We present new abundance determinations of neutron-capture elements Ge , Zr , Os , Ir , and Pt in a sample of 11 metal-poor ( –3.1 \leq [ Fe/H ] \leq –1.6 ) Galactic halo giant stars , based on Hubble Space Telescope UV and Keck I optical high-resolution spectroscopy .
The stellar sample is dominated by r -process-rich stars such as the well-studied CS 22892-052 and BD +17 ^ { \circ } 3248 , but also includes the r -process-poor , bright giant HD 122563 .
Our results demonstrate that abundances of the 3 ^ { rd } r -process peak elements Os , Ir and Pt in these metal-poor halo stars are very well-correlated among themselves , and with the abundances of the canonical r -process element Eu ( determined in other studies ) , thus arguing for a common origin or site for r -process nucleosynthesis of heavier ( Z > 56 ) elements .
However , the large ( and correlated ) scatters of [ Eu , Os , Ir , Pt/Fe ] suggests that the heaviest neutron-capture r -process elements are not formed in all supernovae .
In contrast , the Ge abundances of all program stars track their Fe abundances , very well .
An explosive process on iron-peak nuclei ( e.g . , the \alpha -rich freeze-out in supernovae ) , rather than neutron capture , appears to have been the dominant synthesis mechanism for this element at low metallicities – Ge abundances seem completely uncorrelated with Eu .
The correlation ( with very small scatter ) of Ge and Fe abundances suggests that Ge must have been produced rather commonly in stars – even at early times in the Galaxy – over a wide range of metallicity .
The Zr abundances show much the same behavior as Ge with ( perhaps ) somewhat more scatter , suggesting some variations in abundance with respect to Fe .
The Zr abundances also do not vary cleanly with Eu abundances , indicating a synthesis origin different than that of heavier neutron-capture elements .

Detailed abundance distributions , for CS 22892-052 and BD +17 ^ { \circ } 3248 , combining the new elemental determinations for Os-Pt and recently published Nd and Ho measurements , show excellent agreement with the solar system r -process curve from the elements Ba to Pb .
The lighter n -capture elements , including Ge , in general fall below the same solar system r -process curve that matches the heavier elements .