A New Formation Model for ?;Centauri: A Complex Interplay of Astrophysical Processes

Kenji Bekki, Takuji Tsujimoto

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Abstract

We investigate the formation processes of the Galactic globular cluster (GC) ? Cen with multiple stellar populations based on our original hydrodynamical simulations with chemical enrichment by Type II supernovae (SNe II), asymptotic giant branch (AGB) stars, and neutron star mergers (NSMs). Multiple stellar populations with a wide range of [Fe/H] can be formed from rather massive and compact molecular clouds with a mass of 2;;10(7) M in the central region of its dwarf galaxy within less than a few hundred megayears. Gas ejected from SNe II and AGB stars can mix well to form new stars with higher He abundances (Y) and higher [Fe/H]. The He-rich stars are strongly concentrated in the GC?s central region so that the GC can show a steep negative gradient of Y. Relative ratios of light elements to Fe show bimodal distributions for a given [Fe/H] owing to star formation from original gas and AGB ejecta. [La/Fe] and [Ba/Fe] can rapidly increase until [Fe/H];?;?1.5 and then decrease owing to Fe ejection from SNe II. Although AGB ejecta can be almost fully retained in the intracluster medium, NSM ejecta can be retained only partially. This difference in the retention capability is responsible for the observed unique [Eu/Fe]?[Fe/H] and [La/Eu]?[Fe/H] relations in ? Cen. The observed [O/Na]?[Fe/H] relation and radial [Fe/H] gradient are yet to be well reproduced in the present model. We briefly discuss how the results change for different yields of AGB stars and SNe II.

Original languageEnglish
Article number121
Number of pages25
JournalAstrophysical Journal
Volume886
Issue number2
DOIs
Publication statusPublished - 1 Dec 2019

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