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Kinematics of highly r-process-enhanced halo stars: Evidence for origins in now-destroyed ultra-faint dwarf galaxies

Published online by Cambridge University Press:  14 May 2020

Kaley Brauer Open the ORCID record for Kaley Brauer [Opens in a new window] ,
Alexander P. Ji ,
Kohei Hattori ,
Sergio Escobar  and
Anna Frebel
Kaley Brauer
Affiliation:
Dept. of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA, USA email: kbrauer@mit.edu
Alexander P. Ji
Affiliation:
Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA, USA
Kohei Hattori
Affiliation:
Dept. of Astronomy, University of Michigan, 1085 S. University, Ann Arbor, MI, USA
Sergio Escobar
Affiliation:
Dept. of Physics, California Institute of Technology, 1200 E California Blvd, Pasadena, CA, USA
Anna Frebel
Affiliation:
Dept. of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA, USA email: kbrauer@mit.edu
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Abstract

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The Milky Way’s stellar halo preserves a fossil record of smaller dwarf galaxies that merged with the Milky Way throughout its formation history. Currently, though, we lack reliable ways to identify which halo stars originated in which dwarf galaxies or even which stars were definitively accreted. Selecting stars with specific chemical signatures may provide a way forward. We investigate this theoretically and observationally for stars with r-process nucleosynthesis signatures. Theoretically, we combine high-resolution cosmological simulations with an empirically-motivated treatment of r-process enhancement. We find that around half of highly r-process-enhanced metal-poor halo stars may have originated in early ultra-faint dwarf galaxies that merged into the Milky Way during its formation. Observationally, we use Gaia DR2 to compare the kinematics of highly r-process-enhanced halo stars with those of normal halo stars. R-process-enhanced stars have higher galactocentric velocities than normal halo stars, suggesting an accretion origin. If r-process-enhanced stars largely originated in accreted ultra-faint dwarf galaxies, halo stars we observe today could play a key role in understanding the smallest building blocks of the Milky Way via this novel approach of chemical tagging

Keywords

stars: kinematicsgalaxies: formation
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 14 , Symposium S353: Galactic Dynamics in the Era of Large Surveys , June 2019 , pp. 71 - 74
Copyright
© International Astronomical Union 2020

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