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Title: Finding r-II Sibling Stars in the Milky Way with the Greedy Optimistic Clustering Algorithm
Abstract R-process enhanced stars with [Eu/Fe] ≥ +0.7 (so-calledr-II stars) are believed to have formed in an extremely neutron-rich environment in which a rare astrophysical event (e.g., a neutron-star merger) occurred. This scenario is supported by the existence of an ultra-faint dwarf galaxy, Reticulum II, where most of the stars are highly enhanced inr-process elements. In this scenario, some small fraction of dwarf galaxies around the Milky Way wererenhanced. When each r-enhanced dwarf galaxy accreted to the Milky Way, it deposited manyr-II stars in the Galactic halo with similar orbital actions. To search for the remnants of ther-enhanced systems, we analyzed the distribution of the orbital actions ofN= 161r-II stars in the solar neighborhood by using Gaia EDR3 data. Since the observational uncertainty is not negligible, we applied a newly developed greedy optimistic clustering method to the orbital actions of our sample stars. We found six clusters ofr-II stars that have similar orbits and chemistry, one of which is a new discovery. Given the apparent phase-mixed orbits of the member stars, we interpret that these clusters are good candidates for remnants of completely disruptedr-enhanced dwarf galaxies that merged with the ancient Milky Way.  more » « less
Award ID(s):
2205847 1815403
PAR ID:
10403648
Author(s) / Creator(s):
; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
946
Issue:
1
ISSN:
0004-637X
Format(s):
Medium: X Size: Article No. 48
Size(s):
Article No. 48
Sponsoring Org:
National Science Foundation
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