Lithium 6104 Å in Population II stars

Ford, Alison; Jeffries, R. D.; Smalley, B.; Ryan, Sean G.; Aoki, Wako; Kawanomoto, Satoshi; James, D. J.; Barnes, John

doi:10.1051/0004-6361:20021040

Cited by 15 publications

(22 citation statements)

References 16 publications

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“…We measure the equivalent width to be 37.3 mÅ, which when run in a full synthesis using the line list from Ford et al, 17 results in logǫ(Li) = 2.25; i.e., good agreement with the earlier work. A question, however, arises as to the validity of the detection, given the noise in the spectrum and the fact that the center of the measured line is 0.12Å to the red of the strongest feature in the Li doublet, while the center of the Fe I line at λ6705 is well matched in the data, as can be seen in Fig.…”

supporting

confidence: 80%

Preliminary abundance analysis of galactic bulge main sequence, subgiant, and giant branch stars observed during microlensing with Keck/HIRES

Cavallo

Cook

Minniti

et al. 2003

Discoveries and Research Prospects From 6- To 10-Meter-Class Telescopes II

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We present an abundance analysis of six main sequence turnoff, subgiant, and giant branch stars toward the Galactic bulge that were observed with Keck/HIRES during microlensing events. This is an early look at the first detailed chemical analysis of main sequence stars in the Galactic bulge. Lensing events allow the effective aperture of Keck to be increased beyond its current dimensions; although, some events still stretched its spectroscopic capabilities. Future large telescopes with high resolution and high throughput spectrometers will allow the study of abundances in distant stellar populations and in less evolved stars with greater ease.

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supporting

confidence: 80%

Preliminary abundance analysis of galactic bulge main sequence, subgiant, and giant branch stars observed during microlensing with Keck/HIRES

Cavallo

Cook

Minniti

et al. 2003

Discoveries and Research Prospects From 6- To 10-Meter-Class Telescopes II

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“…In comparison, our spectra have S/N % 500 or better in the relevant wavelength region. Finally, we note that our resolving power is about twice as large as obtained by Ford et al (2002) (110,000 vs. 50,000).…”

Section: Comparison With Results From the LI Resonance Linesupporting

confidence: 44%

“…While we are not in a position to unequivocally identify the reasons for the very different conclusions of Ford et al (2002), we suspect that the key is the quality of the observations. The S/ Ns of the spectra of Ford et al (2002) are between 200 and 300 around the 610.4 nm line, which may still not be sufficient to detect this very weak line in metal-poor turnoff stars (note that this line is about 50% stronger in a subgiant like HD 140283 with T eA % 5700 K than in a turnoff star with T eA % 6200 K for the same Li abundance). Under these circumstances it is easy to overestimate the line strength due to noise and thus derive too high abundances.…”

Section: Comparison With Results From the LI Resonance Linementioning

confidence: 80%

Lithium Isotopic Abundances in Metal‐poor Halo Stars

Asplund

Lambert

Nissen

et al. 2006

ApJ

531

1,081

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Very high quality spectra of 24 metal-poor halo dwarfs and subgiants have been acquired with ESO's VLT/UVES for the purpose of determining Li isotopic abundances. The derived one-dimensional, non-LTE 7 Li abundances from the Li i 670.8 nm line reveal a pronounced dependence on metallicity but with negligible scatter around this trend. Very good agreement is found between the abundances from the Li i 670.8 nm line and the Li i 610.4 nm line. The estimated primordial 7 Li abundance is 7 Li /H ¼ (1:1 1:5) ; 10 À10 , which is a factor of 3-4 lower than predicted from standard big bang nucleosynthesis with the baryon density inferred from the cosmic microwave background. Interestingly, 6 Li is detected in 9 of our 24 stars at the !2 significance level. Our observations suggest the existence of a 6 Li plateau at the level of log 6 Li % 0:8; however, taking into account predictions for 6 Li destruction during the pre-main-sequence evolution tilts the plateau such that the 6 Li abundances apparently increase with metallicity. Our most noteworthy result is the detection of 6 Li in the very metal-poor star LP 815À43. Such a high 6 Li abundance during these early Galactic epochs is very difficult to achieve by Galactic cosmic-ray spallation and -fusion reactions. It is concluded that both Li isotopes have a pre-Galactic origin. Possible 6 Li production channels include protogalactic shocks and late-decaying or annihilating supersymmetric particles during the era of big bang nucleosynthesis. The presence of 6 Li limits the possible degree of stellar 7 Li depletion and thus sharpens the discrepancy with standard big bang nucleosynthesis.

