Lithium in the globular cluster NGC 6397

Hernández, J. I. González; Bonifacio, P.; Caffau, E.; Steffen, M.; Ludwig, H.‐G.; Behara, N. T.; Sbordone, L.; Cayrel, Roger; Zaggia, S.

doi:10.1051/0004-6361/200912713

Cited by 53 publications

(5 citation statements)

References 43 publications

(52 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Li observations have also been performed in some globular clusters. For example, in NGC 6397, González Hernández et al () and Lind et al () found the 7 Li/H values to be (2.34 ± 0.05) × 10 −10 and (1.78 ± 0.04) × 10 −10 , respectively, somewhat higher than the result for field stars, whereas Monaco et al () found a value of 7 Li/H = (1.48 ± 0.41) × 10 −10 in Omega Centauri that is similar to halo star abundances.…”

Section: Introductionmentioning

confidence: 89%

Higher D or Li: probes of physics beyond the standard model

Olive

Petitjean

Vangioni

et al. 2012

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Standard big bang nucleosynthesis (BBN) at the baryon density determined by the microwave anisotropy spectrum predicts an excess of 7 Li compared to observations by a factor of 4-5. In contrast, BBN predictions for D/H are somewhat below (but within 2σ of) the weighted mean of observationally determined values from quasar absorption systems. Solutions to the 7 Li problem which alter the nuclear processes during or subsequent to BBN often lead to a significant increase in the deuterium abundance consistent with the highest values of D/H seen in absorption systems. Furthermore, the observed D/H abundances show considerable dispersion. Here, we argue that those systems with D/H 4 × 10 −5 may be more representative of the primordial abundance and as a consequence, those systems with lower D/H would necessarily have been subject to local processes of deuterium destruction. This can be accounted for by models of cosmic chemical evolution able to destroy in situ deuterium due to the fragility of this isotope.

show abstract

Section: Introductionmentioning

confidence: 89%

Higher D or Li: probes of physics beyond the standard model

Olive

Petitjean

Vangioni

et al. 2012

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…The metal‐poor ([Fe/H]=−2.3 dex) GC M92 shows a mean value of A (Li) = 2.36 ± 0.05 dex, σ= 0.18 (Bonifacio 2002). For NGC 6397 ([Fe/H]=−2.0 dex), different studies point towards A (Li) between 2.25 ± 0.01 (Lind et al 2009a) and 2.30 ± 0.01 dex (González Hernández et al 2009) in stars along the MS or around the TO. The value of A (Li) in nine TO stars of NGC 6752 ([Fe/H]=−1.4 dex) has been measured by Pasquini et al (2005) who found A (Li) = 2.24 ± 0.05 dex (σ= 0.15).…”

Section: Evolution Of A(li)mentioning

confidence: 99%

“…Extensive chemical screenings of the Li content in GC dwarf stars have so far been limited to a few closest objects, such as 47 Tuc (Bonifacio et al 2007; D'Orazi et al 2010), NGC 6397 (Bonifacio et al 2002; Korn et al 2006a; González Hernández et al 2009; Lind et al 2009a), NGC 6752 (Pasquini et al 2005) and M92 (Boesgaard et al 1998; Bonifacio 2002). The metal‐poor GC NGC 6397, in particular, has recently been the object of an intense debate regarding the discrepancy between the cosmological and stellar Li abundance.…”

Section: Introductionmentioning

confidence: 99%

“…Korn et al (2006a) and Lind et al (2009a) found a trend between A (Li) and T eff along the SGB and the early RGB, roughly consistent with models (Richard et al 2005, hereafter R05) that start with the BBNS A (Li) and include atomic diffusion moderated by some ad hoc turbulent mixing that brings back to the surface some of the Li (and other elements) diffused below the convective envelope during the main‐sequence (MS) phase. González Hernández et al (2009) have studied a sample of MS and SGB stars in the same cluster and found A (Li) decreasing with decreasing T eff in both groups of stars, with the SGB stars showing systematically higher values of A (Li) at a given T eff . This pattern cannot be reproduced satisfactorily by any existing theoretical model starting with the BBNS value of A (Li).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Lithium abundance in the globular cluster M4: from the turn-off to the red giant branch bump★

