Non-LTE effects on the lead and thorium abundance determinations for cool stars

Mashonkina, L.; Ryabtsev, A. N.; Frebel, Anna

doi:10.1051/0004-6361/201218790

Cited by 57 publications

(65 citation statements)

References 52 publications

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“…Bergemann et al 2012). In particular, positive corrections of 0.3-0.5 dex are to be expected for the lead abundances of stars in the metallicity range of our observed sample (Mashonkina et al 2012). If we assume an average correction of 0.4 dex, 21 CEMP-s stars (of which 16 are CEMP-s/r) would have [Pb/Fe] ≥ 2.8 and cannot be reproduced by any of our models.…”

Section: The Effect Of M Pmzsupporting

confidence: 51%

“…This correction increases for increasing temperature, and for decreasing metallicity and surface gravity. Positive corrections are typically required also for barium and europium (Mashonkina et al 2012;Niemczura et al 2014). Although the magnitudes of the corrections are of the order of the observational uncertainties ( < ∼ 0.2 dex), they suggest that our models should produce higher abundances of heavy elements for a given amount of carbon.…”

Section: A62 Page 14 Of 16mentioning

confidence: 99%

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Modelling the observed properties of carbon-enhanced metal-poor stars using binary population synthesis

Abate

Pols

Stancliffe³

et al. 2015

A&A

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The stellar population in the Galactic halo is characterised by a large fraction of carbon-enhanced metal-poor (CEMP) stars. Most CEMP stars have enhanced abundances of s-process elements (CEMP-s stars), and some of these are also enriched in r-process elements (CEMP-s/r stars). In one formation scenario proposed for CEMP stars, the observed carbon excess is explained by invoking wind mass transfer in the past from a more massive thermally-pulsing asymptotic giant branch (AGB) primary star in a binary system. In this work we generate synthetic populations of binary stars at metallicity Z = 0.0001 ([Fe/H] ≈ −2.3), with the aim of reproducing the observed fraction of CEMP stars in the halo. In addition, we aim to constrain our model of the wind masstransfer process, in particular the wind-accretion efficiency and angular-momentum loss, and investigate under which conditions our model populations reproduce observed distributions of element abundances. We compare the CEMP fractions determined from our synthetic populations and the abundance distributions of many elements with observations. Several physical parameters of the binary stellar population of the halo are uncertain, in particular the initial mass function, the mass-ratio distribution, the orbital-period distribution, and the binary fraction. We vary the assumptions in our model about these parameters, as well as the wind mass-transfer process, and study the consequent variations of our synthetic CEMP population. The CEMP fractions calculated in our synthetic populations vary between 7% and 17%, a range consistent with the CEMP fractions among very metal-poor stars recently derived from the SDSS/SEGUE data sample. The resulting fractions are more than a factor of three higher than those determined with default assumptions in previous population-synthesis studies, which typically underestimated the observed CEMP fraction. We find that most CEMP stars in our simulations are formed in binary systems with periods longer than 10 000 days. Few CEMP stars have measured orbital periods, but all that do have periods up to a few thousand days. Our results are consistent only if this small subpopulation represents the short-period tail of the underlying period distribution. The results of our comparison between the modelled and observed abundance distributions are significantly different for CEMP-s/r stars and for CEMP-s stars without strong enrichment in r-process elements. For the latter, our simulations qualitatively reproduce the observed distributions of carbon, sodium, and heavy elements such as strontium, barium, europium, and lead. Contrarily, for CEMP-s/r stars our model cannot reproduce the large abundances of neutron-rich elements such as barium, europium, and lead. This result is consistent with previous studies, and suggests that CEMP-s/r stars experienced a different nucleosynthesis history to CEMP-s stars.

