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| Paper: |
Detailed Abundances in a Metal-Poor Stellar Stream |
| Volume: |
432, New Horizons in Astronomy: Frank N. Bash Symposium 2009 |
| Page: |
239 |
| Authors: |
Roederer, I. U.; Sneden, C.; Thompson, I. B.; Preston, G. W.; Shectman, S. A. |
| Abstract: |
We present the results of a detailed abundance analysis of one of
the confirmed building blocks of the Milky Way stellar halo, a
kinematically-coherent metal-poor stellar stream. We have obtained
high resolution and high S/N spectra of 8 confirmed and 4 rejected
stream members using the MIKE spectrograph on the
Magellan-Clay Telescope at Las Campanas Observatory and the 2dCoude
spectrograph on the Smith Telescope at McDonald Observatory. We
have derived abundances or upper limits for nearly 50 species of
more than 40 elements in each of these stars. The stream members
show a range of metallicity (–2.5< [Fe/H] <–1.5) but are
otherwise chemically homogeneous, with the same star-to-star
chemical dispersion in [X/Fe] as halo stars. They show no evolution
in the α or Fe-group elements over the range of metallicity.
The stream does not resemble a globular cluster in that its members
show a range of metallicities, and the small chemical dispersion and
lack of chemical evolution demonstrate that it is also unlike the
classical Milky Way dwarf spheroidal galaxies. Our results support
the notion that a significant fraction of the Milky Way stellar halo
was formed from accreted systems, and these systems likely did not
resemble the present-day globular clusters or luminous dwarf
galaxies. This stream is mildly enriched (in, e.g., [Eu/Fe]) by
material produced by the main and weak components of the rapid
neutron-capture process and shows no evidence for enrichment by the
slow neutron-capture process. Except for the observed metallicity
range of the stream stars, the enrichment pattern of the stream is
nearly identical to that of the massive metal-poor globular cluster
M15. The kinematics of M15 and the stream are also similar. It is
possible that both systems may have originated from a common
progenitor but not likely that the stream originated from M15. |
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