Lithium abundance

Abstract. We present preliminary results of lithium abundances in turnoff stars in the open cluster NGC 2506. Some fifty turnoff stars and a few blue stragglers have been observed using the FLAMES facility on the VLT, during half a night from the French Guaranteed Time on this instrument. 

The lithium abundance, using the Li I 6707 doublet, will be used as a signature of internal mixing to confirm whether or not internal mixing is one of the mechanisms responsible for the existence of blue straggler stars. 

The radial velocities have been computed with the low resolution set-up (more spectral lines, no telluric line), using a cross-correlation technique. When excluding the seven outliers, the peak in centered at 83.0 0.4kms 1 with a dispersion of 1.9 0.2kms 1. Lithium abundance is being determined using Li i 6707.8 A. We used the B — V index to determined the ([3]), and the curve of growth from [7] to derive AT(Li). 

R.Pallavicini, S. Randich, P. Sestito Lithium abundances in intermediate age and old clusters . In 13th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, ed. by F. Favata et al. (ESA, Special Publication), in press (2004)... 

From observations of 11 main-sequence stars belonging to the Galactic halo, Spite Spite [27] concluded that the lithium abundance was essentially independent of metallicity for halo stars hotter than 5600 K, and inferred that the Li abundance was hardly altered from the Big Bang. Two decades of work has followed, increasing the number of stars observed and the range of metallicity that they span, in an effort to establish the primordial Li abundance more securely. 

We have also measured the lithium abundances in the samples of unmixed and mixed stars [6]. When low mass stars, such as those in our sample, evolve through the red giant branch, the degree of dilution of the lithium increases as the convective zone penetrates deeper and thus we expect a decline of the lithium abundance. In the mixed stars the lithium has never been detected, the upper limit of the lithium abundance is log N(Li) < 0.0, on the contrary in all the unmixed stars but one, the lithium line is visible and log N(Li) is > 0.20. In these stars as expected, the lithium abundance decreases when the gravity decreases (Fig. 3-b). 

Abstract. From VLT/UT2 GIRAFFE GTO, we performed a lithium abundance survey along the red giant branch of the metal-rich globular cluster 47 TUC (NGC 104), in order to investigate the efficiency of extra mixing occurring at the RGB bump. 

Fig. 2. (Left panel) evolutionary tracks using FST in the logTefj vs. log g plane (solid line non gray models with rph = 10 by Montalban et al.,2004) and 2D calibrated MLT (dashed line).(Right panel) Lithium evolution for the solar mass with different assumptions about convection and model atmospheres. The dotted line at bottom represents today s solar lithium abundance. MLT models with AH97 model atmospheres down to Tph = 10 and 100 are shown dotted for cum = 1 and dash-dotted for cpr, = 1.9. The Montalban et al. (2004) MLT models with Heiter et al. (2002) atmospheres down to Tph = 10 (lower) and 100 (upper) are dashed The continuous lines show the non gray FST models for rph = 10 and 100, and, in between, the long dashed model employing the 2D calibrated MLT.

As stars become older, lithium at their surface becomes gradually depleted by mixing with deeper layers at temperatures above 2.5 x 106 K where it is destroyed by the (p, a) reaction, Eq. (4.49). This destruction takes place more rapidly in cooler stars with deeper outer convection zones, so that there is a trend for lithium abundance to decrease with both stellar age and diminishing surface temperature in cooler stars some depletion takes place already in the pre-main-sequence stage. Thus, in the young Pleiades cluster ( 108 yr), lithium has its standard abundance down to Teff = 5500 K (type G5), whereas in the older Hyades cluster ( 6 x 108yr) it is noticeably depleted below Tc t = 6300 K (F7) and also in... 

Fig. 4.12. Stellar lithium abundances (log of the number per 1012 H atoms) among main-sequence stars as a function of metallicity. The full-drawn curve shows the prediction of a numerical Galactic chemical evolution model, while the broken-line curve gives the sum of a primordial component and an additional component proportional to iron and normalized to meteoritic abundance. Adapted from Matteucci, D Antona and Timmes (1995).

Dissertation, Universitat Gottingen, Gottingen, Germany Collins AG (1976) Lithium abundances in oilfield waters. Itr. Lithium Resources and Requirements by the Year 2000. Vine JD (ed) U.S. Geol Surv Prof Pap 1005 116-123 Coplen TB (1996) Atomic weights of the elements 1995. Pure Appl Chem 68 2339-2359... 

