Investigation of the Puzzling Abundance Pattern of the Neutron‐Capture Elements in the Ultra–Metal‐poor Star CS 30322‐023

The s-enhanced and very metal-poor star CS 30322-023 shows a puzzlingabundance pattern of the neutron-capture elements, i.e. several neutron-captureelements such as Ba, Pb etc. show enhancement, but other neutron-captureelements such as Sr, Eu etc. exhibit deficient with respect to iron. The studyto this sample star could make people gain a better understanding of s- andr-process nucleosynthesis at low metallicity. Using a parametric model, we findthat the abundance pattern of the neutron-capture elements could be bestexplained by a star that was polluted by an AGB star and the CS 30322-023binary system formed in a molecular cloud which had never been polluted byr-process material. The lack of r-process material also indicates that the AGBcompanion cannot have undergone a type-1.5 supernova, and thus must have had aninitial mass below 4.0M$_\odot$, while the strong N overabundance and theabsence of a strong C overabundance indicate that the companion's initial masswas larger than 2.0M$_\odot$. The smaller s-process component coefficient ofthis star illustrates that there is less accreted material of this star fromthe AGB companion, and the sample star should be formed in the binary systemwith larger initial orbital separation where the accretion-induced collapse(AIC) mechanism can not work.Comment: 13 pages, 2 figure