Lew M. Hobbs

The lithium abundance in halo stars

Spectroscopic observations are reported for 23 population II subdwarfs (selected for age homogeneity) and 31 other stars (mainly population I F and G dwarfs). The spectra were obtained in the 670.7-nm line of Li I using coude spectrographs on the 2.7-m reflector at McDonald Observatory, the 3.0-m reflector at Lick Observatory, and the 4-m Mayall reflector at KPNO during 1983-1985. The results are presented (along with selected published data) in extensive tables and graphs and analyzed. For 12 stars with space velocities v(LSR) = 160 km/s or greater and Fe/H = -1.4 or less, the atmospheric Li/H abundance is shown to depend on T(e), the mean value for T(e) = 5600 K or more being Li/H = (1.2 + or - 0.3) x 10 to the -10th. This result, also found for many of the population I stars, is interpreted as a significant constraint on the cosmic baryon/photon ratio.

Li production in the big bang

Li abundance is determined for 23 halo subdwarfs. About half of the stars show [Fe/H] < −1.4 and a space velocityV > 160 km s−1 Li appears to be present in all our halo stars, with an abundance within about ± 0.2 dex of the value logn (Li) = 2.0 found by Spite & Spite (1982). Thus our results provide confirmation of the main conclusion of Spite & Spite.

Primordial Nucleosynthesis of 7Li

We have observed 23 halo stars with space velocities\( \left| {\begin{array}{*{20}{c}} \to \\ {{v_{LSR}}} \end{array}} \right| \geqslant 100\,km\,{s^{ - 1}} \) and metallicities [Fe/H] ≤ -0.6, Twelve of these 23 show the more extreme properties \( \left| {\begin{array}{*{20}{c}} \to \\ {{v_{LSR}}} \end{array}} \right| \geqslant 160\,km\,{s^{ - 1}} \) and [Fe/H] ≤ -1.4 and should therefore constitute an especially old, homogeneous subgroup. The principal results for these 12 extreme halo stars and 5 similar stars observed in previous studies are that (1) a single, well defined relation, previously discovered and discussed by Spite and Spite, exists without exception between the atmospheric Li/H ratio and Te, and (2) at Te and (2) at T ≤ 5600 K the average lithium abundance is = 1.2 ± 0.3 x -10. The latter value constitutes a lower limit on the ^Li fraction produced in primordial nucleosynthesis and thereby significantly constrains the cosmic ratio of baryons to photons.