A Subaru/High Dispersion Spectrograph Study of Lead (Pb) Abundances in Eight s-Process Element-rich, Metal-poor Stars

By Wak Aoki, S. Ryan, J. Norris, Timothy C. Beers, H. Ando, S. Tsangarides. 2002

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We report the abundances of neutron-capture elements in eight carbon-rich, metal-poor (-2.7 ≤ [Fe/H] ≤ -1.9) stars observed with the Subaru Telescope High Dispersion Spectrograph. The derived abundance patterns indicate that the neutron-capture elements in these objects primarily originated from s-process nucleosynthesis, although the [Ba/Eu] abundance ratios in some objects are lower than that of the solar system s-process component. The present analysis has yielded the Pb abundances for seven objects as well as an upper limit for one object from use of the Pb I λ4057 and λ3683 lines. The values of [Pb/Ba] in these objects cover a wide range, between -0.3 and 1.2. Theoretical studies of s-process nucleosynthesis at low metallicity are required to explain this large dispersion of the [Pb/Ba] values. Variations in radial velocity have been found for two of the eight objects, suggesting that, at least in these instances, the observed excess of s-process elements is due to the transfer of material across a binary system including an AGB star. Comparisons with predictions of AGB nucleosynthesis models are discussed.

Subfields: Astronomy and Astrophysics

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Abundance Variations within Globular Clusters (2004, background): “Second, the abundance distribution among the n-capture elements ranges from r-process dominance (characterized by [Eu/Ba] ∼ +1; e.g., Cowan et al. 2002, Hill et al. 2002, Sneden et al. 2003) to s-process dominance ([Eu/Ba] ∼ –1; e.g., Aoki et al. 2002, Lucatello et al. 2003, Van Eck et al. 2003).”
The s-Process in Low Metallicity Stars. II. Interpretation of High-Resolution Spectroscopic Observations with AGB models (2011, background): “…([Na/Fe] > 1): CS 22942– 019 (Preston & Sneden 2001), CS 29497–34, CS 29528– 028 and CS 30301–015 (Aoki et al. 2007, 2008), CS 30322– 023 (Masseron et al. 2006; Aoki et al. 2007), LP 625–44 (Aoki et al. 2002a), SDSS J1349–0229 (Behara et al. 2010), SDSS 0924+40, and SDSS 1707+58 (Aoki et al. 2008).”
The Hamburg/ESO R-process enhanced star survey (HERES) - III. HE 0338-3945 and the formation of the r + s stars (2006, background): “They noted, however, that the observations of the151Eu/153Eu ratio of this star by Aoki et al. (2002) seem to indicate that the neutron density was rather around the more normal value of 108.”
Stellar Abundances for the Galactic Archeology (SAGA) Database — Compilation of the Characteristics of Known Extremely Metal-Poor Stars (2008, background): “…Ryan et al. 1991; McWilliam et al. 1995; Ryan et al. 1996; Fulbright 2000; Preston & Sneden 2000; Burris et al. 2000; Mishenina & Kovtyukh 2001; Aoki et al. 2002; Cohen et al. 2002; Carretta et al. 2002; Johnson 2002; Nissen et al. 2002; Cayrel et al. 2004; Honda et al. 2004; Cohen et al.…”
HE 1327–2326, an Unevolved Star with [Fe/H] < –5.0. I. A Comprehensive Abundance Analysis (2005, background): “One sees that HE 1327 2326 shares its Mg overabundance with the carbon-enhanced, metal-poor stars CS 22949 037 (McWilliam et al. 1995; Norris et al. 2001; Depagne et al. 2002) and CS 29498 043 (Aoki et al. 2002a, 2004), in contrast with the value for HE 0107 5240.”
Spectroscopic Studies of Extremely Metal-Poor Stars with the Subaru High Dispersion Spectrograph. II. The r-Process Elements, Including Thorium (2004, methodology): “However, the Yb ii 3694.2 8 line may indeed be affected by hyperfine splitting, as pointed out by Aoki et al. (2002b) and Hill et al. (2002), because two of the seven isotopes of this element have odd mass numbers (171Yb and 173Yb).”
