Enrichment of lead (Pb) in the Galactic halo

Abstract

We have determined lead (Pb) abundances for twelve red giants having [Fe/H] between -2.1 and -1.3, and its upper-limits for two lower metallicity objects, as well as the abundances of lanthanum (La) and europium (Eu). The averages of [Pb/Fe] and [Pb/Eu] are -0.3 and -0.6, respectively, and no clear increase of these ratios with increasing metallicity is found. The [La/Eu] values are only slightly higher than that of the r-process component in solar-system material. Combining the previous studies for globular clusters, these results suggest little contribution of the s-process to Pb of the field stars studied here, supporting the estimate of Pb production by the r-process from the solar-system abundances.

6 pages, 2 figures, 4 tables. To appear in Publication of Astronomical Society of Japan (PASJ)