including Thorium (2004, methodology): “A similar result was already reported for CS 31082 001 by Cayrel et al. (2001) and Hill et al. (2002), as mentioned in x 1.”
The rate, luminosity function and time delay of non-Collapsar short GRBs (2014, background): “A critical consideration when proposing ns2 mergers as sources of heavy r-process material is the observations of such elements in some very low metallicity (log10[Fe/H] ≈ 3) stars (Woolf, Tomkin & Lambert 1995; Shetrone 1996; Burris et al. 2000; Cayrel et al. 2001; Hill et al. 2002).”
The Rise of the s-Process in the Galaxy (2004, background): “…strength throughout the near-UV to red spectral regions, and all of them yield consistent abundances from the solar spectrum and from r-process-rich, low-metallicity stars such as BD +17◦3248, BPS CS 22892-052, and BPS BPS CS 31082-001 (Lawler et al. 2001a; Sneden et al. 2003; Hill et al. 2002).”
A SEARCH FOR STARS OF VERY LOW METAL ABUNDANCE. VI. DETAILED ABUNDANCES OF 313 METAL-POOR STARS (2014, result): “Our results for CS 31082–001, another giant with a high level of r-process enrichment, exhibit a similar offset with respect to Hill et al. (2002), Sneden et al. (2009), and others.”
The two metallicity groups of the globular cluster M 22: a chemical perspective (2011, methodology): “The synthesis linelist for the blue CN band is described in Hill et al. (2002).”
Improved Laboratory Transition Probabilities for Nd II and Application to the Neodymium Abundances of the Sun and Three Metal-poor Stars (2003, background): “A sampling of the current literature on such stars (e.g., Westin et al. 2000; Cowan et al. 2002; Hill et al. 2002; Aoki et al. 2001; Sneden et al. 2003) suggests that even when large numbers of Nd ii lines are used, the resulting line-to-line abundance scatter is 0:2 dex.”
Is HE 0107–5240 A Primordial Star? The Characteristics of Extremely Metal-Poor Carbon-Rich Stars (2004, neutral): “Data has been taken from Ryan, Norris & Bessell (2001); Norris, Ryan & Beers (1997,b); Norris, Ryan, Beers (2001); Hill et al (2000, 2002); Aoki et al. (2001, 2002a,b); Depagne et al. (2002); Johnson & Bolte (2002); Cohen et al. (2003); Lucatello et al. (2003); Sneden et al (2003).”
The s-Process in Low Metallicity Stars. II. Interpretation of High-Resolution Spectroscopic Observations with AGB models (2011, positive): “Up to date, several r-II stars have been analysed: most noteworthy are CS 31082–001 by (Hill et al. 2002; Plez et al. 2004) ([Eu/Fe] ∼ 1.6), HD 115444 by Westin et al. (2000) ([Eu/Fe] = 0.85), HE 1523– 0901 by Frebel et al. (2007) ([Eu/Fe] ∼ 1.8), CS 29497– 004 by Christlieb et al. (2004) ([Eu/Fe]…”