Richter FM, Davis AM, DePaolo DJ, Watson EB (2003) Isotope fradionation by chemical diliusion between molten basalt and rhyolite. Geochim Cosmochim Acta 67 3905-3923 Ritzenhoff S, Schroter EH, Schmidt W (1997) The lithium abundance in sunspots. Astron Astrophys 328 695-701... 

Rudnick RL, McDonough WF, Tomascak PB, Zack T (2003) Lithium isotopic composition of eclogites implications for subduction zone processes. Eighth Int Kimberlite Conf Abst Ryan JG, Langmuir CH (1987) The systematics of lithium abundances in young volcanic rocks. Geochim Cosmochim Acta 51 1727-1741... 

You CF, Chan LH, Gieskes JM, Klinkhammer GP (2004) Seawater intrusion through the oceanic crust and carbonate sediment in the Equatorial Pacific Lithium abundance and isotopic evidence. Geophys Res Lett 30 (in press)... 

Figure 2. Variations in twilight lithium abundance at 80 km. altitude following the Teak and Starfish rocket explosions (16)...

OBSERVED LITHIUM ABUNDANCES AS A TEST OF STELLAR INTERNAL STRUCTURE... 

Another explanation of the lithium gap in the Hyades could be found in terms of turbulent diffusion and nuclear destruction. Turbulence is definitely needed to explain the lithium abundance decrease in G stars. If this turbulence is due to the shear flow instability induced by meridional circulation (Baglin, Morel, Schatzman 1985, Zahn 1983), turbulence should also occur in F stars, which rotate more rapidly than G stars. Fig. 2 shows a comparison between the turbulent diffusion coefficient needed for lithium nuclear destruction and the one induced by turbulence. Li should indeed be destroyed in F stars This effect gives an alternative scenario to account for the Li gap in the Hyades. The fact that Li is normal in the hottest observed F stars could be due to their slow rotation. 

ON THE DISTRIBUTION OF THE LITHIUM ABUNDANCE IN NORMAL LATE-TYPE GIANTS... 

The next feature that deserves attention in Fig. 2, is bimodal frequency distribution of lithium line strengths for MO - M4 giants. Here we get some hint at the existence of a gap in the distribution of the lithium abundances of the evolved stars. The results of a more precise abundance analysis of 25 M giants by Luck and... 

Lambert (1982) and 10 M giants by Hanni (1983) also tend to show a discontinuity in the lithium abundances within the sample of stars with similar effective temperature. 

Finally, I would like to stress that the bulk and quality of the lithium abundance data for red giants need to be considerably raised for an adequate statistical analysis. The main task of the present report was to provoke some interest in the problem concerning the distribution of lithium abundances in evolved stars. 

From the isotopic decomposition of normal lithium one finds that the mass-7 isotope, 7Li, is the more abundant of lithium s two isotopes 92.5% of terrestrial Li. The cosmic issues surrounding the lithium abundance are among the most complex and fascinating of any element. Using the total abundance of elemental Li = 57.1 per million silicon atoms in solar-system matter, this isotope has... 

Specific nuclear reactions capable of producing noticeable quantities of noble gas daughters in the Earth ( He and Ne in particular) are initiated by alpha and fission activities of the natural radioelements. Helium-3 is produced through a neutron capture reaction involving Li (HUl, 1941), whereas Ne production occurs through a number of a-induced reactions (Wetherill, 1954). In the case of helium, the He/ He ratio produced is of the order 10 and primarily reflects the lithium abundance at the site of production (Mamyrin and Tolstikhin, 1984). Eor neon, the only conspicuous isotope produced is Ne due to its low natural abundance. The present-day Ne/ He production ratio in the mantle has been calculated at 4.5 X 10 (Yatsevich and Honda, 1997) (see Ballentine and Bumard, 2002 for discussion regarding calculation of this parameter). 

Figure 8. A compilation of the lithium abundance data from stellar observations as a function of metallicity. N(Li) = 1012(Li/H) and [Fe/H] is the usual metallicity relative to solar. Note the Spite Plateau in Li/H for [Fe/H] — 2.

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