Abundances in a sample of turnoff and subgiant stars in NGC 6121 (M 4)

Spite, M.; Spite, F.; Gallagher, A. J.; Monaco, L.; Bonifacio, P.; Caffau, E.; Villanova, S.

doi:10.1051/0004-6361/201628759

Cited by 45 publications

(74 citation statements)

References 37 publications

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“…5 (very close to the mean value) confirms the very small scatter of the lithium abundance in the old galactic stars, in this interval of temperature and metallicity (Spite et al 2012). The abundance A(Li) does not depend on the stellar kinematic or dynamic properties (see also Boesgaard et al 2005).…”

Section: Lithium Abundancesupporting

confidence: 78%

“…5, we plotted the lithium abundance as a function of the effective temperature T eff both for WISE J0725-2351 and for all the field galactic turnoff stars with the Li measurement available in the literature (Charbonnel & Primas 2005;Asplund et al 2006;Bonifacio et al 2007;Aoki et al 2009;Hosford et al 2009;Meléndez et al 2010;Sbordone et al 2010;Schaeuble & King 2012). We only selected the stars with temperatures higher than 5900 K, and a metallicity between [Fe/H] = -2 and [Fe/H] = -2.8, as in Spite et al (2012).…”

Section: Lithium Abundancementioning

confidence: 99%

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Lithium abundance in a turnoff halo star on an extreme orbit

Spite

Caffau

et al. 2015

A&A

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Context. The lithium abundance in turnoff stars of the old population of our Galaxy is remarkably constant in the metallicity interval −2.8 < [Fe/H] < −2.0, defining a plateau. The Li abundance of these turnoff stars is clearly lower than the abundance predicted by the primordial nucleosynthesis in the frame of the standard Big Bang nucleosynthesis. Different scenarios have been proposed for explaining this discrepancy, along with the very low scatter of the lithium abundance around the plateau. Aims. The recently identified very high velocity star, WISE J0725-2351 appears to belong to the old Galactic population, and appears to be an extreme halo star on a bound, retrograde Galactic orbit. In this paper, we study the abundance ratios and, in particular the lithium abundance, in this star. Methods. The available spectra (ESO-Very Large Telescope) are analyzed and the abundances of Li, C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Sr and Ba are determined. Results. The abundance ratios in WISE J0725-2351 are those typical of old turnoff stars. The lithium abundance in this star is in close agreement with the lithium abundance found in the metal-poor turnoff stars located at moderate distance from the Sun. This high velocity star confirms, in an extreme case, that the very small scatter of the lithium plateau persists independent of the dynamic and kinematic properties of the stars.

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Section: Lithium Abundancesupporting

confidence: 78%

Section: Lithium Abundancementioning

confidence: 99%

Lithium abundance in a turnoff halo star on an extreme orbit

Spite

Caffau

et al. 2015

A&A

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“…3 in Spite et al 2012b). In four of the above-mentioned UIP stars the lithium abundance could not be measured, and it is intriguing to consider the possibility that the atmospheres of these stars are indeed totally devoid of lithium.…”

Section: Lithiummentioning

confidence: 99%

TOPoS

Bonifacio

Caffau

Spite

et al. 2015

A&A

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Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. Aims. We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns. Methods. We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D local thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum line formation code. were not able to detect any iron lines, yet we could place a robust (3σ) upper limit of [Fe/H] < −5.0 and measure the Ca abundance, with [Ca/H] = −5.0, and carbon, A(C) = 6.90, suggesting that this star could be even more metal-poor than SDSS J1742+2531. This makes these two stars the seventh and eighth stars known so far with [Fe/H] < −4.5, usually termed ultra-iron-poor (UIP) stars. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li) < 1.8 for both stars. Conclusions. Our measured carbon abundances confirm the bimodal distribution of carbon in CEMP stars, identifying a high-carbon band and a low-carbon band. We propose an interpretation of this bimodality according to which the stars on the high-carbon band are the result of mass transfer from an AGB companion, while the stars on the low-carbon band are genuine fossil records of a gas Article published by EDP Sciences A28, page 1 of 20 A&A 579, A28 (2015) cloud that has also been enriched by a faint supernova (SN) providing carbon and the lighter elements. The abundance pattern of the UIP stars shows a large star-to-star scatter in the [X/Ca] ratios for all elements up to aluminium (up to 1 dex), but this scatter drops for heavier elements and is at most of the order of a factor of two. We propose that this can be explained if these stars are formed from gas that has been chemically enriched by several SNe, that produce the roughly constant [X/Ca] ratios for the heavier elements, and in some cases the gas has also been polluted by the ejecta of a faint SN that contributes the lighter elements in variable amounts. The absence of lithium in four of the five known unevolved UIP stars can be explained by a dominant role of fragmentation in the formation of these stars. This would result either in a destruction of lithium in the pre-main-sequence phase, through rotational mixing or to a lack of late accretion from a reservoir of fresh gas. The phenomenon should have varying degrees of efficiency.

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“…The observed 7 Li abundance appears to be depleted by a factor of about 3 when compared to the prediction of standard BBN in conjunction with CMB data. For recent reviews see Jedamzik & Pospelov (2009), Spite & Spite (2010), Steigman (2010), Fields (2011), Frebel & Norris (2011), Spite et al (2012), and Coc et al (2014). 7 Li is observed in the atmospheres of stars.…”

Section: Introductionmentioning

confidence: 99%

Non-Gaussian error distribution of 7Li abundance measurements

Crandall

Houston

2015

Mod. Phys. Lett. A

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We construct the error distribution of 7 Li abundance measurements for 66 observations (with error bars) used by Spite et al. (2012) that give A(Li) = 2.21± 0.065 (median and 1σ symmetrized error). This error distribution is somewhat non-Gaussian, with larger probability in the tails than is predicted by a Gaussian distribution. The 95.4% confidence limits are 3.0σ in terms of the quoted errors. We fit the data to four commonly used distributions: Gaussian, Cauchy, Student's t, and double exponential with the center of the distribution found with both weighted mean and median statistics. It is reasonably well described by a widened n = 8 Student's t distribution. Assuming Gaussianity, the observed A(Li) is 6.5σ away from that expected from standard Big Bang nucleosynthesis given the P lanck observations (Coc et al. 2014). Accounting for the non-Gaussianity of the observed A(Li) error distribution reduces the discrepancy to 4.9σ, which is still significant.

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Abundances in a sample of turnoff and subgiant stars in NGC 6121 (M 4)

Cited by 45 publications

References 37 publications

Lithium abundance in a turnoff halo star on an extreme orbit

Lithium abundance in a turnoff halo star on an extreme orbit

TOPoS

Non-Gaussian error distribution of 7Li abundance measurements

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