The discovery of anomalously high levels of [Si/Fe] among metal-poor giants in the bulge, disk, and halo of the Milky Way. (arXiv:1904.05884v1 [astro-ph.GA])

The discovery of anomalously high levels of [Si/Fe] among metal-poor giants in the bulge, disk, and halo of the Milky Way. (arXiv:1904.05884v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Fernandez_Trincado_J/0/1/0/all/0/1">Jos&#xe9; G. Fern&#xe1;ndez-Trincado</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Beers_T/0/1/0/all/0/1">Timothy C. Beers</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Placco_V/0/1/0/all/0/1">Vinicius M. Placco</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Martell_S/0/1/0/all/0/1">Sarah L. Martell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moreno_E/0/1/0/all/0/1">Edmundo Moreno</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tang_B/0/1/0/all/0/1">Baitian Tang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alves_Brito_A/0/1/0/all/0/1">Alan Alves-Brito</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Villanova_S/0/1/0/all/0/1">Sandro Villanova</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ortigoza_Urdaneta_M/0/1/0/all/0/1">Mario Ortigoza-Urdaneta</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Minniti_D/0/1/0/all/0/1">Dante Minniti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Perez_Villegas_A/0/1/0/all/0/1">Angeles P&#xe9;rez-Villegas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reyle_C/0/1/0/all/0/1">C&#xe9;line Reyl&#xe9;</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Robin_A/0/1/0/all/0/1">Annie C. Robin</a>

Here, we report the discovery of a unique collection of giants, that exhibit
anomalously high levels of [Si/Fe] and [Al/Fe] without noticeable carbon and
nitrogen enhancement, clearly above typical Galactic levels, distinguishable
from dwarf galaxy populations in most chemical elements; their distinction is
less apparent among other light-elements such as N and Mg. The newly identified
mildly metal-poor sample’s [Si/Fe] appear definitively anomalous, having a
spread in [Si/Fe] from around $+0.6$ to $+1.1$ dex, compared with Galactic
[Si/Fe]$<+0.5$. We confirm that most of the chemically anomalous Si-rich stars are on tight halo-like orbits passing through the bulge, similar to those found in other studies. Their chemical composition is, in general, similar to typical globular cluster stars with extreme abundance, although several differences exist. Furthermore, we did not detect any variation of the radial velocities that would support the binary hypothesis in this unique sample. Thus, the high aluminum and silicon abundances, and enhancements in their textit{s}-process elements relative to Solar abundance ratios, could be due to formation from gas that was already strongly enriched by SNe II.

Here, we report the discovery of a unique collection of giants, that exhibit
anomalously high levels of [Si/Fe] and [Al/Fe] without noticeable carbon and
nitrogen enhancement, clearly above typical Galactic levels, distinguishable
from dwarf galaxy populations in most chemical elements; their distinction is
less apparent among other light-elements such as N and Mg. The newly identified
mildly metal-poor sample’s [Si/Fe] appear definitively anomalous, having a
spread in [Si/Fe] from around $+0.6$ to $+1.1$ dex, compared with Galactic
[Si/Fe]$<+0.5$. We confirm that most of the chemically anomalous Si-rich stars
are on tight halo-like orbits passing through the bulge, similar to those found
in other studies. Their chemical composition is, in general, similar to typical
globular cluster stars with extreme abundance, although several differences
exist. Furthermore, we did not detect any variation of the radial velocities
that would support the binary hypothesis in this unique sample. Thus, the high
aluminum and silicon abundances, and enhancements in their textit{s}-process
elements relative to Solar abundance ratios, could be due to formation from gas
that was already strongly enriched by SNe II.

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