We determine the abundances of neutron-capture elements from Sr to Eu for five very-metal-poor stars ( -3 < [ Fe/H ] < -2 ) in the Milky Way halo to reveal the origin of light neutron-capture elements .
Previous spectroscopic studies have shown evidence of at least two components in the r-process ; one referred to as the “ main r-process ” and the other as the “ weak r-process , ” which is mainly responsible for producing heavy and light neutron-capture elements , respectively .
Observational studies of metal-poor stars suggest that there is a universal pattern in the main r-process , similar to the abundance pattern of the r-process component of solar-system material .
Still , it is uncertain whether the abundance pattern of the weak r-process shows universality or diversity , due to the sparseness of measured light neutron-capture elements .
We have detected the key elements , Mo , Ru , and Pd , in five target stars to give an answer to this question .
The abundance patterns of light neutron-capture elements from Sr to Pd suggest a diversity in the weak r-process .
In particular , scatter in the abundance ratio between Ru and Pd is significant when the abundance patterns are normalized at Zr .
Our results are compared with the elemental abundances predicted by nucleosynthesis models of supernovae with parameters such as electron fraction or proto-neutron-star mass , to investigate sources of such diversity in the abundance patterns of light neutron-capture elements .
This paper presents that the variation in the abundances of observed stars can be explained with a small range of parameters , which can serve as constraints on future modeling of supernova models .