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“…Lithium appears in a stellar absorption spectrum with few transitions, namely the resonant line at 670.7 nm, and a much weaker signature at 610.4 nm, only recently explored in the most metal-poor stars (cf. Bonifacio & Molaro 1998;Ford et al 2002). The 670.7 nm line falls in a clean spectral region, especially in metal-deficient stars.…”

Section: Stellar Parameters: I Gravity Metallicity and Microturbulmentioning

confidence: 99%

“…Fulbright (2000) 50 000 >100 s/s/s O 13. Ford et al (2002 ) 50 000 >150 l/l/l O a T eff /log g/[Fe/H]: l = literature; s = spectroscopy; p = photometry. b O = new set of observations; T = new T eff scale (with Li EW collected from literature).…”

Section: The "Lithium Plateau Debate"?mentioning

confidence: 99%

The lithium content of the Galactic Halo stars

Charbonnel

Primas

2005

A&A

137

148

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Thanks to the accurate determination of the baryon density of the universe by the recent cosmic microwave background experiments, updated predictions of the standard model of Big Bang nucleosynthesis now yield the initial abundance of the primordial light elements with unprecedented precision. In the case of 7 Li, the CMB+SBBN value is significantly higher than the generally reported abundances for Pop II stars along the so-called Spite plateau. In view of the crucial importance of this disagreement, which has cosmological, galactic and stellar implications, we decided to tackle the most critical issues of the problem by revisiting a large sample of literature Li data in halo stars that we assembled following some strict selection criteria on the quality of the original analyses. In the first part of the paper we focus on the systematic uncertainties affecting the determination of the Li abundances, one of our main goal being to look for the "highest observational accuracy achievable" for one of the largest sets of Li abundances ever assembled. We explore in great detail the temperature scale issue with a special emphasis on reddening. We derive four sets of effective temperatures by applying the same colour-T eff calibration but making four different assumptions about reddening and determine the LTE lithium values for each of them. We compute the NLTE corrections and apply them to the LTE lithium abundances. We then focus on our "best" (i.e. most consistent) set of temperatures in order to discuss the inferred mean Li value and dispersion in several T eff and metallicity intervals. The resulting mean Li values along the plateau for [Fe/H] ≤ -1.5 are A(Li) NLTE = 2.214 ± 0.093 and 2.224 ± 0.075 when the lowest effective temperature considered is taken equal to 5700 K and 6000 K respectively. This is a factor of ∼2.48 to 2.81 (depending on the adopted SBBN model and on the effective temperature range chosen to delimit the plateau) lower than the CMB+SBBN determination. We find no evidence of intrinsic dispersion. Assuming the correctness of the CMB+SBBN prediction, we are then left with the conclusion that the Li abundance along the plateau is not the pristine one, but that halo stars have undergone surface depletion during their evolution. In the second part of the paper we further dissect our sample in search of new constraints on Li depletion in halo stars. By means of the Hipparcos parallaxes, we derive the evolutionary status of each of our sample stars, and re-discuss our derived Li abundances. A very surprising result emerges for the first time from this examination. Namely, the mean Li value as well as the dispersion appear to be lower (although fully compatible within the errors) for the dwarfs than for the turnoff and subgiant stars. For our most homogeneous dwarfs-only sample with [Fe/H] ≤ -1.5, the mean Li abundances are A(L) NLTE = 2.177 ± 0.071 and 2.215 ± 0.074 when the lowest effective temperature considered is taken equal to 5700 K and 6000 K respectively. This is a factor of 2.52 to 3.06...

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Lithium 6104 Å in Population II stars

Cited by 15 publications

References 16 publications

Preliminary abundance analysis of galactic bulge main sequence, subgiant, and giant branch stars observed during microlensing with Keck/HIRES

Preliminary abundance analysis of galactic bulge main sequence, subgiant, and giant branch stars observed during microlensing with Keck/HIRES

Lithium Isotopic Abundances in Metal‐poor Halo Stars

The lithium content of the Galactic Halo stars

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