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Section: The Effect Of M Pmzsupporting

confidence: 51%

Section: A62 Page 14 Of 16mentioning

confidence: 99%

Modelling the observed properties of carbon-enhanced metal-poor stars using binary population synthesis

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Pols

Stancliffe³

et al. 2015

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“…24 shows the results for CS 30351-029 (upper panel) and HE 0524-2055 (lower panel), using Eu II 4129.72 Å line. Mashonkina et al (2012) present NLT corrections for Eu abundances in cool stars, but the estimated values are lower than ∆ NLT E = +0.10 dex for our sample stars. After checking seven Gd II lines, the gadolinium abundance was derived for six of our program stars.…”

Section: Second-peak Region Elementscontrasting

confidence: 59%

High-Resolution Abundance Analysis of Very Metal-Poor R-I Stars

Siqueira-Mello

Hill²,

Barbuy

et al. 2015

Proceedings of XIII Nuclei in the Cosmos — PoS(NIC XIII)

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Context. Moderately r-process-enriched stars (r-I; +0.3 ≤ [Eu/Fe] ≤ +1.0) are at least four times as common as those that are greatly enriched in r-process elements (r-II; [Eu/Fe] > +1.0), and the abundances in their atmospheres are important tools for obtaining a better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak. Aims. The main aim of this work is to derive abundances for a sample of seven metal-poor stars with −3.4 ≤ [Fe/H] ≤ −2.4 classified as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is(are) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars. Methods. We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph, using spectra in the wavelength ranges 3400 -4500 Å, 6800 -8200 Å, and 8700 -10,000 Å, with resolving power R ∼ 40 000 (blue arm) and R ∼ 55 000 (red arm). The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code Turbospectrum. Results. We have derived abundances of the light elements Li, C, and N, the α-elements Mg, Si, S, Ca, and Ti, the odd-Z elements Al, K, and Sc, the iron-peak elements V, Cr, Mn, Fe, Co, and Ni, and the trans-iron elements from the first peak (Sr, Y, Zr, Mo, Ru, and Pd), the second peak (Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), the third peak (Os and Ir, as upper limits), and the actinides (Th) regions. The results are compared with values for these elements for r-II and "normal" very and extremely metal-poor stars reported in the literature, ages based on radioactive chronometry are explored using different models, and a number of conclusions about the r-process and the r-I stars are presented. Hydrodynamical models were used for some elements, and general behaviors for the 3D corrections were presented. Although the abundance ratios of the second r-process peak elements (usually associated with the main r-process) are nearly identical for r-I and r-II stars, the first r-process peak abundance ratios (probably associated with the weak r-process) are more enhanced in r-I stars than in r-II stars, suggesting that differing nucleosynthesis pathways were followed by stars belonging to these two different classifications.

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“…It is important to note that Mashonkina et al (2012) presented NLTE abundance corrections for the Eu II 4129 Å line in cool stars. Using a model with T eff = 5780 K and log g = 4.4 [cgs], they found ∆ NLTE (Eu) = +0.03 dex in stars with solar metallicity.…”

Section: Discussionmentioning

confidence: 99%

Origin of the heavy elements in HD 140283

Mello¹,

Barbuy²,

Spite³

et al. 2012

A&A

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Context. HD 140283 is a nearby (V = 7.7) subgiant metal-poor star, extensively analysed in the literature. Although many spectra have been obtained for this star, none showed a signal-to-noise (S/N) ratio high enough to enable a very accurate derivation of abundances from weak lines. Aims. The detection of europium proves that the neutron-capture elements in this star originate in the r-process, and not in the s-process, as recently claimed in the literature. Methods. Based on the OSMARCS 1D LTE atmospheric model and with a consistent approach based on the spectrum synthesis code Turbospectrum, we measured the europium lines at 4129 Å and 4205 Å, taking into account the hyperfine structure of the transitions. The spectrum, obtained with a long exposure time of seven hours at the Canada-France-Hawaii Telescope (CFHT), has a resolving power of 81 000 and a S/N ratio of 800 at 4100 Å. Results. We were able to determine the abundance A(Eu) = −2.35 ± 0.07 dex, compatible with the value predicted for the europium from the r-process. The abundance ratio [Eu/Ba] = +0.58 ± 0.15 dex agrees with the trend observed in metal-poor stars and is also compatible with a strong r-process contribution to the origin of the neutron-capture elements in HD 140283.

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Non-LTE effects on the lead and thorium abundance determinations for cool stars

Cited by 57 publications

References 52 publications

Modelling the observed properties of carbon-enhanced metal-poor stars using binary population synthesis

Modelling the observed properties of carbon-enhanced metal-poor stars using binary population synthesis

High-Resolution Abundance Analysis of Very Metal-Poor R-I Stars

Origin of the heavy elements in HD 140283

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