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Abstract The light element lithium is formed by nucleosynthesis during the Big Bang. Its abundance can help to define the parameters of the early Universe. To find this primordial value, it is necessary to determine Li abundances in the oldest stars because it is readily destroyed by nuclear reactions in stellar interiors. We have made high-resolution (∼45,000) spectroscopic observations of five identical unevolved turnoff stars in the 13 Gyr old globular cluster M5. In our analysis we find a range in Li abundance of a factor of 2; the spread is 5 times the individual error. The comparison of these results with those for turnoff stars from five other globular clusters reveals a similarly large range in Li. Lithium in M5 and the other clusters all have stars above the field star Li plateau, but none are as high as the predictions for primordial Li. The maximum values for Li are the same in all six clusters. Multiple generations of stars are found in many globular clusters; those later generations are expected to have formed from Li-depleted gas. Such second- and later-generation stars would have no Li. However, only one of the six clusters has a few unevolved stars with upper limits on the Li abundance.
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Primordial Lithium from Globular Cluster Turnoff Stars: M13 and M71
Abstract During Big Bang nucleosynthesis (BBN) in the first 15 minutes of the Universe, some7Li was created along with isotopes of H and He. The determination of that primordial value of Li can help constrain the conditions at that time. The oldest stars with known ages can be found in globular clusters which have well-determined ages through stellar evolution models. High-resolution spectra of Li have been obtained with the Keck I Telescope and HIRES in several unevolved stars in the clusters M13 and M71 withVmagnitudes of 17.6–17.9. Abundances of Li have been determined with spectrum synthesis techniques and show a range of a factor of 4. We attribute that spread to differences in initial angular momentum resulting in different amounts of spin-down, related mixing, and destruction of Li. Our results are compared with similar results for main-sequence and turnoff stars in other globular clusters. The range in age of these clusters is 11.2–14.2 Gyr for an age span of 3 Gyr. These clusters range in [Fe/H] from −0.75 to −2.24 corresponding to a factor of 30 in metallicity. The maximum in the Li abundance for these unevolved stars in all eight clusters is the same corresponding to Li/H = 3.16 × 10−10, while the predicted Li abundance, based on the deuterium abundance and the BBN predictions, is 5.24 × 10−10.
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- PAR ID:
- 10539127
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 972
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 136
- Size(s):
- Article No. 136
- Sponsoring Org:
- National Science Foundation
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