Mucciarelli

Salaris

Lovisi

et al. 2010

Monthly Notices of the Royal Astronomical Society

104

105

View full text Add to dashboard Cite

We present Li and Fe abundances for 87 stars in the globular cluster M4, obtained by using high‐resolution spectra collected with GIRAFFE at the Very Large Telescope. The targets range from the turn‐off up to the red giant branch bump. The Li abundance in the turn‐off stars is uniform, with an average value equal to A(Li)= 2.30 ± 0.02 dex (σ= 0.10 dex), consistent with the upper envelope of Li content measured in other globular clusters and in the halo field stars, confirming also for M4 the discrepancy with the primordial Li abundance predicted by Wilkinson Microwave Anisotropy Probe+ big bang nucleosynthesis (WMAP+BBNS). The global behaviour of A(Li) as a function of the effective temperature allows us to identify the two main drops in the Li evolution due to the first dredge‐up and to the extra‐mixing episode after the red giant branch bump. The measured iron content of M4 results to [Fe/H]=−1.10 ± 0.01 dex (σ= 0.07 dex), with no systematic offsets between dwarf and giant stars. The behaviour of the Li and Fe abundances along the entire evolutionary path is incompatible with theoretical models including pure atomic diffusion, pointing out that an additional turbulent mixing below the convective region needs to be taken into account, able to inhibit the atomic diffusion. The measured value of A(Li) and its homogeneity in the turn‐off stars allow us to put strong constraints on the shape of the Li profile inside the M4 turn‐off stars. The global behaviour of A(Li) with the effective temperature can be reproduced with different pristine Li abundances, depending on the kind of adopted turbulent mixing. One cannot reproduce the global trend that starts from the WMAP+BBNS A(Li) and adopts the turbulent mixing described by Richard, Michaud & Richer with the same efficiency as that used by Korn et al. to explain the Li content in NGC 6397. In fact, such a solution is not able to well reproduce simultaneously the Li abundance observed in turn‐off and red giant branch stars. However, the WMAP+BBNS A(Li) can be reproduced assuming a more efficient turbulent mixing able to reach deeper stellar regions where the Li is burned. We conclude that the cosmological Li discrepancy cannot be easily solved with the present, poor understanding of the turbulence in the stellar interiors, and a future effort to well understand the true nature of this non‐canonical process is needed.

show abstract

“…Beyond this series of papers, studies of lithium in metal-poor stars have provided crucial mass- and metallicity-dependent constraints (González Hernández et al. 2009 , 2019; Meléndez et al. 2010 ; Nissen & Schuster 2012 ).…”

Section: Introductionmentioning

confidence: 99%

Atomic diffusion and mixing in old stars – VIII. Chemical abundance variations in the globular cluster M4 (NGC 6121)

Nordlander,

Gruyters,

Richard

et al. 2023

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Variations in chemical abundances with evolutionary phase have been identified among stars in globular and open clusters with a wide range of metallicities. In the metal-poor clusters, these variations compare well with predictions from stellar structure and evolution models considering the internal diffusive motions of atoms and ions, collectively known as atomic diffusion, when moderated by an additional mixing process with a fine-tuned efficiency. We present here an investigation of these effects in the Galactic globular cluster NGC 6121 (M4) ([Fe/H] = −1.13) through a detailed chemical abundance analysis of 86 stars using high-resolution ESO/VLT FLAMES spectroscopy. The stars range from the main-sequence turnoff point (TOP) to the red giant branch (RGB) just above the bump. We identify C-N-O and Mg-Al-Si abundance anti-correlations, and confirm the presence of a bimodal population differing by 1 dex in nitrogen abundance. The composition of the second-generation stars imply pollution from both massive (20–40 $\rm M_{\odot}$) and asymptotic giant branch stars. We find evolutionary variations in chemical abundances between the TOP and RGB, which are robust to uncertainties in stellar parameters and modelling assumptions. The variations are weak, but match predictions well when employing efficient additional mixing. Without correcting for Galactic production of lithium, we derive an initial lithium abundance 2.63 ± 0.10, which is marginally lower than the predicted primordial BBN value.

show abstract

Lithium in the globular cluster NGC 6397

Cited by 53 publications

References 43 publications

Higher D or Li: probes of physics beyond the standard model

Higher D or Li: probes of physics beyond the standard model

Lithium abundance in the globular cluster M4: from the turn-off to the red giant branch bump★

Atomic diffusion and mixing in old stars – VIII. Chemical abundance variations in the globular cluster M4 (NGC 6121)

Contact Info

Product

Resources

About