The Hamburg/ESO R-process enhanced star survey (HERES). II. Spectroscopic analysis of the survey sample (2005, background): “Figure 28 also identifies a number of mildly carbonenhanced stars without enhancement of neutron-capture elements, a class of objects identified by Aoki et al. (2002a).”
Spectroscopic Studies of Very Metal-poor Stars with the Subaru High Dispersion Spectrograph. III. Light Neutron-Capture Elements (2005, background): “…implies that the process that produces heavy neutron-capture elements like Ba also forms light neutron-capture elements such as 14 Some CEMP-s stars exhibit very high Ba abundances with a moderate excess of Sr (e.g., LP 706-7 = CS 31062-012: log (Ba) ¼ 1:65 and log (Sr) ¼ 0:67; Aoki et al. 2002b).”
Neutron-Capture Elements in the Very Metal Poor Star HD 122563 (2006, background): “The main s-process is also excluded as a possible source of light neutron-capture elements, because that yields even lower abundance ratios between light and heavy neutron-capture elements at low metallicity (e.g., Busso et al. 1999; Aoki et al. 2002).”
The s process: Nuclear physics, stellar models, and observations (2010, background): “An illustrative case are the high Eu abundances, relative to Ba and other s-process elements, in some CEMP stars, which can not be explained by standard s-process models (Aoki et al., 2002b; Cohen et al., 2003; Hill et al., 2000).”
Near-Ultraviolet Observations of HD 221170: New Insights into the Nature of r-Process-rich Stars (2006, background): “In studies of metal-poor stars with s+r enhancements (see e.g. Aoki et al 2002; Johnson & Bolte 2004), [Er/Eu] can be ∼1 regardless of whether or not the stars possess strong r-process enhancements.”
GALACTIC CHEMICAL EVOLUTION AND SOLAR s-PROCESS ABUNDANCES: DEPENDENCE ON THE 13C-POCKET STRUCTURE (2014, background): “…stellar populations (planetary nebulae, post-AGB, MS, S, C(N), Ba, CH, and CEMP s stars; see, e.g., Smith & Lambert 1990; Péquignot & Baluteau 1994; Aoki et al. 2002; Abia et al. 2002; Allen & Barbuy 2006; Jonsell et al. 2006; Sharpee et al. 2007; Sterling & Dinerstein 2008; Reyniers et al. 2007;…”
Neutron-Capture Elements in the Early Galaxy (2008, background): “…l/ F e ] MAGB ini ~ 1.3 M ; case: ST/12 [r /Fe]ini = 2.0; [α/Fe] = 0.5 dil = 0.0 dex T eff = 6250 K; log g = 3.7 [Fe/H] = –2.26 0 10 20 30 40 50 60 70 80 90 Atomic number CS 22898-027 Aoki et al. (2007a) Aoki et al. (2002c) Aoki et al. (2002d) 280 Sneden · Cowan · Gallino A n n u .”
THE DISCOVERY AND ANALYSIS OF VERY METAL-POOR STARS IN THE GALAXY (2005, background): “From Aoki et al. 2004 with permission. in these stars are overabundant, as compared with “normal” EMP stars, such as CD −38◦ 245 and CS 22885-096 (Aoki et al. 2002b, 2004; Israelian et al. 2004).”
Carbon-enhanced Metal-poor Stars. I. Chemical Compositions of 26 Stars (2006, methodology): “This object was more recently studied by Tsangarides (2005), who compared in some detail their results with those of Aoki et al. (2002d).”
The role of binaries in the enrichment of the early Galactic halo (2015, background): “Aoki et al. (2002a) and Ryan et al. (2005) first called attention to the apparent contrast in the heavy-element abundance patterns among several subclasses of CEMP stars and speculated about their likely origin.”
Is HE 0107–5240 A Primordial Star? The Characteristics of Extremely Metal-Poor Carbon-Rich Stars (2004, methodology): “The abundances of many neutron-rich elements vary considerably from star to star even among those stars which have the abundance ratio [Ba/Eu] very close to the solar r-process value (McWilliam 1998; Aoki et al. 2002a; Honda et al. 2004).”
The Binary Frequency Among Carbon-enhanced, s-Process-rich, Metal-poor Stars (2004, methodology): “…enhancements in their n-capture elements (hereafter, CEMP-no; Norris, Ryan & Beers 1997b; Aoki et al. 2002a), at least two of which (CS 29498-043; Aoki et al. 2002d,e and CS 22949-037; Depagne et al. 2002) also appear to exhibit large enhancements in N, O, and the α-elements, while a single case…”