A Study of Elemental Abundance Pattern of the r-II Star HD 222925

HD 222925 is a rare r-process enhanced star in the Milky Way because of its metal abundance([Fe/H]=-1.46±0.10)and Eu abundance([Eu/Fe]=1.32±0.08).Based on the very complete set of elemental abundances of HD 222925,we use the abundance decomposition method to fit the observed abundances of 58elements in the sample star,which is also the largest number of elemental abundances fitted at the same time for a fixed star.We analyze the astrophysical origins of elements in HD 222925 by its abundance ratios and component ratios.It is found that the light elements and the iron group elements in HD 222925 mainly originate from the primary process of the TypeⅡsupernovae(SNeⅡ)with the progenitor mass M>10 M_(⊙)and have no contribution from SNe Ia and the first generation of very massive stars.The contribution of the weak r-process to Ga,Ge,and As is superior to that of the other processes,and its contribution decreases linearly with increasing atomic number.The main r-process that is likely derived from a neutron star merger plays a key role in the formation of neutroncapture elements(Z≥38)in HD 222925.

Study of the puzzling abundance pattern of the neutron-capture elements in LMC star J053253.51–695915.1

Object J053253.51–695915.1(J053253)in the Large Magellanic Cloud(LMC)is reported as a young stellar object(YSO).Its chemical abundances reflect the initial composition of the gas cloud in which the star formed.However,the discovery that this star shows the enhancement of the neutron(n)-capture elements and the higher ratio of the heavier n-capture elements relative to the lighter n-capture elements is puzzling.Using an abundance decomposed method,we explore the astrophysical origins of the n-capture elements in this star.We find that the abundance characteristic of the higher ratio of the heavier n-capture elements to the lighter n-capture elements can be explained by the pollution of the r-process event and the contamination of the s-process material.

Pollution tracks of r-process material in[Sr/Ba]vs.[Ba/Fe]space for the early Galaxy

In the early Galaxy,elemental abundances of the extremely metal-poor(EMP)stars contain abundant information about the neutron-capture nucleosynthesis and the chemical enrichment history.In this work,we study the abundance characteristics of Sr and Ba for the EMP stars in the[Sr/Ba]vs.[Ba/Fe]space.We find that there are three boundaries for the distribution region of the EMP stars.The weak rprocess star CS 22897-008 lies on the upper end and the main r-process stars lie on the right end of the region.Near the right boundary of the distribution region,there is an Fe-normal belt.For the EMP stars in the belt,element Fe dominantly originates from the normal massive stars.The low-Sr stars([Sr/Fe]6−0.3)distribute in the region of the lower left of the Fe-normal belt and their Fe should originate partly from the prompt inventory.We find that the formation of the lower boundary of the distribution region is due to the pollution of the main r-process material and the formation of the right boundary could be explained by the combination of the weak r-and main r-process material.Furthermore,the formation of the left boundary is due to the pollution of the weak r-process material.Although the[Sr/Ba]ratios are related to the relative importance of the weak r-process material,the scatter of[Sr/Ba]ratios for the EMP stars mainly depends on the abundance ratio of the weak r-process.