The stellar record of elemental abundances in satellite galaxies is important to identify the origin of r-process because such a small stellar system could have hosted a single r-process event , which would distinguish member stars that are formed before and after the event through the evidence of a considerable difference in the abundances of r-process elements , as found in the ultra-faint dwarf galaxy Reticulum II ( Ret II ) .
However , the limited mass of these systems prevents us from collecting information from a sufficient number of stars in individual satellites .
Hence , it remains unclear whether the discovery of a remarkable r-process enrichment event in Ret II explains the nature of r-process abundances or is an exception .
We perform high-resolution spectroscopic measurements of r-process abundances for twelve metal-poor stars in the Draco dwarf galaxy in the metallicity range of -2.5 < [ Fe/H ] < -2 .
We found that these stars are separated into two groups with r-process abundances differing by one order of magnitude .
A group of stars with high abundances of r-process elements was formed by a single r-process event that corresponds to the event evidenced in Ret II .
On the other hand , the low r-process abundance group was formed by another sporadic enrichment channel producing a far fewer r-process elements , which is clearly identified for the first time .
Accordingly , we identified two populations of stars with different r-process abundances , which are built by two r-process events that enriched gases at levels that differ by more than one order of magnitude .